Fast spreading of surface ozone in both temporal and spatial scale in Pearl River Delta

Surface ozone (O3) is a major air pollutant and draw increasing attention in the Pearl River Delta (PRD), China. Here, we characterize the spatial-temporal variability of ozone based on a dataset obtained from 57 national monitoring sites during 2013-2019. Our results show that: (1) the seasonal difference of ozone distribution in the inland and coastal areas was significant, which was largely affected by the wind pattern reversals related to the East Asian monsoon, and local ozone production and destruction; (2) the daily maximum 8hr average (MDA8 O3) showed an overall upward trend by 1.11 ppbv/year. While the trends in the nine cities varied differently by ranging from -0.12 to 2.51 ppbv/year. The hot spots of ozone were spreading to southwestern areas from the central areas since 2016. And ozone is becoming a year-round air pollution problem with the pollution season extending to winter and spring in PRD region. (3) at the central and southwestern PRD cities, the percentage of exceedance days from the continuous type (defined as ≥3 days) was increasing. Furthermore, the ozone concentration of continuous type was much higher than that of scattered exceedance type (<3 days). In addition, although the occurrence of continuous type starts to decline since 2017, the total number of exceedance days during the continuous type is increasing. These results indicate that it is more difficult to eliminate the continuous exceedance than the scatter pollution days and highlight the great challenge in mitigation of O3 pollution in these cities.

Ecological risk assessment of the typical anti-epidemic drugs in the Pearl River Delta by tracing their source and residual characteristics

Since the outbreak of the COVID-19 pandemic, the anti-epidemic drugs have been used in extraordinary quantities with high intensity, and concerns have grown about their potential ecological risks due to their continued release and persistence in the receiving environments. A systematic investigation, covering the samples from hospital wastewater, effluent from wastewater treatment plants and receiving water bodies in the Pearl River Delta Region (PRDR), was carried out and aimed at tracing the sources and fate of 30 typical anti-epidemic in different water matrixes and evaluating their ecological risk. The results showed that these typical anti-epidemic drugs residues were detected in most of the sampling sites, with the highest concentration measured in hospital wastewater, whose concentrations were as high as ppb level, while the highest concentration of the surface water samples in tributaries was lower than ppb level. Anti-epidemic drugs contained in hospital wastewater and effluent from WWTPs were the main sources of drug residues in the surface water of this region. In the surface water of PRDR, although the detected concentration anti-epidemic drugs were basically in the range of 0-10 ng/L. The risk quotient of several anti-epidemic drugs, including Ciprofloxacin (CFX), Ofloxacin (OFX), Erythromycin (ETM), Clindamycin (CLI), and Sulfamethoxazole (SMX), was calculated to be a high value, which indicated that they might cause non-negligible ecological risk to the aquatic environment.

Maximizing ozone control by spatial sensitivity-oriented mitigation strategy in the Pearl River Delta Region, China

The Pearl River Delta (PRD) has long been plagued by severe O3 pollution, particularly during the autumn. A regional O3 pollution episode influenced by the Western Pacific Subtropical High in September 2021 was characterized by near-surface O3 escalation due to strong photochemical reactions within the planetary boundary layer. This event was targeted to develop effective control strategies through investigation of precursor control type and scope based on the high-order decoupled direct method (HDDM) and integrated source apportionment method (ISAM) of CMAQ. Generally, the majority of areas (67.0 %) were under NOx-limited regime, which should strengthen afternoon NOx control inferred by positive convex O3 responses. However, high emission and heavily polluted areas located in central PRD were under VOC-limited regime (11.6 %) or mixed regime (15.0 %). The remaining areas (6.4 %) were under NOx-titration or insensitive conditions. Regarding source apportionment, Guangdong province contributed 32.3 %-58.4 % to MDA8 O3 of PRD, especially higher proportion (>50 %) to central areas. Overall, local-focused NOx/VOC emission reductions had limited effects on O3 mitigation for receptor cities compared to regional-cooperative regulation. When region-wide VOC emission reduction was implemented, MDA8 O3 in VOC-limited grids exhibited the largest declines (2.3 %-4.1 %, 3.9- 7.0 μg·m-3). However, unified NOx control contributed to increasing MDA8 O3 in VOC-limited grids (most stations located for air quality evaluation) whereas decreased MDA8 O3 by 2.1 %- 5.7 %, 3.0- 8.2 μg·m-3 in large-scale NOx-limited grids. The sensitivity-oriented regional control avoided O3 rebound and achieved the greatest decline of 3.4 %- 5.0 %, 5.7- 8.4 μg·m-3 in VOC-limited grids; additionally, time-refined dynamic aggressive NOx control decreased peak O3 by an extra 1.2- 6 μg·m-3, both of which facilitate the regulation for the forecasting O3 episodes. These findings suggest that in heavily polluted environments, the enhancement of O3 regulation benefits requires meticulous, coordinated, and dynamic NOx and VOC controls spanning the entire region based on high-resolution analysis of heterogeneous O3-NOx-VOC sensitivity. Furthermore, emission reduction gains should be more reasonably reflected through increasing in-situ observations covering multi-sensitivity regions.

Importance of secondary decomposition in the accurate prediction of daily-scale ozone pollution by machine learning

Machine learning (ML) models have been proven as a reliable tool in predicting ambient pollution concentrations at various places in the world. However, their performance in predicting the maximum daily 8-h averaged ozone (MDA8 O3), the metric often used for O3 pollution assessment and management, is relatively poorer. This is largely resulted from more irregular data fluctuations of the MDA8 O3 levels governed collectively by the synoptic condition, local photochemistry, and long-range transport. In order to improve the prediction accuracy of MDA8 O3, this study developed a secondary decomposition ML model framework which coupled the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) as the primary decomposition, the variational mode decomposition (VMD) as secondary decomposition, and the gate recurrent unit (GRU) ML model. By applying this secondary decomposition model framework on MDA8 O3 prediction for the first time, we showed that the prediction accuracy of MDA8 O3 is largely improved from R2 of 0.46 and RMSE of 30.4 μg/m3 for GRU without decomposition to R2 of 0.91 and RMSE of 12.6 μg/m3 over the Pearl River Delta of China. We also found that the prediction accuracy rate of O3 pollution non-attainments, an essential indicator for initiating contingency O3 pollution control, improved greatly from 14.9 % for GRU without decomposition to 72.5 %. The performance of O3 pollution non-attainment prediction is relatively higher in southwestern PRD, which is mainly due to greater number and severity of O3 non-attainments in southwestern cities located downwind of the emission hotspot area at central PRD. This study underscored the importance of secondary decomposition in accurately predicting daily-scale O3 concentration and non-attainments over the PRD, which can be extended to other photochemically active region worldwide to improve their O3 prediction accuracy and assist in O3 contingency control.

Assessing the Foodshed and Food Self-Sufficiency of the Pearl River Delta Megacity Region in China

Food self-sufficiency has long been regarded as essential for understanding and managing urban and regional food systems; however, few studies have examined the food self-sufficiency of megacity regions within a comprehensive framework that distinguishes different types of agricultural land (i.e., arable land, horticultural landscapes, and waters). To fill these gaps, we took the Pearl River Delta as a case study and quantified the foodsheds of different types of agricultural land by calculating the land footprint of food consumption. On this basis, food self-sufficiency is defined as the ratio of available and required agricultural area for regional food demand. The results indicated that the self-sufficiency level provided by the arable land in the Pearl River Delta is low and cannot realize self-sufficiency at the regional and urban levels. The horticultural landscapes can provide self-sufficiency at the regional level, whereas the regions with water cannot, as their foodsheds extend over the boundary of the Pearl River Delta. For arable land, establishing a localized regional food system requires expanding the foodshed size. These findings provide evidence that megacity regions may face increasing difficulties in achieving self-sufficiency in the near future. This research can improve policymakers' understanding of the sustainability and resilience of regional food systems in megacity regions.

Key factors influencing pollution of heavy metals and phenolic compounds in mangrove sediments, South China

Concentrations of heavy metals (HMs) and phenolic compounds with factors which potentially affected their spatial distribution were investigated in mangrove sediments, South China. Compared to Qi'ao, Futian sediments exhibited higher levels of Pb and nonylphenol (NP), but lower levels of Co and Ni. Seasonal variation showed higher concentrations of Pb, Cr, Co, NP and bisphenol A (BPA), while lower concentration of methylparaben (MP) in wet than dry season. Contaminant levels in sediments collected at different tidal heights showed insignificant variations, except for Zn and NP. MP was found negatively correlated with nearly all HMs and BPA, whereas the latter exhibited positive correlations with each other. Sedimentary total carbon, total nitrogen, C/N and N/P ratios were screened as the most influential factors affecting the distribution of these contaminants. Additionally, both salinity and total phosphate exhibited positive, while both pH and sedimentary particle size registered negative correlation, with one or more contaminants.

