Gupta, P; Khan, MN; da Silva, A; Patadia, F (2013). MODIS aerosol optical depth observations over urban areas in Pakistan: quantity and quality of the data for air quality monitoring. ATMOSPHERIC POLLUTION RESEARCH, 4(1), 43-52.
Ten years (2001-2010) of aerosol optical depth (AOD) observations from the MODerate resolution Imaging SpectroRadiometer (MODIS) over two large urban centers in Pakistan have been analyzed for atmospheric aerosol loading and surface level particulate matter air quality assessments. MODIS Level 2 AOD data over Karachi and Lahore were analyzed for availability of aerosols data, spatial gradients, and long term trends. MODIS AOD used in this analysis is retrieved using the dark target algorithm. Availability of AOD data over Karachi and its surroundings is seriously impacted by the presence of bright surfaces - a well known limitation of the retrieval algorithm. The Lahore region does not experience this problem due to its relatively darker surface, and therefore permits a more in-depth analysis. Due to the lack of available AOD data, analysis over Karachi has not been performed. A spatial gradient of 0.2/degree in AOD have been found over Lahore, which indicate high aerosol loading near the city center as compared to outside the city area. Long-term trend analysis over Lahore shows a decreasing trend in AOD with slope of -0.07 over the last decade. The surface level particulate matter estimates using AOD-PM relationship suggest that Lahore experience unhealthy air quality on more than 80% days in any given year.