Missing peroxy radical sources within a summertime ponderosa pine forest

Wolfe, G. M.; Cantrell, C. A.; Kim, S.; Mauldin, R. L.; Karl, T.; Harley, P. C.; Turnipseed, Andrew A.; Zheng, Weiwei; Flocke, Frank; Apel, E. C.; Hornbrook, R. S.; Hall, Samuel R.; Ullmann, Kirk; Henry, S. B.; DiGangi, J. P.; Boyle, Erin S.; Kaser, L.; Schnitzhofer, R.; Hansel, Armin; Graus, M.; Nakashima, Yoshihiro; Kajii, Yoshizumi; Guenther, Alex; Keutsch, Frank N.

doi:10.5194/acp-14-4715-2014

Cited by 63 publications

(68 citation statements)

References 87 publications

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“…All analyses in this work were done using estimated in-canopy concentrations, which were inferred by applying these empirical relationships to the continuous 25 m inlet measurements. This scaling technique has been used before, producing similar results when applied to measurements during the summer 2010 BEACHON-ROCS (BEACHON-Rocky Mountain Organic Carbon Study) campaign at the same field location Wolfe et al, 2014).…”

Section: Sampling Strategy and Measurementsmentioning

confidence: 58%

In situ secondary organic aerosol formation from ambient pine forest air using an oxidation flow reactor

et al. 2016

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Abstract. An oxidation flow reactor (OFR) is a vessel inside which the concentration of a chosen oxidant can be increased for the purpose of studying SOA formation and aging by that oxidant. During the BEACHON-RoMBAS (Bio-hydroatmosphere interactions of Energy, Aerosols, Carbon, H 2 O, Organics & Nitrogen-Rocky Mountain Biogenic Aerosol Study) field campaign, ambient pine forest air was oxidized by OH radicals in an OFR to measure the amount of SOA that could be formed from the real mix of ambient SOA precursor gases, and how that amount changed with time as precursors changed. High OH concentrations and short residence times allowed for semicontinuous cycling through a large range of OH exposures ranging from hours to weeks of equivalent (eq.) atmospheric aging. A simple model is derived and used to account for the relative timescales of condensation of low-volatility organic compounds (LVOCs) onto particles; condensational loss to the walls; and further reaction to produce volatile, non-condensing fragmentation products. More SOA production was observed in the OFR at nighttime (average 3 µg m −3 when LVOC fate corrected) compared to daytime (average 0.9 µg m −3 when LVOC fate corrected), with maximum formation observed at 0.4-1.5 eq. days of photochemical aging. SOA formation followed a similar diurnal pattern to monoterpenes, sesquiterpenes, and toluene+p-cymene concentrations, including a substantial increase just after sunrise at 07:00 local time. Higher photochemical aging (> 10 eq. days) led to a decrease in new SOA formation and a loss of preexisting OA due to heterogeneous oxidation followed by fragmentation and volatilization. When comparing two different commonly used methods of OH production in OFRs (OFR185 and OFR254-70), similar amounts of SOA formation were observed. We recommend the OFR185 mode for future forest studies. Concurrent gas-phase measurements of air after OH oxidation illustrate the decay of primary VOCs, production of small oxidized organic compounds, and net production at lower ages followed by net consumption of terpenoid oxidation products as photochemical age increased. New particle formation was observed in the reactor after oxidation, especially during times when precursor gas concentrations and SOA formation were largest. Approximately 4.4 times more SOA was formed in the reactor from OH oxidation than could be explained by the VOCs measured in ambient air. To our knowledge this is the first time that this has been shown when comparing VOC concentrations with SOA formation measured at the same time, rather than comparing measurements made at different times. An SOA yield of 18-58 % from those compounds can explain the observed SOA formation. S/IVOCs were the only pool of gas-phase carbon that was large enough to explain the observed SOA formation. This work suggests that these typically unmeasured gases play a substantial role in ambient SOA formation. Our results allow ruling out condensation sticking coefficients much lower than 1. These measurements help clarify the magnitu...

