Direct measurements of urban OH reactivity during Nashville SOS in summer 1999

Kovacs, Thomas; Brune, William H.; Harder, Hartwig; Martínez, Mònica; Simpas, James Bernard; Frost, G. J.; Williams, E. J.; Jobson, T.; Stroud, Craig; Young, V.; Fried, Alan; Wert, B.

doi:10.1039/b204339d

Cited by 130 publications

(186 citation statements)

References 20 publications

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“…However, other studies suggest that the missing reactivity is due to unmeasured oxidation products of measured primary emitted VOCs (Kovacs et al, 2003;Hofzumahaus et al, 2009;Lou et al, 2010). This role of oxidation products is supported by recent observations by Kim et al (2011) of OH reactivity within branch enclosures on four different tree species, where no significant oxidation chemistry had taken place, which found that the observed OH loss rate could be accounted for by the measured BVOCs.…”

Section: P M Edwards Et Al: Oh Reactivity In a South East Asian Trsupporting

confidence: 66%

OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

et al. 2013

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Abstract. OH (hydroxyl radical) reactivity, the inverse of the chemical lifetime of the hydroxyl radical, was measured for 12 days in April 2008 within a tropical rainforest on Borneo as part of the OP3 (Oxidant and Particle Photochemical Processes) project. The maximum observed value was 83.8 ± 26.0 s −1 with the campaign averaged noontime maximum being 29.1 ± 8.5 s −1 . The maximum OH reactivity calculated using the diurnally averaged concentrations of observed sinks was ∼ 18 s −1 , significantly less than the observations, consistent with other studies in similar environments. OH reactivity was dominated by reaction with isoprene (∼ 30 %). Numerical simulations of isoprene oxidation using the Master Chemical Mechanism (v3.2) in a highly simplified physical and chemical environment show that the steady state OH reactivity is a linear function of the OH reactivity due to isoprene alone, with a maximum multiplier, to account for the OH reactivity of the isoprene oxidation products, being equal to the number of isoprene OH attackable bonds (10). Thus the emission of isoprene constitutes a significantly larger emission of reactivity than is offered by the primary reaction with isoprene alone, with significant scope for the secondary oxidation products of isoprene to constitute the observed missing OH reactivity. A physically and chemically more sophisticated simulation (including physical loss, photolysis, and other oxidants) showed that the calculated OH reactivity is reduced by the removal of the OH attackable bonds by other oxidants and photolysis, and by physical loss (mixing and deposition). The calculated OH reactivity is increased by peroxide cycling, and by the OH concentration itself. Notable in these calculations is that the accumulated OH reactivity from isoprene, defined as the total OH reactivity of an emitted isoprene molecule and all of its oxidation products, is significantly larger than the reactivity due to isoprene itself and critically depends on the chemical and physical lifetimes of intermediate species. When constrained to the observed diurnally averaged concentrations of primary VOCs (volatile organic compounds), O 3 , NO x and other parameters, the model underestimated the observed diurnal mean OH reactivity by 30 %. However, it was found that (1) the short lifetimes of isoprene and OH, compared to those of the isoprene oxidation products, lead to a large variability in their concentrations and so significant variation Published by Copernicus Publications on behalf of the European Geosciences Union. P. M. Edwards et al.: OH reactivity in a South East Asian tropical rainforestin the calculated OH reactivity; (2) uncertainties in the OH chemistry in these high isoprene environments can lead to an underestimate of the OH reactivity; (3) the physical loss of species that react with OH plays a significant role in the calculated OH reactivity; and (4) a missing primary source of reactive carbon would have to be emitted at a rate equivalent to 50 % that of isoprene to account for the missing OH s...

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Section: P M Edwards Et Al: Oh Reactivity In a South East Asian Trsupporting

confidence: 66%

OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

et al. 2013

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“…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 …”

Section: Urbanmentioning

confidence: 99%

“…For example, additional species (such as more reactive NMHCs or more reactive reaction intermediates) and their chemistry could be included in the model. However observations indicate that this approach would still leave outstanding missing reactivity (Edwards et al, 2013;Elshorbany et al, 2012;Kaiser et al, 2016;Kovacs et al, 2003;Lee et al, 2009;Lou et al, 2010;Mao et al, 2012;Mogensen 25 et al, 2011;Yang et al, 2017). In this work, we have taken a different, simpler approach.…”

mentioning

confidence: 99%

“…15 In an attempt to account for the additional OH reactivity potentially arising from unmeasured oxidation intermediates, a number of studies invoked box modelling to determine the abundance of these species and their contribution to kOH. These efforts have been met with mixed results: while some managed to reconcile the total kOH with the sum of reactivities once the oxidation intermediates were taken into account (Whalley et al, 2016), others obtained different degrees of improvement on the agreement between the two, leaving different fractions of kOH still unaccounted for (Edwards et al, 2013;Elshorbany et al, 20 2012;Kaiser et al, 2016;Kovacs et al, 2003;Lee et al, 2009;Lou et al, 2010;Mao et al, 2012;Mogensen et al, 2011;Yang et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Ferracci¹,

