Snowmelt Leads to Seasonal Nitrous Acid Formation Across Northwestern China

28 snowpack samples were collected across northern Xinjiang, northwestern China in January 2018. 16 of these liquid snowmelt samples, 15 with pH < 6.8 and one with the highest nitrate anion (NO3-) concentration, were selected to investigate the photochemical gaseous nitrous acid (HONO) production rate (P(HONO)((g))), which was observed to range from 4.0 to 180.9 ppt min(-1) at room temperature. Surprisingly, the ratio of HONO production rate and NO3- concentration (P(HONO)((g))/[NO3 ˉ]) was significantly higher than those obtained from the photolysis of aqueous NO3- solutions with similar pH, due to the complex organic compounds present in the snowmelt samples, enhancing HONO formation or the coexistence of other photochemical HONO sources. We also found that P(HONO)((g)) was highly correlated with the pH of snowmelt samples, which were significantly lower in rural/remote areas than those from urban/industrial sites, suggesting a significant influence of anthropogenic activities on pH and P(HONO)((g)) of snowmelt.

Automated summary

28 snowpack samples were collected in northern Xinjiang, China in January 2018. The study focused on investigating the production rate of gaseous nitrous acid (HONO) in liquid snowmelt samples, and found that the rate was influenced by the presence of complex organic compounds and other photochemical HONO sources. The pH of the snowmelt samples was also found to be closely correlated with the production rate of HONO, with lower pH values in rural/remote areas compared to urban/industrial sites, indicating the influence of anthropogenic activities.