Air-sea exchange and gas-particle partitioning of polycyclic aromatic hydrocarbons over the northwestern Pacific Ocean: Role of East Asian continental outflow

Spatial Variations of Atmospheric Alkylated Polycyclic Aromatic Hydrocarbons across the Western Pacific to the Southern Ocean: Unexpected Increasing Deposition

Spatial variations of atmospheric alkylated polycyclic aromatic hydrocarbons (Alk-PAHs) are key to understanding their long-range atmospheric transport (LRAT). However, limited Alk-PAHs data have hindered their LRAT characterizations on a global scale. In this study, 49 Alk-PAHs were measured in the atmospheric samples collected across the Western Pacific to the Southern Ocean. The summed concentration of 39 frequently detected Alk-PAHs (Σ39Alk-PAHs) was 25.8 ± 25.3 ng m-3. The concentrations of Σ39Alk-PAHs significantly declined with the decrease in latitude (°N). Higher concentrations (55.8 ± 33.8 ng m-3) were linked to continental air mass compared to oceanic/Antarctica air mass (17.0 ± 13.6 ng m-3), highlighting continental emissions as the primary source of marine atmospheric Alk-PAHs. An unexpected increase in the G/P partitioning ratio (KP) was found in samples farther away from the continent, which cannot be explained by the influence of temperature on the partitioning process. Deposition analysis suggested that gaseous concentrations and the G/P partitioning largely influenced deposition patterns. Hypothetical scenario analysis indicated that increased KP under snowy conditions could enhance the total Alk-PAH deposition. These findings emphasize the need for accurate characterization of partitioning and deposition processes when studying the global fate of Alk-PAHs, particularly in remote and polar regions.

Air-water exchange: Toxicities, risks and PAHs compounds in the three gorges reservoir of China

Air-water exchange is inevitably accompanied by the transportation of contaminants between atmosphere and water, which significantly leads to the alterations of toxicity and risks. However, the resulting changes of toxicity and risk in water and air due to the cross-interfacial transport of pollutants are still unclear. In this study, the water and atmospheric samples at the Pengxi River located in the Three Gorges Reservoir (TGR), China, were collected in winter and summer seasons respectively. The contaminated water exhibited higher toxicity effects than air in multiple toxicity endpoint tests. Besides, waters collected during winter exhibited greater toxicity effects than in summer. The concentrations of ΣPAHs were 48.0-445 ng L-1 in the water and 9.44-82.3 ng/m3 in the air, with ΣPAHs significantly higher in winter than in summer for water samples. Notably, the 2-3 ring PAHs showed a tendency to volatilize from water to air and may increase atmospheric toxicity, whereas the 4-6 ring PAHs tend to be deposited from air to water and may heighten toxicity in the water. Correlation analysis indicated that PAHs were important toxicants in the air, posing higher incremental carcinogenic risk, particularly during winter. Thus, the changes in toxicity and risk caused by the water-air exchange of pollutants cannot be ignored. This research contributes to a deeper understanding of the changes in toxicity effects and health risks caused by the air-water exchange of pollutants. The importance of considering the toxic effects and health concerns of micropollutants in the air as important as in water is emphasized.

Distribution and provenance analysis of polycyclic aromatic hydrocarbons in surface sediments of the East China Sea

A total of 32 surface sediment samples were collected from the East China Sea (ECS) to investigate the distribution of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments and evaluate their sources. The content of PAHs in the ECS surface sediments ranged from 2.3 ng/g to 57.8 ng/g. The source analysis revealed that the combustion of such fuels as petroleum is the main contribution source of PAHs in the ECS surface sediments, and oil spill is another important contribution source. The study also showed that the content of PAHs in the ECS surface sediments is low and does not cause adverse ecological risks.

Air-sea exchange of PAHs in the Taiwan Strait: Seasonal dynamics and regulation mechanisms revealed by machine learning approach

In this study, to understand the seasonal dynamics of air-sea exchange and its regulation mechanisms, we investigated polycyclic aromatic hydrocarbons (PAHs) at the air-sea interface in the western Taiwan Strait in combination with measurements and machine learning (ML) predictions. For 3-ring PAHs and most of 4- to 6-ring, volatilization and deposition fluxes were observed, respectively. Seasonal variations in air-sea exchange flux suggest the influence of monsoon transitions. Results of interpretable ML approach (XGBoost) indicated that volatilization of 3-ring PAHs was significantly controlled by dissolved PAH concentrations (contributed 24.0 %), and the gaseous deposition of 4- to 6-ring PAHs was related to more contaminated air masses originating from North China during the northeast monsoon. Henry's law constant emerged as a secondary factor, influencing the intensity of air-sea exchange, particularly for low molecular weight PAHs. Among environmental parameters, notably high wind speed emerges as the primary factor and biological pump's depletion of PAHs in surface seawater amplifies the gaseous deposition process. The distinct dynamics of exchanges at the air-water interface for PAHs in the western TWS can be attributed to variations in primary emission intensities, biological activity, and the inconsistent pathways of long-range atmospheric transport, particularly within the context of the monsoon transition.

