Analytical study of the effect of nitrogen oxides, volatile organic compounds, and ambient temperature on ozone in Tehran

The aim of this study is to evaluate the effect of nitrogen oxides, volatile organic compounds, and ambient temperature on ozone concentration in the city of Tehran. In this regard, the hourly concentration for ozone and nitrogen oxides for the first half of 1396-98 were used. Also the 2-weeks averaged data for BTEX monitored by passive sampling method and 30-minutes averaged temperature data monitored at Mehrabad airport were used. First, daily variations of ozone and nitrogen oxides with their corresponding indexes were analyzed. Then, the role of nitrogen oxide and nitrogen dioxide on ozone concentration were investigated by statistical analysis. The results show a meaningful relationship between ozone and both nitrogen oxide and nitrogen dioxide with the coefficient of determinations of 0.83 and 0.8, respectively. Although an apparent increasing trend in ozone concentrations has been observed in recent years, however, no similar trends are detected for nitrogen oxide and nitrogen dioxide. The limited available data for BTEX, shows a 17.3% increase from 1394 to 1398. The daytime temperature analysis for the 30 days with the highest ozone concentrations showed an increasing trend from 1396 to 1398. Therefore, it can be concluded that the increasing trends of BTEX concentrations and ambient temperature were probably responsible for the increasing trend of ozone concentration in the study period.