Size Distributions and Health Risks of Particulate Polycyclic Aromatic Hydrocarbons in the Atmosphere at Coastal Areas in Ningbo, China.

Most current research focusing on the health risk assessments of particulate polycyclic aromatic hydrocarbons (PAHs) have not analyzed the size distributions and human respiratory deposition rates. In the present study, size-separated particulate matter (PM) was collected in the coastal area of Ningbo using an Anderson eight-stage air sampler over a 1-year period (2014-2015). The 16 US Environmental Protection Agency priority PAHs associated with PM were pretreated with rapid solvent extraction and analyzed by gas chromatography-mass spectrometry. The respiratory exposure assessment was determined using the multiple-path particle dosimetry (MPPD) model. The results show that all PAHs exhibited bimodal distribution with one mode peak in accumulation mode (0.43-0.65 µm) and another mode peak in coarse mode (4.7-5.8 µm). In addition, a low coefficient of divergence of PAHs between PM2.1 and PM2.1-10 indicated a high spatial heterogeneity in source factor contribution and formation mechanism. The deposition fluxes (tracheobronchial + pulmonary) of PM were highest for children in the size range of 3.3 µm < particle diameter (Dp) < 9 µm, while for males and females the highest fluxes occurred in the size range of 1.1 µm < Dp < 2.1 µm. The depositions of coarse PM in children were significantly higher than those in adults. The benzo[a]pyrene equivalent (BaPeq) depositions of dibenz[a,h]anthracene ranged from 1.4e-04 to 0.015 ng h-1, which were highest among the PAHs. The PAHs on particles with Dp >4.7 µm contributed approximately three times more to children than to males and females. Therefore, the toxicity of coarse PM to children needed attention. The incremental lifetime cancer risks (ILCR) for children, males, and females were estimated to be 2.92 × 10-7, 1.82 × 10-7, and 2.38 × 10-7, respectively, which were below the cancer risk guideline value (10-6). These ILCR values were much lower than the risks calculated without considering particle size distributions and respiratory depositions. The combination of the size-segregated sampling technique and the MPPD model can effectively avoid the overestimation of human respiratory exposure. Environ Toxicol Chem 2024;43:1364-1377. © 2024 SETAC.

Nitrate sources and its formation in precipitation during typhoons (In-fa and Chanthu) in multiple cities, East China.

A clear understanding of the factors governing dual isotopes (δ15N-NO3- and δ18O-NO3-) in typhoons is essential for understanding their NO3- sources and its formation mechanisms. In this study, sequential precipitation samples during typhoons, including In-fa and Chanthu, were collected from Ningbo, Hangzhou and Huzhou. The chemical compositions, nitrogen and oxygen isotopes of NO3- and oxygen isotopes of H2O (δ18O-H2O) were measured. The results showed that the δ15N-NO3- and δ18O-NO3- values ranged from -6.3‰ to 6.0‰, and 38.0‰ to 66.5‰, respectively. The lower δ18O-NO3- values (less than 52‰) indicated the importance of peroxy radicals (RO2 or HO2) in NOx oxidation to NO3- formation pathways. By the Monte Carlo simulation of δ18O-NO3- values of typhoons, the calculated oxidation proportions of NO by RO2 (or HO2) during the OH· pathway ranged from 0% to 27% of In-fa and from 0% to 32% of Chanthu, respectively, in the three cities. More NOx emissions from marine microbial processes caused the lower δ15N-NO3- values of typhoons in Ningbo than those in Hangzhou and Huzhou. The variation in δ15N-NO3- values in sequential samples in In-fa reflected the decreased marine sources (lightning) and the increased anthropogenic sources in land (coal combustion and microbial N cycle) from Phrase I to Phrase II and III. Based on the improved Bayesian model with nitrogen isotopic fractionation, the contributions of lightning + biomass burning, coal combustion, mobile sources and the microbial N cycle were 35.7%, 22.5%, 27.1% and 14.7% in In-fa, and 28.3%, 32.3%, 28.0% and 11.4% in Chanthu, respectively, in the three cities, emphasizing the influence of marine NOx sources (lightning). The results highlight the importance of RO2 (or HO2) in NOx oxidation pathways in typhoons and provide valuable insight into the NOx sources of typhoons.

