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Recently, increasing urban aerosol NO 3 − deposition have aroused widespread attention. To reveal its sources and formation processes, the water-soluble inorganic ions (WSIIs) and NO 3 − dual isotopes (i.e., δ15N and δ18O) were measured in fine particles (i.e., PM 2.5), which were collected during rush hours in the morning and afternoon, and non-rush hours at noon, discretely in winter and in summer at urban Guiyang, southwest China. Results showed the sulfate, nitrate, and ammonium together accounted for more than 90% of the total WSIIs in both seasons. Both NO 3 − and its dual isotopes were distinctly higher in winter than in summer. While only NO 3 − and δ15N were observed significantly higher during rush hours than the non-rush hours in summer, which could be potentially controlled by the temperature, relative humidity and ambient NH 3 contents. The gradual but insignificant increase of δ18O during from morning to afternoon were ascribed to the decreasing contributions of •OH oxidation pathway. By using the Bayesian isotope mixing model, we revealed the coal combustion and biomass burning accounted for the predominant NO x sources in contributing to the particulate NO 3 − in winter, followed by vehicular and soil biogenic emissions. Whereas in summer, biomass burning played the most important role, since the coal combustion proportion sharply decreased. Moreover, the particle NO 3 − source contributions showed minor difference during diurnal periods in winter, while the difference was larger in summer, especially for that during between morning rush and noon non-rush hours, which were likely due to the changes of NO x emissions (e.g. from vehicular and soil biogenic source), as well as the meteorological conditions. • The urban p-NO 3 − during rush hours are not mainly determined by nearby vehicular NO x • The δ15N of urban p-NO 3 − was influenced by HNO 3(g) partitioning processes in summer • The •OH oxidation pathway decreased during from morning to afternoon in both seasons [ABSTRACT FROM AUTHOR]

Sulfate, nitrate and ammonium (SNA) are the dominant components of water-soluble ions (WSIs) in PM2.5, which are of great significance for understanding the sources and transformation mechanisms of PM2.5. In this study, daily PM2.5 samples were collected from September 2017 to August 2018 within the Guiyang urban area and the concentrations of the major WSIs in the PM2.5 samples were characterized. The results showed that the average concentration of SNA (SO42−, NO3−, NH4+) was 15.01 ± 9.35 μg m−3, accounting for 81.05% (48.71–93.76%) of the total WSIs and 45.33% (14.25–82.43%) of the PM2.5 and their possible chemical composition in PM2.5 was (NH4)2SO4 and NH4NO3. The highest SOR (sulfur oxidation ratio) was found in summer, which was mainly due to the higher temperature and O3 concentrations, while the lowest NOR (nitrogen oxidation ratio) found in summer may ascribe to the volatilization of nitrates being accelerated at higher temperature. Furthermore, the nitrate formation was more obvious in NH4+-rich environments so reducing NH3 emissions could effectively control the formation of nitrate. The results of the trajectory cluster analysis suggested that air pollutants can be easily enriched over short air mass trajectories from local emission sources, affecting the chemical composition of PM2.5. [ABSTRACT FROM AUTHOR]

Total suspended particles (TSP) and their source-related samples from Guiyang, Southwest China, were collected and analyzed for their lead (Pb) concentrations and Pb isotopic compositions, to identify the sources of atmosphere lead in urban Guiyang. Coals from Guizhou Province had significantly high radiogenic Pb, different to those from North China. Local vehicle exhaust had similar Pb isotope ratios to those of other areas in China. Pb isotopic compositions of atmospheric aerosols, rainwaters, plant samples, and acid-soluble fraction of street dusts were similar to each other. The results clearly suggest that the Pb–Zn ore-related industrial emission, and/or vehicle exhaust, rather than the local coal combustion, are the main sources of atmospheric Pb in Guiyang. Furthermore, binary mixing model indicates that the contribution of coal combustion to the local atmospheric Pb decreased from about 40% in 1988 to about 10% in 2013. [ABSTRACT FROM AUTHOR]