Abstract
This study was aimed at presenting a continuous and spatially coherent picture of ammonia (NH3) distribution over the Indo-Gangetic Plain (IGP) by exploiting satellite observations. Atmospheric columns of ammonia were mapped over South Asia by using TES observations on board NASA’s Aura satellite. Monthly mean data were used to identify emission sources of atmospheric ammonia across the South Asian region. Data were analysed to explore temporal trends, seasonal cycles, and hot spots of atmospheric ammonia within the study area. The results show that the IGP region has the most ammonia concentrations in terms of column densities, and hence this region has been identified as an ammonia hot spot. This is attributed majorly to extensive agricultural activity. Time series showed a slight increase in ammonia column densities over the study area from 2004 to 2011. Different seasonal cycles were identified across the IGP region with maximum NH3 columns observed during the month of July in most of the subregions. Seasonality in an ammonia column is driven by different cropping patterns and meteorological conditions in the IGP subregions. Global emission inventories of atmospheric ammonia were largely overestimating as compared to satellite observations.
Highlights
Ammonia (NH3) is a highly reactive and soluble alkaline gas [1] in the atmosphere having a short lifetime of 1 day [2, 3] and plays an important role in several environmental processes and their consequent impacts
It is evident that the ammonia columns are higher in the area marked by red polygons. e area marked by red polygons basically consists of plains of the Indus and Ganges river basins. is area is generally known as the Indo-Gangetic Plain (IGP). e plain extends from the Arabian Sea to the Bay of Bengal and from the Himalayan foothills to the Indian peninsula. e region covers a total of 21% of the geographic area of India, 14% of the territory of Nepal, 24% of the area of Pakistan, and 100% of the area of Bangladesh. e IndoGangetic Plain (IGP) region is prominent as the world’s largest food basket and hosts extensive agriculture activities. e main causes of NH3 emissions are the production and use of ammoniabased fertilizers [6]
Extensive agricultural activity with more use of synthetic fertilizers is one of the pronounced causes of ammonia emissions in the atmosphere. e time series generated for the various regions of the study area clearly depicted that the ammonia column density is higher over the agricultureintensive areas of South Asia, commonly termed as the IndoGangetic Plain. e results show a 6% in overall ammonia columns over the study region with pronounced seasonality, which is maximum during the month of July every year, with few exceptions over some regions (IGP-4, 5)
Summary
Ammonia (NH3) is a highly reactive and soluble alkaline gas [1] in the atmosphere having a short lifetime of 1 day [2, 3] and plays an important role in several environmental processes and their consequent impacts. Ammonia combines with other gases and causes the formation of fine particulates which are hazardous to human health [6]. Reactions with other pollutants like oxides of sulphur lead to the formation of fine particulates [7]. Like oxides of nitrogen and sulphur as well as HCl, cause the formation of ammonium ions (NH4+). Large uncertainties exist in atmospheric emissions, chemistry, transport, and deposition of nitrogen compounds such as ammonia [9]. Agriculture sector is considered as the greatest source contributing to global atmospheric ammonia [10]. Vegetation fires have been attributed to Advances in Meteorology the second most important source contributing to 16% of the total emissions [9]. Relative contribution and importance of these sources can vary on both local and regional scales
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