Mapping nationwide concentrations of sulfate and nitrate in ambient PM2.5 in South Korea using machine learning with ground observation data.

Particulate matter (PM) is a major air pollutant in Northeast Asia, with frequent high PM episodes. To investigate the nationwide spatial distribution maps of PM2.5 and secondary inorganic aerosols in South Korea, prediction models for mapping SO42- and NO3- concentrations in PM2.5 were developed using machine learning with ground-based observation data. Specifically, the random forest algorithm was used in this study to predict the SO42- and NO3- concentrations at 548 air quality monitoring stations located within the representative radii of eight intensive air quality monitoring stations. The average concentrations of PM2.5, SO42-, and NO3- across the entire nation were 17.2 ± 2.8, 3.0 ± 0.6, and 3.4 ± 1.2 µg/m3, respectively. The spatial distributions of SO42- and NO3- concentrations in 2021 revealed elevated concentrations in both the western and central regions of South Korea. This result suggests that SO42- concentrations were primarily influenced by industrial activities rather than vehicle emissions, whereas NO3- concentrations were more associated with vehicle emissions. During a high PM2.5 event (November 19-21, 2021), the concentration of SO42- was primarily influenced by SOX emissions from China, while the concentration of NO3- was affected by NOX emissions from both China and Korea. The methodology developed in this study can be used to explore the chemical characteristics of PM2.5 with high spatiotemporal resolution. It can also provide valuable insights for the nationwide mitigation of secondary PM2.5 pollution.

Mapping the spatial distribution of primary and secondary PM2.5 in a multi-industrial city by combining monitoring and modeling results.

Industrial cities are strongly influenced by primary emissions of PM2.5 from local industries. In addition, gaseous precursors, such as sulfur oxides (SOX), nitrogen oxides (NOX), and volatile organic compounds (VOCs), emitted from industrial sources, undergo conversion into secondary inorganic and organic aerosols (SIAs and SOAs). In this study, the spatial distributions of primary and secondary PM2.5 in Ulsan, the largest industrial city in South Korea, were visualized. PM2.5 components (ions, carbons, and metals) and PM2.5 precursors (SO2, NO2, NH3, and VOCs) were measured to estimate the concentrations of secondary inorganic ions (SO42-, NO3-, and NH4+) and secondary organic aerosol formation potential (SOAFP). The spatial distributions of SIAs and SOAs were then plotted by combining atmospheric dispersion modeling, receptor modeling, and monitoring data. Spatial distribution maps of primary and secondary PM2.5 provide fundamental insights for formulating management policies in different districts of Ulsan. For instance, among the five districts in Ulsan, Nam-gu exhibited the highest levels of primary PM2.5 and secondary nitrate. Consequently, controlling both PM2.5 and NO2 emissions becomes essential in this district. The methodology developed in this study successfully identified areas with dominant contributions from both primary emissions and secondary formation. This approach can be further applied to prioritize control measures during periods of elevated PM levels in other industrial cities.

Distributions of PCDD/Fs, PCBs, and PCNs in coastal sediments collected from major industrial bays in South Korea.

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs) were assessed in coastal sediments from industrial bays in South Korea to evaluate the pollution levels and their environmental impact. The mean sediment concentrations of Σ17 PCDD/Fs, Σ18 PCBs, and Σ15 PCNs were 198 ± 140, 3427 ± 7037, and 85 ± 336 pg/g dw, respectively. Generally, pollutant concentrations in the inner bay were higher than those in the outer bay, indicating the influence of industrial emissions and harbor activities. The primary sources were identified as steel manufacturing and wastewater treatment plants for PCDD/Fs, harbor and shipbuilding activities for PCBs, and combustion-related sources for PCNs. Notably, PCDD/F concentrations exceeded sediment guideline values. The combined effects of PCDD/Fs and PCBs demonstrated adverse impacts on aquatic organisms. Hence, the release of toxic pollutants into the marine environment could have potential biological effects due to the combined impact of these various compounds.

Passive air sampling of VOCs, O3, NO2, and SO2 in the large industrial city of Ulsan, South Korea: spatial-temporal variations, source identification, and ozone formation potential.