Chemodynamics of Polycyclic Aromatic Hydrocarbons and Their Alkylated and Nitrated Derivatives in the Yellow Sea and East China Sea

The occurrence of continuously released polycyclic aromatic hydrocarbons (PAHs) in marginal seas is regulated by hydrological and biogeochemical processes; however, scarce knowledge is about their derivatives in marine environments. In this study, the dissolved and particulate PAHs and their alkylated/nitrated derivatives (A-PAHs/N-PAHs) in surface seawater of the southwestern Yellow Sea (YS) and northwestern East China Sea (ECS) during September 2022 were comprehensively discussed. Results confirm higher levels of Σ26PAHs (9.3-70 ng/L) and Σ43A-PAHs (13-76 ng/L) than Σ20N-PAHs (0.80-6.6 ng/L). The spatial heterogeneity of contaminants was regulated by substantial riverine runoff and ocean currents. Lagrangian Coherent Structure analysis further revealed the existence of a transport barrier at the shelf break of the southwestern YS where contaminants hardly crossed and tended to accumulate. The relationship between dissolved compounds and chlorophyll a indicated both biodegradation and the biological pump contributed to the depletion of PAHs and A-PAHs from surface seawater while the biological pump was the major driver for N-PAHs, despite their complicated water-particle partition behavior due to variations in physicochemical properties in the presence of nitro groups. Source identification demonstrated that pyrogenic and petrogenic sources dominated the YS and ECS, respectively, while photochemical transformations appeared more active in the YS.

PAHs in the monsoonal open ocean: Homogeneous spatial pattern and wind-driven significant seasonal variations

PAHs enter the ocean via surface runoff and atmospheric transport pathways, and the distribution of PAHs is highly variable in coastal seas due to the influence of direct human activities, inputs of surface runoff, and strong biological activities. However, highly temporal variability of PAHs has also been widely observed in the open oligotrophic tropical and subtropical oceans without the influence of three types of factors mentioned above. This study developed a method to quantify the variability of oceanic PAHs based on wind frequency and wind-speed-weighted wind frequency using in-situ survey data from three cruises in the Philippine Sea, and tested the validity of this method using publicly available data from other monsoonal open oceans. The result showed that the wind frequency could better explain the variation of dissolved PAHs and particulate PAHs in the surface ocean, while the wind-speed-weighted wind frequency could better explain the variation of particulate PAHs. This study suggests that the influence of seasonal atmospheric transport cannot be ignored when describing and interpreting the distribution patterns of PAHs in the monsoon-influenced low and mid-latitude open oceans and also provides a reference method for a better understanding of the global-scale distribution patterns of PAHs in the ocean.

PM2.5-bound polycyclic aromatic hydrocarbons of a megacity in eastern China: Source apportionment and cancer risk assessment

Ninety-six fine particulate matter (PM_2.5) samples covering four seasons from October 2020 to August 2021 were collected at a 'super' site in Hangzhou, a megacity in eastern China. These samples were analyzed to determine the sources and potential cancer risks to humans of 16 United States Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs). The average concentrations of the PAHs in PM_2.5 in autumn, winter, spring, and summer were 8.35 ± 4.90, 27.9 ± 13.6, 8.3 ± 5.97, and 1.05 ± 0.50 ng/m³, respectively, and with an annual average of 11.9 ± 13.2 ng/m3. The source apportionment by positive matrix factorization analysis indicated that, based on the yearly average, the major sources of PAHs were traffic emissions (38.2 %), coal combustion (28.9 %), coke (21.7 %), and volatilization (11.1 %). Strong correlations between high concentrations of carbonaceous aerosols and high-molecular-weight PAHs in winter could be attributed to incomplete combustion. Long-range transport of air from the sea to the southeast resulted in low concentrations of carbonaceous aerosols and low-molecular-weight PAHs in summer. Trajectory clustering and the potential source contribution function both indicated that the Yangtze River Delta was the main source region of PAHs for PM_2.5 in Hangzhou in spring and summer. In autumn and winter, it was dominated by long-range transport from northern China. Lifetime lung cancer risk assessment revealed that the PAHs in PM_2.5 impose moderate human health risks in Hangzhou due to traffic emissions. The results of this study provide important information for policymakers to establish abatement strategies to reduce PAH emissions in Hangzhou, and perhaps other urban centers across China.

Considering zooplankton as a black box in determining PAH concentrations could result in misjudging their bioaccumulation

Zooplankton play an important role in energy transfer in the marine food web and form the dietary basis for the size of important fish stocks and the maintenance of their resources. Although zooplankton include numerous taxa with significantly different ecological characteristics and the interspecific differences in optimum body size and taxonomic specificity in fish feeding on zooplankton are remarkable, they are always considered as a whole (like a "black box") in current studies about the transport of persistent organic pollutants through the food chain. This approach might result in misjudgment of their bioaccumulation. In this study, the distribution properties of each taxa of zooplankton community were discerned using data from two cruise surveys conducted in the northern South China Sea. Twelve groups of zooplankton were identified, all of which had distinct ecological and functional characteristics. The carbon-based community structure of zooplankton could explain their variability with respect to polycyclic aromatic hydrocarbons (PAHs). Smaller-sized zooplankton (smaller calanoids and cyclopoids) were more likely to accumulate low molecular weight PAHs (LMW-PAHs), while larger-sized zooplankton (larger calanoids) were more likely to accumulate high molecular weight PAHs (HMW-PAHs). The bioaccumulation capacity of the zooplankton community for LMW-PAHs was negatively correlated with the proportion of omnivores and carnivores, while the opposite was true for HMW-PAHs. These results suggested that the effects of complex community structure within plankton communities should be taken into account when assessing the transfer and bioaccumulation effects of PAHs in the marine food chain.

