Reply on RC3

Abstract

Ammonia (NH3) is the most important alkaline gas in the atmosphere, which has negative effects on biodiversity, ecosystems, soil acidification and human health. China has largest NH3 emissions in the world mainly associated with agricultural sources including nitrogen fertilizer and livestock. However, there is still a limited number of ground monitoring sites in China, hindering our understanding of both surface NH3 concentrations and emissions. In this study, using the polar-orbiting satellite (IASI) and Fengyun-4 geostationary satellite (GIIRS), we analyzed the changes of hourly NH3 concentrations, and estimated surface NH3 concentrations and NH3 emissions in China. GIIRS-derived NH3 concentration in daytime was generally higher than that at night, with high values during 8:00–18:00. Satellite-derived surface NH3 concentration was generally consistent with the ground observation data with R-square at 0.72–0.81 and slope equal to 1.03. Satellite-based NH3 emissions ranged from 12.99–17.77 Tg N yr-1 during 2008–2019. Spatially, high values of NH3 emissions mainly occurred in the North China Plain, Northeast China and Sichuan Basin, while low values were mainly distributed in western China (Qinghai-Tibet Plateau). Our study shows a high predictive power of using satellite data to estimate surface NH3 concentration and NH3 emissions over multiple temporal and spatial scales, which provide an important reference for understanding NH3 changes over China.