Radical budget analysis in a suburban European site during the MEGAPOLI summer field campaign

Abstract

Chemical Ionisation Mass Spectrometer measurements of hydroxyl radical (OH) and the sum of hydroperoxy and organic peroxy (HO<sub>2</sub>+RO<sub>2</sub>) radicals were conducted during the MEGAPOLI summer field campaign at the SIRTA observatory near Paris, France, in July 2009. OH and (HO<sub>2</sub>+RO<sub>2</sub>) showed a typical diurnal variation with averaged daytime maxima values around 5×10<sup>6</sup> and 1.2×10<sup>8</sup> molecule cm<sup>−3</sup>, respectively. Simultaneously, a large number of ancillary measurements, such as NO<sub>x</sub>, O<sub>3</sub>, HONO, HCHO and other VOCs were also conducted. These data provide an opportunity to assess our understanding of the radical chemistry in a suburban environment by comparing the radical observations to calculations. First, OH mixing ratios were estimated by a simple Photo Stationary State (PSS) calculation. PSS calculations overestimate the OH mixing ratio by 50%, especially at NO<sub>x</sub> mixing ratios lower than 10 ppb, suggesting that some loss processes were missing in the calculation at low NO<sub>x</sub>. Then, a photochemical box model simulation based on the Master Chemical Mechanism (MCM) and constrained by ancillary measurements was run to calculate radical concentrations. Three different modelling procedures were tested, varying the way the unconstrained secondary species were estimated, to cope with the unavoidable lack of their measurements. They led to significant differences in simulated radical concentrations. OH and (HO<sub>2</sub>+RO<sub>2</sub>) concentrations estimated by two selected model version were compared with measurements. These versions of the model were chosen because they lead, respectively, to the higher and lower simulated radical concentrations and are thus the two extremes versions. The box model showed better results than PSS calculations, with a slight overestimation of 12% and 5%, for OH and (HO<sub>2</sub>+RO<sub>2</sub>) respectively, in average for the reference model, and an overestimation of approximately 20% for OH and an underestimation for (HO<sub>2</sub>+RO<sub>2</sub>) for the other selected model version. Thus, we can conclude from our study that OH and (HO<sub>2</sub>+RO<sub>2</sub>) radical levels agree on average with observations within the uncertainty range. Finally, an analysis of the radical budget, on a daily basis (06:00–18:00 UTC), indicates that HONO photolysis (~35%), O<sub>3</sub> photolysis (~23%), and aldehydes and ketones photolysis (~16% for formaldehyde and 18% for others) are the main radical initiation pathways. According to the MCM modelling, the reactions of RO<sub>2</sub> with NO<sub>2</sub> (~19%), leading mainly to PAN formation, is a significant termination pathway in addition to the main net loss...

Radical budget and ozone chemistry during autumn in the atmosphere of an urban site in central China

“…The high OH + NO 2 reaction rate was mainly caused by the relatively high daily average NO x concentration during the study period, with a value of 44 ppbv. The reaction rate of HO 2 + NO in this study is lower than that reported by Liu et al [] (19.8 ppbv h −1 , in Beijing) and Michoud et al [] (10.9 ppbv h −1 , in France). The main reason for this discrepancy is that those two studies were performed during summer, when the photolysis rate is at its highest for the year.…”

Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

“…In urban environments, measured HO 2 concentrations were sometimes found to agree with model predictions Emmerson et al, 2007; Published by Copernicus Publications on behalf of the European Geosciences Union. 96 M. M. Lew et al: Hydroperoxy radical in the atmosphere using laser-induced fluorescence 2009b; Michoud et al, 2012;Lu et al, 2013;Ren et al, 2013;Griffith et al, 2016), while other times the measurements were found to be both lower (George et al, 1999;Konrad et al, 2003) and higher than model predictions Ren et al, 2003;Emmerson et al, 2005;Kanaya et al, 2007a;Chen et al, 2010;Sheehy et al, 2010;Czader et al, 2013;Griffith et al, 2016). In forested environments, measured HO 2 concentrations were sometimes found to agree with model predictions (Tan et al, 2001;Ren et al, 2005Ren et al, , 2006 but were often found to be either lower (Carslaw et al, 2001;Kanaya et al, 2007bKanaya et al, , 2012Whalley et al, 2011;Mao et al, 2012;Griffith et al, 2013) or higher than model predictions (Carslaw et al, 2001;Kubistin et al, 2010;Kim et al, 2013;Hens et al, 2014).…”

Decadal simulation and comprehensive evaluation of CESM/CAM5.1 with advanced chemistry, aerosol microphysics, and aerosol‐cloud interactions

“…FSNS is overpredicted over Europe (see Figure ), allowing more photolytic reactions to produce OH (e.g., photolytic reactions of O 3 and VOCs), and therefore more OH can oxidize NO 2 to produce HNO 3 . In addition, the observed surface OH concentrations vary from 0 to 6 × 10 6 molecules cm −3 , with a mean maximum value of 4.2 × 10 6 molecule cm −3 in summer over Europe [ Michoud et al ., ]. The summer (JJA) average of simulated OH over Europe is about 0.05–0.35 ppt (or 1–7 × 10 6 molecules cm −3 ), indicating possible OH overpredictions.…”