Occurrence, spatial patterns, air-seawater exchange, and atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) from the Northwest Pacific to Arctic Ocean

Numerous studies have elucidated the characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Arctic; however, their behavior in different environments has not been studied at a large scale. To investigate the occurrence, spatial trends, air-seawater exchange and atmospheric deposition of 16 polycyclic aromatic hydrocarbons (PAHs), this study takes sample from the Northwest Pacific Ocean. to the Arctic Ocean.The concentrations of 16 PAHs in air and seawater ranged from 27 to 5658 pg/m³ and 34-338 ng/L, respectively. The air-seawater exchange flux of the region was calculated with a Whitman two-film model to be -82681-24613 ng/m²/day. Meanwhile, low-ring PAHs were transported from seawater to the air, while high-ring PAHs were transported from air to seawater. A correlation analysis between multiple environmental factors and particle phase ratio suggested that temperature might be the major driving factor for PAHs in the long-range atmospheric transport (LRAT) process. Moreover, the dry atmospheric deposition fluxes in the region were analyzed by considering environmental factors and the physicochemical properties of each PAHs monomer, these fluxes ranged from 0.001 to 696 ng/m²/day and were greater inshore than offshore and at higher latitudes. This study highlights that PAHs are affected by LRAT during their transport from Asia to Northwest Pacific and further to the Arctic Ocean, while emphasizing that air-seawater exchange plays an important role in air-sea interactions in the open ocean.

Measurement of the mixing state of PAHs in individual particles and its effect on PAH transport in urban and remote areas and from major sources

Although recent laboratory simulations have demonstrated that organic matter prevents the degradation of polycyclic aromatic hydrocarbons (PAHs), their role in the long-range transport of PAHs in the real atmosphere remains poorly understood. In this study, we measured the chemical composition and mixing state of PAHs-containing individual particles in aerosols from three sources, one urban area and one remote area. PAHs-containing particles were classified into five types: organic carbon (OC), potassium mixed with organic carbon (KOC), potassium mixed with sodium (KNa), Krich and PAH-rich. The PAH-rich and KOC particles were the main types of particles produced by vehicle exhaust/coal burning and biomass burning, respectively, accounting for >50% of the PAHs-containing particles. It was found that organic matter enhancement of PAHs-containing particles occurs in the ambient atmosphere, with organic-rich (OC and KOC) particles accounting for >90%. Further analysis revealed that the increase in the fractions of PAHs was related to the mixing state with organic compounds due to the protection of organics against PAHs and/or the aging of PAHs-containing particles. The results of this study improve our understanding of the chemical composition and mixing state of PAHs particles in atmospheric aerosols from emission sources and urban and remote areas, and provide field observation evidence to support the promotion of the study of long-range transport of PAHs by organics.

Land-Ocean Exchange Mechanism of Chlorinated Paraffins and Polycyclic Aromatic Hydrocarbons with Diverse Sources in a Coastal Zone Boundary Area, North China: The Role of Regional Atmospheric Transmission

The marine environment is regarded as a crucial "sink" of numerous land-origin pollutants. As typical boundary regions, the coastal and offshore areas are used to evaluate the dominating transfer process and land-ocean exchange mechanism of semivolatile organic compounds. In air samples collected from a coastal area in North China over a whole year, chlorinated paraffins (CPs), including short-chain CPs and medium-chain CPs, and prior control 16 polycyclic aromatic hydrocarbons (PAHs) were determined, with mean concentrations of 25.8 and 94.7 ng/m³, respectively. Results of different gas-particle partitioning models indicated that the steady-state hypothesis provides a better description of the possible land-ocean exchange molecular mechanism. The source-sink influences for CPs and PAHs were affected by the predominant atmospheric motion, which alternated between gaseous diffusion and particulate sedimentation in different seasons. Source apportionment results indicated that different transfer characteristics contributed to the source divergence of ambient CPs and PAHs within 12 nautical miles in the same area. Coal/biomass combustion and diesel/natural gas combustion were the main PAH sources in the coast site (43.1%) and sea site (35.3%), respectively. Similar industrial sources CP-52 and CP-42 were the main CP sources in the coast site (41.4%) and sea site (40.8%), respectively.

Dissolved PAHs impacted by air-sea interactions: Net volatilization and strong surface current transport in the Eastern Indian Ocean

In the Indian Ocean, the marine fate of polycyclic aromatic hydrocarbons (PAHs) is impacted by the unique air-sea interactions with great monsoon characters. By collecting water-column samples during the monsoon transition period, we found PAHs (∑₈PAH: 1.1-27 ng L^-1) showed significantly different distributions from the Bay of Bengal, Equatorial Indian Ocean, Eastern Indian Ocean, and the South China Sea (p < 0.001). Their vertical profiles showed natural logarithm relationships with depth in the Bay of Bengal and Equatorial Indian Ocean. PAHs were mainly from wood/coal combustion and vehicle emission. The estimation of PAHs' air-seawater exchange flux revealed net volatilizations from seawater except in the Eastern Indian Ocean. The Wyrtki Jet, a surface current driven by the westerly wind, was observed in the equatorial area. This swift current could transport PAHs eastward efficiently with a mass flux of 636 ± 188 g s^-1. The subsurface current, Equatorial Undercurrent, played a less crucial role in PAHs' lateral transport with a flux of 115 ± 31.3 g s^-1. This study preliminarily revealed the role of air-sea interactions on PAHs' transport and fate in the open ocean. The coupled air-sea interactions with biogeochemical processes should be considered in future work.