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Section: Sampling Strategy and Measurementsmentioning

confidence: 58%

In situ secondary organic aerosol formation from ambient pine forest air using an oxidation flow reactor

et al. 2016

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“…However, the RO 2 simulations result in lower levels as HPALD formation depletes the RO 2 pool, which mostly composed of isoprene peroxy radicals. These results suggest that direct HO 2 and RO 2 observations can provide pivotal information about radical recycling and isoprene peroxy radical chemistry (Kim et al, 2013c;Wolfe et al, 2014). More studies on characterizing existing techniques to quantify HO 2 (Fuchs et al, 2011) and developing new techniques (Horstjann et al, 2014) are needed.…”

Section: Discussionmentioning

confidence: 99%

“…Recently developed isoprene photo-oxidation mechanisms shown in Archibald et al (2010b) are also incorporated in the model. In addition, Kim et al (2013c) and Wolfe et al (2014) applied the model in the identical fashion as used for this study to probe radical distributions using comprehensive observational data sets. This study used the UWCM to simulate the diurnal variations of radical pool (OH + HO 2 + RO 2 ) distributions as observational parameters such as CO, NO x , ozone, and VOCs are constrained.…”

Section: Uwcm Box Modelmentioning

confidence: 99%

Impact of isoprene and HONO chemistry on ozone and OVOC formation in a semirural South Korean forest

Kim

Lee³

et al. 2015

Atmos. Chem. Phys.

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Abstract. Rapid urbanization and economic development in East Asia in past decades has led to photochemical air pollution problems such as excess photochemical ozone and aerosol formation. Asian megacities such as Seoul, Tokyo, Shanghai, Guangzhou, and Beijing are surrounded by densely forested areas, and recent research has consistently demonstrated the importance of biogenic volatile organic compounds (VOCs) from vegetation in determining oxidation capacity in the suburban Asian megacity regions. Uncertainties in constraining tropospheric oxidation capacity, dominated by hydroxyl radical, undermine our ability to assess regional photochemical air pollution problems. We present an observational data set of CO, NO x , SO 2 , ozone, HONO, and VOCs (anthropogenic and biogenic) from Taehwa research forest (TRF) near the Seoul metropolitan area in early June 2012. The data show that TRF is influenced both by aged pollution and fresh biogenic volatile organic compound emissions. With the data set, we diagnose HO x (OH, HO 2 , and RO 2 ) distributions calculated using the University of Washington chemical box model (UWCM v2.1) with nearexplicit VOC oxidation mechanisms from MCM v3.2 (Master Chemical Mechanism). Uncertainty from unconstrained HONO sources and radical recycling processes highlighted in recent studies is examined using multiple model simulations with different model constraints. The results suggest that (1) different model simulation scenarios cause systematic differences in HO x distributions, especially OH levels (up to 2.5 times), and (2) radical destruction (HO 2 + HO 2 or HO 2 + RO 2 ) could be more efficient than radical recycling (RO 2 + NO), especially in the afternoon. Implications of the uncertainties in radical chemistry are discussed with respect to ozone-VOC-NO x sensitivity and VOC oxidation product formation rates. Overall, the NO x limited regime is assessed except for the morning hours (8 a.m. to 12 p.m. local standard time), but the degree of sensitivity can significantly vary depending on the model scenarios. The model results also suggest that RO 2 levels are positively correlated with oxygenated VOCs (OVOCs) production that is not routinely constrained by observations. These unconstrained OVOCs can cause higher-than-expected OH loss rates (missing OH reactivity) and secondary organic aerosol formation. The series of modeling experiments constrained by observations strongly urge observational constraint of the radical pool to enable precise understanding of regional photochemical pollution problems in the East Asian megacity region.

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“…Besides oxidation by OH radicals, direct solar photolysis of hydroxyketones may represent a significant degradation pathway and source of free radicals in the atmosphere. It should be noted that several studies have underlined the difficulties to satisfactorily model radical levels in the atmosphere, invoking possible lacking sources of radicals (Wolfe et al, 2014;Stone et al, 2012;Kanaya et al, 2012). In addition, OH reactivity measurements often disagree with models, the reasons invoked being unmeasured secondary oxygenated reaction products (Yang et al, 2016).…”

Section: Introductionmentioning

confidence: 95%

Kinetics of the photolysis and OH reaction of 4-hydroxy-4-methyl-2-pentanone: Atmospheric implications

Aslan

Laversin

Coddeville

et al. 2017

Atmospheric Environment

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Missing peroxy radical sources within a summertime ponderosa pine forest

Cited by 63 publications

References 87 publications

In situ secondary organic aerosol formation from ambient pine forest air using an oxidation flow reactor

In situ secondary organic aerosol formation from ambient pine forest air using an oxidation flow reactor

Impact of isoprene and HONO chemistry on ozone and OVOC formation in a semirural South Korean forest

Kinetics of the photolysis and OH reaction of 4-hydroxy-4-methyl-2-pentanone: Atmospheric implications

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