Eastern Atlantic Spring Experiment 1997 (EASE97) 2. Comparisons of model concentrations of OH, HO₂, and RO₂ with measurements

Abstract

[1] An observationally constrained box model has been used to investigate the chemistry of the marine boundary layer at the Mace Head Atmospheric Research Station, a remote site on the west coast of Ireland. The model aims to simulate concentrations of the hydroxyl (OH) and hydroperoxy (HO 2 ) radicals measured by an in situ fluorescence assay by gas expansion instrument, and the sum of peroxy radicals , respectively, between 1100 and 1500 hours: the level of agreement is better for all three sets of radicals in the cleanest air mass. Possible reasons for the observed discrepancies are discussed. In addition, a rate of production analysis is used to identify key OH and HO 2 reactions in the three air masses. The rate of OH production from HO 2 with NO exceeds that from ozone photolysis by factors of 2-6 in the polluted air masses studied. In cleaner air from the northern polar region, primary production from ozone photolysis exceeds that from HO 2 + NO by a factor of 2.5. HO 2 and CH 3 O 2 dominate the peroxy radical composition in all air masses, but peroxy radicals derived from the oxidation of nonmethane hydrocarbons are more important in polluted air masses.

Hohenpeissenberg Photochemical Experiment (HOPE 2000): Measurements and photostationary state calculations of OH and peroxy radicals

“…The peroxy radical chemical amplifier technique (Hastie et al, 1991;Cantrell et al, 1984) has been used in a large number of campaigns (e.g. Platt et al, 2002;Carslaw et al, 2002;Monks et al, 1996;Cantrell et al, 1996). In a recent field campaign (Platt et al, 2002), it was shown to compare well with direct RO x measurements made using Matrix Isolation/Electron Spin Resonance (MIESR) (Mihelcic et al, 1990).…”

“…Model results have tended to overestimate the OH concentration (Carslaw et al, 2002(Carslaw et al, , 1999George et al, 1999), with the PROPHET campaign representing a significant exception. Constraining the HO 2 or RO x concentration using measured values tends to result in much better agreement between model results and measurements (e.g.…”

“…However, only a few campaigns have been reported in which measurements of both OH and RO x (RO x =OH+RO+HO 2 +RO x ) radicals were made (e.g. Carslaw et al, 2002;Platt et al, 2002;Carslaw et al, 1999;Cantrell et al, 1996).…”

“…HCHO and CH 3 CHO, can be a significant source of peroxy radicals (e.g. Poppe et al, 1994;Carslaw et al, 2002) and by the conversion of the H atom generated in Reaction 7 following Reaction 4. A further source of peroxy radicals is the oxidation of alkenes by the nitrate radical, NO 3 , and a small yield from the oxidation of alkenes by ozone.…”

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

“…The role of halogens in HO x chemistry was demonstrated during the NAMBLEX campaign in Mace Head, Ireland , following several studies which attributed box model overestimates of HO 2 observations in marine environments to unmeasured halogen monoxides (Carslaw et al, 1999Kanaya et al, 2001Kanaya et al, , 2002Kanaya et al, , 2007. Simultaneous measurements of OH and HO 2 by laserinduced fluorescence (LIF) (Bloss et al, 2005a;Smith et al, 2006) and halogen species by a combination of DOAS (for BrO or IO, OIO and I 2 ) and broadband cavity ring-down spectroscopy (BBCRDS) (for OIO and I 2 ) (Bitter et al, 2005) during NAMBLEX enabled box model calculations to fully explore the impacts of halogens on the local composition.…”