High population density and intense industrial activity has resulted in various forms of pollution in megacities. Air pollution ranks at the top of this list. This study investigated long-term changes in air pollutant parameters (SO2, CO, NO, NO2, NOx) in Istanbul City, Turkey, using data from air-quality measurement stations on the Asian and European sides of Istanbul. The results show decreases from 2002 to 2010 in the amounts of SO2 (one of the main pollutants released as a result of the burning of fossil fuels) and CO (indicative of incomplete combustion). However, NOx concentrations showed fluctuations over time, rather than a steady decline throughout the study period.