Concerns about volatile organic compounds (VOCs) have increased due to their toxicity and secondary reaction with nitrogen oxides (NOX) to form ozone (O3). In this study, passive air sampling of VOCs, O3, NO2, and SO2 was conducted in summer, fall, winter, and spring from 2019 to 2020 at six industrial and ten urban sites in Ulsan, the largest industrial city in South Korea. Over the entire sampling period, the concentration of toluene (mean: 8.75 µg/m3) was the highest of the 50 target VOCs, followed by m,p-xylenes (4.52 µg/m3), ethylbenzene (4.48 µg/m3), 3-methylpentane (4.40 µg/m3), and n-octane (4.26 µg/m3). Total (Σ50) VOC levels did not statistically differ between seasons, indicating that large amounts of VOCs are emitted into the atmosphere throughout the year. On the other hand, O3, NO2, and SO2 exhibited strong seasonal variation depending on the meteorological conditions and emission sources. The spatial distribution of Σ50 VOCs, NO2, and SO2 indicated that industrial complexes were major sources in Ulsan, while O3 had the opposite spatial distribution. Using a positive matrix factorization model, five major sources were identified, with industrial effects dominant. Aromatic compounds, such as m,p,o-xylenes, toluene, and 1,2,4-trimethylbenzene, significantly contributed to O3 formation. The VOC/NO2 ratio and O3 concentrations suggested that reducing VOC emissions is more effective than reducing NO2 emissions in terms of preventing the secondary formation of O3. The findings of this study allow for a better understanding of the relationship between VOCs, O3, NO2, and SO2 in industrial cities.

Particulate matter concentration effects on attention to environmental issues: a cross-sectional study among residents in Korea's Pohang Industrial Complex.

Background: With modernization, air pollution has become increasingly serious, and its effects on health have been revealed. As a result, public interest in environmental pollution has become critical for regulating air pollution. In our study, we aim to evaluate the impact of air pollution levels on public attention to environmental issues and examine whether awareness of the residential environment's impact on health acts as a mediator in this relationship. Methods: We conducted an analysis on 400 individuals surveyed in the preliminary feasibility study on adverse health effects in the Pohang Industrial Complex, to examine the relationship between particulate matter 2.5 (PM2.5) and attention to environmental issues. Logistic regression analysis was performed, and mediation analysis was used to determine whether awareness of the residential environment's impact on health mediated the relationship. Results: The logistic regression analysis results showed that PM2.5 levels were associated with attention to environmental issues (adjusted odds ratio [AOR]: 2.1; 95% confidence interval [CI]: 1.3-3.5; p = 0.003) and awareness of health impacts (AOR: 3.4; 95% CI: 1.6-7.1; p = 0.001). The PM2.5 levels showed 9.9% (95% CI: 5.4-14.0) increase in the prevalence of high attention to environmental issues, of which, only 1.0% (95% CI: 0.2-2.3) were mediated by health impact awareness. In the overall analysis, 10% of the total effect of PM2.5 on attention to environmental issues was mediated by health impact awareness. Conclusions: According to this study's results, there was a correlation between air pollution levels and attention to environmental issues. Awareness of the health impacts of air pollution partially mediated the effect of air pollution levels on attention to environmental issues. In future studies, it is recommended to identify other mediators to further understand this structure.

Roles of ambient temperature and relative humidity on the relationship between fine particulate matter and gaseous pollutants in the largest industrial city of Ulsan, South Korea.

Although meteorological conditions play a significant role in air pollution, research on their effects on the relationship between air pollutants is limited. In this study, trends of six criteria air pollutants were investigated from 15 air quality monitoring stations (AQMSs) in Ulsan, a multi-industrial city in South Korea, during 2015-2019. Unlike CO and O3, SO2, NO2, PM10, and PM2.5 showed statistically significant decreasing trends over the period. The companion relationship between PM2.5 and gaseous pollutants was evaluated by their correlations [R (PM2.5-GPs)]. R (PM2.5-NO2) was relatively high at almost all AQMSs, whereas high R (PM2.5-SO2) was observed near the petrochemical industrial complex, suggesting a great influence of local emissions (vehicles and industries). R (PM2.5-CO) and the standardized regression coefficients of CO obtained from the multiple linear regression model were the highest, indicating that combustion processes may significantly contribute to PM2.5. The effect of temperature (T) was more apparent on R (PM2.5-GPs) than that of relative humidity, with significant values under T > 15 °C. Moreover, R (PM2.5-O3) was positive at the T range of 12-18 °C, suggesting that reducing GPs emitted by industrial facilities during May-June may control PM2.5 and O3 in Ulsan. The methodology demonstrated in this study can be further used for a better understanding of the influences of environmental factors on the secondary PM2.5 formation from gaseous precursors and the R (PM2.5-O3).

