Role of PM2.5 in the photodegradation of the atmospheric benzene

Long-term ambient ozone exposure and lung cancer mortality: a nested case-control study in Korea

The link between long-term exposure to tropospheric ozone (O3) and risk of lung cancer mortality remains uncertain. We aimed to provide new insights into the association between long-term O3 exposure and lung cancer mortality in Korea. A nested case-control study was conducted within a cancer-free cohort of 1,731,513 individuals who underwent health screenings provided by the National Health Insurance Service in 2006-2007. A total of 7,133 lung cancer deaths that occurred from January 1, 2012, to December 31, 2021, were matched to 28,532 controls at a 1:4 ratio based on propensity scores. Daily 24-hour and 8-hour maximum O3 concentrations, averaged year-round and during the warm season from 2006 to 2010, were estimated for participants based on their residential addresses using the Community Multiscale Air Quality model. O3 concentrations rise during the daytime, also exhibiting seasonal variations, with the highest levels occurring in the warm season. Elevated risk of lung cancer mortality was observed among participants in the highest quartile of O3 exposure compared with those in the lowest quartile, yielding odds ratios ranging from 1.15 to 1.27. However, when exposure to particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) was further adjusted for, the adverse risk of long-term O3 exposure was attenuated, even tending to be protective. Notably, participants with both high O3 and high PM2.5 exposures had an increased risk of lung cancer mortality. Furthermore, regional differences were observed, with a significantly higher risk in rural areas. Findings of this study suggest that long-term exposure to O3, especially in combination with PM2.5 exposure, is associated with an excess risk of lung cancer mortality, underscoring the importance of addressing the O3 and PM2.5 interaction in lung cancer prevention.

Combating regional air pollution significantly enhance the photodegradation of atmospheric benzo(a)pyrene

Air pollution control strategies aim to reduce the levels of primary pollutants, but unexpectedly induce changes in atmospheric photochemistry. This may create favorable condition for the photodegradation of atmospheric Benzo(a) pyrene (BaP), leading to new environmental challenges because of the more toxic derivatives. Based on the field observations from 1998 to 2021 at Tsuen Wan (TW) and Central & Western District (CWD) sites in Hong Kong, Coupling detrended fluctuation analysis (CDFA) has been applied to quantitatively describe the photodegradation degree of BaP in real atmosphere. From the temporal evolution process, it has been discovered that BaP photodegradation exhibits a significant increase trend since 2019 in Hong Kong. Correlation analysis shows that degree of BaP photodegradation is positively correlated with factors (T, RH, hv, O3 and NO2/NOx), while is negatively correlated with factor (PM2.5/PM10). Due to the impact of sea salt aerosols, the effect of O3 and NO2 on BaP photodegradation at CWD site is less significant than that at TW site. Furthermore, the relative contribution of major atmospheric oxidants NO2 and O3 to BaP photodegradation in real atmosphere has been determined. The results suggest that contribution of NO2 to BaP photodegradation is greater than that of O3, and the contribution of O3 is gradually increasing in Hong Kong. This work has discovered a new environmental effect that may be caused by air pollution control strategies. New insights have significant implications for improving ecological risk assessment.

Fractal analysis of impact of PM2.5 on surface O3 sensitivity regime based on field observations

Properties of PM_2.5 that can change aerosol chemistry and photolysis rates have great impacts on O₃ sensitivity regime, further affecting the production rate of surface O₃. However, responses of O₃ sensitivity regime to changes in PM_2.5 levels are difficult to be accurately determined, due to the complexity and nonlinearity of atmospheric chemistry. Here, based on long-term time series (2016-2020) of air quality variables in north and south Taiwan, fractal analysis along with Pearson correlation analysis are used to directly reveal the impacts of PM_2.5 on O₃ sensitivity regime in real atmosphere, by capturing the nonlinear dynamic relations among air pollutants. Great regional and seasonal difference in impacts of PM_2.5 on O₃ sensitivity regime may be ascribed to meteorological factors, PM_2.5 components and levels of SO₂, NO, NO₂, etc. For north Taiwan, increased PM_2.5 level can enhance the sensitivity of O₃ formation to VOC in spring and summer, whereas the opposite effect can be observed in winter. But for south Taiwan, the influence of PM_2.5 on O₃ sensitivity regime is not statistically significant, excluding spring. Furthermore, feasibility and availability of fractal analysis is tested by simulations with Empirical Kinetics Modeling Approach (EKMA). The results demonstrate the capability of fractal analysis to identify the impacts of PM_2.5 on O₃ sensitivity regime in real atmosphere, which can provide suggestions for PM_2.5-O₃ coordinated control strategies in regions suffering combined air pollution.

