Impact of HONO on global atmospheric chemistry calculated with an empirical parameterization in the EMAC model

Abstract

The photolysis of HONO is important for the atmospheric HO<sub>x</sub> (OH+HO<sub>2</sub>) radical budget and ozone formation, especially in polluted air. Nevertheless, owing to the incomplete knowledge of HONO sources, realistic HONO mechanisms have not yet been implemented in global models. We investigated measurement data sets from 15 field measurement campaigns conducted in different countries worldwide. It appears that the HONO/NO<sub>x</sub> ratio is a good proxy predictor for HONO mixing ratios under different atmospheric conditions. From the robust relationship between HONO and NO<sub>x</sub>, a representative mean HONO/NO<sub>x</sub> ratio of 0.02 has been derived. Using a global chemistry-climate model and employing this HONO/NO<sub>x</sub> ratio, realistic HONO levels are simulated, being about one order of magnitude higher than the reference calculations, which only consider the reaction OH+NO-> HONO. The resulting enhancement of HONO significantly impacts HO<sub>x</sub> levels and photo-oxidation products (e.g, O<sub>3</sub>, PAN), mainly in polluted regions. Furthermore, the relative enhancements in OH and secondary products were higher in winter than in summer, thus enhancing the oxidation capacity in polluted regions, especially in winter, when the other photolytic OH sources are of minor importance. Our results underscore the need to improve the understanding of HONO chemistry and its representation in atmospheric models

Impacts of Additional HONO Sources on Concentrations and Deposition of NO_y in the Beijing-Tianjin-Hebei Region of China

“…The extended model with the additional HONO sources succeeded to capture the magnitude and the diurnal variations of the observed data (Table S1), e.g., promising improvement in the model performance is found for predictions of O 3 peaks in urban areas (Li et al 2011). Our results agree with other studies (Li et al 2010;Elshorbany et al 2012;Gonçalves et al 2012), showing that at least the Het and the Emis should be included in models, since their impact on second- (2010) and Spataro et al (2013). Case R is a reference case; Case E includes NO 2 * chemistry, the NO 2 heterogeneous reaction on aerosol surfaces and HONO emissions.…”

Implementation and refinement of a surface model for heterogeneous HONO formation in a 3-D chemical transport model

“…The first mechanism is the photolysis of surface adsorbed nitric acid (HNO 3 ) (Zhou et al, , 2011Beine et al, 2002;Dibb et al, 2002;Zhou et al, 2003;Ramazan et al, 2004;Clemitshaw, 2006). This mechanism is believed to be important under low-NOx conditions (e.g., Zhou et al, 2003;Elshorbany et al, 2012). The second is the photo-enhanced conversion of gas-phase NO 2 on organic films or surfaces commonly found on the ground or aerosols (e.g., George et al, 2005;Stemmler et al, 2006Stemmler et al, , 2007.…”

“…Nitrous acid (HONO) plays an important role in atmospheric chemistry, since its photolysis leads to the rapid formation of the hydroxyl radical, OH, during the early morning hours and even during the daytime in urban areas with high NOx levels (e.g., Elshorbany et al, 2012). The hydroxyl radical is extremely reactive and is the most important oxidizing species in the atmosphere.…”

Large conversion rates of NO2 to HNO2 observed in air masses from the South China Sea: Evidence of strong production at sea surface?

“…Current global and regional chemical transport models that consider the heterogeneous production of HONO on the ground surfaces either do not distinguish sea and land [Elshorbany et al, 2012] or do not consider the HONO formation on the sea at all [Goncalves et al, 2012;Sarwar et al, 2008;Zhang et al, 2012]. Our study indicates that HONO may be produced at a faster rate on the sea; if this finding is confirmed and applicable to other regions, current chemical transport models may need to consider HONO formation on the sea and to adopt different parameterizations for reactions on land and sea.…”