Distribution characteristics of photoinitiators and their flux estimation from the Pearl River Delta to the coastal waters of the South China Sea

Photoinitiators (PIs) are widely used in industrial polymerization processes. It has been reported that PIs are ubiquitous in indoor environments and that humans are exposed to PIs, but the occurrence of PIs in natural environments are rarely known. In the present study, 25 PIs, including 9 benzophenones (BZPs), 8 amine co-initiators (ACIs), 4 thioxanthones (TXs) and 4 phosphine oxides (POs), were analyzed in water and sediment samples collected from eight riverine outlets of the Pearl River Delta (PRD). Eighteen, 14, and 14 of the 25 target PIs were detected in water, suspended particulate matter (SPM) and sediment samples, respectively. The total concentrations of PIs in water, SPM, and sediment were in the ranges of 2.88‒96.1 ng/L, 9.25‒923 ng/g dry weight (dw), and 3.79‒56.9 ng/g dw, with geometric mean concentration (GM) of 10.8 ng/L, 48.6 ng/g dw, and 17.1 ng/g dw, respectively. A significant linear regression was observed between the log partitioning coefficients (K_d) values of PIs and their log octanol water partition coefficient (K_ow) values (R² = 0.535, p < 0.05). The annual riverine input of PIs to the coastal waters of the South China Sea via eight main outlets of the PRD was estimated to be 4.12 × 10³ kg/year, and the ∑BZPs, ∑ACIs, ∑TXs and ∑POs contributed to 1.96 × 10³, 1.24 × 10³, 89.6 and 830 kg/year, respectively. This is the first report of a systematic description of the occurrence characteristics of PIs exposure in water, SPM, and sediment. The environmental fate and risks of PIs in aquatic environments need further investigations.

Spatio-temporal dynamics and sensitive distance of nighttime light environment in Pearl River Delta Protected Areas, China

Protected areas (PAs) are important barriers to ensure the ecological security of territory. Light pollution is a threat to PAs, which is particularly obvious in the urban agglomeration environment. We used multi-source big data (satellite remote sensing light data, land cover types and points of interest) to quantitatively analyze the temporal and spatial dynamics of nighttime light in the PAs of the Pearl River Delta (PRD) urban agglomeration from 2000 to 2018, the correlation between the night light environment within the PAs and human activity intensity outside, as well as the sensitive distance of the PAs to artificial light interference. The results showed that the total value of nighttime light data of PAs in the PRD increased from 71107 nanoW·cm-2·sr-1 to 127682 nanoW·cm-2·sr-1 from 2000 to 2018, the mean value per pixel increased from 15.3 nanoW·cm-2·sr-1 to 23.7 nanoW·cm-2·sr-1, and the lighted ratio increased from 73.3% to 86.4%, indicating that the nighttime light environment of PAs in the region were facing cumulative deterioration risks and serious challenges. The nighttime light intensity of the PAs in the core area of the PRD was much higher than that in the peripheral areas such as Zhaoqing and Huizhou, whereas the expansion degree of the PAs in the peripheral areas was higher than that in the core area. The nighttime light environment inside the PAs was positively correlated with the intensity of human activities around it. The most sensitive distance of the PAs to the artificial light interference around it was 10 km, and the interference degree tended to be stable after 30 km. We proposed that 0-10 km area outside the boundary of the PAs should be the light control core zone and 10-20 km area as the control buffer zone.

The derivation of soil generic assessment criteria for polychlorinated biphenyls under the agricultural land scenario in Pearl and Yangtze River Delta regions, China

The agricultural soils in China are suffered from serious polychlorinated biphenyls (PCBs) contamination, however, the valid management standards for farmland are absent to efficiently control the health risks of PCBs exposure. This study analyzed the contamination characteristics and main composition of PCBs in agricultural soils of the southeastern China from the published literature over the past 20 years, and derived the regional generic assessment criteria (GAC) using an exposure modelling approach for individual and total PCBs (∑PCBs) via multiple exposure pathways such as ingestion of soil and dust, consumption of vegetables, dermal contact with soil and dust, ingestion of soil attached to vegetables, and inhalation of soil vapour and soil-derived dust outdoors under the agricultural land scenario. It is identified that the averaged ∑PCBs concentration of 80.03 ng g^-1 under the 95 % lower confidence limit with an unacceptable health risk of 4.8 × 10^-6 has significantly exceeded the integrated generic assessment criteria (expressed as GAC_int) of 16.5 ng g^-1. Accordingly, the exposure pathways from the consumption of agricultural produces and indirect ingestion of soil attached to vegetables contributed up to 62 %-88 % of the total exposure, followed by 11 %-33 % of the soil ingestion and 2 %-6 % of dermal contact. The derived GAC_int for ∑PCBs is extremely valuable to effectively assess and manage the PCBs contamination in agricultural soils of China.

Large scale occurrence of aluminium-rich shallow groundwater in the Pearl River Delta after the rapid urbanization: Co-effects of anthropogenic and geogenic factors

Aluminium(Al)-rich (> 0.2 mg/L) groundwater has received more concerns because of its harmful to human beings. Origins of large-scale occurrence on Al-rich groundwater in urbanized areas such as the Pearl River Delta (PRD) are still little known. The current work was conducted to investigate spatial distribution of Al-rich groundwater in the PRD, and to discuss its origins in various aquifers. For that, 265 groundwater samples and 15 river water samples were collected, and 21 hydrochemical parameters including Al were analyzed by using conventional analytical procedures. The results showed that groundwater Al concentrations were up to 22.64 mg/L, and Al-rich groundwater occurred in 15% of the area occupied by the PRD. Al-rich groundwater in the coastal-alluvial aquifer was about 2 times those in alluvial-proluvial and fissured aquifers, whereas the karst aquifer was absent. In the coastal-alluvial aquifer, Al-rich groundwater in the peri-urban area was 2 or more times those in urbanized and agricultural areas, whereas the remaining area was absent. By contrast, in the alluvial-proluvial aquifer, Al-rich groundwater in the remaining area was 1.5-3.5 times that in other areas; in the fissured aquifer, the distribution of Al-rich groundwater was independent of land-use types. The infiltration of wastewater from township enterprises was main anthropogenic source for Al-rich groundwater in urbanized and peri-urban areas, whereas irrigation of Al-rich river water was the main one in the agricultural area. Naturally dissolution of Al-rich minerals in soils/rocks, triggered by both of pH decrease resulted from nitrification of contaminated ammonium (e.g., sewage leakage, the use of nitrogen fertilizer) and acid deposition, was the main geogenic source for Al-rich groundwater in the PRD. The contribution of anthropogenic sources to Al-rich groundwater in the coastal-alluvial aquifer was more than that in alluvial-proluvial and fissured aquifers, whereas the contribution of geogenic sources was opposite. In conclusion, the discharge of township enterprises wastewater and ammonium-rich sewage, the emission of nitrogen-containing gas, and the use of nitrogen fertilizer should be preferentially limited to decrease the occurrence of Al-rich groundwater in urbanized areas such as the PRD.

Linking Ecosystem Service Supply and Demand to Evaluate the Ecological Security in the Pearl River Delta Based on the Pressure-State-Response Model

The increase in population and economic development has made environmental issues more serious and threatens regional ecological security and sustainable development. Currently, most indicators in the related research field of ecological security tend to be socio-economic and neglect depicting the state of the ecosystems. This study, therefore, assessed the ecological security by constructing the evaluation index system embedded in the ecosystem service supply and demand based on the pressure-state-response model and identified the key obstacles to ecological security in the Pearl River Delta from 1990 to 2015. Our results showed that soil retention, carbon sequestration, and water yield increased with fluctuation except for grain production and habitat quality. The grain demand, carbon emission, and water demand increased sharply by 10.1%, 769.4%, and 17.5%, respectively. The ecosystem service supply areas were mainly located in the low hills, while the demand regions were mainly in the low plain areas. The ecological security index's decline in vitality was caused by the decrease in the pressure index, indicating that the ecological security showed an inevitable deterioration and increased pressure on the ecosystem. During the study period, the source of the five key obstacle factors changed from the state layer and response layer to the pressure layer. The accumulative degree of the five top obstacle factors was above 45%. Therefore, governments should grasp the key indicators to improve ecological security as this study provides the theoretical basis and scientific information for sustainable development.

Anthropogenic impact on long-term riverine CODMn, BOD, and nutrient flux variation in the Pearl River Delta

In the Pearl River Delta (PRD), population growth and economic development have steadily increased the anthropogenic nutrient discharge into coastal waters. In this study, we employed the observed concentration and model reproduced runoff to quantify the interannual variation and the long-term (1985-2021) trends in riverine chemical oxygen demand (COD_Mn), biochemical oxygen demand (BOD), and nutrient fluxes. The annual COD_Mn and BOD fluxes increased slightly between 1999 and 2021. In comparison, the mean annual dissolved inorganic nitrogen (DIN) fluxes of the four eastern outlets increased significantly from 2.05 × 10⁵ t/a in 1985-1995 to 3.11 × 10⁵ t/a in 1999-2011 and then to 3.91 × 10⁵ t/a in 2014-2021. The outlets with the largest contributions to the COD_Mn, BOD, and DIN fluxes were Humen and Modaomen, which are both located near large cities. By calculating the COD_Mn fluxes upstream of the PRD, we found that the COD_Mn fluxes from downstream in the PRD increased faster than the fluxes from upstream. It follows that the increase in COD_Mn at outlets was mostly driven by the contributions of downstream major cities. In addition, the proportion of ammonia nitrogen flux in the DIN flux decreased from over 50 % to under 10 % at most outlets. This indicates that the toxicity of DIN fluxes has been mitigated. The DIN fluxes also showed a positive correlation with surface chlorophyll a and a negative correlation with bottom dissolved oxygen outside the Pearl River Estuary (PRE). This implies that the changes in phytoplankton growth and oxygen levels outside the PRE are closely linked to the variation in river-delivered nutrients, and the increasing riverine nutrient input may result in the expansion of intensified low-oxygen conditions outside the PRE.

