In this study, spatial and temporal distributions of tropospheric NO 2 vertical column densities over Pakistan during the time period of 2002-2012 are discussed. Data products from the satellite instrument SCIAMACHY are used. The results show a large NO 2 growth over major cities of Pakistan, particularly the areas with rapid urbanization. Different seasonal cycles were observed in different regions of Pakistan. In the provinces of Punjab (north east), Khyber Paktunkhwa (north west) and Sindh (south east), NO 2 columns are maximum in winter and minimum in summer months while a reversed seasonality was observed in the province of Baluchistan (south west). We compared the observed spatio-temporal patterns to existing emission inventories and found that for the most populated provinces the NO x emissions are clearly dominated by anthropogenic sources. In these areas also the strongest positive trends were observed. NO x released from soils and produced by lightning both together contribute about 20% for the provinces of Punjab, Sindh, and Khyber Paktunkhwa, while its contribution in Baluchistan is much stronger (~50%). NO x emissions from biomass burning are negligible. This finding can also explain the observed summer maximum in Baluchistan, since the highet lightning activity occurs during the Monsoon season. Our comparison also indicates that the inventories of anthropogenic NO x emissions over Pakistan seem to underestimate the true emissions by about a factor of two.
This study primarily focuses on monitoring of tropospheric formaldehyde (HCHO) column densities over Pakistan during the time period of year 2003 to 2012. Observations from two satellite instruments SCIAMACHY (Scanning imaging absorption spectrometer for atmospheric chartography, on-board ENVISAT-1) and GOME-2 (Global ozone monitoring experiment, on-board Metop-A) were used. Spatial and temporal distributions of HCHO column densities over Pakistan are analysed. Spatial maps were generated in order to see the distribution of HCHO and to identify major hotspots across the country. Seasonal cycle of HCHO over all provinces of Pakistan showed the summer maximum attributed to increase in biogenic emissions and biomass burning activities. Further emphasis was made on source identification of HCHO emissions. It revealed that agriculture fires and extensive use of compressed natural gas (CNG) as fuel also contribute to tropospheric HCHO in Pakistan. World fire atlas data from along track scanning radiometer (ATSR) was used to identify effect of agriculture waste burning on HCHO concentration in Pakistan. Significant correlation was observed between agricultural fires and increased HCHO column densities.
This study uses the tropospheric ozone data derived from combined observations of Ozone Monitoring Instrument/Microwave Limb Sounder instruments by using the tropospheric ozone residual method. The main objective was to study the spatial distribution and temporal evolution in the troposphere ozone columns over Pakistan during the time period of 2004 to 2014. Results showed an overall increase of 3.2 ± 1.1 DU in tropospheric ozone columns over Pakistan. Spatial distribution showed enhanced ozone columns in the Punjab and southern Sindh consistent to high population, urbanization, and extensive anthropogenic activities, and exhibited statistically significant temporal increase. Seasonal variations in tropospheric ozone columns are driven by various factors such as seasonality in UV-B fluxes, seasonality in ozone precursor gases such as NO and volatile organic compounds (caused by temperature dependent biogenic emission) and agricultural fire activities in Pakistan. A strong correlation of 96% (r = 0.96) was found between fire events and tropospheric ozone columns in Pakistan.
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