Abstract
Abstract. Ammonia (NH3), as an alkaline gas in the atmosphere, can cause direct or indirect effects on the air quality, soil acidification, climate change and human health. Estimating surface NH3 concentrations is critically important for modeling the dry deposition of NH3 and for modeling the formation of ammonium nitrate, which have important impacts on the natural environment. However, sparse monitoring sites make it challenging and difficult to understand the global distribution of surface NH3 concentrations in both time and space. We estimated the global surface NH3 concentrations for the years of 2008–2016 using satellite NH3 retrievals combining vertical profiles from GEOS-Chem. The accuracy assessment indicates that the satellite-based approach has achieved a high predictive power for annual surface NH3 concentrations compared with the measurements of all sites in China, the US and Europe (R2=0.76 and RMSE = 1.50 µg N m−3). The satellite-derived surface NH3 concentrations had higher consistency with the ground-based measurements in China (R2=0.71 and RMSE = 2.6 µg N m−3) than the US (R2=0.45 and RMSE = 0.76 µg N m−3) and Europe (R2=0.45 and RMSE = 0.86 µg N m−3) at a yearly scale. Annual surface NH3 concentrations higher than 6 µg N m−3 are mainly concentrated in the North China Plain of China and northern India, followed by 2–6 µg N m−3 mainly in southern and northeastern China, India, western Europe, and the eastern United States (US). High surface NH3 concentrations were found in the croplands in China, the US and Europe, and surface NH3 concentrations in the croplands in China were approximately double those in the croplands in the US and Europe. The linear trend analysis shows that an increase rate of surface NH3 concentrations (> 0.2 µg N m−3 yr−1) appeared in eastern China during 2008–2016, and a middle increase rate (0.1–0.2 µg N m−3 yr−1) occurred in northern Xinjiang over China. NH3 increase was also found in agricultural regions in the central and eastern US with an annual increase rate of lower than 0.10 µg N m−3 yr−1. The satellite-derived surface NH3 concentrations help us to determine the NH3 pollution status in the areas without monitoring sites and to estimate the dry deposition of NH3 in the future.
Highlights
Ammonia (NH3), emitted primarily by agricultural activities and biomass burning, is an important alkaline gas in the atmosphere (Van Damme et al, 2018; Warner et al, 2017)
Estimation of surface NH3 concentrations is critically important in modeling the dry deposition of NH3, which may comprise a large part of atmospheric nitrogen (N) deposition, and could cause acidification in the soil, eutrophication in the aquatic ecosystems, and contamination in drinking water (Basto et al, 2015; Kim et al, 2014; Lamarque et al, 2005; Larssen et al, 2011; Reay et al, 2008)
NH3 vertical profiles were fitted by a Gaussian function based on the 47 layers’ NH3 concentrations from GEOS-Chem, and the fitting accuracy was determined by R2
Summary
Ammonia (NH3), emitted primarily by agricultural activities and biomass burning, is an important alkaline gas in the atmosphere (Van Damme et al, 2018; Warner et al, 2017). Schiferl et al (2016) evaluated the modeled NH3 concentrations during 2008–2012 from GEOS-Chem, and found an approximately 26 % underestimation compared with the ground-based measurements, which can be related to the relatively large uncertainties in NH3 emissions used for driving GEOS-Chem (Schiferl et al, 2016). A number of previous studies have used satellite NO2 columns to estimate the surface NO2 concentrations combining NO2 vertical profiles from CTMs (Geddes et al, 2016; Lamsal et al, 2013; Nowlan et al, 2014; Liu et al, 2017c). CTMs can provide valuable information of NH3 vertical profiles (Whitburn et al, 2016; Liu et al, 2017b), and IASI-derived surface NH3 concentrations combining NH3 vertical profiles from CTMs in China and Europe were evaluated previously (Liu et al, 2017b; van der Graaf et al, 2018). This study followed these studies to estimate the satellite-derived global surface NH3 concentrations using IASI NH3 retrievals and the vertical profiles from GEOSChem, and the present study aims to estimate the global surface NH3 concentration from a satellite perspective
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