An analysis of energy efficiency of the Pearl River Delta of China based on super-efficiency SBM model and Malmquist index

With the rapid growth rate of China's economy, the extensive pattern of economic growth of "high energy consumption and low output" has magnified the constraints of energy issues on China's economic development and environmental protection, which highlights the importance of improving energy efficiency. As one of the three major economic zones in China, the Pearl River Delta region also faces high energy consumption and pollution emissions while developing at a high speed. Hence, improving the energy efficiency of the Pearl River Delta region is needed, as it not only is conducive to driving its development of the surrounding green economy, but also promotes the subsequent sustainable economic development. However, there are few literatures on the calculation and analysis of energy efficiency in the Pearl River Delta, and lacking a systematic analysis of input-output index system of energy efficiency measurement. Therefore, this paper calculates the energy efficiencies and the Malmquist indexes based on the panel data of the nine cities in the Pearl River Delta from 2005 to 2019 through super-efficiency SBM model and Malmquist index method by using MAXDEA and MATLAB software. The result illustrates that all regions in the Pearl River Delta except Guangzhou and Shenzhen show obvious energy inefficiency, which is mainly caused by the imbalance between technical efficiency and scale efficiency. Based on the calculation results, this paper gives some relevant suggestions for the further approach of energy reform in the Pearl River Delta according to the calculation results.

Assessing natural background levels of geogenic contaminants in groundwater of an urbanized delta through removal of groundwaters impacted by anthropogenic inputs: New insights into driving factors

Knowledge on driving forces controlling natural background levels (NBLs) of geogenic contaminants (GCs) in groundwater of coastal urbanized areas are still limited because of complex hydrogeological conditions and anthropogenic activities. This study assesses NBLs of two GCs including arsenic (As) and manganese (Mn) in four groundwater units of the Pearl River Delta (PRD) with large scale urbanization by using a preselection method composed of the chloride/bromide mass ratio versus chloride concentration and the oxidation capacity with the combination of Grubbs' test. More importantly, driving factors controlling NBLs of As/Mn in groundwater of the PRD are discussed. Results showed that groundwater As/Mn concentrations in residual datasets were independent of land-use types, while those in original datasets in different land-use types were distinct because of various human activities, indicating that the used preselection method in this study is valid for NBLs-As/Mn assessment in groundwater of the PRD. NBL-As in coastal-alluvial aquifers was >6 times that in other groundwater units. NBL-Mn in coastal-alluvial aquifers was 1.4 times that in alluvial-proluvial aquifers, and both were >4 times that in other two groundwater units. High NBLs-As/Mn in coastal-alluvial aquifers is mainly attributed to reduction of FeMn oxyhydr(oxides) induced by mineralization of organic matter in Quaternary sediments. Elevated pH also contributes higher NBL-As in coastal-alluvial aquifers. By contrast, higher NBL-Mn in alluvial-proluvial aquifers than in other two groundwater units mainly ascribes to reduction of FeMn oxyhydr(oxides) in Quaternary sediments triggered by irrigation of reducing river waters. In addition, more occurrence of As/Mn-rich sediments and the infiltration of As/Mn-rich river water are also important factors for high NBLs-As/Mn in coastal-alluvial aquifers. This study shows that revealing natural driving factors of GCs-rich groundwater in coastal urbanized areas on the basis of identification of contaminated groundwaters via the used preselection methods is acceptable.

Refined Carbon Emission Measurement Based on NPP-VIIRS Nighttime Light Data: A Case Study of the Pearl River Delta Region, China

The accurate measurement of CO₂ emissions is helpful for realizing the goals of "carbon neutralization" and "carbon peak". However, most current research on CO₂ emission measurements utilizes the traditional energy balance coefficient and top-down methods. The data granularity is large, and most studies are concentrated at the national, provincial, municipal, or district/county administrative unit scale. As an important part of the Guangdong-Hong Kong-Macao Greater Bay Area of China, the Pearl River Delta region has good nighttime light vitality and faces huge carbon emission pressure. Using the Pearl River Delta as the research area, this study constructed an optimized pixel-scale regression model based on NPP-VIIRS (The Visible Infrared Imaging Radiometer Suite on the Suomi National Polar-Orbiting Partnership spacecraft) nighttime light data and CO₂ emissions data at the district and county levels for 2017. In addition, the spatial pattern of CO₂ emissions in the Pearl River Delta was analyzed based on the predicted CO₂ emission status. The results showed that the spatial pattern of CO₂ emissions in the Pearl River Delta had the distinct characteristics of the "center-edge" effect, the spatial spillover effect, and high-value aggregation, which should be considered when making related social or public decisions.

Occurrence and distribution of organic corrosion inhibitors (OCIs) in riverine sediments from the Pearl River Delta, South China

Although soluble organic corrosion inhibitors (OCIs) have been observed globally in surface water, data on their exposures in sediments are still scarce. In this study, a comprehensive investigation on spatial variations and potential sources of OCIs were conducted in riverine sediments from the Pearl River Delta (PRD), one of the most developed and urbanized areas in China. Of 12 OCIs, 7 were detected with the total concentrations ranging from 81.8 to 401.2 ng/g. When the results were compared with those of the water phase, OCIs in the riverine sediments exhibited relatively low concentrations, which was likely due to their low K_ow, and they were not expected to be adsorbed onto sediments. The spatial variation of OCIs suggested that the discharge of sewage treatment plants (STPs) effluent could be a major source of OCIs in the PRD region. The total concentrations of OCIs had a significant positive correlation with total organic carbon (TOC) contents, suggesting that they have similar sources. This study strongly indicated that the high consumption of OCIs have led to their wide exposure in different environments in the PRD region and additional ecotoxicological data are needed to evaluate their potential risks in riverine sediments in the future.

A cold front induced co-occurrence of O3 and PM2.5 pollution in a Pearl River Delta city: Temporal variation, vertical structure, and mechanism

In this study, the spatiotemporal variabilities and characteristics of ozone (O₃) and fine particulate matter (PM_2.5) were reconstructed, and the interaction between meteorological conditions and the co-occurrence of O₃ and PM_2.5 in Zhuhai, a city in the Pearl River Delta (China), was analysed. The vertical distributions of lower tropospheric O₃, aerosol extinction coefficient, and wind velocity were measured using a ground-based LiDAR system. The diurnal variations in air pollutant concentrations and meteorological conditions at ground level were examined from 28 November to December 8, 2020 considering the weather conditions in Zhuhai. Heavy pollution episodes with increased concentrations of O₃ and PM_2.5 were observed from 6 to 7 December after a period of cold air invasion. The maximum hourly average concentrations of O₃ and PM_2.5 at the ground level reached up to 190 μg/m³, 98 μg/m³, respectively. The horizontal wind speed rapidly decreased to less than 2 m/s during the heavy pollution episodes driven by O₃ and PM_2.5, whereas the vertical wind velocity was dominated by the downdraught. When the large-scale synoptic winds were weak, a strengthening sea breeze in the afternoon could promote the landward propagation of warm marine air masses, and a lower surface wind speed was driven by the convergence of cold air from the north and warm air from the south. In turn, this increased the residence time of air pollutants and promoted their conversion to secondary pollutants. Regarding the pollution sources, the results indicated that the Pearl River Estuary represented a 'pool' of O₃ and PM_2.5 pollution. In addition, the contribution of regional pollutant transport could not be ignored when considering the accumulative increase in air pollution. Overall, the relatively weak synoptic winds, low mixing height, and high generation of pollution around Zhuhai collectively resulted in high concentrations of O₃ and PM_2.5.

Identification of close relationship between large-scale circulation patterns and ozone-precursor sensitivity in the Pearl River Delta, China

To curb the continuous deterioration of ozone (O₃) pollution in China, identifying the O₃-precursor sensitivity (OPS) and its driving factors is a prerequisite for formulating effective O₃ pollution control measures. Traditional OPS identification methods have limitations in terms of spatiotemporal representation and timeliness; therefore, they are not appropriate for making OPS forecasts for O₃ contingency control. OPS is not only influenced by local precursor emissions but is also closely related to meteorological conditions governed by large-scale circulation (LSC). In this study, a localized three-dimensional numerical modeling system was used to investigate the relationship between LSC and OPS in the Pearl River Delta (PRD) of China during September 2017, a month with continuous O₃ pollution. Our results highlighted that there was a close relationship between LSC and OPS over the PRD, and the four dominant LSC patterns corresponded well to the NO_x-limited, NO_x-limited, VOC-limited, and transitional regimes, respectively. The clear linkage between LSC and OPS was mainly driven by the spatial heterogeneity of NO_x and VOC emissions within and beyond the PRD along the prevailing winds under different LSC patterns. A conceptual model was developed to highlight the intrinsic causality between the LSC and OPS. Because current technology can accurately forecast LSC 48-72 h in advance, the LSC-based OPS forecast method provided us with a novel approach to guide contingency control and management measures to reduce peak O₃ at a regional scale.

