Abstract
The impact of nitrous acid (HONO) chemistry on regional ozone and particulate matter in Pearl River Delta region was investigated using the community multiscale air quality (CMAQ) 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 NOx, 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 HONO. To improve the model performance for HONO, 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 HONO compared with observed data. The addition of HONO sources enhances daily maximum 8-hour ozone by up to 6 ppbV (8%) and daily mean PM2.5by up to 17 ug/m3(12%). They also affected ozone control strategy in Pearl River Delta region.
Highlights
The importance of nitrous acid (HONO) to tropospheric chemistry is well recognized due to its contribution to HOx (OH + HO2) budget, which may lead to the enhancement of overall oxidation capacity of the atmosphere [1,2,3,4,5,6,7,8,9,10]
Consistent with the results reported, Sarwar et al [46] predicted nighttime HONO was 30%–67% lower than the values obtained with carbon bond 2005 (CB05)+EM+HT+SP and 66%–236% lower than the observed data
This study investigated the contribution of HONO sources to the photochemistry over PRD using the MM5-SMOKECMAQ model system
Summary
The importance of nitrous acid (HONO) to tropospheric chemistry is well recognized due to its contribution to HOx (OH + HO2) budget, which may lead to the enhancement of overall oxidation capacity of the atmosphere [1,2,3,4,5,6,7,8,9,10]. Accumulated HONO at night would undergo photolysis after sunrise to become an important source of hydroxyl radical (OH). It is especially important in the early morning when other major OH sources are still small. Analysis of measured HONO in urban area of Europe suggested that reaction (R1) contributes more than 30% of the integrated photolytic HOx formation [6, 7]. Box model studies by considering the importance of HONO photolysis to HOx budget demonstrated its impact on O3 buildup [1, 2]
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