Polycyclic Aromatic Hydrocarbons in the Marine Atmosphere from the Western Pacific to the Southern Ocean: Spatial Variability, Gas/Particle Partitioning, and Source Apportionment

The spatial variability of polycyclic aromatic hydrocarbons (PAHs) in the marine atmosphere contributes to the understanding of the global sources, fate, and impact of this contaminant. Few studies conducted to measure PAHs in the oceanic atmosphere have covered a large scale, especially in the Southern Ocean. In this study, high-volume air samples were taken along a cross-section from China to Antarctica and analyzed for gaseous and particulate PAHs. The data revealed the spatial distribution, gas-particle partitioning, and source contributions of PAHs in the Pacific, Indian, and Southern Oceans. The median concentration (gaseous + particulate) of ∑₂₄PAHs was 3900 pg/m³ in the Pacific Ocean, 2000 pg/m³ in the Indian Ocean, and 1200 pg/m³ in the Southern Ocean. A clear latitudinal gradient was observed for airborne PAHs from the western Pacific to the Southern Ocean. Back trajectories (BTs) analysis showed that air masses predominantly originated from populated land had significantly higher concentrations of PAHs than those from the oceans or Antarctic continents/islands. The air mass origins and temperature have significant influences on the gas-particle partitioning of PAHs. Source analysis by positive matrix factorization (PMF) showed that the highest contribution to PAHs was from coal combustion emissions (52%), followed by engine combustion emissions (27%) and wood combustion emissions (21%). A higher contribution of PAHs from wood combustion was found in the eastern coastal region of Australia. In contrast, engine combustion emissions primarily influenced the sites in Southeast Asia.

Non-equilibrium influence on G/P partitioning of PAHs: Evidence from the diurnal and nocturnal variation

Gas/particle (G/P) partitioning is an important behavior for the atmospheric transport of polycyclic aromatic hydrocarbons (PAHs). In this study, paired daytime and nighttime air samples were collected for one year in order to study the diurnal and nocturnal variations of concentration and G/P partitioning of PAHs. Higher PAHs concentrations in total phase were observed in nighttime. The geomean (GM) concentrations of Σ₁₅PAHs in total phase were 69.6 and 52.8 ng/m³ in nighttime and daytime, respectively. More obviously diurnal and nocturnal variations were observed in non-heating season, with the GM ratios of Σ₁₅PAHs in nighttime to daytime of 1.65 and 1.06 in non-heating season and heating season, respectively. The results could be attributed to emission sources and meteorological conditions. The values of particulate phase fraction (ϕ_P) and G/P partitioning quotient (log K_P) were used to quantify the phase distribution of PAHs. For most high molecular weight PAHs, the values of ϕ_P and log K_P in nighttime were higher than those in daytime, which could be mainly attributed to the lower temperature in nighttime. However, for the three light molecular weight PAHs (Acy, Ace and Flu), higher values of ϕ_P and log K_P were observed in daytime. The regression of log K_P against log K_OA for the three PAHs in daytime differed from those in nighttime. The chemical losses of PAHs in different phases might be responsible for the result. These findings suggested that the chemical loss of PAHs in gas phase should be considered for the G/P partitioning process.

Prediction of the gas/particle partitioning quotient of PAHs based on ambient temperature

Gas/particle (G/P) partitioning is an important influencing factor for the environmental fate of semi-volatile organic compounds (SVOCs). The G/P partitioning of polycyclic aromatic hydrocarbons (PAHs) is an integrated complex process due to its formation and growth concurrently with particles. Based on the large dataset of gaseous and particulate samples in a wide ambient temperature range of 50 °C, the simple empirical equations based on ambient temperature were established to predict the G/P partitioning quotient (K_P) of PAHs at the temperature range from 252 K to 307 K (-21 °C to 34 °C). The performance of the empirical equations was validated by comparison with the monitoring K_P of PAHs worldwide. The empirical equations exhibited good performance for the prediction of K_P of PAHs based on ambient temperature. Two deviations with the prediction lines of the previous G/P partitioning models from the monitoring data of K_P were observed. It was found that the deviations might be attributed to some non-considered influencing factors with the previous G/P partitioning prediction models. Therefore, further research should be conducted to study the mechanism of the G/P partitioning of PAHs, and more influencing factors should be introduced into the establishment of G/P partitioning models of PAHs. In summary, the result of the present study provided a convenient method for the prediction of K_P of PAHs, which should be useful for the study of environmental fate of PAHs in atmosphere.

Method Development for Low-Concentration PAHs Analysis in Seawater to Evaluate the Impact of Ship Scrubber Washwater Effluents

