Conditions optimization and application for determining concentrations of HNO₃ and HNO₂ in atmosphere of Beijing by annular denuders method

In order to study the pollution characteristics of HNO₃ and HNO₂ in ambient air of Beijing City, the experiments for determining the optimal concentrations of annular denuders coatings were performed, and application study carried out in Beijing in the autumn of 2014. The results showed that when the concentration of Na₂CO₃ coating solution was 2%, the removal rate of acid gases in the atmosphere reached over 90%. The concentrations of HNO₃ and HNO₂ in air sampled in downtown Beijing were determined by the optimization approach. The concentrations of HNO₃ and HNO₂ in the measurement period ranged from 0.77 to 3.23 μg/m ³ and from 1.12 to 5.51 μg/m ³, with an average value of 2.33 μg/m ³ and 2.96 μg/m ³, respectively. HNO₂ concentration was higher than that of HNO₃ in the study area. The weak light during sampling might result in HNO₂ photolysis reduction. Also, because of the sampling point nearby trunk road, the homo- and heterogeneous reactions of NO_x from automobile exhaust may lead to a higher HNO₂ concentration. The highest concentration of HNO₃ occurred in haze day, followed by sunny day, while HNO₂ had the highest concentration in haze day, which was far more than that in sunny day.