[Variety of the Composition and Sources of VOCs During the Spring Festival and Epidemic Prevention in the Pearl River Delta]

Volatile organic compounds (VOCs) are the key precursors of the ozone (O₃) formation processes in the troposphere and are important control objects for the coordinated governance of O₃ and PM_2.5. The Spring Festival of 2020 was affected by the novel coronavirus (COVID-19) pneumonia epidemic:companies stopped work and production, and traffic was restricted, providing scientific experimentation opportunities for pollutant emission reduction research. This study analyzed the variety of the composition, chemical reaction activity, and sources of VOCs in the Pearl River Delta during the Spring Festival and the epidemic control period, using real-time online monitoring data of VOCs obtained at four sites(Guangzhou, Dongguan, Zhongshan, and Duanfen)in the Pearl River Delta from January 1, 2020 to February 29, 2020. The results showed that during the Spring Festival and the epidemic control period, the average of φ (VOCs) in the Pearl River Delta was 15.89×10^-9, and the maximum hourly average concentration was 45.43×10^-9, values that were 44% and 60% lower, respectively, than those before the Spring Festival holiday. Among the VOCs component concentration decreases, the aromatic hydrocarbon component decreased the most, and the decrease in the urban area of the Pearl River Delta (74%) was significantly greater than that in the suburban area (56%). As a result, the contribution rate of aromatic hydrocarbons to the total VOCs was reduced to less than 10%. The analysis of the·OH reaction activity of VOCs(L_·OH)and ozone formation potential(OFP)showed that the L_·OH and OFP of VOCs decreased significantly in the Pearl River Delta during the Spring Festival and the epidemic control period. Compared with those before the Spring Festival holiday, the total L_·OH and total OFP decreased by an average of 60% and 63% in the urban area of the Pearl River Delta, respectively. Additionally, the atmospheric oxidation had also been significantly reduced, which showed a 28% decrease in ρ(O_x). The ratio of toluene/benzene showed that the influence of industrial sources had almost disappeared during the Spring Festival and the epidemic control period, and the total points of the representative components of industrial-related solvent-use sources such as toluene, ethylbenzene, and m/p-xylene dropped by 72% to 91%. The results of this study suggest that solvent-use sources and vehicle exhaust emission sources are the current sources of VOCs that need to be paid attention to in the prevention and control of O₃ pollution in the Pearl River Delta region, and the impact of petrochemical sources cannot be ignored in the work of further reducing the background concentration of O₃.

Heavy metals and Pb isotopes in a marine sediment core record environmental changes and anthropogenic activities in the Pearl River Delta over a century

Heavy metal accumulation in marine sediments is associated with changes in both the natural environment and human activities. This study used heavy metals and Pb isotopes in a precisely dated (by ²¹⁰Pb and ¹³⁷Cs) sediment core from the Macao Sea to reconstruct the historical changes in anthropogenic activities and the environment in the western Pearl River Estuary (PRE). The distribution of heavy metals in the sediment core could be divided into four stages (pre-1950, 1950-1976, 1976-2000, and post-2000), which corresponded to the changes in anthropogenic activities and environment of the Pearl River Delta during the past 100 years. The contribution of anthropogenic metals (Pb and Zn) in the sediments increased gradually over time. However, the concentrations, enrichment factors, and fluxes of heavy metals in the sediments all displayed a downward trend since 2010, revealing a decline in metal pollutant input due to strict emission reduction policies implemented in the last decade. The Pb isotopes in the sediments showed a similar trajectory to the heavy metals, reflecting the changes in Pb sources in the sediments at different stages. Based on a binary Pb isotope mixing model, the calculated proportions of anthropogenic and natural Pb in the sediments were 0-50.9% (mean 15.9%) and 49.1-100% (mean 84.1%), respectively, suggesting that the Pb in the PRE sediments is mainly controlled by natural sources.

Assessment of groundwater sustainable development considering geo-environment stability and ecological environment: a case study in the Pearl River Delta, China

Groundwater resources have an important impact on the geo-environment and ecological environment. The exploitation of groundwater resources may induce geo-environmental issues and has a negative impact on the ecological environment. The assessment of groundwater sustainable development can provide reasonable suggestions for the management of groundwater resources in coastal cities. In this study, an assessment method for groundwater sustainable development based on the resource supply function, geo-environment stability function, and ecological environment function was provided. Considering the groundwater quantity and quality; the vulnerability of karst collapse, land subsidence, and seawater intrusion; and the distribution of groundwater-dependent ecosystems (GDEs) and soil erosion, the groundwater in the Pearl River Delta was divided into concentrated groundwater supply area (21.97%) and decentralized groundwater supply area (48.22%), ecological protection area (20.77%), vulnerable geo-environment area (8.94%), and unsuitable to exploit groundwater area (0.10%). ROC curve and single-indicator sensitivity analysis were applied in the assessment of geo-environment vulnerability, and the results showed that the VW-AHP model effectively adjusted the weights of the indicators so that the assessment results were more in line with the actual situation in the Pearl River Delta, and the accuracy of the VW-AHP model was higher than that of the AHP model. This study provides a scientific basis for groundwater management in the Pearl River Delta and an example for the assessment of groundwater sustainable development in coastal cities.

Spatiotemporal distribution, source apportionment and risk assessment of typical hormones and phenolic endocrine disrupting chemicals in environmental and biological samples from the mariculture areas in the Pearl River Delta, China

The present work studied the levels, distribution, potential sources, ecological and human health risks of typical hormones and phenolic endocrine disrupting chemicals (EDCs) in the mariculture areas of the Pearl River Delta (PRD), China. The environmental levels of 11 hormones (6 estrogens, 4 progestogens, and 1 androgen) and 2 phenolic EDCs were quantified in various matrices including water, sediment, cultured fish and shellfish. Ultrahigh performance liquid chromatography-triple quadrupole tandem mass spectrometry analyses showed that all the 13 target compounds were detected in biotic samples, whereas 10 were detected in water and sediment, respectively. The total concentrations ranged from 35.06-364.53 ng/L in water and 6.31-29.30 ng/g in sediment, respectively. The average contaminant levels in shellfish (Ostrea gigas, Mytilus edulis and Mimachlamys nobilis) were significantly higher than those in fish (Culter alburnus, Ephippus orbis and Ephippus orbis). Source apportionment revealed that the pollution of hormones and phenolic EDCs in PRD mariculture areas was resulted from the combination of coastal anthropogenic discharges and mariculture activities. The hazard quotient values of the contaminants were all less than 1, implying no immediate human health risk. Overall, the present study is of great significance for scientific mariculture management, land-based pollution control, ecosystem protection, and safeguarding human health.

Accelerated toluene degradation over forests around megacities in southern China

Toluene is a typical anthropogenic pollutant that has profound impacts on air quality, climate change, and human health, but its sources and sinks over forests surrounding megacities remain unclear. The Nanling Mountains (NM) is a large subtropical forest and is adjacent to the Pearl River Delta (PRD) region, a well-known hotspot for toluene emissions in southern China. However, unexpectedly low toluene concentrations (0.16 ± 0.20 ppbv) were observed at a mountaintop site in NM during a typical photochemical period. A backward trajectory analysis categorized air masses received at the site into three groups, namely, air masses from the PRD, those from central China, and from clean areas. The results revealed more abundant toluene and its key oxidation products, for example, benzaldehyde in air masses mixed with urban plumes from the PRD. Furthermore, a more than three times faster degradation rate of toluene was found in this category of air masses, indicating more photochemical consumption in NM under PRD outflow disturbance. Compared to the categorized clean and central China plumes, the simulated OH peak level in the PRD plumes (15.8 ± 2.2 × 106 molecule cm-3) increased by approximately 30% and 55%, respectively, and was significantly higher than the reported values at other background sites worldwide. The degradation of toluene in the PRD plumes was most likely accelerated by increased atmospheric oxidative capacity, which was supported by isoprene ozonolysis reactions. Our results indicate that receptor forests around megacities are not only highly polluted by urban plumes, but also play key roles in environmental safety by accelerating the degradation rate of anthropogenic pollutants.

[Geochemical Characteristics and Driving Factors of High-Iodine Groundwater in Rapidly Urbanized Delta Areas: A Case Study of the Pearl River Delta]

The source of iodine in the groundwater of coastal urbanization areas is complex, and high-iodine groundwater is a potential threat to the safety of drinking water. Based on this, this study took the Pearl River Delta, which is developing rapidly in urbanization, as the research area. Additionally, the occurrence characteristics and driving factors of iodide in shallow groundwater of different aquifers and different urbanization levels in the Pearl River Delta were studied using mathematical statistics, principal component analysis, and other methods. The results showed that the concentration of iodide in the shallow groundwater was 2.34 mg·L^-1 and undetected in the form of I^-. Among 1567 groundwater samples in the study area, there were 120 groups of groundwater with high iodine content greater than 0.1 mg·L^-1, accounting for 7.7%. Among them, 84 and 36 groups were detected in shallow porous and shallow fissure high-iodine groundwater, respectively, whereas no high-iodine groundwater was detected in the karst aquifer. The proportion of high-iodine groundwater was 8.0% in the shallow porous aquifer and 7.5% in the shallow fissure aquifer. Both the porous aquifer and the fissured aquifer with high iodine content were mainly distributed in the urbanized areas, the proportion of which was more than three times that of the non-urbanized areas. The chemical types of the high-iodine groundwater were mainly HCO₃·Cl-Ca·Na and Cl-Na type water, which have the characteristics of high pH and low redox potential. The reduction and dissolution of iodine-containing Fe/Mn (oxygen) hydroxides and the decomposition of iodine-rich organics in sediments may be the main sources of high-iodine groundwater in the shallow porous aquifers of the Pearl River Delta Plain. The degradation and urbanization of organic matter in carbonate-rich rocks is accompanied by the leakage of reducing sewage, which may be the main source of high-iodine groundwater in shallow fissured aquifers. The neutral to weakly alkaline reduction environment with rich organic matter was the main cause of high-iodine groundwater in the Delta Plain area. Weathering, leaching, cation exchange, and sea-land interactions are the main hydrogeochemical processes in the evolution of high-iodine groundwater in the Pearl River Delta.

