Long-term trends of Nitrogen oxides and surface ozone concentrations in Tehran city, 2002-2011

Background and aim: Tropospheric ozone is a problem with multi aspects - hazard to human health, plant, and welfare and a key factor to climate change, air pollution and atmosphere chemistry, as well. Behavior of ozone and nitrogen oxides (NO, and NO2) concentration is highly complex and variable; therefore, their trends as short and long-term were significantly attended. Most of the studies were carried out on the behavior of pollutant concentrations in North America, Europe, and East Asia, but few studies have been conducted in west Asia. The aim of this study was to assess daily changes and long- term trend of ozone and nitrogen oxides concentrations in Tehran city, Iran from March 2002 to September 2011. Material and methods: Data were collected from 18 air quality monitoring stations. The data were sorted as daily mean of 10 years (daily changes) and annual mean for each year (long- term trend). One-sample test was used to assess the statistical significance. Results: Current findings indicated that changes of ozone, NO, and NO2 concentrations are dependent from job shifts and photochemical reactions. Annual mean concentrations of ozone and NO2 were gradually increased, long- term trend of ozone and NO2 concentration indicated. The correlation between long term trend of ozone and NO2 was significant (p < 0.05). Conclusion: The controlling program was the most important factor in long- term concentration of ozone, and nitrogen oxides, but some problems and difficulties were accounted to perform controlling program.