资源环境科技发展态势分析平台

Recently, increasing urban aerosol NO₃⁻ deposition have aroused widespread attention. To reveal its sources and formation processes, the water-soluble inorganic ions (WSIIs) and NO₃⁻ 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 NO₃⁻ and its dual isotopes were distinctly higher in winter than in summer. While only NO₃⁻ 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 NH₃ 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 NO₃⁻ 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 NO₃⁻ 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.