A naval ship’s exhaust gas scrubber may discharge polycyclic aromatic hydrocarbons (PAHs) into seawater. Due to the high lipophilicity and low water solubility of PAHs, their concentrations in seawater are extremely low, making them difficult to detect or accurately determine. To accurately assess the impact of scrubber washwater effluent on the PAHs concentration of seawater, appropriate analysis methods must be established. In this study, a large-volume pre-concentration water sampler was used onboard to concentrate PAHs in surface seawater (100 L) from four sites offshore of southern Taiwan. The quantitative and qualitative analysis of dissolved PAHs in seawater and quality control samples were implemented using a GC/MS system with the aid of internal and surrogate standards. Results showed that the field and equipment blank samples of quality control samples were lower than twice the detection limit. The detection limit of individual PAHs is between 0.001 (naphthalene, NA) and 0.014 ng/L (dibenzo[a,h]anthracene, DBA), which meets the requirements for evaluating PAHs in seawater (that is, less than the maximum permissible concentrations (MPCs)). The concentration of total PAHs (TPAHs) in the four seawater samples ranged from 2.297 to 4.001 ng/L and had an average concentration of 3.056 ± 0.727 ng/L. The concentrations of 16 PAHs were determined in each seawater sample, indicating that the analytical method in this study is suitable for the determination of low-concentration PAHs in seawater. Phenanthrene (PHE) is the most dominant compound in seawater samples accounting for 59.6 ± 12.6% of TPAHs, followed by fluorine (FL) accounting for 8.5 ± 3.7%. The contribution of high-ring PAHs to TPAHs is not high (0.5–9.2%), but the observed concentrations can cause a higher risk to aquatic organisms than low-ring PAHs. The diagnostic ratio showed that the sources of PAHs in the seawater collected offshore of southern Taiwan may include mixed sources such as petrogenic, petroleum combustion, and biomass combustion. The results can be used for regular monitoring, which contributes to pollution prevention and management of the marine environment.

Spatial distribution of polycyclic aromatic hydrocarbons in the Philippine Sea, Western Pacific and the impact factors analysis

Knowing the polycyclic aromatic hydrocarbons (PAHs) pollution properties in ocean is highly needed to protect the open sea. In July to August of 2020, twenty surface water samples were obtained from the East China Sea to the Philippine Sea. The ranges of Σ₁₅PAHs concentrations were 3.188-5.29 ng L^-1 in dissolved phase, 0.455-1.305 ng L^-1 in particulate phase in the Philippine Sea. 3, 4-Ring PAHs were the most abundant PAHs. Their spatial differences in dissolved phase were mainly caused by human activities, the summer monsoon from the Philippine Islands and the Northern Equatorial Current, and the Kuroshio Current and Subtropical Countercurrent. The source analysis showed that PAHs in surface water in the Philippine Sea may come from coal combustion. It is the first time to analyze the occurrence and distribution of PAHs in the Philippine Sea.

Dissolved polycyclic aromatic hydrocarbons from the Northwestern Pacific to the Southern Ocean: Surface seawater distribution, source apportionment, and air-seawater exchange

Polycyclic aromatic hydrocarbons (PAHs) as a group of toxic and carcinogenic compounds are large scale globally emitted anthropogenic pollutants mainly emitted into the atmosphere. However, atmospheric transport cannot fully explain the spatial variability of PAHs in the marine atmosphere and seawater. It is hypothesized that PAHs accumulated in seawater and ocean circulation can also influence PAHs observed in air above the ocean. In order to investigate PAHs in seawater as a potential secondary source to air, we collected paired air and seawater samples during a research cruise from China to the Antarctic in 2018-2019, covering the Pacific Ocean, the Indian Ocean, and the Southern Ocean. Summed concentrations of 28 analyzed PAHs in seawater were highest in the Pacific Ocean (4000 ± 1400 pg/L), followed by the Indian Ocean (2700 ± 1000 pg/L), and the Southern Ocean (2300 ± 520 pg/L). Three-ringed PAHs dominated the composition profile. We found that PAH levels in the Pacific and Indian Oceans were strong inversely correlated with salinity and distance to the coastline. This suggests that riverine inputs and continental discharges are important sources of PAHs to the marine environment. Derived air-seawater fugacity ratios suggest that net fluxes of PAHs were from seawater to the air in the Pacific and Indian Oceans at 9.0-8100 (median: 1600) ng/m²/d and 290-2000 (median: 1300) ng/m²/d, respectively. In the Southern Ocean, the net flow of PAHs was from air to seawater with a flux of -1000-450 (median: -82) ng/m²/d. Source apportionment from two different models suggested that the largest contribution to total PAHs was from petrogenic sources (44-57%), followed by coal/wood combustion (30-31%), fossil fuel combustion (15%), and engine combustion emissions (2.8-9.5%). Higher contributions from petrogenic sources were found at sites close to coastal regions. Both coal/wood combustion and petrogenic sources are responsible for the PAH concentrations detected in the Indian and Southern Oceans.

Persistent organic pollutants (POPs) in deep-sea sediments of the tropical western Pacific Ocean

Persistent organic pollutants (POPs) are toxic compounds that can persist for extended periods in the environment. The marine environment is considered an important sink for POPs. However, information regarding POPs in deep-sea environments remains limited. In this study, surface sediments from depths below 2,000 m were collected in the western Pacific Ocean to analyze polycyclic aromatic hydrocarbons (PAHs), organic pesticides, and polychlorinated biphenyls (PCBs). The concentrations of PAHs were highest (5.2-24.6 ng g^-1 dw). Hexachlorocyclohexanes (HCHs) were the predominant organic pesticide (30-1,730 pg g^-1 dw). Dicofol, chlorpyrifos, and malathion were detected only at a few sites. PCBs were not detected in the study area. A principal component analysis with multiple linear regression (PCA-MLR) indicated that PAHs in sediments mainly originated from biomass and coal combustion (∼62%) and petrogenic (∼38%) sources. This study revealed the distribution and potential sources of POPs in sediments of a deep-sea region in the western Pacific Ocean. Further studies of the transformations, sedimentation, and biological interactions of POPs are needed to better understand the fates of POPs in the marine environment and the ecological risks they pose.

