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 PM_1.0 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 PM_1.0 was 0.7 ± 0.7 ppb, and 20.1 ± 8.8 μg m⁻³, respectively. A clear increase in the NO₃⁻ concentration in PM_1.0 was observed on high pollution days (PM_1.0 ≥ 20 μg 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 NO_x 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.