Constraining East Asia ammonia emissions through satellite observations and iterative Finite Difference Mass Balance (iFDMB) and investigating its impact on inorganic fine particulate matter

Abstract

Uncertainty in ammonia (NH₃) emissions causes the inaccuracy of fine particulate matter simulations, which is associated with human health. To address this uncertainty, in this work, we employ the iterative finite difference mass balance (iFDMB) technique to revise NH₃ emissions over East Asia using the Cross-track Infrared Sounder (CRIS) satellite for July, August, and September 2019. Compared to the emissions, the revised NH₃ emissions show an increase in China, particularly in the North China Plain (NCP) region, corresponding to agricultural land use in July, August, and September and a decrease in South Korea in September. The enhancement in NH₃ emissions resulted in a remarkable increase in concentrations of NH₃ by 5 ppb. in July and September, there is an increase in ammonium (NH₄⁺) and nitrate (NO₃^-) concentrations by 5 μg/m3, particularly in the NCP region, while in August, both NH₄⁺ and NO₃^- concentrations exhibit a decrease. For sulfate (SO₄^2-), in August and September, the concentrations decreased over most regions of China and Taiwan, as a result of the production of ammonium sulfate; increased concentrations of SO₄^2-, however, were simulated over South Korea, Japan, and the southern region of Chengdu, caused by higher relative humidity (RH). In contrast, during the month of July, our simulations showed an increase in SO₄^2- concentrations over most regions of China. To gain a more comprehensive understanding, we defined a sulfur conversion ratio ( [Formula: see text] ), which explains how changes in sulfur in the gas phase affect changes in sulfate concentrations. A subsequent sensitivity analysis performed in this study indicated the same relationship between changes in ammonia and its effect on inorganic fine particulate matter (PM_2.5). This study highlights the challenge of controlling and managing inorganic PM_2.5 and indicates that reducing the emissions of air pollutants do not necessarily lead to a reduction in their concentrations.

Keywords: Ammonia; CrIS; East Asia; Inorganic particulate matter; Inverse modeling; iFDMB.