Polycyclic aromatic hydrocarbon contamination along roads based on levels on vehicle window films

Vehicular emissions are known to be major contributors of airborne polycyclic aromatic hydrocarbons (PAHs) in cities. In order to assess the long-term contamination of PAHs along roads, we collected organic films from vehicle windows (26 private cars and 4 buses, in Shanghai, China) and used mathematical models to convert the film-bound PAH concentrations to the airborne PAH concentrations. The field measurements of airborne PAHs revealed that the partitioning and Level III fugacity model was suitable to estimate the airborne concentrations of high and low volatile PAHs (expect for naphthalene), respectively. The total airborne PAH concentrations along roads in Shanghai ranged from 0.83 to 3.37 μg m^-3 and the incremental lifetime cancer risks (ILCR_total) by exposure to PAHs along roads were greater than the USEPA lower guideline of 10^-6, indicating non-negligible carcinogenic risks to drivers and passengers, especially via ingestion processes. This study provided a practicable method to investigate long-term air contamination of PAHs in vehicles and along roads based on film-bound PAH on vehicle windows. In addition, it was also possible to investigate the health risk in vehicles as a result of exposure to PAHs. Comparisons of PAHs between roads and shipping lanes also facilitated the delineation of vehicular and shipping PAH inventories. A capsule that summarizes the main finding of the work: Investigating film-bound PAH on vehicle windows is a practicable pathway to investigate the long-term contamination of PAHs in vehicles and along roads. This method can not only simplify the sampling processes, but the model calculations. The results also enabled investigations into ILCR in vehicles and specified source apportionment of traffic PAHs.

Tracing human footprint and the fate of atmospheric polycyclic aromatic hydrocarbons over the Pearl River Estuary, China: Importance of particle size

Few studies have focus on size-segregated particulate polycyclic aromatic hydrocarbons (PAHs) in the oceanic atmosphere. To better understand the impacts of anthropogenic activities on atmospheric PAHs, a heavily human-impacted estuary, the Pearl River Estuary (PRE), was chosen as a case study. We collected gaseous and size-segregated particulate samples of ambient air at two sites in the PRE, as well as from the exhaust emissions of the cruise ship used in the sampling campaign. In addition, surface seawater samples were collected. Size distribution patterns of high molecular-weight (HMW) particulate PAHs were bimodal at one site and unimodal at the other, suggesting PAHs at the former site were derived not only from long-range atmospheric transport but also from local sources. Gas-particle partition coefficients of HMW PAHs in size-segregated particles varied with particle sizes, mostly higher in fine particles (<1.8 μm). Dry deposition flux of Σ₂₃PAHs (defined as the sum of 23 PAHs) was contributed mainly from coarse particles (>1.8 μm), and HMW PAHs with lower dry deposition velocities could be transported farther away. With respect to air-water exchange, lower MW PAHs tended to have net volatilization, whereas higher MW PAHs were likely to have net deposition. This study sheds new lights on the origins and fate of atmospheric PAHs over the PRE, and suggests the emissions of maritime traffics should be regulated. Collected near the metropolitan regions, atmospheric PAHs over the PRE were highly affected by anthropogenic activities, especially for HMW PAHs, which could pose a long-lasting impact to the oceanic atmosphere and marine organisms.

Distribution and gas-particle partitioning of polycyclic aromatic hydrocarbons over the East China Sea and Yellow Sea in spring: Role of atmospheric transport transition

To elucidate the variations in the East Asian monsoon system during seasonal changes and their impacts on continental outflow of polycyclic aromatic hydrocarbons (PAHs), sixteen integrated air samples were collected during a research cruise covering the Yellow Sea (YS) and East China Sea (ECS) in mid-spring of 2017. The concentrations of total suspended particle (TSP), aerosol-phase PAH fractions, ratios of organic to elemental carbon (OC/EC) and gas-particle partitioning of atmospheric PAHs exhibited clear regional differences associated with variations in the monsoon regime. The total concentrations of 16 USEPA priority PAHs (Σ₁₆PAHs) varied from 3.11 to 13.4 ng/m³ throughout the cruise, with medium-to-high molecular weight (MW) PAHs more enriched over the YS and north ECS than the south ECS. Together with the relatively low gaseous PAH fraction over the YS and north ECS (78 ± 4%) relative to the south ECS (95 ± 13%), this result indicates the pattern of regional atmospheric transport. The ratio of organic to elemental carbon varied significantly between the south ECS (lower than 4) and the YS and north ECS (greater than 4), indicating contributions from vehicle emissions and coal combustion or biomass burning, respectively, following different atmospheric input pathways of carbonaceous aerosols, as supported by backward trajectory analysis. Considering the gas-particle partitioning of PAHs, soot adsorption was the main partitioning mechanism in the study region; while high-MW PAHs in the YS and north ECS were influenced by both absorption and adsorption. The K_oa absorption model provided better predictions for high-MW PAHs when continental air masses prevailed, despite underestimating the partition coefficients (k_p) of low-MW PAHs. Meanwhile, predicted k_p for medium MW PAHs was better estimated over the YS and ECS when K_sa was included.

