This study was carried out to apply principal component analysis (PCA) as a tool to identify the major sources responsible stand behind air pollution variation in a sector of Mosul city for the first time. In addition, Besides, PCA was used to construct a temporal overall air quality assessment index to find the period of best air quality along the year. The data was collected through a monitoring station located in the public library on a side of a very crowded highway and near a traffic light intersection in Mosul city. It The data involves the measurements of O₃, NO, NO₂, NO_x, SO₂, CO, CO₂, CH₄, TH, NMHC and PM₁₀ for a year. Air quality parameters were analyzed using PCA seasonally and yearly. The study found that the pollutants produced by vehicular traffic exhibited more variation with a percentage of 56.91 to 73.75%. The results showed that traffic pollution is the main contributor to air quality variation with 56.91 to 73.75%. It is verified by the gases CO, NO, NO_x, O₃, THC and CO₂. The temporal assessment of monthly air quality showed that the Best air quality was recorded in March followed by April. Whereas, the worst air quality was observed in January. The study concluded that the application of PCA to air quality data had drawn the parameters responsible for air quality variation and detect the sources of air pollution efficiently. In addition, The results of PCA can be helpful in the design of the program of measurements in the monitoring station.