A joint study by the Indian Space Research Organisation (ISRO) and National Aeronautics and Space Administration (Nasa) of the US, which had commenced after satellite images showed the presence of an aerosol layer over the Asia region, has confirmed the same and has also found the presence of nitrate, which is a new finding. Aerosol, the sub-micron size particles suspended in air are produced from a variety of man-made and natural processes such as vehicle exhaust, waste-burning, wind blown dust, volcanic eruptions et al, are mostly restricted to the first few kilometers from the surface of Earth’s atmosphere—Upper Troposphere and Lower Stratosphere (UTLS). According to ISRO, measurements by the joint team has “confirmed the presence of aerosol layer seen in satellite measurements over the Asian region and it also shows a sharp increase of aerosol concentration near 16.5-18.5 km (from Earth’s surface).” This layer, ISRO says, has distinct size distribution as opposed to that from background mineral aerosol dust that is naturally present in the atmosphere. “This layer contains particles of size less than 0.25 micron and are 90 per cent volatile. It appears the aerosol is formed from precursor pollutant gases which are transported via convection from the ground,” ISRO has said. Preliminary chemical analysis of samples collected in this campaign indicates dominant presence of nitrate, which is a new finding and the converging air masses over northern part of India during Asian Monsoon which is generally active during July and August is found to be the main forcing for vertical transport of the aerosols and trace gases to the UTLS region along with long-range transport from northern parts of India. However, detailed analysis yet to be carried out with all the data collected during the campaign. Aerosols, Radiation and Trace Gases Group (ARTG) of National Atmospheric Research Laboratory, ISRO, and a team from Nasa have been studying air quality around India as part of this campaign.According to the joint team, one additional campaign during winter months for obtaining the background conditions is planned. Presence of different pollutants which results from interplay of different circulation patterns and pollutant source regions also necessitates multiple campaigns spread over a few years (until 2020) to comprehensively characterise the aerosol layer in the UTLS region and study its impact on radiation budget and ozone chemistry. Additionally, this campaign seeks to use balloon-borne measurements of aerosol, water vapor, and ozone to validate measurements from Nasa’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite and Nasa’s Stratospheric Aerosol and Gas Experiment (SAGE) III instrument along with Cloud-Aerosol Transport System (CATS) on the International Space Station.
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