Probabilistic storm surge hazard using a steady-state surge model for the Pearl River Delta Region, China

Storm surges caused by tropical cyclones (TCs) are one of the costliest threats to coastal communities in southern China. Numerical surge models remain computationally challenging when used to simulate the large number of TC events required for probabilistic hazard assessments at regional scale. The present study demonstrates the applicability of a simple 1D steady-state storm surge representation for such regional scale hazard assessment. The surge setups from wind shear stress and barometric pressure difference are calculated with the meteorological forcing derived from parametric wind models and TC track information. Being computationally efficient, the surge model results do not require further empirical coefficients derived from correlation against observed data as compared to the previous statistical and semi-empirical surge estimations. Using the Pearl River Delta (PRD) region in China as a case study, the root-mean-square errors between the estimated and reported peak storm surges along the PRD coastline are 0.37 m and 0.45 m using two different TC best track inputs, respectively, covering 118 observed surge records from 39 historical TC events. Probabilistic surge hazard maps are further developed for the PRD coastline using the two TC best track datasets covering 1951-2018 as inputs. The mean surge heights along the coastline are in the range of 1.5-3.2 m and 2.0-3.5 m under 100-year and 200-year return periods, respectively. Areas in the west and near the estuary outlet are more prone to higher surge levels due to more frequent TCs affecting the areas historically. Differences in TC characteristics exist between the two best track datasets, which gives rise to localised difference in surge heights along the PRD coastline. The maximum differences in the 100-year and 200-year return period surge levels from the two best track datasets are 0.51 m and 0.64 m, respectively.

Novel Insights into Dissolved Organic Matter Processing Pathways in a Coastal Confined Aquifer System with the Highest Known Concentration of Geogenic Ammonium

High levels of geogenic ammonium in groundwater is a highly neglected nitrogen pool in coastal aquatic systems. Although organic matter (OM) mineralization is known to significantly influence geogenic ammonium enrichment, the detailed mechanism underlying ammonium enrichment based on dissolved organic matter (DOM) characterization in coastal aquifer systems remains unclear. In this study, we characterized the optical and molecular signatures of DOM coupled with hydrogeochemistry and multiple isotopes (H/O/C/N) to elucidate in detail the mechanisms underlying the anomalously high ammonium in the coastal confined aquifer system of the Pearl River Delta, which exhibits the highest reported geogenic ammonium concentration in groundwater on the Earth. We identified three DOM fluorescent components, a marine humic-like component (C1) and two other humic-like components (C2 and C3). The autochthonous OM was first processed to the C1 component, which was further transformed to C2 and C3 components. In terms of molecular classes, the processing pathway from bacterial- or algal-derived OM to aliphatic compounds and highly unsaturated-low O compounds was identified, and highly unsaturated-low O compounds were accumulated as the main products. Compounds containing two or three N atoms were processed, and compounds with one N atom gradually accumulated, which was further degraded into CHO compounds. The ammonium (up to 179 mg/L as N) was gradually enriched due to the decomposition of CHO+3N to CHO+2N, CHO+1N, and CHO compounds. Owing to the longer residence time and less frequent fresh water flushing, the produced ammonium was retained in the aquifer as a "long-term result". The contrasting DOM characteristics, together with the differing depositional and hydrogeological conditions, give rise to the higher levels of geogenic ammonium in coastal confined aquifer systems compared with inland alluvial-lacustrine confined aquifer systems. To our knowledge, this is the first study to characterize DOM and its relationship with geogenic ammonium in coastal aquifer systems.

[Geochemical Characteristics and Driving Factors of NO3-Type Groundwater in the Rapidly Urbanizing Pearl River Delta]

In response to rapid economic development, nitrate pollution of groundwater is becoming a serious issue in many parts of China. Urbanization and industrialization are the main drivers of NO₃-type groundwater expansion. Focusing on the Pearl River Delta, the occurrence and driving factors of shallow nitrate groundwater are discussed. Overall, groundwater nitrate concentrations are generally high in this region. Of 1538 groundwater samples, 5.7% had nitrate concentrations higher than the groundwater quality standard(88.6 mg·L^-1) and 18.5% were classified as NO₃-type waters, which are mainly distributed in the hilly and piedmont areas. Guangzhou, Dongguan, Foshan, Zhuhai and other areas show high total dissolved solid(TDS)-concentration NO₃-type waters, which are affected by urbanization and industrialization. In comparison, low-TDS NO₃-type waters are distributed in the hilly and valley areas. In the Xijiang and Dongjiang plains, the TDS concentrations on groundwater increased significantly due to inputs of industrial wastewater and saline seawater. The NO₃^- concentration in the groundwater in this area exceeded the class III water standard but did not change the hydrochemical type classification. However, industrialization has led to the frequent appearance of SO₄-type water in this area. The NO₃-type water occurs in acidic or weakly acidic environments, typically characterized by low TDS and total hardness concentrations, and high Cl^-, SO₄^2-, and K⁺ concentrations. The formation of NO₃-type water is mainly affected by domestic sewage, industrial wastewater, agricultural nitrogen fertilizer, septic tank outflows, and landfill leachate leakage. Generally, the pollution loads of high-TDS NO₃-type waters are higher than low-TDS NO₃-type waters. The delineation of NO₃-type waters, especially the low-TDS type, is helpful for identifying groundwaters posing greater risks for human activities, and those with low nitrate concentrations but potential pollution risk, which is of great significance in the prevention and control of groundwater pollution.

[Pollution Characteristics and Source Analysis of Atmospheric VOCs in the Coastal Background of the Pearl River Delta]

As an important precursor of ozone, volatile organic compounds (VOCs) have attracted much attention. This study analyzed the temporal variation and composition of atmospheric VOCs in the coastal background of the Pearl River Delta, using real-time online monitoring data of VOCs obtained at the Yangmeikeng Ecological Environment Monitoring Station from August 2019 to July 2020. The major sources of VOCs were identified using a receptor model based on the PMF (positive matrix factorization) and HYSPLIT (hybrid single particle Lagrangian integrated trajectory) models. The results showed that the annual mean concentration of anthropogenic VOCs in the coastal background area of the Pearl River Delta was 9.30×10^-9(volume fraction). There was obvious seasonal variation of VOCs in this area, with higher values in autumn and winter and lower values in summer. The coastal background area of the Pearl River Delta exhibited a different diurnal variation pattern to that of cities and other backgrounds. While the peak of VOCs concentration mainly occurred in the morning, from 10:00 to 11:00, concentration remained at a low level during the early morning and after 15:00. Ethylene, propylene, toluene, isopentane, isoprene, m/p-xylene, n-butane, and acetylene were the key species that affected the chemical composition of VOCs. The air masses affecting the coastal background area of the Pearl River Delta were mainly short-distance air masses from elsewhere in the province (25%), ocean air masses (27%), coastal air masses (31%), and inland air masses outside the province (17%). Among them, the average concentration of VOCs was lowest under the influence of ocean air masses, which is mainly affected by the mixed source of ship emissions and aging VOCs, gasoline volatilization, and vehicle emissions. In comparison, the concentration level of VOCs increased by 70.1% to 148.8% under the influence of other air masses. The transmission effects of industrial sources, LNG and LPG volatiles, and petrochemical sources were more prominent. Generally, the atmosphere of coastal background areas was severely affected by anthropogenic pollution, especially by air pollution masses transported from the land, while the impact of pollution by ships near shore and tourist traffic cannot be ignored.

Occurrence, source identification, and ecological risk assessment of polycyclic aromatic hydrocarbons in sediments of the Pearl River Delta, China

The pollution characteristics, sources, and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in surface sediment samples from the river networks and outlets of the Pearl River Delta (PRD) were investigated. The total PAH concentrations were in the range of 69.1-1297 ng g^-1 in river networks and 56.6-617 ng g^-1 in river outlets. The results of source identification showed that PAHs in sediments were mainly derived from combined sources of coke tar and liquid fossil fuel combustion, coal/wood combustion, and petroleum contamination. The ecological risks of PAHs were evaluated based on sediment quality guidelines (SQG), mean probable effects levels quotient values (PEL-Q), and the toxicity equivalence factor (TEQ_BaP) method. The ecological risks of PAHs in sediments were at moderate levels in the Pearl River Delta. Although no high risk was found, regular and continuous monitoring of PAHs in sediments needs to be performed.

DDT, Chlordane, and Hexachlorobenzene in the Air of the Pearl River Delta Revisited: A Tale of Source, History, and Monsoon

Although organochlorine pesticides (OCPs) have been banned for more than three decades, their concentrations have only decreased gradually. This may be largely attributable to their environmental persistence, illegal application, and exemption usage. This study assessed the historic and current regional context for dichlorodiphenyltrichloroethane (DDT), chlordane, and hexachlorobenzene (HCB), which were added to the Stockholm Convention in 2001. An air sampling campaign was carried out in 2018 in nine cities of the Pearl River Delta (PRD), where the historical OCP application was the most intensive in China. Different seasonalities were observed: DDT exhibited higher concentrations in summer than in winter; chlordane showed less seasonal variation, whereas HCB was higher in winter. The unique coupling of summer monsoon with DDT-infused paint usage, winter monsoon with HCB-combustion emission, and local chlordane emission jointly presents a dynamic picture of these OCPs in the PRD air. We used the BETR Global model to back-calculate annual local emissions, which accounted for insignificant contributions to the nationally documented production (<1‰). Local emissions were the main sources of p,p'-DDT and chlordane, while ocean sources were limited (<4%). This study shows that geographic-anthropogenic factors, including source, history, and air circulation pattern, combine to affect the regional fate of OCP compounds.