Isotopic investigation of sources and processes affecting gaseous and particulate bound mercury in the east coast, South Korea.

Understanding sources and processes affecting atmospheric mercury (Hg) are key to enabling targeted Hg managements under the Minamata Convention on Mercury. We employed stable isotopes (δ202Hg, Δ199Hg, Δ201Hg, Δ200Hg, Δ204Hg) and backward air trajectories to characterize sources and processes affecting total gaseous Hg (TGM) and particulate bound Hg (PBM) in a coastal city, South Korea, subjected to atmospheric Hg sources of a local steel manufacturing industry, coastal evasion from the East Sea, and long-distance transport from East Asian countries. Based on the simulated airmasses and the isotopic comparison with TGM characterized from other urban, remote, and coastal sites, TGM evaded from the coastal surface of the East Sea (warm seasons) and from the land surface in high latitude regions (cold seasons) act as important sources relative to local anthropogenic emissions at our study location. Conversely, a significant relationship between Δ199Hg and concentrations of PBM (r2 = 0.39, p < 0.05) and a seasonally uniform Δ199Hg/Δ201Hg slope (1.15), except for summer (0.26), suggest that PBM is generally sourced from local anthropogenic emissions and subjected to Hg2+ photo-reduction on particles. The striking isotopic similarity between our PBM (δ202Hg; -0.86 to 0.49 ‰, Δ199Hg; -0.15 to 1.10 ‰) and those previously characterized along the coastal and offshore regions of the Northwest Pacific (δ202Hg; -0.78 to 1.1 ‰, Δ199Hg; -0.22 to 0.47 ‰) infer that anthropogenically emitted PBM from East Asia and those processed in the coastal atmosphere serves as a regional isotopic end-member. The implementation of air pollution control devices can reduce local PBM, while regional and/or multilateral efforts are required to manage TGM evasion and transport. We also anticipate that the regional isotopic end-member can be used to quantify the relative influence of local anthropogenic Hg emissions and complex processes affecting PBM in East Asia and other coastal regions.

Nationwide assessment of atmospheric organochlorine pesticides over a decade during 2008-2017 in South Korea.

Long-term nationwide atmospheric monitoring of organochlorine pesticides (OCPs) was performed in South Korea during 2008-2017. Their occurrences, seasonal and temporal variability, sources, and effect of ambient temperature were investigated. The OCPs are pronounced with a mean concentration of total OCPs ranging from 5.2 to 256 pg/Sm3. However, a decrease of 54 % was observed in the mean concentration of total OCPs from 2008 to 2017 associated with regulatory actions. OCP concentrations did not show any variations between the different site types, and OCPs were ubiquitously present at all site types. The mean concentration of total OCPs in summer was two-fold higher than in winter. The concentrations of DRINs, DDTs, ENDOs, and HCHs were significantly higher in summer, but the concentrations of chlordane and heptachlor were higher in winter. The diagnostic ratios identified major sources as ongoing sources, past use, and atmospheric transport. Clausius Clapeyron plots strongly suggested the re-emission of α-endosulfan, ß-endosulfan, α-HCH, and ß-HCH, and ΔHsa (enthalpy of surface air exchange) values suggested the influence of the transport and/or new sources on aldrin, dieldrin, and chlordane. The occurrence of OCPs due to re-emissions, ongoing sources, and long-range atmospheric transport could be a challenge towards the complete phase-out of OCPs in South Korea.

Optimization and application of passive air sampling method for gaseous elemental mercury in Ulsan, South Korea.

