In order to assess the extent of air quality within the major urban environments in Pakistan, PM2.5 pollutant has been analyzed during the period 2007–2011 in Islamabad; and 2007 to 2008 in Lahore, Peshawar and Quetta (high elevation, 1680 m MSL). Seasonal and diurnal variations of PM2.5 mass concentration formation and accumulation within these areas have been analyzed. Air quality monitoring data and meteorological data (both QA/QCed) were obtained from Federal and Provincial Pakistan Environmental Protection Agencies. In Islamabad, the annual average PM2.5 mass concentrations were 81.1 ± 48.4 µg/m3, 93.0 ± 49.9 µg/m3, 47.8 ± 33.2 µg/m3, 79.0 ± 49.2 µg/m3, and 66.1 ± 52.1 µg/m3 during 2007 to 2011 respectively. Comparison of the four cities during summer 2007 to spring 2008 shows that all the four cities had PM2.5 concentration exceeding the Pakistan National Environmental Quality Standards (annual average concentration of 25 µg/m3; and 24 hourly average concentration of 40 µg/m3) for ambient air. During the same time period, the highest seasonal PM2.5 mass concentrations for Islamabad were observed as 98.5 µg/m3 during spring 2008; 150.4 ± 87.9 µg/m3; 104.1 ± 51.1 µg/m3 and 72.7 ± 55.2 µg/m3 for Lahore, Peshawar, and Quetta during fall 2007, respectively. Wind speed and temperature have a negative correlation with the mass concentration of PM2.5. Diurnal profile for all the cities suggests an association of PM2.5 with vehicular traffic. Back trajectory analysis conducted using the NOAA HYSPLIT model indicates that air trajectories, during high pollution episodes, influencing the urban regions commonly originate from either western India, especially in summer as part of the prevailing monsoon circulation; or are located in eastern Afghanistan. The source areas in Western India i.e., states of Gujarat, Rajasthan and Punjab have high concentration of industrial activities and crop residue burning, and are likely sources of enhanced PM2.5 concentrations, in addition to the local sources.