Articles | Volume 17, issue 20
Research article
25 Oct 2017
Research article |  | 25 Oct 2017

Summertime OH reactivity from a receptor coastal site in the Mediterranean Basin

Nora Zannoni, Valerie Gros, Roland Sarda Esteve, Cerise Kalogridis, Vincent Michoud, Sebastien Dusanter, Stephane Sauvage, Nadine Locoge, Aurelie Colomb, and Bernard Bonsang

Abstract. Total hydroxyl radical (OH) reactivity, the total loss frequency of the hydroxyl radical in ambient air, provides the total loading of OH reactants in air. We measured the total OH reactivity for the first time during summertime at a coastal receptor site located in the western Mediterranean Basin. Measurements were performed at a temporary field site located in the northern cape of Corsica (France), during summer 2013 for the project CARBOSOR (CARBOn within continental pollution plumes: SOurces and Reactivity)–ChArMEx (Chemistry and Aerosols Mediterranean Experiment). Here, we compare the measured total OH reactivity with the OH reactivity calculated from the measured reactive gases. The difference between these two parameters is termed missing OH reactivity, i.e., the fraction of OH reactivity not explained by the measured compounds. The total OH reactivity at the site varied between the instrumental LoD (limit of detection  =  3 s−1) to a maximum of 17 ± 6 s−1 (35 % uncertainty) and was 5 ± 4 s−1 (1σ SD – standard deviation) on average. It varied with air temperature exhibiting a diurnal profile comparable to the reactivity calculated from the concentration of the biogenic volatile organic compounds measured at the site. For part of the campaign, 56 % of OH reactivity was unexplained by the measured OH reactants (missing reactivity). We suggest that oxidation products of biogenic gas precursors were among the contributors to missing OH reactivity.

Short summary
Our paper presents results of hydroxyl radical (OH) reactivity from a field study conducted during summer 2013 in a western Mediterranean coastal site (Corsica, France). Here, the total OH reactivity, measured with the comparative reactivity method, is compared with the summed OH reactivity from the reactive gases measured with a multitude of different technologies. Our results demonstrate the relatively high observed reactivity and the large impact of biogenic compounds.
Final-revised paper