We compared uptake rates and concentrations of gaseous elemental mercury (GEM) by passive sampling conditions and investigated the spatial distribution of GEM in Ulsan, the largest industrial city in South Korea. For the optimization of sampling conditions, two outer sampling containers (cylindrical polyethylene terephthalate and two stainless steel bowls), two different sulfur contents of the sorbent (16.3% and 26.3%), and three sampling periods (1, 2, and 3 months) were considered. The uptake rates of GEM were not statistically different by the sampling container, but they were increased with the sulfur contents of activated carbon. A sampling condition using two stainless bowls and lower sulfur contents of activated carbon for 2-3 months was preferred with the highest precision of GEM concentrations. With the same method, passive air samples were collected for 3 months in duplicate from 10 sites in Ulsan. The concentrations of GEM ranged from 3.13 to 11.2 ng/m3 (mean 4.65 ng/m3), and the highest concentration was measured at a non-ferrous industrial complex. A zinc smelter in the non-ferrous industrial complex was identified as a major mercury source in Ulsan. This study is the first passive air sampling study investigating the spatial distributions of GEM in different types of industrial areas as well as residential areas of Ulsan.

Organochlorine pesticides in the urban, suburban, agricultural, and industrial soil in South Korea after three decades of ban: Spatial distribution, sources, time trend, and implicated risks.

Organochlorine pesticides in soil samples across urban, suburban, agricultural, and industrial sites were analyzed every year between 2013 and 2016 in South Korea. The study aims to understand the residual status, diminution of occurrence from the South Korean environment, and its risk to humans after three decades of the ban. A general decreasing trend of OCPs has been observed over the years. The OCP concentrations were below the guideline values prescribed for soil pollution. Metabolites like p,p'-DDD and endosulfan sulfate contributed a major portion to the total OCP concentration over the years. The agricultural sites showed higher OCP levels than other site types. Compositional profile and diagnostic ratios suggested that the occurrence of DDT and endosulfan residues were due to historical inputs, but those of HCH and chlordane reflect recent usage in some pockets. The calculated incremental lifetime cancer risk was within the safety limit for all age groups across the genders in the majority of the sites. It is evident that the OCP load on soil is decreasing since the ban on usage. However, regular monitoring with a special focus on metabolites can be an effective control measure to regulate and eliminate the contamination of OCPs.

Characteristics of volatile organic compounds in the metropolitan city of Seoul, South Korea: Diurnal variation, source identification, secondary formation of organic aerosol, and health risk.

Atmospheric volatile organic compounds (VOCs) in Seoul, the capital of South Korea, have attracted increased attention owing to their emission, secondary formation, and human health risk. In this study, we collected 24 hourly samples once a month at an urban site in Seoul for a year (a total of 288 samples) using a sequential tube sampler. Analysis results revealed that toluene (9.08 ± 8.99 µg/m3) exhibited the highest annual mean concentration, followed by ethyl acetate (5.55 ± 9.09 µg/m3), m,p-xylenes (2.79 ± 4.57 µg/m3), benzene (2.37 ± 1.55 µg/m3), ethylbenzene (1.81 ± 2.27 µg/m3), and o-xylene (0.91 ± 1.47 µg/m3), indicating that these compounds accounted for 77.8-85.6% of the seasonal mean concentrations of the total (Σ59) VOCs. The concentrations of the Σ59 VOCs were statistically higher in spring and winter than in summer and fall because of meteorological conditions, and the concentrations of individual VOCs were higher during the daytime than nighttime owing to higher human activities during the daytime. The conditional bivariate probability function and concentration weighted trajectory analysis results suggested that domestic effects (e.g., vehicular exhaust and solvents) exhibited a dominant effect on the presence of VOCs in Seoul, as well as long-range atmospheric transport of VOCs. Further, the most important secondary organic aerosol formation potential (SOAFP) compounds included benzene, toluene, ethylbenzene, and m,p,o-xylenes, and the total SOAFP of nine VOCs accounted for 5-29% of the seasonal mean PM2.5 concentrations. The cancer and non-cancer risks of the selected VOCs were below the tolerable (1 × 10-4) and acceptable (Hazard quotient: HQ < 1) levels, respectively. Overall, this study highlighted the feasibility of the sequential sampling of VOCs and hybrid receptor modeling to further understand the source-receptor relationship of VOCs.