Stable nitrogen isotope composition of NOx of biomass burning in China.

Owing to the local characteristics of stable nitrogen isotopes in nitrogen oxides (δ15N-NOx) emitted from biomass burning, the lack of data on δ15N-NOx values associated with biomass burning in China limits the use of this parameter in identifying and quantifying the sources of atmospheric nitrate (NO3-) and NOx. The results showed that the δ15N-NOx values of open burning and rural cooking stoves in China ranged from -3.7‰ to 3.1‰ and -11.9‰ to 1.5‰, respectively. The δ15N values of nine biomass fuel sources (δ15N-biomass) ranged from 0.1‰ to 4.1‰. Significant linear relationships between the δ15N-biomass values and δ15N-NOx values of open burning (δ15N-NOx = 1.1δ15N-biomass - 2.7; r2 = 0.63; p < 0.05) and rural cooking stoves (δ15N-NOx = 1.7δ15N-biomass - 9.8; r2 = 0.72; p < 0.01) suggested that the variations in δ15N-NOx values from biomass burning were mainly controlled by the biomass fuel source. The isotopic fractionation of nitrogen during the biomass burning process might have led to the higher δ15N-NOx values from open burning in comparison to rural cooking stoves. By combining the δ15N-NOx values of biomass burning with biomass burning emission inventory data, a model for calculating the δ15N-NOx values of biomass burning in different regions of China was established, and the estimated δ15N-NOx value of biomass burning at the national scale was -0.8 ± 1.2‰. But the limited δ15N-biomass values increase the uncertainty of model in national scale.

Combining dual isotopes and a Bayesian isotope mixing model to quantify the nitrate sources of precipitation in Ningbo, East China.

Nitrate (NO3-) is becoming a significant contributor to acid deposition in many cities in China. Based on the chemical compositions and stable isotopes of NO3- in precipitation (δ15N-NO3- and δ18O-NO3-), the NO3- sources and their formation pathways were determined to aid in reducing NOx emissions in Ningbo, an important port city. The acid rain frequency in Ningbo was 67%, and the mean SO42-/NO3- ratio was 1.07. The δ18O-NO3- (49.5‰-82.8‰) and δ15N-NO3- values (-4.3‰-2.7‰) both varied seasonally, with high values during the cold season and low values during the warm season. The seasonal variations in the δ18O-NO3- values were mainly controlled by the NO3- formation pathways, following the OH· pathway during the warm season and N2O5 pathway during the cold season. The Monte Carlo simulation results indicated that the contributions of the OH· pathway ranged from 28.3% to 75.4%, with the remainder contributed by the N2O5 pathway. The improved Bayesian model incorporating nitrogen (N) isotopic fractionation (Ԑ = 4‰) indicated that mobile sources, including ship emissions (35.0%) > coal combustion (26.0%) > biomass burning (20.0%) > soil emissions (19.0%), were the major sources of NOx emissions in Ningbo. The results indicate that the influence of isotopic fractionation on source apportionment must be considered in a Bayesian model.

Stable isotopic characteristics of precipitation related to the environmental controlling factors in Ningbo, East China.

Hydrogen and oxygen stable isotopes (δ2H and δ18O) in precipitation were analysed from June 2018 to May 2020 in Ningbo and were influenced by the subtropical monsoon climate in East China. The δ2H and δ18O values of precipitation in Ningbo varied from -90.0 to 6.0‰ and from -13.5 to -1.6‰, respectively. The local meteoric water line (LMWL) in Ningbo was obtained as δ2H = 9.27 δ18O + 35.95 and had a larger slope and intercept compared to the global meteoric water line (GMWL) because its water vapour sources were oceans. The more negative δ18O values and lower deuterium excess (D-excess) of precipitation in summer were due to water vapour sources from the East China Sea, the South Sea and the Western Pacific, which are controlled by the southeasterly monsoon. In contrast, the less negative δ18O and higher D-excess of precipitation in winter were influenced by water vapour sources from the North Asian continent and North China transported by the northwesterly monsoon. The precipitation amount effect was significant in Ningbo, especially in summer. The inverse temperature effect was appeared in Ningbo, except winter. These two effects may be caused mainly by the monsoon climate rather than by the secondary evaporation effect.

