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20 September 2020 Satellite derived spatio-temporal trends of formaldehyde (HCHO) and nitrogen oxides (NO2) over Delhi and its outer region
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Levels of formaldehyde (HCHO) and nitrogen dioxide (NO2) were analyzed in Delhi (the capital of India) and its surrounding region from January 2010 to December 2014, using the Aura satellite’s OMI sensor data of spatial resolution 0.25°x0.25°. Time sequence plots show that formaldehyde concentrations were the maximum during monsoon period and minimum during the winter months. Nitrogen dioxide concentrations on the other hand were found to be the minimum during the monsoon months and the maximum during the winter months. The scatter plot between the formaldehyde and NO2 levels along with the time sequence plots suggest the presence of a significant anti-correlation between the two. Seasonal wind rose plots which showed that the wind generally blows from west to east which is due to the subtropical westerlies. Seasonal wind speed temporal plot showed that the wind blows with maximum speed in the summer season, then in monsoon followed by winter and the minimum speed of wind is in the post monsoon season. Spatial maps of nitrogen dioxide and formaldehyde in the study area using ArcGIS were plotted and hot spots were identified. For nitrogen dioxide, the east side of Delhi was found to be having higher concentrations as compared to other parts of Delhi. But hot spots for formaldehyde were not easy to demarcate as they were changing with season which is possibly due to the complex chemistry of formaldehyde in the troposphere. A possible explanation has been suggested on the basis of atmospheric photochemistry of formaldehyde and nitrogen dioxide for the observed variations. The results suggest the presence of highly complex chemistry among them.
Conference Presentation
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Sneha Dhankar and Krishan Kumar "Satellite derived spatio-temporal trends of formaldehyde (HCHO) and nitrogen oxides (NO2) over Delhi and its outer region", Proc. SPIE 11531, Remote Sensing of Clouds and the Atmosphere XXV, 1153106 (20 September 2020);

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