Combining chemical components with stable isotopes to determine nitrate sources of precipitation in Hangzhou and Huzhou, SE China

Özet

The chemical components, air pollutants and stable isotopes of $N{O^-}_3$ were used to determine $N{O^-}_3$ sources inprecipitation and reveal $NO_x$ transformation mechanisms from 2015 to 2017 in the cities of Hangzhou andHuzhou, which are representative of most cities in Southeastern China (SE China). The mean concentrations(monthly weighted-mean values) of $N{O^-}_3$ were 49.52 μmol $L^{-1}$ in Hangzhou, and were higher than $N{O^-}_3$concentrations (39.35 μmol $L^{-1}$) in Huzhou. Both $delta^{15}N_{-NO_3}$ values (−4.4‰–3.7‰) and $delta^{18}O_{-NO_3}$ values(27.9‰–83.4‰) varied widely in the study areas. It was demonstrated that the main $N{O^-}_3$ sources in Hangzhouand Huzhou included coal consumption, traffic emissions and soil emissions. Higher levels of traffic emissions inHangzhou were responsible for the spatial variations in $N{O^-}_3$concentrations and $delta^{15}N_{-NO_3}$ values betweenHangzhou and Huzhou. The different NO2 oxidation pathways are particularly important in seasonal variation ofoxygen stable isotope in $N{O^-}_3$ Due to the oxidation of $NO_2$ via $O_3$ forming $HNO_3$ in the $N_2O_5$ pathway, thehighest $delta^{18}O_{-NO_3}$ values were observed in the winter. The lowest $delta^{18}O_{-NO_3}$ values were explained by the $NO_x$oxidation forming $HNO_3$ via the OH pathway in the summer. The seasonal variation of $delta^{15}N_{-NO_3}$ values wasinfluenced by the changing contributions of the main $N{O^-}_3$sources in precipitation collected from the studyareas: soil emissions increased in summer and coal consumption emissions increased because of coal consumption for winter heating from northern China in Hangzhou and Huzhou.