Recent trends in tropospheric NO2 over India observed by SCIAMACHY: Identification of hot spots

Satellite remote sensing technology has a great potential to measure the properties of atmosphere and has shown marked advancements through the last decade, in monitoring nitrogen oxide species (NOX) in troposphere. NO2 in troposphere is one of the key factors which determine the air quality and has serious implications on human health and plant growth. It is also well known for its indirect contribution to climate change. The identification of spatial and temporal variations of NO2 is necessary for any effective mitigation plan to curb its obnoxious abundance. Tropospheric NO2 measurements provided by the satellite remote sensor “SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY” (SCIAMACHY) are utilized here to identify the regions across India where a concentration of NO2 exceeds the permissible healthy level. A new approach based on empirical approximation is attempted to normalize the unit of satellite measurement with the unit of existing air quality standard. Trend analysis for all the regions are carried out by means of a non–linear regression method. The geospatial and statistical analysis of monthly tropospheric NO2 data from the full operational period of SCIAMACHY (2002 August–2012 March) have resulted in the identification of 12 hot spot regions across India among which most of them exhibited a significant increasing trend. Some of the rural districts which were not previously implicated for NO2 pollution risk are also recognized here. This study illustrates the possibility of the use of satellite measurements in air quality monitoring and management in regional spatial scale. The effects of seasonal climatic changes in India on the ambient NO2 pollution level are also explained.