Abstract
Ozone (O3), oxides of nitrogen (NOx), and carbon monoxide (CO) were monitored at CSIR National Physical Laboratory, New Delhi, during May and October, 2014. One-hour O3 concentrations exceeding more than 120 ppb were observed for 9 days in May and 16 days in October months with concurrent high NOx and CO values. The higher ozone episodes in October 2014 as compared to May 2014 may be due to contribution of biomass burning. The nitrogen oxide (NO), nitrogen dioxide (NO2), O3, and the photolysis rate of NO2 (i.e., JNO2) values of May and October, 2014, were used to evaluate the photo-stationary state ratio (or Leighton ratio, ϕ) for clear sky conditions. Leighton ratio ranged from 0.4 to 2.6 (average values 0.89 ± 0.4) for May 2014 and from 0.3 to 3.6 (average value 1.01 ± 0.52) for October 2014. The observed NOy values in October 2014 indicated the production of O3 through hydrocarbon-sensitive O3 chemistry. The sum of reactive nitrogen species’ (i.e., NOy) mixing ratios recorded during October 2014 varied from 259.4 to 10.4 ppb with an average value of 80.5 ± 39 ppb. The averaged diurnal ratio of NOx–NOy of > 0.3 indicated the presence of freshly emitted pollutants.
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