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

Abstract

Abstract. Many field experiments have found high nitrous acid (HONO) mixing ratios in both urban and rural areas during daytime, but these high daytime HONO mixing ratios cannot be explained well by gas-phase production, HONO emissions, and nighttime hydrolysis conversion of nitrogen dioxide (NO 2 ) on aerosols, suggesting that an unknown daytime HONO source (P unknown ) could exist. The formula P unknown ≈ 19.60[NO 2 ] · J (NO 2 ) was obtained using observed data from 13 field experiments across the globe. The three additional HONO sources (i.e., the P unknown , nighttime hydrolysis conversion of NO 2 on aerosols, and HONO emissions) were coupled into the WRF-Chem model (Weather Research and Forecasting model coupled with Chemistry) to assess the P unknown impacts on the concentrations and budgets of HONO and peroxy (hydroxyl, hydroperoxyl, and organic peroxy) radicals (RO x ) (= OH + HO 2 + RO 2 ) in the coastal regions of China. Results indicated that the additional HONO sources produced a significant improvement in HONO and OH simulations, particularly in the daytime. High daytime average P unknown values were found in the coastal regions of China, with a maximum of 2.5 ppb h −1 in the Beijing-Tianjin-Hebei region. The P unknown produced a 60-250 % increase of OH, HO 2 , and RO 2 near the ground in the major cities of the coastal regions of China, and a 5-48 % increase of OH, HO 2 , and RO 2 in the daytime meridionalmean mixing ratios within 1000 m above the ground. When the three additional HONO sources were included, the photolysis of HONO was the second most important source in the OH production rate in Beijing, Shanghai, and Guangzhou before 10:00 LST with a maximum of 3.72 ppb h −1 and a corresponding P unknown contribution of 3.06 ppb h −1 in Beijing, whereas the reaction of HO 2 + NO (nitric oxide) was dominant after 10:00 LST with a maximum of 9.38 ppb h −1 and a corresponding P unknown contribution of 7.23 ppb h −1 in Beijing. The whole RO x cycle was accelerated by the three additional HONO sources, especially the P unknown . The daytime average OH production rate was enhanced by 0.67 due to the three additional HONO sources; [0.64]

Updated emission inventories of power plants in simulating air quality during haze periods over East China

“…Similar underestimations were previously simulated in eastern China (Gao et al, 2015;Liao et al, 2015;. The mean NMB and NME of O 3 in MOD1, calculated at −53.97 and 67.00 %, respectively (Table S1 in the Supplement), were comparable to previous China studies (Li et al, 2012;Tang et al, 2015;Zhou et al, 2017), while the mean NMB and NME of O 3 in MOD2 were ameliorated to −45.83 and 63.61 %, respectively. The SO 2 changes were generally captured in the two simulations in terms of MFB and MFE, but with an overestimation and a low R. In addition to emissions, the absence of pathways converting SO 2 to sulfate in the current WRF-Chem model, such as aqueous-phase oxidation of dis- 3 ) by dissolved NO 2 under conditions of high ammonia (NH 3 ) and NO 2 concentrations (X.…”

Explicit diagnosis of the local ozone production rate and the ozone-NOx-VOC sensitivities

“…The turning point of the contour lines would shift to higher NO x reactivity, which means a more NO x -limited regime appears. Tang et al [37] found that the unknown HONO source could also play a role in the ozone production rate, which improves the O 3 simulation in the Jing-Jin-Ji region. However, the HONO concentrations were constraint to measurement in our study.…”

Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote atmosphere in Cyprus

“…Currently, the HONO formation processes, especially during daytime, are still not fully understood. Recent ground-based field measurements showed unexpectedly high daytime concentrations of HONO, which could not be solely explained by atmospheric gas-phase reactions (R1-R3) Su et al, 2008a;Sörgel et al, 2011a;Su et al, 2011;Michoud et al, 2014;Czader et al, 2012;Wong et al, 2013;Tang et al, 2015;Oswald et al, 2015, Meusel et al, 2016 …”