Heimann²,

Abraham³

et al. 2018

Preprint

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Abstract. The hydroxyl radical (OH) plays a crucial role in the chemistry of the atmosphere as it initiates the removal of most trace gases. A number of field campaigns have observed the presence of a "missing" OH sink in a variety of regions across the planet. Comparison of direct measurements of the OH loss frequency, also known as total OH reactivity (kOH), with the 10 sum of individual known OH sinks (obtained via the simultaneous detection of species such as volatile organic compounds and nitrogen oxides) indicates that, in some cases, up to 80 % of kOH is unaccounted for. In this work, the UM-UKCA chemistry-climate model was used to investigate the wider implications of the missing reactivity on the oxidising capacity of the atmosphere. Simulations of the present-day atmosphere were performed and the model was evaluated against an array of field measurements to verify that the known OH sinks were reproduced well, with a resulting good agreement found for most 15 species. Following this, an additional sink was introduced to simulate the missing OH reactivity as an emission of a hypothetical molecule, X, which undergoes rapid reaction with OH. The magnitude and spatial distribution of this sink were underpinned by observations of the missing reactivity. Model runs showed that the missing reactivity accounted for on average 6 % of the total OH loss flux at the surface, and up to 50 % in regions where emissions of the additional sink were high. The lifetime of the hydroxyl radical was reduced by 3 % in the boundary layer, while tropospheric methane lifetime increased by 20 2 % when the additional OH sink was included. The UM-UKCA simulations also allowed us to establish the atmospheric implications of the newly characterised reactions of peroxy radicals (RO2) with OH. While the effects of this chemistry on kOH were minor, the reaction of the simplest peroxy radical, CH3O2, with OH was found to be a major sink for CH3O2 and source of HO2 over remote regions at the surface and in the free troposphere. Inclusion of this reaction in the model increased tropospheric methane lifetime by up to 3 %, depending on its product branching. Simulations based on the latest kinetic and 25 product information showed that this reaction cannot reconcile models with observations of atmospheric methanol, in contrast to recent suggestions.Atmos. Chem. Phys. Discuss., https://doi

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“…(3)) and OH reactivities (Eq. (2); in units of s À1 ; Kovacs et al, 2003;Di Carlo et al, 2004) are not directly comparable. Although both quantities depend on the OH reaction rate coefficients, the former quantity depends on the BVOC production rates, and the latter depends on the ambient BVOC concentrations.…”

Section: Effect Of Terpenoid Emissions On Oh Reactivitymentioning

confidence: 99%

Flux estimates and OH reaction potential of reactive biogenic volatile organic compounds (BVOCs) from a mixed northern hardwood forest

Ortega

Helmig

Guenther

et al. 2007

Atmospheric Environment

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Diurnal branch-level emission rates of biogenic volatile organic compounds (BVOC) including isoprene, monoterpenes (MT), and sesquiterpenes (SQT) were determined at the University of Michigan Biological Station for the tree species red maple (Acer rubrum), red oak (Quercus rubra), paper birch (Betula papyrifera), white pine (Pinus strobus), and big tooth aspen (Populus grandidentata). These emission rates were combined with detailed biomass distribution and meteorological data and incorporated into the canopy model, model of emissions of gasses and aerosols from nature (MEGAN), for estimating whole-canopy fluxes of isoprene. The modeled half-hour fluxes ðmg C m À2 h À1 Þ and cumulative seasonal fluxes ðmg C m À2 Þ compared favorably with results from direct, canopy-level eddy covariance (EC) isoprene measurements; modeled cumulative seasonal flux deviated less than 30% from the EC results. Significant MT emissions were found from four of the five tree species. MT emissions from three of these were both light-and temperature-dependent and were approximately one order of magnitude greater than light-independent MT emissions. SQT emissions were identified from three of the five tree species. The model was modified to incorporate SQT and both light-dependent and light-independent MT emissions for determining fluxes. Isoprene comprised 495% of the total terpenoid flux with MT and SQT comprising 4% and 0.3%, respectively. The average cumulative fluxes (in mg C m À2 ) from June through September were 2490 for isoprene, 105 for MT, and 7 for SQT. A simple box model analysis was used to estimate the contribution of the isoprene, MT, and SQT emissions to the total OH reactivity. These results confirm that isoprene dominates OH reactions especially during daytime hours. Emissions of reactive MT and SQT increase the BVOC+OH reactivity, but are still lower than estimates of BVOC fluxes at this site necessary for affecting OH reactivity to the significant degree suggested by recent reports. r

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Direct measurements of urban OH reactivity during Nashville SOS in summer 1999

Cited by 130 publications

References 20 publications

OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

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

Flux estimates and OH reaction potential of reactive biogenic volatile organic compounds (BVOCs) from a mixed northern hardwood forest

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