Impacts of dust events on chemical characterization and associated source contributions of atmospheric particulate matter in northern China

Sand and dust have significant impacts on air quality, climate, and human health. To investigate the influences of dust storms on chemical characterization and source contributions of fine particulate matter (PM_2.5) in areas with different distances from dust source regions, PM_2.5 and associated chemical composition were measured in two industrial cities with one near sand sources (i.e., Wuhai) and the other far from sand sources (i.e., Jinan) in northern China in March 2021. Results showed that PM mass concentrations significantly increased and exceeded the Chinese National Ambient Air Quality standard during the dust events, with absolute concentrations and fractional contributions of PM_2.5-bound crustal and trace elements increased while secondary inorganic ions decreased at both sites. Crustal materials dominated the increased PM_2.5 mass from non-dust period to dust period in both cities. These were further evidenced by PM_2.5 source apportionment results from positive matrix factorization model. During the dust events, dust sources contributed up to 88% of PM_2.5 mass in Wuhai and ∼38% of PM_2.5 mass in Jinan, a city about thousands of kilometers away from the sand source. Besides, the measurement data indicated that dust from northwest China may also bring along with high abundance of organic matter and vanadium. Secondary and traffic sources were two of the most important source contributors to PM_2.5 in both cities during the non-dust periods. However, the near sand source city was more susceptible to the aggravating effects of dust and minerals, with much higher contributions by crustal materials (∼47%, from the aspect of chemical components) and dust-related sources (∼26%, from the aspect of sources) to PM_2.5 mass even during non-dust periods. This study highlighted the urgent need for more action and effective control of sand sources to reduce the impact on air quality in downstream regions.

PM2.5-mediated photochemical reaction of typical toluene in real air matrix with identification of products by isotopic tracing and FT-ICR MS

The sight into photoconversion of toluene, a ubiquitous typical pollutant, attentively by the involvement of PM2.5 in the real air environment is crucial for controlling haze pollution. Compared with the large-size PM2.5 on normal day (PM2.5-ND), the PM2.5 on haze day (PM2.5-HD) formed of small particle agglomerates featured greater oxidation capability, evidenced by the valence distribution of sulfur species. Notably, PM2.5-HD had abundant O₂^-• and •OH and participated in the photochemical reaction of toluene, giving it a greater toluene conversion with a first-order kinetic rate constant of 0.4 d^-1 on haze day than on normal day (0.2 d^-1). During the toluene photoconversion, isotopic labelling traced small molecules including benzene and newfound pentane, ethylbenzene, 1,3,8-p-menthatriene and 4-methyl-1-pentanone benzene that could be formed by methyl breakage, ring opening, fragmentation reforming and addition reaction of toluene. Given ADMET properties, 1,3,8-p-menthatriene was assigned high priority since it had poor metabolism, low excretion and severe toxicity, while benzene and 4-methyl-1-pentanone benzene should also be noticeable. FT-ICR MS results indicated that toluene could create multiple macromolecular products that are more sensitive to SOA generation in haze air matrix with broader carbon number and O/C, more oxygenated substitution with CHO/CHON occupying by 81.4%, lower DBE_average at 4.66 and higher OS_C‾ at -1.60 than normal air matrix. Accordingly, a photochemical reaction mechanism for toluene in real air atmosphere was proposed. The stronger oxidation property of PM2.5 not only facilitated toluene to generate small molecules but also boosted the conversion of intermediates to oxygenated macromolecular products, contributing to the formation of SOA.

Spatial Characteristics Analysis for Coupling Strength among Air Pollutants during a Severe Haze Period in Zhengzhou, China

This paper investigates the multifractal characteristics of six air pollutants using the coupling detrended fluctuation analysis method. The results show that coupling correlations exist among the air pollutants and have multifractal characteristics. The sources of multifractality are identified using the chi square test. The coupling strengths between different pollutants are quantified. In addition, the coupling contribution of a series in the haze system is calculated, and SO₂, as the main pollutant, plays a key role in the pollution system. Moreover, the Kriging interpolation method is used to analyze the spatial characteristic on coupling contribution of SO₂. The spatial analysis of coupling strength for air pollutants will provide an effective approach for pollution control.

