Diel peroxy radicals in a semi-industrial coastal area: nighttime formation of free radicals

Abstract

Peroxy radicals were measured by a PeRCA (Peroxy Radical Chemical Amplifier) instrument in the boundary layer during the DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) campaign at a coastal, forested site influenced by urban-industrial emissions in southern Spain in late autumn. Total peroxy radicals (RO₂* = HO₂ + &Sigma;RO₂) generally showed a daylight maximum between 10 and 50 pptv at 13:00 UTC, with an average of 18 pptv over the 15 days of measurements. Emissions from the industrial area of Huelva often impacted the measurement site at night during the campaign. The processing of significant levels of anthropogenic organics leads to an intense nocturnal radical chemistry accompanied by formation of organic peroxy radicals at comparable levels to those of summer photochemical conditions with peak events up to 60–80 pptv. The RO₂ production initiated by reactions of NO₃ with organic trace gases was estimated to be significant, but not sufficient to account for the concentrations of RO₂* observed in air masses carrying high pollutant loading. The nocturnal production of peroxy radicals in those periods seems therefore to be dominated by ozonolysis of volatile organic compounds, in particular alkenes of industrial petrochemical origin. <br><br> RO₂* diurnal variations were consistent with HO₂ measurements available at the site. HO₂/RO₂* ratios generally varied between 0.3 and 0.6, though on some occasions this ratio was likely to have been affected by instrumental artifacts (overestimated HO₂) associated with high RO₂ loads

Insights into HO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; and RO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; chemistry in the boreal forest via measurement of peroxyacetic acid, peroxyacetic nitric anhydride (PAN) and hydrogen peroxide

“…Methylglyoxal is formed at high yield from the OHinitiated oxidation of several biogenic (especially isoprene) and anthropogenic VOCs, e.g. via degradation of aromatic hydrocarbons (Arey et al, 2009;Obermeyer et al, 2009) and is found in biomass-burning-impacted air masses (Fu et al, 2008;Akagi et al, 2011;Stockwell et al, 2015) and those influenced by urban emissions of aromatics (Liu et al, 2010). It is also formed at yields of several percent from the ozonolysis of monoterpenes such as α-Pinene and 3 -carene (Yu et al, 1998;Fick et al, 2003), which were both present at high concentrations during HUMPPA-COPEC-2010.…”

“…Biacetyl is formed in the photo-oxidation of aromatic hydrocarbons in the presence of NO x (Atkinson et al, 1980;Arey et al, 2009;Obermeyer et al, 2009) and is also expected to be present in biomass-burning-impacted air masses. The proposed intermediacy of dicarbonyls such as methylglyoxal and biacetyl in forming PAA in this study is consistent with the dominant role for di-and trialkyl benzenes in PAA formation found by Zhang et al (2010).…”

Missing peroxy radical sources within a summertime ponderosa pine forest

“…Nighttime peroxy radicals are low but consistently above the PeRCIMS detection limit of 2 pptv, with mean mixing ratios from 00:00 to 05:00 of 4 ± 2 pptv and 6 ± 2 pptv for HO * 2 and HO 2 + RO 2 , respectively. Observations in at least one semipolluted area have suggested that NO 3 (nitrate radical) and/or ozone-driven chemistry can drive significant nighttime peroxy radical production in the presence of alkenes (Andres-Hernandez et al, 2013). For the conditions of BEA-CHON, Fry et al (2013) have demonstrated that the oxidation of monoterpenes by NO 3 chemistry can be a significant source of particulate organic nitrates.…”

Night-time measurements of HO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; during the RONOCO project and analysis of the sources of HO&lt;sub&gt;2&lt;/sub&gt;

“…Missing night-time reactivity attributed to unmeasured secondary organic compounds. Lou et al (2010); Lu et al (2012Lu et al ( , 2013 Andrés- Hernández et al (2013) HO x concentrations in polluted or semi-polluted environments. Highlights from these studies are discussed here, with particular attention paid to those involving measurements of HO x , NO 3 , and O 3 and to those in which the contributions made by O 3 and NO 3 to night-time radical chemistry have been considered.…”