Insight into the characteristics of carbonaceous aerosols at urban and regional sites in the downwind area of Pearl River Delta region, China

Carbonaceous aerosols (CAs) take up a substantial fraction of fine particle (PM_2.5) in the atmosphere, yet high temporal resolution and seasonal variations of their emission sources and formation mechanisms are still poorly characterized in the regions with strong anthropogenic activities. In this study, the spatiotemporal characteristics of CAs and their subfractions, i.e., organic carbon (OC) and elemental carbon (EC), were studied in one of China's key city clusters, the Pearl River Delta (PRD) region. Results show that the annual mean OC and EC concentrations are 5.89 ± 3.32 μg/m³ and 1.60 ± 1.00 μg/m³ at the urban site, respectively. Such levels are consistently higher than those at the regional site (4.94 ± 3.34 μg/m³ of OC and 1.45 ± 0.82 μg/m³ of EC), suggesting the strong impact of human activities on OC and EC concentration. Moreover, the OC concentration peak sharply appears at 19:00 across all seasons at the urban site due to the direct influence of traffic exhaust and cooking activities. At regional site, OC peaks in fall afternoon due to intensive photochemical reactions derived combustion-related secondary organic carbon (SOC_com) contributions to the downwind PRD region. Correlations between SOC_com and influence factors were found at both regional and urban sites, suggesting that SOC_com formation is more regionally homogenous and mainly originates from the Zhaoqing-Foshan-Jiangmen belt. In addition, there are significantly different formation mechanisms of non-combustion-related secondary organic carbon (SOC_non-com) in the downwind PRD region. This study provides a solid evidence for collaborative efforts in the mitigation of secondary aerosols in the PRD region.

Emission source-based ozone isopleth and isosurface diagrams and their significance in ozone pollution control strategies

In the past decade, ozone (O₃) pollution has been continuously worsening in most developing countries. The accurate identification of the nonlinear relationship between O₃ and its precursors is a prerequisite for formulating effective O₃ control measures. At present, precursor-based O₃ isopleth diagrams are widely used to infer O₃ control strategy at a particular location. However, there is frequently a large gap between the O₃-precursor nonlinearity delineated by the O₃ isopleths and the emission source control measures to reduce O₃ levels. Consequently, we developed an emission source-based O₃ isopleth diagram that directly illustrates the O₃ level changes in response to synergistic control on two types of emission sources using a validated numerical modeling system and the latest regional emission inventory. Isopleths can be further upgraded to isosurfaces when co-control on three types of emission sources is investigated. Using Guangzhou and Foshan as examples, we demonstrate that similar precursor-based O₃ isopleths can be associated with significantly different emission source co-control strategies. In Guangzhou, controlling solvent use emissions was the most effective approach to reduce peak O₃ levels. In Foshan, co-control of on-road mobile, solvent use, and fixed combustion sources with a ratio of 3:1:2 or 3:1:3 was best to effectively reduce the peak O₃ levels below 145 ppbv. This study underscores the importance of using emission source-based O₃ isopleths and isosurface diagrams to guide a precursor emission control strategy that can effectively reduce the peak O₃ levels in a particular area.

Prey decline leads to diet shift in the largest population of Indo-Pacific humpback dolphins?

The Pearl River Delta (PRD) region on the southeast coast of China has long been known as a highly productive fishing ground. Since the late 1980s, fishing pressure in the PRD has been intense, which warrants concerns of potential fishery-related impacts on the food resources and foraging ecology of apex marine predators in this region, such as the Indo-Pacific humpback dolphin (Sousa chinensis). In this study, we examined 54 stomachs with food remains, collected from beached carcasses of humpback dolphins recovered during fifteen years between 2003 and 2017. The 6043 identified prey items represent 62 teleost taxa, primarily small estuarine fish, but also larger reef fish. The dolphins appear to be opportunistic foragers, hunting across the water-column, with preference for shoaling and meaty fishes (e.g. Collichthys lucidus IRI% = 38.6%, Johnius belangerii IRI% = 23.1%, Mugil cephalus IRI% = 14.0%). Our findings suggest a dietary shift in recent years, from primarily demersal (as previously reported) to greater intake of neritic and pelagic fish. Dolphin foraging group size has decreased in recent years, which corresponds with declining size and numbers of prey items retrieved from dolphin stomachs. We suggest that these are indicators of declining food resources. Faced with a shortage of preferred prey, humpback dolphins may have broadened their dietary spectrum to maintain their daily energy intake, while their foraging group size decreased in response to the altered tradeoff between the costs and benefits of group foraging.

Emission Inventories and Particulate Matter Air Quality Modeling over the Pearl River Delta Region

The Pearl River Delta (PRD) region is located on the southeast coast of mainland China and it is an important economic hub. The high levels of particulate matter (PM) in the atmosphere, however, and poor visibility have become a complex environmental problem for the region. Air quality modeling systems are useful to understand the temporal and spatial distribution of air pollution, making use of atmospheric emission data as inputs. Over the years, several atmospheric emission inventories have been developed for the Asia region. The main purpose of this work is to evaluate the performance of the air quality modeling system for simulating PM concentrations over the PRD using three atmospheric emission inventories (i.e., EDGAR, REAS and MIX) during a winter and a summer period. In general, there is a tendency to underestimate PM levels, but results based on the EDGAR emission inventory show slightly better accuracy. However, improvements in the spatial and temporal disaggregation of emissions are still needed to properly represent PRD air quality. This study’s comparison of the three emission inventories’ data, as well as their PM simulating outcomes, generates recommendations for future improvements to atmospheric emission inventories and our understanding of air pollution problems in the PRD region.

Examining the Effects of Land Use on Carbon Emissions: Evidence from Pearl River Delta

Land-use change accounts for a large proportion of the carbon emissions produced each year, especially in highly developed urban agglomerations. In this study, we combined remote sensing data and socioeconomic data to estimate land-use-related carbon emissions, and applied the logarithmic mean Divisia index (LMDI) method to analyze its influencing factors, in the Pearl River Delta (PRD) of China in 1990–2015. The main conclusions are as follows: (1) The total amount of land-use-related carbon emissions increased from 684.84 × 10⁴ t C in 1990 to 11,444.98 × 10⁴ t C in 2015, resulting in a net increase of 10,760.14 × 10⁴ t (16.71 times). (2) Land-use-related carbon emissions presented a “higher in the middle and lower on both sides” spatial distribution. Guangzhou had the highest levels of carbon emissions, and Zhaoqing had the lowest; Shenzhen experienced the greatest net increase, and Jiangmen experienced the least. (3) The land-use-related carbon emissions intensity increased from 4795.76 × 10⁴ Yuan/t C to 12,143.05 × 10⁴ Yuan/t C in 1990–2015, with the greatest increase seen in Huizhou and the lowest in Zhongshan. Differences were also found in the spatial distribution, with higher intensities located in the south, lower intensities in the east and west, and medium intensities in the central region. (4) Land-use change, energy structure, energy efficiency, economic development, and population all contributed to increases in land-use-related carbon emissions. Land-use change, economic development and population made positive contributions, while energy efficiency and energy structure made negative contributions. At last, we put forward several suggestions for promoting low-carbon development, including development of a low-carbon and circular economy, rationally planning land-use structure, promoting reasonable population growth, improving energy efficiency and the energy consumption structure, and advocating low-carbon lifestyles. Our findings are useful in the tasks related to assessing carbon emissions from the perspective of land-use change and analyzing the associated influencing factors, as well as providing a reference for realizing low-carbon and sustainable development in the PRD.

Urbanization and climate change impacts on future flood risk in the Pearl River Delta under shared socioeconomic pathways

Climate change and urbanization are converging to challenge the flood control in the Pearl River Delta (PRD) due to their adverse impacts on precipitation extremes and the urban areas environment. Previous studies have investigated temporal changes in flood risk with various single factor, few have considered the joint effects of climate change, urbanization and socio-economic development. Here, based on the representative concentration pathway (RCP) scenarios, we conducted a comprehensive assessment of future (2030-2050) flood risk over the PRD combined with a thorough investigation of climate change, urbanization and socio-economic development. Precipitation extremes were projected using the regional climate model RegCM4.6, and urbanization growth was projected based on the CA-Markov model. The economic and population development was estimated by the shared socio-economic pathways (SSPs). Flood risk mapping with different RCPs-urbanization-SSPs scenarios was developed for the PRD based on the set pair analyze theory. The results show that climate change and urbanization are expected to exacerbate flood risk in most parts of the PRD during the next few decades, concurrently with more intense extreme precipitation events. The high flood risk areas are projected mainly in the urban regions with unfavorable terrain and dense population. The highest flood risk areas are expected to increase by 8.72% and 19.80% under RCP4.5 and RCP8.5 scenarios, respectively. Reducing greenhouse gas emissions may effectively mitigate the flood risk over the PRD. This study highlight the links between flood risk and changing environment, suggesting that flood risk management and preventative actions should be included in regional adaptation strategies.

Occurrence and spatial distribution of legacy and novel brominated flame retardants in seawater and sediment of the South China sea

The occurrence and spatial distribution of polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (NBFRs) in seawater and surficial sediment samples (N = 19 and 45, respectively) from the South China Sea (SCS) in 2018 were investigated, and the correlation between BFRs and site parameters (total organic carbon, depth, etc.) were assessed by principal component analysis. The concentration ranges of ΣPBDEs in seawater and sediments were 0.90-4.40 ng/L and 0.52-22.67 ng/g dry weight (dw), respectively, while those of ΣNBFRs were 0.49-37.42 ng/L and 0.78-82.29 ng/g dw, respectively. BDE-209 and decabromodiphenyl ethane were the predominant BFRs, accounting for 38.65% and 36.94% in seawater and 26.71% and 68.42% in sediments, respectively. Notably, tris(2,3-dibromopropyl)isocyanurate and 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, seldomly detected in aquatic matrices worldwide, were detected for the first time in the study area, and their relatively high levels and detection frequencies indicate the ubiquitous application of these NBFRs in the Pearl River Delta. Zhuhai and Jiangmen are the main sources of NBFRs in the SCS. Preliminary risk assessment on NBFRs using hazard quotient indicates low to medium risks to marine organisms at some sites. The occurrence of NBFRs in the SCS highlights the prioritization of more toxicological information on these compounds.