Identification of source areas of polycyclic aromatic hydrocarbons in Ulsan, South Korea, using hybrid receptor models and the conditional bivariate probability function.

This study identifies the emission source areas for the atmospheric polycyclic aromatic hydrocarbons (PAHs) detected in Ulsan, South Korea. To achieve this, in addition to a conditional bivariate probability function (CBPF), two hybrid receptor models - the three-dimensional potential source contribution function (3D-PSCF) model and the 3D concentration weighted function (3D-CWT) model - were used, both of which adopt trajectory segments within the mixing layer. Notably, the fraction-weighted trajectory (FWT), a combination of PAH gas/particle partitioning with a hybrid receptor model, was introduced for the first time in this study to support the identification of emission source areas using other approaches (i.e., 3D-PSCF, 3D-CWT, and CBPF). Consequently, it was found that gaseous PAHs in Ulsan mostly originated from local emission sources (i.e., transportation and industrial emissions) throughout the year, whereas particulate PAHs were likely to originate from emission sources in China (e.g., Shandong, Hebei, and Liaoning) during spring and winter via long-range transport. However, in summer and fall, the influence of local emissions on particulate PAHs appeared to be stronger. The FWT was able to distinguish between local and distant sources more effectively, especially in summer and fall, i.e., the periods when local sources increased their contribution. This study thus increases the understanding of the long-range transport of PAHs in Northeast Asia, and the novel FWT approach exhibits the potential to be employed in the source area identification of various semi-volatile organic chemicals.

Application of gas chromatographic retention times to determine physicochemical properties of nitrated, oxygenated, and parent polycyclic aromatic hydrocarbons.

Nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) are receiving attention because of their high toxicity compared with parent PAHs. However, the experimental data of their physicochemical properties has been limited. This study proposed the gas chromatographic retention time (GC-RT) technique as an effective alternative one to determine octanol-air partition coefficients (KOA) and sub-cooled liquid vapor pressures (PL) for 11 NPAHs, 10 OPAHs, and 19 parent PAHs. The slopes and intercepts of the linear regressions between temperature versus KOA and PL were provided and can be used to estimate KOA and PL for the 40 targeted compounds at any temperature. The internal energies of phase transfer (ΔUOA) and enthalpies of vaporization (ΔHL) for all targeted compounds were also calculated using the GC-RT technique. High-molecular-weight compounds may release or absorb higher heat energy to transform between different phases. NPAHs and OPAHs had a non-ideal solution behavior with activity in octanol (γoct) in the range of 19-53 and 18-1,078, respectively, which is larger than the unity threshold. A comparison among four groups of PAH derivatives showed that a functional group (nitro-, oxygen-, chloro-, and bromo-) in PAH derivatives increased γoct for corresponding parent PAHs by tens (mono-group) to hundreds of times (di-group). This study suggests that the GC-RT method is applicable for indirectly measuring the physicochemical properties of various groups of organic compounds.

Driving factors to air pollutant reductions during the implementation of intensive controlling policies in 2020 in Ulsan, South Korea.

Evaluation for the controlling policy's effectiveness to mitigate criteria air pollutants (CAPs) in South Korea during December 1, 2019-March 31, 2020 is difficult because of its coincidence with the COVID-19 social distancing. In this study, we differentiated the influence of three major driving factors (intensive controlling policy by the government, meteorological conditions, and social distancing) to the CAP variation in Ulsan, the largest industrial city in South Korea. In 2013-2019, the concentrations of PM2.5 (2015-2019), PM10, SO2, and NO2 decreased by 6.7, 1.6, 4.2, and 3.3%/year, respectively, whereas the O3 concentration slightly increased by 0.7%/year. Trend analysis was used to predict the CAP concentrations before (January 1-February 21) and during (February 22-March 31) the social distancing in 2020. The difference between the measured and predicted concentrations was designated as the contribution of the three factors. The controlling policy was the most important driver of the CAP reductions. In particular, its contributions were 94.1% (January 1-February 21) and 87.4% (February 22-March 31) to the PM2.5 decrease. The change in meteorological conditions considerably affected the CAP reductions, with the highest contributions of 35.2% (January 1-February 21) and 39.2% (February 22-March 31) to the O3 decrease. On February 22-March 31, the effects of social distancing were 1.6, 0.6, 1.3, and 1.4% to the reduction of SO2, NO2, PM10, and PM2.5, respectively. Overall, a decrease in the CAP concentrations was apparent during January-March 2020 in Ulsan primarily due to the intensive controlling policies, not by the COVID-19 social distancing.

