Investigating air quality status and air pollutant trends over the Metropolitan Area of Tehran, Iran over the past decade between 2005 and 2014.

Studies on the trend of air pollution in Tehran, Iran, as one of the most polluted metropolis in the world are scant, and today Tehran is known for its high levels of air pollutants. In this study, the trend of air pollution concentration was evaluated over the past 10 years (2004-2015). The data were collected from 22 stations of the Air Quality Control Company. Daily concentrations of CO, NO₂, SO₂, O₃, PM₁₀ were analyzed using SPSS 16 based on the statistical method, repeated measures, and intra-group test to determine the pattern of each pollutant changes. As a result of the 22 air pollution monitoring stations, NO₂ and SO₂ concentrations have been increasing over the period of 10 years. The highest anomaly is related to SO₂. The CO concentrations represent a descending pattern over the period, although there was a slight increase in 2013 and 2014. The O₃ concentrations declined in the following years. The average concentration of PM₁₀ has been rising during the period. Also we evaluated changes of each pollutant in different months and calculated the number of clean, healthy, unhealthy days for sensitive, unhealthy, very unhealthy, and dangerous groups. The study findings illustrated the necessity for larger investment in air pollution abatement. Overall, trends have been progressed to worsening, the number of healthy days has been declined and the number of unhealthy days has been increased in recent years.