Quantifying Agricultural Ammonia Emissions in India

Abstract:

Atmospheric ammonia (NH₃) is the most abundant alkaline gas in the atmosphere. It is a major constituent of the nitrogen cycle and is key in the formation of atmospheric aerosols and fine particulate matter (PM_2.5). Globally, the predominant source of ammonia is from agricultural activities, contributing more than 80% of total emissions. The main component of this comes from nitrogen-based fertilizer application, however animal waste and feed also contribute significantly. Southern Asia, notably China and India accounts for over 50% of global NH₃ emissions, however the spatiotemporal distribution of NH₃ in India is poorly understood and no national monitoring network with sufficient spatial coverage exists. Using the ammonia products from the satellite-based Infrared Atmospheric Sounding Interferometer (IASI) and Cross-track Infrared Sounder (CrIS) instruments we produce a combined NH₃ product oversampled to high resolution (0.02x0.02°) over India for the period 2013-2017. A k-means clustering technique was used to calculate the seasonal distribution of NH₃ columns in India to determine regions of distinct spatiotemporal NH₃ emissions profiles.

The regional NH₃ emissions have been studied in the context of fertilizer application practices in major agricultural regions of India. Using this analysis, we estimate that fertilization of wheat and rice production contribute 24% and 9%, respectively, of total ammonia emissions in India. Across the central and western Indo-Gangetic Plain, where wheat is the major crop, show annual maxima in mid-summer when the Kharif crop is planted. During this period, fertilizers for wheat farming contribute 51% of NH₃ emissions. Regions in which rice is the major crop show an emissions peak in March/April, consistent with the timing of fertilizer application for this crop, accounting for 23% of total NH₃ emissions during Spring in India. This top-down approach has also been used to estimate ammonia emissions at state level in India for the purpose of improving the understanding of NH₃ emissions sources in this highly polluted region.