Health risk assessment of exposure to organochlorine pesticides in the general population in Seoul, Korea over 12 years: A cross-sectional epidemiological study.

This study evaluated the 12-year trends in serum levels of 28 organochlorine pesticides (OCPs) in 880 adults living in Seoul, Korea. The OCP levels decreased from 2006 to 2017, and p,p'-dichlorodiphenyldichloroethylene was a predominant compound. OCP levels were higher in females than in males, and showed positive associations with BMI and age. The OCP concentrations had inverted U-shaped associations with low-density lipoprotein cholesterol and total cholesterol. Concentrations of ß-hexachlorocyclohexane were significantly higher in patients with hypertension than in participants that were normotensive. OCP levels showed positive associations with uric acid, creatinine, and thyroid-stimulating hormone, but negative associations with free thyroxine. Participants with diabetes had significantly higher OCP levels than those without it. Principal component analysis suggested possible differences in disease manifestation depending on the composition of OCPs. These results suggest that OCPs might disturb renal transport and thyroid homeostasis. To our knowledge, the inverted U-shaped associations of heptachlor epoxide and endosulfan with cholesterol, the epidemiological associations of trans-nonachlor and endosulfan with thyroid hormones, and the association of p,p'-DDE with hyperuricemia have not been previously reported in general population. This is the first long-term study to show trends of 28 OCPs in serum and associations with various health indicators in Korea.

Dietary exposure and potential human health risk of dioxins in South Korea: Application of deterministic and probabilistic methods.

Following the reduction of incinerator emission, enacted by the Korean Government in 2001, the levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in the air (-96%) have significantly decreased. However, their levels in the human serum of the general Korean population have not reduced at the same rate (-36%), indicating that humans may also be unintentionally exposed to these compounds, primarily through food ingestion. In this study, the risk of dietary exposure was assessed on a large scale, to provide toxicological information and guide the development of food safety policies. The food consumption data of the extreme (95th percentile) group and various subgroups (by age, pregnancy, and lactation), as well as the average group, were utilized. Compared to the tolerable daily intake (TDI) established by the World Health Organization (WHO), the average daily dietary exposure of the general Korean population, calculated using a deterministic method, was 11.9% of the WHO TDI (4 pg-TEQWHO05 kg body weight-1 d-1). For additional comparison, a probabilistic method using a Monte Carlo simulation was applied to the same data. Finally, the associated potential health risk was quantitatively characterized, and the results suggest the importance of non-dioxin-like congeners in future risk assessments.

Monitoring and risk assessment of arsenic species and metals in the Taehwa River in Ulsan, the largest industrial city in South Korea.

Toxic metals, As, and As species were monitored at 18 stations along the Taehwa River in Ulsan. The concentrations of Ni (98.4 µg/L) at stations near industrial areas were relatively high and exceeded the WHO's drinking water guidelines (70 µg/L) and the US EPA's national recommended water quality criteria (52 µg/L). Principal component analysis and cluster analysis revealed that Ni and Cu were more strongly influenced by industrial activity than other elements in the Taehwa River estuary. Analysis of the hazard quotient (HQ) and cancer risk (CR) indicated that As was of the greatest non-carcinogenic and carcinogenic concern. Notably, the HQ and CR of AsIII at suburban stations exceeded 1 and 10-4, respectively, representing a significant health risk. These results indicate that As speciation testing is crucial for the development of effective management plans based on health risks because the toxicity and mobility of As depend on its chemical form.

Source apportionment of PM2.5 and sulfate formation during the COVID-19 lockdown in a coastal city of southeast China.

