Investigation of Temporal and Spatial Trends of Air Pollutants in the City of Karaj

One of the significant challenges metropolises faces is air pollution, which has many adverse effects on human health and the environment. Karaj, as an industrial city situated close to the country's major industries and power plants, is severely affected by air pollution from both mobile and stationary sources. This study measured air quality in stations equipped with the analyzers of four gaseous pollutants, including ozone, carbon monoxide, nitrogen dioxide, and sulfur dioxide, along with two particulate pollutants, including particulates smaller than 2.5 and 10 microns. Furthermore, the city's air quality index, obtained from the total of monitoring stations, was analyzed. The study finds that particulate matter smaller than 2.5 microns and ozone are the main pollutants in Karaj in hot and cold seasons, respectively. The other pollutants exceed the allowable air quality index, rarely. For a period of one-year, particulate matter smaller than 2.5 microns and ozone put the air quality index in the range of unhealthy for sensitive groups and unhealthy for the entire city of Karaj for 94 and 18 days, respectively. Due to the secondary nature of Karaj's main pollutants, such as ozone in the warm season and a high portion of suspended particles smaller than 2.5 microns in the cold season, it is necessary to reduce air pollution through modeling that incorporates photochemical reactions in the atmosphere.