Groundwater Quality in Agricultural Lands Near a Rapidly Urbanized Area, South China

Understanding the groundwater quality and its factors is a key issue in the context of the use and protection of groundwater resources in agricultural areas near urbanized areas. This study assessed the groundwater quality in agricultural areas in the Pearl River Delta (PRD) by a fuzzy synthetic evaluation method and determined the main factors controlling the groundwater quality by principal component analysis (PCA). Results showed that approximately 85% of groundwater sites in agricultural lands in the PRD were good-quality (drinkable). Drinkable groundwater was 95% and 80% in fissured aquifers and porous aquifers, respectively. Poor-quality groundwater in porous aquifers was controlled by four factors according to the PCA, including the seawater intrusion; the lateral recharge and irrigation of surface water and geogenic sources for As, Fe, NH₄⁺, and Mn; the wastewater infiltration; and the geogenic sources for iodide. By contrast, another four factors, including the infiltration of wastewater and agricultural fertilizers, the geogenic sources for heavy metals, the geogenic sources for iodide, and the irrigation of contaminated river water, were responsible for the poor-quality groundwater in fissured aquifers. Therefore, in the future, the groundwater protection in agricultural lands in the PRD should be strengthened because the majority of groundwater in these areas was good-quality and suitable for drinking and agricultural purposes. In addition, poor-quality groundwater in agricultural lands in the PRD was a small proportion and negligible because the factors for poor-quality groundwater are complicated.

Cross-regional transport of PM2.5 nitrate in the Pearl River Delta, China: Contributions and mechanisms

Cross-regional transport potentially contributes to PM_2.5 nitrate (pNO₃), and this can occur as indirect transport, through which pNO₃ precursors are transported to targeted regions, wherein they subsequently react with locally emitted ones to produce pNO₃. However, the process has been rarely studied, which limits its comprehensive understanding. We applied the CMAQ model to study the contributions and mechanisms of pNO₃ transport during autumn in the Pearl River Delta (PRD), a metropolitan region under the growing influence of cross-regional transport on PM_2.5 pollution. Results showed that cross-regional transport contributed to 58% pNO₃ monthly in the PRD, and this mostly occurred as indirect transport contributions (accounting for 43% among all contributions). For the first time, we identified the mechanism of indirect pNO₃ transport in the PRD, which mainly involves transported O₃ and locally emitted NO_x reacting to produce pNO₃ through N₂O₅ heterogeneous hydrolysis. pNO₃ contributions in different periods and regions indicated differences in the indirect transport contributions to N₂O₅ heterogeneous hydrolysis under varying O₃ availability conditions, which are determined by wind fields and the intensity of NO_x emissions. On the regional scale, the pNO₃ level is controlled by both transported O₃ and local NO_x emissions, but pNO₃ sensitivity to these two precursors varies among cities. This study demonstrates the notable effect and complex process of cross-regional pNO₃ transport in the PRD. Considering the important role of transported O₃ for pNO₃, O₃ reduction within a larger scale is required to achieve PM_2.5 pollution control target.

Effects of Soil pH and Mineral Nutrients on Cadmium Uptake by Rice Grain in the Pearl River Delta, China

Alluvial soils are rich in mineral nutrients, and contain high heavy metals, especially Cd. The interactions of mineral nutrients with Cd in soil-rice grain systems on natural condition of alluvial plain are highlighted in this study. 110 pairs of rice grain and soil (0-20 cm) samples from the Pearl River Delta were investigated and measured. The results indicated that pH, organic matter, cation exchange capacity, clay, Ca, Cd, Fe, Mn and Zn are the most important soil characteristics controlling Cd uptake by rice grain. There are synergetic interactions between Cd and mineral elements in the soils, and antagonistic interactions between them in the rice grains. It could provide useful information for the risk assessment of heavy metals in the soils of alluvial plain.

Isotopic and hydrochemical evidence for the salinity origin in the coastal aquifers of the Pearl River Delta, Guangzhou, China

To better understand the origin of the saline groundwater in the Pearl River Delta (PRD), China, water samples were collected from local aquifers, rainfall regions and rivers for isotopic and hydrochemical analysis. The hydraulic connections between the aquifers in the study area were tested by analyzing a series of water samples from different months in one hydrological year (January 2017-January 2018). The total dissolved solids (TDS) results show that the highly saline groundwater only occurs in the granites, which indicates that the TDS distribution depends on the permeability of the aquifer material. Variations in the TDS and stable hydrogen and oxygen isotope ratios (δ²H and δ¹⁸O, respectively) of the water samples from different months reflect a dynamic balance among evaporation and precipitation in a hydrological year. Additionally, the very old radiocarbon (¹⁴C) ages and undetectable amounts of tritium (³H) in most of the groundwater samples suggest that the residence time of the groundwater in the aquifer is high. In general, the saline groundwater (TDS >5 g/L) in the area mainly originated primarily from seawater intrusion in the past. Meanwhile, the water contents of saline groundwater were affected by evaporation and long-term geochemical processes, such as water-rock, sulfate reduction, methanogenesis and ion exchange. The fresh groundwater in the area is from modern meteoric precipitation recharge.

Impact of trophic levels on partitioning and bioaccumulation of polycyclic aromatic hydrocarbons in particulate organic matter and plankton

The distribution and bioconcentration of polycyclic aromatic hydrocarbons (PAHs) in water, suspended particulate material (SPM), algae, and zooplankton samples from the Pearl River Delta (PRD), South China, were investigated. The PAHs in the water and SPM samples is significantly associated with chlorophyll a (Chl a), implying the important role of the aquatic productivity on PAH distribution. PAHs in the water or SPM samples were strongly correlated to dissolved organic carbon (DOC) or algal particulate organic carbon (A-POC). Moreover, the log bioconcentration factor (BCF) values (mL g^-1) of PAHs in both the algae and zooplankton samples were linearly related to their log octanol-water coefficient (Kow) values. However, the slopes of these relationships were negatively correlated with Chl a, attributing to the difference in the dominant plankton species or the non-equilibrium exchange between air-water-biota. The above results indicate the important role of trophic levels on the distribution and bioaccumulation of PAHs.

Scenario-based flood risk assessment for urbanizing deltas using future land-use simulation (FLUS): Guangzhou Metropolitan Area as a case study

Preparing cities for sea-level rise is one of the critical challenges of the twenty-first century. Extreme weather events, natural hazards, and the failure of climate mitigation and adaptation are substantial risks. These risks are especially significant in fast-urbanizing deltas, such as the Pearl River Delta in China, because the conflict between urbanization and flooding caused by climate change will be more significant in the future. This paper elaborates on an approach that employs a future land-use simulation (FLUS) model for scenario-based 100-year coastal flood risk assessment. Storylines of future scenarios from the Intergovernmental Panel on Climate Change (IPCC), called the representative concentration pathways (RCPs) 2.6 and 8.5, are utilized in the present study. The Guangzhou Metropolitan Area (GMA) is used as a case study to explore the probable implications of future land-use changes due to the ongoing urbanization process in the region in relation to projected environmental changes (sea-level rise, storm surge, and land subsidence). The results indicate that there will be a significant increase in flooded urban areas in the future. The simulations show that, as compared to 2015, the built-up area in the GMA will increase by 246.57 km² in 2030 and 513.03 km² in 2050. As compared to 2015, the flooding of built-up areas in 2030 and 2050 will respectively increase by about 31.32 km² and 48.49 km² under the RCP 8.5 scenario. It is also found that, as the main driving factor, urbanization will increase the flooding of built-up areas in Guangzhou in 2030 and 2050 by about 1.9 km² and 5.9 km², respectively, under the RCP 2.6 scenario as compared to 2015. Additionally, due to environmental changes, the flooding of built-up areas in Guangzhou will increase by about 24.2 km² and 26.8 km², respectively, under the RCP 8.5 scenario by 2030 and 2050 as compared to 2015. This increasing flood risk information determined by the simulation provides insight into the spatial distribution of future flood-prone urban areas to facilitate the development and prioritization of flood mitigation measures at the most critical locations in the region.

Changes in dissolved inorganic carbon in river water due to urbanization revealed by hydrochemistry and carbon isotope in the Pearl River Delta, China

Under natural conditions, the dissolved inorganic carbon (DIC) in river water is dominantly derived from carbonate or silicate dissolution by carbonic acid. However, sulfuric and nitric acids produced by human activities provide additional acidity for chemical weathering, which would affect the DIC flux and change its isotopic composition. To identify the natural and anthropogenic impacts on DIC, the major ion concentrations and stable carbon isotopes of the DIC (δ¹³C-DIC) of river waters were measured in the Pearl River Delta (PRD) region, which is one of the most developed and populated areas in China. The mass balance calculations for DIC-apportionment showed that carbonate dissolution by carbonic acid was the dominant origin of DIC in the Beijiang (BJ) River (67%) and Xijiang (XJ) River (78%) and silicate dissolution by carbonic acid was the dominant origin of DIC in the Guangzhou (GZ) Channel (37%) and Dongjiang (DJ) River (50%), which was related to the lithology of the catchment. The contribution of carbonate dissolution by sulfuric and nitric acids, which represented the contribution of human activities to the total DIC concentrations in river water, showed high proportions in the GZ Channel and DJ River, with averages of 42% and 34%, respectively, which were associated with a high degree of urbanization. Evidence of hydrochemical parameters and δ¹³C-DIC signatures indicated that human activities had impacts on the DIC pool. Carbonate dissolution by sulfuric and nitric acids caused by human activities changed DIC apportionments rather than the DIC flux, and this part of DIC would ultimately become a source of CO₂ to the atmosphere on the geological timescale and affects the CO₂ budget. An increase in nutrient concentration due to increased sewage discharge in the urbanized area could promote phytoplankton photosynthesis, which could change the DIC pool and increase the δ¹³C-DIC value. This study quantitatively highlights the influence of human activities on DIC apportionment in river water, suggesting that anthropogenic impacts should be seriously considered when evaluating the evolution of DIC.