Revealing the changes in chemical compositions and sources of PM2.5 is important for understanding aerosol chemistry and emission control strategies. High time-resolved characterization of water-soluble inorganic ions, elements, organic carbon (OC), and elemental carbon (EC) in PM2.5 was conducted in a coastal city of southeast China during the COVID-19 pandemic. The results showed that the average concentration of PM2.5 during the city lockdown (CLD) decreased from 46.2 µg m-3 to 24.4 µg m-3, lower than the same period in 2019 (PM2.5: 37.1 µg m-3). Concentrations of other air pollutants, such as SO2, NO2, PM10, OC, EC, and BC, were also decreased by 27.3%-67.8% during the CLD, whereas O3 increased by 28.1%. Although SO2 decreased from 4.94 µg m-3to 1.59 µg m-3 during the CLD, the concentration of SO42- (6.63 µg m-3) was comparable to that (5.47 µg m-3) during the non-lockdown period, which were attributed to the increase (16.0%) of sulfate oxidation rate (SOR). Ox (O3+NO2) was positively correlated with SO42-, suggesting the impacts of photochemical oxidation. A good correlation (R2 = 0.557) of SO42- and Fe and Mn was found, indicating the transition-metal ion catalyzed oxidation. Based on positive matrix factorization (PMF) analysis, the contribution of secondary formation to PM2.5 increased during the epidemic period, consisting with the increase of secondary organic carbon (SOC), while other primary sources including traffic, dust, and industry significantly decreased by 9%, 8.5%, and 8%, respectively. This study highlighted the comprehensive and nonlinear response of chemical compositions and formation mechanisms of PM2.5 to anthropogenic emissions control under relatively clean conditions.

Spatial distribution and temporal variation of polycyclic aromatic hydrocarbons in runoff and surface water.

This study aims to investigate the spatial distribution of and temporal variation in the phase distribution, emission sources, and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in runoff and in surface water mixed with runoff discharge. The samples were collected at semi-rural, residential, and industrial sites in Ulsan, South Korea, from April to October 2016. The industrial site had the highest PAH concentrations in the runoff and surface water due to the higher PAH levels found in the surrounding environmental media. The PAH phase distributions were relatively similar between the sampling sites, with dissolved PAHs (2- to 4-ring species) dominant. In July, the PAHs in the surface water were more commonly found in the dissolved phase due to the higher water temperature and dissolved organic carbon concentration. The emission sources for the PAHs were identified using principal component analysis (PCA), a dimension reduction technique, and the k-nearest neighbor (KNN) classifier, a supervised learning algorithm. It was determined that the PAHs in the runoff and surface water were likely to share similar petrogenic and pyrolysis sources for most of the sampling periods. The ecological risk of the surface water was 1.5-4.5 times lower after being mixed with runoff water, mainly due to dilution effects. The ecological risk for surface water was highest in July because of the higher PAH concentrations. This study contributes to the understanding of PAHs in runoff and in surface water affected by runoff discharge.

Air pollution increases human health risks of PM2.5-bound PAHs and nitro-PAHs in the Yangtze River Delta, China.

Identifying the nature and extent of atmospheric PM2.5-bound toxic organic pollutants is beneficial to evaluate human health risks of air pollution. Seasonal observations of PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) in the Yangtze River Delta (YRD) were investigated, along with criteria air pollutants and meteorological parameters. With the elevated PM2.5 level, the percentage of 4-ring PAHs and typical NPAH including 3-Nitrobiphenyl (3-NBP) and 2-Nitrofluoranthene (2-NFLT) increased by 19-40%. PM2.5-bound 2-NFLT was positively correlated with O3 and NO2, suggesting the contribution of atmospheric oxidation capacity to enhance the secondary formation of NPAHs in the atmosphere. Positive matrix factorization (PMF) analysis indicated that traffic emissions (44.9-48.7%), coal and biomass combustion (27.6-36.0%) and natural gas and volatilization (15.3-27.5%) were major sources of PAHs, and secondary formation (39.8-53.8%) was a predominant contributor to total NPAH concentrations. Backward trajectory analysis showed that air masses from North China transported to the YRD region increased PAH and NPAH concentrations. Compare to clean days, the BaP equivalent concentrations of total PAHs and NPAHs during haze pollution days were enhanced by 10-25 and 2-6 times, respectively. The Incremental Lifetime Cancer Risks (ILCRs) of PAHs by inhalation exposure also indicated high potential health risks in the YRD region. The results implied that the health risks of PM2.5-bound PAHs and NPAHs could be sharply enhanced with the increase of PM2.5 concentrations.