Stable isotopes and chemical characteristics of precipitation in Hangzhou and Huzhou, East China.

Atmospheric precipitation is a very important link in the water cycle. The characteristics of major ions (n = 341) and stable isotopes (δ2H, δ18O; n = 157) were analysed in Hangzhou and Huzhou, which are economically prosperous cities in East China. The δ2H and δ18O values of precipitation ranged from - 109.70 to 21.30‰ and from - 14.87 to - 0.95‰, respectively. Compared with the local meteoric water line (LMWL) of China, the slope and intercept of the LMWL were much higher in Hangzhou and Huzhou, which is related to the effects of the humid climate and less secondary evaporation. The δ2H and δ18O values were highest in spring because of the influence of air masses from the northern Asian continent and other nearby sources. In contrast, the air masses from the South China Sea and the western Pacific Ocean in the summer had the lowest δ2H and δ18O. The dominant ions in precipitation indicate that Ca2+, HCO3-, SO42-, NH4+ and NO3- are the main ions of precipitation in Hangzhou and Huzhou, and the dilution of precipitation leads to lower concentrations of ions in spring and summer, similar to the values found in most Chinese cities. The increase in motor vehicle use resulted in a lower [SO42-]/[NO3-] ratio (1.64) of precipitation, indicating mixed acid rain in Hangzhou and Huzhou (HZS). Based on a combination of the correlation analysis, enrichment factors and source contributions, we determined that SO42- and NO3- were introduced mainly from anthropogenic activities such as coal combustion and vehicle exhaust, accounting for 89% and 99%, respectively. The strong correlation between Cl- and Na+, as well as Ca2+, Mg2+ and K+, indicates that these ions commonly have marine and crustal origins, respectively, and 40% of Mg2+ comes from a marine source.

Quantifying nitrate sources in a large reservoir for drinking water by using stable isotopes and a Bayesian isotope mixing model.

Drinking water reservoirs are threatened globally by anthropogenic nitrogen pollution. Hydrochemistry and isotopes were analyzed to identify spatial and temporal varieties of main nitrate sources in a large drinking water reservoir in East China. The results showed that NO3- was the main nitrogen form in both the dry and wet seasons, but dissolved organic nitrogen (DON) was increased in the wet season. The δ15N-NO3- values (+ 1.3‰ to + 11.8‰) and δ18O-NO3- values (+ 2.5‰ to + 13.5‰), combined with principal component analysis (PCA), indicated that chemical fertilizer was the main nitrate source during the dry season, while chemical fertilizer, soil N, and sewage/manure were the main nitrate sources during the wet season in the Qiandao Lake area. And, the nitrate isotopes showed the significant nitrification and assimilation in the Qiandao Lake area. A Bayesian isotopic mixing model (Stable Isotope Analysis in R) was applied to the spatial and seasonal trends in the proportional contribution of four NO3- sources (chemical fertilizer (CF), soil nitrogen (SN), sewage and manure (SM), and atmospheric deposition (AD)) in the Qiandao Lake area. It was revealed that CF was the most important nitrate source in the dry season, accounting for 53.4% with 19.2% of SM and 18.9% of SN, while the contribution of SN increased in the wet season, accounting for 31.6%, followed by CF (30.8%) and then SM (24.2%). The main nitrate sources in the urban area, rural area, and central lake area were CF and SN, accounting for 66.1% in the urban area, 71.7% in the rural area, and 68.2% in the central lake area. Measures should be made to improve chemical fertilizer use efficiency and to reduce nitrogen loss in the Qiandao Lake area. Graphical abstract .