Temporal Record of Atmospheric Nitrogen Dioxide (No2) Column Densities Over Pakistan By Using Satellite Observations

Abstract

In this study, the spatial and temporal distributions of tropospheric NO2 Vertical Column Densities (VCDs) over Pakistan are presented. The data products from three satellite instruments SCIAMACHY, OMI and GOME-2 are used. This study provides first database of NO2 concentration over Pakistan useful for various stakeholders concerned with air quality and its regulations. The spatial, seasonal and overall trend of NO2 column densities over Pakistan were determined from 2002 – 2012. Identification of sources for increased NO2 column densities is also discussed. The results show a large NO2 growth over the major cities of Pakistan particularly the areas with rapid urbanization and economic growth. Overall temporal increase of 58% was observed over Pakistan. Different seasonal cycles were observed in the eastern and western sides of Pakistan. In the east and south of Pakistan, NO2 maximum is found in winters while low in summer and vice versa trend was observed in the west. On the eastern side, the increase can be attributed to the anthropogenic emissions as these are the areas with high population density and industrial activities. While on the western side, natural emissions such as from soil and lightning dominate. The vehicle population showed a positive correlation with NO2 column densities in the major provinces of Punjab, Sindh and KPK with exception of Balochistan. Similarly, the areas with major industrial activity showed high amount of NO2 concentration. The data of three satellite instruments compare well with each other. Auto correlation function (ACF) and regression analysis was also performed to test the statistical significance of the data used in this study.