Seasonality in a tidal reach: Existence, impact and a possible approach for design flood level estimation

Heterogeneity caused by seasonality could lead to the estimation error of the design flood level (DFL). This research intended to examine the existence of seasonality in the extreme water levels in a tidal reach and to quantify its impact on the DFL estimation. The mixed-distribution, a commonly used method for design value estimation with heterogeneous samples, was tested. A case study was carried out in the Pearl River Delta, South China. Results showed that a significant seasonality existed in the extreme water levels that were generated from the flood-tide interactions in the delta. If the DFL was estimated with a single distribution, the DFL with a return period smaller than 1.1 years would be underestimated and more information of the non-flood season would be lost. The mixed-distribution was superior in its consideration of seasonality, however, when the return period was over 10 years or smaller than 5 years, the DFL estimation results of this approach were only shifted by <1% from that of a single distribution.

Distribution and risk assessment of phthalates in water and sediment of the Pearl River Delta

Phthalate esters (PAEs) are widely used industrial raw materials that are well known for their environmental contamination and toxicological effects as "endocrine disruptors." In this study, environmental levels of PAEs and eco-toxicological risk assessments were determined in the eight estuaries of the Pearl River (Estuaries), main upstream tributary (Xijiang River), urban river network (River network), and nature reserve reservoir (Reservoirs). Water and sediment samples from the above water systems were collected during the low-water period (May) and the high-water period (August) between 2012 and 2014. Solid phase and ultrasonic methods were used to extract 14 different PAEs that were analyzed by gas chromatography. The analytical average recovery of PAEs in water and sediment was 75.4% ± 4.9% and 121.5% ± 8.9%, respectively. The results showed that PAEs were detected in all of the samples, and the di-n-butyl phtalate (DBP) and benzyl butyl phthalate (BBP) monomers had a detection rate of 100% in water. Similarly, in sediment samples, the detection rates of diisobutyl phthalate (DiBP), DBP, dimethoxyethyl phthalate (DMEP), BBP, di-n-octyl phthalate (DnOP), and DNP ranged from 66.7 to 100%. Among these, in sediment samples, di(2-ethylhexyl) phthalate (DEHP) and phthalic acid bis(2-butoxyethyl) ester (DBEP) had detection rates of 95.8% to 100% in the Estuaries, Xijiang River, and River network. The concentrations of Σ₁₄PAEs in water samples and sediments ranged from 12.95 ± 1.97 to 6717.29 ± 112.37 ng/L and 71.99 ± 8.72 to 17,340.04 ± 227.83 ng/g-dw, respectively. During the low-water period, the average concentration of Σ₁₄PAEs in water and sediment was 1159.58 ± 97.22 ng/L and 2842.50 ± 178.21 ng/g-dw, respectively, and during the high-water period, 822.83 ± 53.19 ng/L and 1936.42 ± 111.31 ng/g-dw, respectively. In water, the average concentration of Σ₁₄PAEs in 2013 and 2014 was 963.39 ± 19.55 ng/L and 2815.35 ± 176.32 ng/L, respectively. In sediment, the average concentrations of Σ₁₄PAEs in 2012 to 2014 were 990.10 ± 23.33 ng/g-dw, 1084.20 ± 112.12 ng/g-dw, and 1816.89 ± 79.97 ng/g-dw, respectively, with concentrations showing an increasing trend year after year (2014 > 2013 > 2012). Potential risk assessment of water ecological, the results show that exceeding environmental risk level (ERL) value in higher molecular weight plasticizer (DEHP, DMEP, DNOP, DNP) was mainly distributed in water, the lower molecular weight plasticizer (BMP, DiBP) was mainly distributed in sediment.

Shipping emission inventories in China's Bohai Bay, Yangtze River Delta, and Pearl River Delta in 2018

Pollutant emissions from ships could increase with expanding international trade and shipping fleet size, posing a severe but often overlooked threat to public health. China houses the three biggest port clusters in the world: the Bohai Bay (BB), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD) and must combat pollutant emissions. This study examines the emissions of key pollutants (i.e., NO_X, PM₁₀, PM_2.5, HC, CO, SO_X, CO₂, NMVOC, and CH₄) utilizing a bottom-up methodology with the aid of automatic identification system data. Our results show that among the three regions studied, ships in the YRD produce the most emissions, accounting for 47.84% of the combined total emissions in 2018. We evaluate the emissions from different ship types, operation modes, and discharge equipment. Container ships account for ~50% of all emissions, which are mainly generated during the cruising phase. Different power sources produce varying levels of pollutants owing to power, load, and discharge variations. In addition, ship emissions have seasonal characteristics, which are reflected by the decline trend recorded in February, July, August, and December. This baseline dataset could aid comparisons with historic or future emission data and help establish regulatory actions to improve air quality.

Elevated manganese concentrations in shallow groundwater of various aquifers in a rapidly urbanized delta, south China

High concentration of manganese (Mn) in groundwater is a major concern because of its harmful to human health, and the origin of which in urbanized areas is often complicated. The present study aims to delineate spatial distributions of groundwater Mn in various aquifers and in areas with different urbanization levels in the Pearl River Delta (PRD), and to identify the origins of groundwater Mn in this region. Nearly 400 groundwater samples collected, and 14 chemicals were analyzed. The results show that approximately 20% groundwater in granular aquifers showed elevated-Mn (>0.4 mg/L), and was more than two times of that in fissured aquifers, while that in karst aquifers was absent. The proportions of elevated-Mn groundwater in urbanized areas and peri-urban areas were higher than that in non-urbanized areas. The decomposition of organic matter and reduction of Fe (hydr)oxides in sediments with reducing condition was likely to be the main factor controlling elevated-Mn groundwater in granular aquifers at a regional scale. By contrast, elevated-Mn groundwater in fissured aquifers was likely mainly affected by the urbanization accompanied with the leakage of low-oxygen domestic sewage and the industrialization accompanied by the leakage of industrial wastewater. In addition, Mn-rich surface water was also probably an important source for groundwater Mn in river network areas. Therefore, it is necessary to make a long-term monitoring for groundwater Mn in granular aquifers, especially in urbanized areas and river network areas, because of the high proportion of elevated-Mn.

The sequential collaborative relationship between economic growth and carbon emissions in the rapid urbanization of the Pearl River Delta

In a rapid urbanization context, socio-economic development has caused large increases in carbon emissions. In this study, various techniques such as cointegration analysis, vector autoregression, and decoupling elastic function methods are applied to analyze the sequential collaborative relationship between economic development and carbon emissions in the process of urbanization in terms of the time-series lag relationship and the decoupling relationship. The main findings are as follows: (1) urbanization and carbon emissions displayed a temporal correlation relation with a lag of order 4, according to stability tests, and (2) the development of urbanization, economic growth, and changes in land use may be responsible for the time lag in carbon emissions. Furthermore, the mechanisms behind the effect of urbanization on carbon emissions are investigated to assist future carbon emissions reduction efforts. (3) From 1990 to 2014, carbon emissions and economic development showed a temporal evolution trend of "weak decoupling-expansionary coupling-weak decoupling" in the Pearl River Delta region, and there was an overall weak decoupling state: carbon emissions increased with growth in economic development, but the emissions growth rate was lower than the speed of economic development. (4) From 1990 to 2014, economic development showed a trend of sustained growth in the Pearl River Delta region, and differences were detected in the decoupling status between carbon emissions and economic development at different times. The overall decoupling status of the nine cities in the region was one of weak decoupling; however, the decoupling index, carbon emissions, and economic development levels displayed differences, whereby cities with high carbon emissions and high economic development levels were not necessarily the cities in which environmental pressures from economic development were the most severe. Our results have important theoretical and practical significance as they clarify the impact of economic development on carbon emissions in the process of urbanization, as well as the carbon emissions reduction work that must be undertaken in urban systems.

Occurrence of organophosphate esters and their diesters degradation products in industrial wastewater treatment plants in China: Implication for the usage and potential degradation during production processing

Influent, effluent and sludge samples were collected from eight industrial wastewater treatment plants (WWTPs) in the Pearl River Delta, China. Samples were investigated for the occurrence of 10 organophosphate esters (OPEs) and 7 organophosphate diesters (Di-OPs). Most of the 10 OPEs were detected at total concentrations of OPEs (∑OPEs) ranging from 65.8 to 2842 ng L^-1 in influent samples and exhibited different composition profiles. The results indicated that OPEs were widely used with different proportions in versatile OPE-containing products. Meanwhile, ∑OPEs in effluent were found in the range of 6.37-2710 ng L^-1; these residuals were subsequently transported to municipal WWTPs for further treatment and posed extra pressure on the plants. Seven Di-OPs, possible degradation products of the OPEs, were also detected in influent, effluent and sludge. The results suggested that OPEs underwent degradation during rigorous industrial manufacturing procedures, such as thermal processes, highly alkaline pH, or processes that involved metal/metal oxide. In addition, high levels of dibutyl phosphate, di(2-ethylhexyl) phosphate and diphenyl phosphate were found in influent suggesting their possible industrial application.