Estimation of Tropospheric Ozone Column over Pakistan

Abstract

Air pollution has become a serious environmental problem across the densely populated Asian countries, especially Pakistan, being the sixth largest populous country in the world. Dramatic growth in population along with the significant increase in vehicles and industries have contributed to higher air pollutants concentrations i.e., TCO and its precursor gases. This study aimed to develop a database to analyse the spatio-temporal distribution of TCO and its precursors (Nitrogen dioxide and Formaldehyde) over Pakistan. The datasets used were; tropospheric ozone columns derived from Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) onboard Aura satellite based on Tropospheric Ozone Residual Technique (TOR), while nitrogen dioxide and formaldehyde from TEMIS OMI. Tropospheric ozone column showed strong seasonality with monsoon (Jun, Jul, Aug) maximum and winter (Dec, Jan, Feb) minimum. The seasonal formaldehyde variation was similar to that of tropospheric ozone column, whereas nitrogen dioxide showed different patterns with higher concentration in post-monsoon and winter as compared to lower concentration in monsoon and pre-monsoon. Tropospheric ozone column presented an overall increase of 2.15±1.5 Dobson Unit, over Pakistan during the study period of 2004 - 2017. Backward HYSPLIT trajectory model was used to determine the long-range transport of TCO from over the hotspots of Baluchistan with relatively less populated and industrial activities. The source attribution, showed that the fire events influence the concentration of TCO and its precursors. And for UVB radiation, TCO presented a highly significant correlation (0.91), HCHO presented positive correlation (0.43) but NO2 showed an insignificant correlation (-0.13).