High efficiency of nitric acid controls in alleviating particulate nitrate in livestock and urban areas in South Korea

Remarkably, enhanced particulate nitrate (NO3-) concentrations occur in many environments during particulate matter (PM) pollution; however, information on the formation mechanism and alleviation strategies is still limited. Herein, to explore the NO3- formation mechanism and conditions, we measured the concentrations of water-soluble inorganic ions in PM1.0 as well as the inorganic gas concentrations of HNO3, NO2, and NH3 in Gimje, a highly dense livestock area, from June to July 2020 and January to February 2021. At the monitoring site, extremely high atmospheric NH3 was measured with an hourly average of 96.9 +/- 48.1 ppb, and the daily average of HNO3 and PM1.0 was 0.7 +/- 0.7 ppb, and 20.1 +/- 8.8 mu g m(-3), respectively. A clear increase in the NO3- concentration in PM1.0 was observed on high pollution days (PM1.0 >= 20 mu g m(-3)), suggesting that HNO3 and NH3 contributed to NO3- formation. Moreover, we applied the thermodynamic model ISORROPIA-II to predict the NO3- response to the reduction of total HNO3 (TN), total NH3 (TA), and SO42-. The results showed that controlling TN could be more effective in alleviating particulate NO3- than controlling SO42- and TA in the livestock area. We also compared this result to that of a nearby urban area, Jeonju. A similar result was observed, with efficient HNO3 control, which reduced the NO3- concentration in Jeonju. These measurements and simulations indicated that NOx control could be the most effective approach to reduce particulate NO3- concentrations in both livestock and urban areas. Our results provide a significant contribution to developing a strategy for alleviating particulate NO3- pollution.