Satellite Remote Sensing of Aerosols and Gaseous Pollution over Pakistan

Abstract

The trace gases–aerosols–climate interaction is an important subject regarding climate change, air quality studies, and modeling. This study focuses on the spatiotemporal variability, trends, and seasonality of aerosols and important trace gases such as NO2, CH4, O3, and CO over Pakistan using satellite remote sensing. In the present work, to assess the total aerosol burden, we have analyzed the Aqua-MODIS derived deep blue aerosol optical depth (AOD) at 550 nm for the period July 2002 to June 2015. We have also compared AOD from Aqua with that of Terra and MISR. High correlation (R = 0.832) was observed between Aqua-AOD and Terra-AOD while relatively low correlation (0.666) was found between Aqua-AOD and MISR-AOD. The AOD starts to increase from February and becomes maximum (0.55) in July and then decreases afterwards. We have also discussed seasonal and annual mean AOD derived from Aqua-MODIS over six megacities of Pakistan. Annual mean value of tropospheric NO2 column derived from OMI (Ozone Monitoring Instrument) is found to be 1.187 ± 0.018 × 1015 molecules/cm2 during 2005–2015. NO2 column exhibits two peaks, i.e., primary peak in June (1.325 ± 0.079 × 1015 molecules/cm2) and secondary peak in December (1.258 ± 0.099 × 1015 molecules/cm2). Atmospheric Infrared Sounder (AIRS) observations reveal an annual averaged value of CO to be 123.165 ± 6.67 (ppbv). AIRS data show large spatial and temporal variations of lower-tropospheric O3 retrieved at 850 hPa. Yearly time and space averaged value of O3 is 42.27 ± 0.35 ppbv with increasing trend of 0.17% per year. SCIAMACHY data show that total column of CH4 is elevating with the rate of 0.41% per year with an annual mean value of 1787 ± 22 ppbv during the study period.