Measurements of total hydroxyl radical reactivity during CABINEX 2009 – Part 1: field measurements

Abstract

Abstract. Total hydroxyl radical (OH) reactivity was measured at the PROPHET (Program for Research on Oxidants: PHotochemistry, Emissions, and Transport) forested field site in northern Michigan during the 2009 Community Atmosphere–Biosphere INteraction EXperiment (CABINEX). OH reactivity measurements were made with a turbulent-flow reactor instrument at three heights from the forest floor above (21 and 31 m) and below (6 m) the canopy at three different time periods during the CABINEX campaign. In addition to total OH reactivity measurements, collocated measurements of volatile organic compounds (VOCs), inorganic species, and ambient temperature were made at the different heights. These ancillary measurements were used to calculate the total OH reactivity, which was then compared to the measured values. Discrepancies between the measured and calculated OH reactivity, on the order of 1–24 s−1, were observed during the daytime above the canopy at the 21 and 31 m heights, as previously reported for this site. The measured OH reactivity below the canopy during the daytime was generally lower than that observed above the canopy. Closer analysis of the measurements of OH reactivity and trace gases suggests that the missing OH reactivity could come from oxidation products of VOCs. These results suggest that additional unmeasured trace gases, likely oxidation products, are needed to fully account for the OH reactivity measured during CABINEX.

Global modelling of the total OH reactivity: investigations on the missing OH sink and its atmospheric implications

“…10 An exponential temperature dependence of the missing reactivity was observed during two campaigns carried out in the same North American forest, consistent with either primary biogenic emissions (Di Carlo et al, 2004) or with their oxidation products (Hansen et al, 2014). Some of the campaigns carried out in other forested environments also observed a similar trend (Kaiser et al, 2016;Mao et al, 2012;Zannoni et al, 2017), whereas others found no evidence for this correlation (Ren et al, 2006b;Sinha et al, 2010).…”

“…For instance, measurements taken during the INTEX-B campaign (Mao et al, 2009) found that the missing reactivity correlated with formaldehyde concentrations; the authors concluded that this indicated that the missing reactivity potentially arose from VOCs that formed formaldehyde upon oxidation. Similarly, measurements performed in a forest in Michigan during the CABINEX campaign showed good correlation between the missing reactivity and both isoprene and its oxidation products 15 (methyl vinyl ketone, MVK, and methacrolein, MACR) when the missing reactivity was highest (Hansen et al, 2014).…”

“…Nashville, USA (SOS) 11.0 3.8 (Kovacs et al, 2003) New York, USA (PMTACS-NY2001) 18.8 0.7 (Ren et al, 2003a(Ren et al, , 2003b New York, USA (PMTACS-NY2004) 25.1 4.0 (Ren et al, 2006a) Mexico City, Mexico (MCMA-2003) 47.5 14.3 (Shirley et al, 2006) Houston, USA (TexAQS) 9.4 0.4 (Mao et al, 2010) Houston, USA (TRAMP2006) 12.24 0.03 (Mao et al, 2010) Paris, France (MEGAPOLI) 40.3 22.8 (Dolgorouky et al, 2012) Lille, France 7.4 0 (Hansen et al, 2015) London, UK (ClearfLo) 18.1 5.9 2.7 † (Whalley et al, 2016) Remote Michigan, USA (Prophet2000) 7.8 2.6 (Di Carlo et al, 2004) Hyytiälä, Finland (BFORM) 8.6 3.9 (Sinha et al, 2010) Hyytiälä, Finland (HUMPPA-COPEC2010) 11.5 8.9 (Nölscher et al, 2012) Rocky Mountains, USA (BEACHON-SRM08) 6.7 2.1 (Nakashima et al, 2014) Michigan, USA (CABINEX) 11.6 6.3 (Hansen et al, 2014) Amazon, Brazil (ATTO) dry season 49.6 35.8 …”

“…Many studies have attempted to identify the missing sink: while some authors have attributed the missing reactivity to the presence of primary emissions that escaped detection (Holzinger et al, 2005;Kaiser et al, 2016;Sinha et al, 2010), others have pointed at the reactions of OH with short-lived oxidation intermediates (Hansen et al, 2014;Nakashima et al, 2014), which are notoriously challenging to measure in the field. 10 An exponential temperature dependence of the missing reactivity was observed during two campaigns carried out in the same North American forest, consistent with either primary biogenic emissions (Di Carlo et al, 2004) or with their oxidation products (Hansen et al, 2014).…”

Comment on "Observation and modelling of HO<sub>x</sub> radicals in a boreal forest" by Hens et al. (2014)

“…After publication of Mogensen et al (2011), several measurement and modelling papers have followed investigating the vertical dimension of the OH reactivity (e.g. Mao et al, 2012;Pratt et al, 2012;Hansen et al, 2014).…”