An optimized approach for estimating benzene in ambient air within an air quality monitoring network

Benzene is a carcinogenic air pollutant for which European legislation has set an annual limit and criteria for the number of fixed monitoring sites within air quality networks (AQMN). However, due to the limited number of fixed sites for benzene measurement, exposure data are lacking. Considering the relationship between benzene levels and other variables monitored within an AQMN, such as NO₂, O₃, temperature, solar radiation, and accumulated precipitation, this study proposes an approach for estimating benzene air concentrations from the related variables. Using the data of the aforementioned variables from 23 fixed stations during 2016-2017, the proposed approach was able to forecast benzene concentration for 2018 with high confidence, providing enriched data on benzene exposure and its trends. Moreover, the spatial distribution of the estimated versus the most representative benzene levels was quite similar. Finally, an artificial neural network identified the most representative fixed benzene monitoring sites within the AQMN.

A review on methodology in O3-NOx-VOC sensitivity study

Gaining insight into the response of surface ozone (O₃) formation to its precursors plays an important role in the policy-making of O₃ pollution control. However, the real atmosphere is an open and dissipative system, and its complexity poses a great challenge to the study of nonlinear relations between O₃ and its precursors. At present, model-based methods based on reductionism try to restore the real atmospheric photochemical system, by coupling meteorological model and chemical transport model in temporal and spatial resolution completely. Nevertheless, large inconsistencies between predictions and true values still exist, due to the great uncertainty originated from emission inventory, photochemical reaction mechanism and meteorological factors. Recently, based on field observations, some nonlinear methods have successfully revealed the complex emergent properties (long-term persistence, multi-fractal, etc) in coupling correlation between O₃ and its precursors at different time scales. The emergent properties are closely associated with the intrinsic dynamics of atmospheric photochemical system. Taking them into account when building O₃ prediction model, is helpful to reduce the uncertainty in the results. Nonlinear methods (fractal, chaos, etc) based on holism can give new insights into the nonlinear relations between O₃ and its precursors. Changes of thinking models in methodology are expected to improve the precision of forecasting O₃ concentration. This paper has reviewed the advances of different methods for studying the sensitivity of O₃ formation to its precursors during the past few decades. This review highlights that it is necessary to incorporate the emergent properties obtained by nonlinear methods into the modern models, for assessing O₃ formation under combined air pollution environment more accurately. Moreover, the scaling property of coupling correlation detected in the real observations of O₃ and its precursors could be used to test and improve the simulation performance of modern models.

Revealing adsorption and the photodegradation mechanism of gas phase o-xylene on carbon quantum dots modified TiO2 nanoparticles

Here, we report the photocatalytic oxidation (PCO) of o-xylene on carbon quantum dots (CQDs) modified TiO₂ nanoparticles. The results demonstrated that with 1 wt% CQDs loading, 87 % of o-xylene (50 ppm) can be photodegraded, which is 55.3 % higher than pure TiO₂ (56 %) under UV/visible light. This improved photocatalytic activity is associated with the important role of CQDs on TiO₂ surface, which increased the o-xylene adsorption and facilitated the photogenerated hole-electron separation process. Also, the 1 wt%CQDs/TiO₂ nanocomposite showed photocatalytic activity in the visible region (λ > 400 nm) compared to pure TiO₂ (inactive). The DFT study revealed that o-xylene strongly adsorb on TiO₂ (001) surface than (101) through π electrons of the aromatic ring. The in situ DRIFTS study showed that free OH groups on the photocatalyst surface could act as effective Lewis sides for the o-xylene adsorption. The interaction of π electrons of the aromatic ring and isolated OH groups was also observed. The FTIR peaks for CO₂ increased in the case of CQDs/TiO₂ nanocomposite contrasted to pure TiO₂, which suggested that the presence of CQDs improved the mineralization potency of TiO₂. These findings should affect the quest for a better photocatalyst to photodegrade VOCs.