Volatilization of polycyclic aromatic hydrocarbons (PAHs) over the North Pacific and adjacent Arctic Ocean: The impact of offshore oil drilling

Air and seawater samples were collected in 2016 over the North Pacific Ocean (NPO) and adjacent Arctic Ocean (AO), and Polycyclic Aromatic Hydrocarbons (PAHs) were quantified in them. Atmospheric concentrations of ∑₁₅ PAHs (gas + particle phase) were 0.44-7.0 ng m^-3 (mean = 2.3 ng m^-3), and concentrations of aqueous ∑₁₅ PAHs (dissolved phase) were 0.82-3.7 ng L^-1 (mean = 1.9 ng L^-1). Decreasing latitudinal trends were observed for atmospheric and aqueous PAHs. Results of diagnostic ratios suggested that gaseous and aqueous PAHs were most likely to be related to the pyrogenic and petrogenic sources, respectively. Three sources, volatilization, coal and fuel oil combustion, and biomass burning, were determined by the PMF model for gaseous PAHs, with percent contributions of 10%, 44%, and 46%, respectively. The 4- ring PAHs underwent net deposition during the cruise, while some 3- ring PAHs were strongly dominated by net volatilization, even in the high latitude Arctic region. Offshore oil/gas production activities might result in the sustained input of low molecular weight 3- ring PAHs to the survey region, and further lead to the volatilization of them. Compared to the gaseous exchange fluxes, fluxes of atmospheric dry deposition and gaseous degradation were negligible. According to the extrapolated results, the gaseous exchange of semivolatile aromatic-like compounds (SALCs) may have a significant influence on the carbon cycling in the low latitude oceans, but not for the high latitude oceans.

Cross-interface transfer of polycyclic aromatic hydrocarbons (PAHs) in a shallow urban lake in Shanghai, China based on the fugacity model

Shallow urban lakes are important urban ecosystems; however, these systems are subject to severe polycyclic aromatic hydrocarbons (PAHs) contamination. An understanding of the distribution and dynamics of PAHs in lakes is required to restore the functions of lake ecosystems and to ensure the ecological security of urban water sources. The Quantitative Water Air Sediment Interaction (QWASI) model and partition coefficient and fugacity fraction methods were applied to estimate the multimedia transfers of PAHs in Dianshan Lake, a typical shallow lake in Shanghai, China. In addition, some new concepts and methods related to PAH transfers were introduced. The results showed that while the gas-solid partition in the area remained in non-equilibrium, the influence of pollution sources tended to weaken. Atmospheric advection was the main source of PAHs to the lake, and a portion of the net loss of advection was transformed into total flux of cross-interface transfers, in which transport fluxes from air to water and from water to sediment were dominant, with a significant correlation between the two types of transfer. The large resuspension of high molecular weight (HMW)-PAHs occurred, possibly related to frequent hydrodynamic disturbances. Furthermore, this study explored the distribution of PAHs among different compartments and the seasonal variation of multimedia transfers. Sensitivity analysis showed that the model is remarkably sensitive to four parameters including temperature and advection. Monte Carlo uncertainty analysis verified that the simulation results were stable and reliable. The results can provide a theoretical basis for the monitoring and control of shallow lake pollution.

Atmospheric legacy organochlorine pesticides and their recent exchange dynamics in the Northwest Pacific Ocean

The occurrence and air-sea gas exchange of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and chlordanes were determined in the Northwest Pacific Ocean (NWP) in spring to elucidate their current pollution status and fate. ΣHCHs, ΣDDTs, and Σchlordanes in air (sum of gaseous and aerosol phase) ranged from 9.37 to 102, from 1.73 to 12.8, and from 0.24 to 14.9 pg/m³, respectively, with their dissolved levels being 30.7-518, 7.10-80.5, and 0.25-7.10 pg/L, respectively. HCHs, DDTs, and chlordanes cause substantial contamination of the air and seawater of the East China Sea (ECS), indicating significant OCP inputs from China. Isomer ratios of HCHs and DDTs provided a fingerprint of East Asian emissions of legacy OCPs, with the pollution profiles of HCHs and DDTs dominated by lindane and combined dicofol-type and weathered technical DDTs, respectively. The former result is consistent with the apparent decline in air α-HCH levels over the ECS. Different from still net deposition of gaseous α- and γ-HCH in the NWP, outgassing of trans-chlordane, cis-chlordane, and DDTs other than dicofol-sourced o,p'-DDT was indicated. This observation attributes to intensive historical usage of technical HCHs and the prevalence of lindane pollution in East Asia, and demonstrates the transitioning role of seawater as a source for residual OCPs in the East Asia-NWP region. Significant subcooled liquid vapor pressure-based relationships for legacy OCPs were identified mainly in marine air masses; these were different from land-sourced polybrominated diphenyl ethers, and suggested a heterogeneous role of ocean- and land-based sources in atmospheric partitioning of these pollutants.

Occurrence, air-sea exchange, and gas-particle partitioning of atmospheric polybrominated diphenyl ethers from East Asia to the Northwest Pacific Ocean

The occurrence, air-sea exchange, and gas-particle partitioning of polybrominated diphenyl ethers (PBDEs) were analyzed during a 2015 research expedition from the East China Sea (ECS) to the open Northwest Pacific Ocean (NWP). The sum of 13 PBDEs (Σ₁₃PBDEs) in air and surface seawater varied in the range of 0.54-14.5. pg m^-3 and 0.60-13.5 pg L^-1, respectively, with the highest concentrations observed in the ECS. The Clausius-Clapeyron approach and air mass origin analysis indicated that continued primary emissions of PBDEs, particularly BDE-209, from East Asian sources governed the spatial variability of air PBDEs over the NWP through long-range atmospheric transport (LRAT). Net air-to-seawater gas deposition of PBDEs was evidenced based on the fugacity calculation with sum fluxes of seven selected PBDEs ranging from -45 to -582 pg m^-2 d^-1. Following the substantial advection of aerosol phase BDE-209 over the ECS, dry particle deposition dominated the input pathway of PBDEs into the ECS, whereas in the open NWP, relatively free from the influence of the land emissions, fluxes in PBDE absorption and in dry particle deposition were comparable. This suggests an impact of continental outflow on the fate of atmospheric PBDEs over the NWP. Regarding gas-particle partitioning, PBDEs over the NWP were obviously absorbed into continental organic aerosols during atmospheric transport, except for BDE-209, which tended to remain within the steady state.

