Estimating global surface ammonia concentrations inferred from satellite retrievals

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.

Northwestward cropland expansion and growing urea-based fertilizer use enhanced NH<sub>3</sub> emission loss in the contiguous United States

“…The seven subregions are the Northeast (NE), the Midwest (MD), the Northern Great Plains (NGP), the Northwest (NW), the Southern Great Plains (SGP), the Southeast (SE), and the Southwest (SW). corn and spring wheat expansion together greatly boosted the NH 3 loss proportion, which may contribute to the decreasing crop NUE in these regions (Lu et al, 2019) (Fig. 4).…”

“…The predictable rise in food demand may lead to more N fertilizer consumption in the coming decades (Alexandratos and Bruinsma, 2012;David et al, 1997). However, 5 %-9 % of the N applied was lost to the atmosphere through ammonia (NH 3 ) volatilization (0.5-1 Tg N annually) across the US at the beginning of this century, which lowered the N use efficiency (NUE) of crops and caused numerous environmental issues (Bouwman et al, 2002;Cassman et al, 2002;Lu et al, 2019;Tilman et al, 2002). Nationwide, synthetic Nfertilizer-induced NH 3 volatilization, contributing to 15 %-30 % of annual total NH 3 emission, has been identified as the second contributor to atmospheric NH 3 only next to livestock production (Park et al, 2004;Paulot et al, 2014;Reis et al, 2009;US EPA, 2020).…”

Dry deposition of ammonia around paddy fields in the subtropical hilly area in southern China

“…Thus, the NH 3 emissions intensity for the farmland source in this region is relatively small, which leads to a higher ratio of near-source NH 3 deposition to NH 3 emissions, and a lower ratio of long-range-transported NH 3 to NH 3 emissions. This may also be one of the reasons for the relatively low atmospheric NH 3 concentration in subtropical hilly areas (Liu et al 2019). In this study, the paddy area was relatively small, which resulted in a small source strength.…”

“…This pattern of distribution of croplands or animal farms accompanying the surrounding natural ecosystems may result in a higher near-source deposition ratio of NH 3 in the subtropical hilly region than that in the plain areas. Recent observations also showed that the concentration of NH 3 in the subtropical hilly areas of China was not very high (Liu et al 2019), which indirectly indicates that there may be a high near-source deposition of NH 3 in the subtropical hilly areas, but there is no direct experimental evidence.…”

Northwestward Cropland Expansion and Growing Urea-Based Fertilizer Use Enhanced NH<sub>3</sub> Emission Loss in the Contiguous United States

“…However, it is challenging to quantify fertilizer-induced NH3 emissions due to the paucity of information on spatially and temporally varied environmental conditions and various agricultural practices (Behera et al, 2013;Bouwman et al, 2002;Pinder et al, 2006;Sommer et al, 2004). Inverse modeling of atmospheric observations such as N deposition and satellite images has been developed as an indirect approach to estimate seasonal NH3 emission at the regional and national scale (Gilliland et al, 2006;Liu et al, 2019)). However, this "top-down" approach has difficulty in separating contribution of each individual source of NH3 emission due to the observations contain all sources of NH3 emissions.…”