Impact of nitrous acid chemistry on air quality modeling results over the Pearl River Delta region

Abstract. The impact of nitrous acid chemistry on regional ozone and particulate matter in Pearl River Delta region was investigated using the Community Mutilscale Air Quality modeling system and the CB05 mechanism. Model simulations were conducted for a ten-day period in October 2004. Compared with available observed data, the model performance for NO_x, SO₂, PM₁₀, and sulfate is reasonably good; however, predictions of HONO are an order of magnitude lower than observed data. The CB05 mechanism contains several homogenous reactions related to nitrous acid. To improve the model performance for nitrous acid, direct emissions, two heterogeneous reactions, and two surface photolysis reactions were incorporated into the model. The inclusion of the additional formation pathways significantly improved simulated nitrous acid compared with observed data. The addition of nitrous acid sources enhance daily maximum 8-h ozone by up to 6 ppb V (8 %) and daily mean PM_2.5 by up to 17 μg m⁻³ (12 %). They also affected ozone control strategy in Pearl River Delta region.