Impacts of an unknown daytime HONO source on the mixing ratio and budget of HONO, and hydroxyl, hydroperoxyl, and organic peroxy radicals, in the coastal regions of China

摘要

Many field experiments have found high nitrous acid (HONO) mixing ratios inboth urban and rural areas during daytime, but these high daytime HONOmixing ratios cannot be explained well by gas-phase production, HONOemissions, and nighttime hydrolysis conversion of nitrogen dioxide(NO) on aerosols, suggesting that an unknown daytime HONO source() could exist. The formula ≈ 19.60[NO] ·(NO) was obtained using observed data from 13 field experiments acrossthe globe. The three additional HONO sources (i.e., the ,nighttime hydrolysis conversion of NO on aerosols, and HONO emissions)were coupled into the WRF-Chem model (Weather Research and Forecasting modelcoupled with Chemistry) to assess the impacts on theconcentrations and budgets of HONO and peroxy (hydroxyl, hydroperoxyl, andorganic peroxy) radicals (RO) (= OH + HO + RO) inthe coastal regions of China. Results indicated that the additional HONOsources produced a significant improvement in HONO and OH simulations,particularly in the daytime. High daytime average values werefound in the coastal regions of China, with a maximum of 2.5 ppb h inthe Beijing–Tianjin–Hebei region. The produced a60–250 % increase of OH, HO, and RO near the ground in themajor cities of the coastal regions of China, and a 5–48 % increaseof OH, HO, and RO in the daytime meridional-mean mixing ratioswithin 1000 m above the ground. When the three additional HONO sources wereincluded, the photolysis of HONO was the second most important source in theOH production rate in Beijing, Shanghai, and Guangzhou before 10:00 LST witha maximum of 3.72 ppb h and a corresponding contribution of 3.06 ppb h in Beijing, whereas the reaction ofHO + NO (nitric oxide) was dominant after 10:00 LST with a maximumof 9.38 ppb h and a corresponding contribution of 7.23 ppb h in Beijing. The whole RO cycle was accelerated by thethree additional HONO sources, especially the . The daytimeaverage OH production rate was enhanced by 0.67 due to the three additionalHONO sources; [0.64], due to the , to 4.32 [3.86] ppb h, viathe reaction of HO + NO, and by 0.49 [0.47] to 1.86 [1.86] ppb h, via the photolysis of HONO. The OH daytime average loss ratewas enhanced by 0.58 [0.55] to 2.03 [1.92] ppb h, via the reaction ofOH + NO, and by 0.31 [0.28] to 1.78 [1.64] ppb h, via thereaction of OH + CO (carbon monoxide) in Beijing, Shanghai, and Guangzhou.Similarly, the three additional HONO sources produced an increase of 0.31[0.28] (with a corresponding contribution) to1.78 [1.64] ppb h, via the reaction of OH + CO, and 0.10 [0.09] to 0.63 [0.59] ppb h, via the reaction of CHO (methylperoxy radical) + NO in the daytime average HO production rate, and 0.67 [0.61] to 4.32[4.27] ppb h, via the reaction of HO + NO in the daytimeaverage HO loss rate in Beijing, Shanghai, and Guangzhou. The aboveresults suggest that the considerably enhanced the ROconcentrations and accelerated RO cycles in the coastal regions ofChina, and could produce significant increases in concentrations ofinorganic aerosols and secondary organic aerosols and further aggravate hazeevents in these regions.