Record high levels of atmospheric ammonia over India: Spatial and temporal analyses

Atmospheric ammonia (NH₃) is an alkaline gas and a prominent constituent of the nitrogen cycle that adversely affects ecosystems at higher concentrations. It is a pollutant, which influences all three spheres such as haze formation in the atmosphere, soil acidification in the lithosphere, and eutrophication in water bodies. Atmospheric NH₃ reacts with sulfur (SO_x) and nitrogen (NO_x) oxides to form aerosols, which eventually affect human health and climate. Here, we present the seasonal and inter-annual variability of atmospheric NH₃ over India in 2008-2016 using the IASI (Infrared Atmospheric Sounding Interferometer) satellite observations. We find that Indo-Gangetic Plains (IGP) is one of the largest and rapidly growing NH₃ hotspots of the world, with a growth rate of +1.2% yr^-1 in summer (June-August: Kharif season), due to intense agricultural activities and presence of many fertilizer industries there. However, our analyses show insignificant decreasing trends in annual NH₃ of about -0.8% yr^-1 in all India, about -0.4% yr^-1 in IGP, and -1.0% yr^-1 in the rest of India. Ammonia is positively correlated with total fertilizer consumption (r = 0.75) and temperature (r = 0.5) since high temperature favors volatilization, and is anti-correlated with total precipitation (r = from -0.2, but -0.8 in the Rabi season: October-February) as wet deposition helps removal of atmospheric NH₃. This study, henceforth, suggests the need for better fertilization practices and viable strategies to curb emissions, to alleviate the adverse health effects and negative impacts on the ecosystem in the region. On the other hand, the overall decreasing trend in atmospheric NH₃ over India shows the positive actions, and commitment to the national missions and action plans to reduce atmospheric pollution and changes in climate.