Multimedia modeling of the PAH concentration and distribution in the Yangtze River Delta and human health risk assessment

Emissions of polycyclic aromatic hydrocarbons (PAHs) in China remain at a high level compared to those in developed countries. The Yangtze River Delta (YRD) is an economic and industrial center in China with an extremely large population. The potentially high emissions and excess cancer risk from human exposure in this region cannot be neglected. This study applied a multimedia model to estimate the concentrations of 16 US EPA priority PAHs in the environment in the YRD with a well-developed PAH-emission inventory for 2014. The model predicted that the average concentrations of ΣPAHs were 274 ng/m³ in the air, 255 ng/g in the soil, 15 ng/g in vegetation, 147 ng/L in freshwater and 144 ng/g in sediment, as well as 99 ng/L and 80 ng/g in seawater and sediment, respectively. Soil is the PAH sink in this region, and the net flux of the total PAHs is always from air to soil for each isomer. A deterministic assessment observed that the ELCR (excess lifetime cancer risk) ranged from 2.5 × 10^-6 to 3.0 × 10^-5 for exposure by air inhalation and from 3.5 × 10^-7 to 7.9 × 10^-6 for exposure by soil ingestion. The probabilistic results did not find any probability of ELCR >10^-4 by exposure via soil ingestion in the YRD. The probabilistic ELCR induced by inhalation exposure varied from 8.1 × 10^-7 to 3.1 × 10^-4 in the YRD. This study provided a comprehensive overview of PAHs occurrence in natural environments and of the relevant human health risks. The information presented in this study could help authorities to enact a strategy regarding emission reduction and pollution control relevant to PAHs.

CAPSULE

Multimedia modeling predicted distributions and compositions of PAHs in different environmental compartments, and deterministic and probabilistic ELCRs induced by air inhalation and soil ingestion were also provided.

Seasonal variation, air-water exchange, and multivariate source apportionment of polycyclic aromatic hydrocarbons in the coastal area of Dalian, China

The concentrations and seasonal variations of polycyclic aromatic hydrocarbons (PAHs) in air and seawater dissolved samples from the coastal area of Dalian were investigated, as well as their air-water exchanges. The average concentrations of PAHs were 27.5 ± 14.6 ng/m³ and 49.5 ± 20.5 ng/L in the air and water, respectively. Phenanthrene was the dominant congener in both air and water dissolved phase. Seasonality was discovered in the air with the concentrations higher in winter than in summer, but not in the water dissolved phase. Air-water exchange trends also displayed apparent seasonality with 3-4 ring PAHs generally being volatilization or equilibrium in summer but deposition in winter, which highlighted the important influence of temperature on the air-water exchange direction of PAHs. The air-water exchange fluxes of individual PAH congeners ranged from -24331 to 6541 ng/m²/d, and the highest deposition and volatilization fluxes both appeared at the industrial areas, which emphasized the influence of point source emission to the magnitude of air-water diffusion flux of PAHs. Multivariate source apportionment approaches, including principle component analysis, diagnostic ratios, and positive matrix factorization, were conducted, which suggested that PAHs in water originated from multiple sources. Frequent port transport correlated vehicle/ship emission rather than coal combustion may be the primary contributor of PAHs to the coastal air and water.

Fossil Fuel-Derived Polycyclic Aromatic Hydrocarbons in the Taiwan Strait, China, and Fluxes across the Air-Water Interface

On the basis of the application of compound-specific radiocarbon analysis (CSRA) and air-water exchange models, the contributions of fossil fuel and biomass burning derived polycyclic aromatic hydrocarbons (PAHs) as well as their air-water transport were elucidated. The results showed that fossil fuel-derived PAHs (an average contribution of 89%) presented the net volatilization process at the air-water interface of the Taiwan Strait in summer. Net volatile fluxes of the dominant fluorene and phenanthrene (>58% of the total PAHs) were 27 ± 2.8 μg m^-2 day^-1, significantly higher than the dry deposition fluxes (average 0.43 μg m^-2 day^-1). The Δ¹⁴C contents of selected PAHs (fluorene, phenanthrene plus anthracene, fluoranthene, and pyrene) determined by CSRA in the dissolved seawater ranged from -997 ± 4‰ to -873 ± 6‰, indicating that 89-100% (95 ± 4%) of PAHs were supplied by fossil fuels. The South China Sea warm current originating from the southwest China in summer (98%) and the Min-Zhe coastal current originating from the north China in winter (97%) input more fossil fuel PAHs than the Jiulong River estuary (90%) and Xiamen harbor water (93%). The more radioactive decayed ¹⁴C of fluoranthene (a 4-ring PAH) than that of phenanthrene and anthracene (3-ring PAHs) represented a greater fossil fuel contribution to the former in dissolved seawater.