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C A Cantrell - One of the best experts on this subject based on the ideXlab platform.
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missing Peroxy Radical sources within a summertime ponderosa pine forest
Atmospheric Chemistry and Physics, 2014Co-Authors: G M Wolfe, C A Cantrell, R L Mauldin, T KarlAbstract:Organic Peroxy (RO2) and hydroPeroxy (HO2) Radicals are key intermediates in the photochemical pro- cesses that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of Peroxy Radical chemistry presents a sig- nificant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present Peroxy Radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro- atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen - Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total Peroxy Radical mixing ra- tios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the compre- hensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of Peroxy Radicals below the forest canopy. The base chem- ical mechanism underestimates total Peroxy Radicals by as much as a factor of 3. Since primary reaction partners for Peroxy Radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO 2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 inde- pendently of sun-driven photochemistry, such as ozonolysis
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Peroxy Radical behavior during the transport and chemical evolution over the pacific trace p campaign as measured aboard the nasa p 3b aircraft
Journal of Geophysical Research, 2003Co-Authors: C A Cantrell, Richard E. Shetter, F L Eisele, G. D. Edwards, S Stephens, R L Mauldin, Mark A Zondlo, E Kosciuch, B L LeferAbstract:[1] Peroxy Radical concentrations were measured aboard the NASA P-3B aircraft during the Transport and Chemical Evolution over the Pacific (TRACE-P) campaign in the spring of 2001 and varied in ways that depended on Radical production rates and reactive nitrogen concentrations. Measurements of HO2 ,H O2 +R O2, and OH during this study allowed calculation of Radical ratios, examination of functional relationships of these ratios on controlling variables, and comparison with numerical model estimations. Radical production terms show changes in relative contributions at low, middle, and high total production rates that are understandable in terms of systematic variations in the controlling components (trace gas concentrations and photolysis rate coefficients). Ozone tendency calculations indicate net ozone production in the western Pacific basin because the concentrations of critical precursor trace gases (e.g., NOx, hydrocarbons) are highest there. The dependence of ozone tendency follows the concentration of NO systematically. Peroxy Radical levels on the two aircraft (HO2 +R O2 on the P-3B and HO2 on the DC-8) during two relatively short prescribed intercomparison periods were in good agreement in one instance and poorer in another given reasonable assumptions about the apportioning of Radicals between HO2 and RO2. Recommended changes to CH2O photolysis quantum yields, HO2 self reaction, and O( 1 D) quenching kinetics lead to small changes (<5%) in calculated Peroxy Radical levels for TRACE-P conditions. There is evidence from this campaign that Peroxy Radicals are lost by interaction with aerosols and cloud droplets. INDEX TERMS: 0317 Atmospheric Composition and Structure: Chemical kinetic and photochemical properties; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: photochemistry, Peroxy Radicals, ozone
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intercomparison of Peroxy Radical measurements at a rural site using laser induced fluorescence and Peroxy Radical chemical ionization mass spectrometer percims techniques
Journal of Geophysical Research, 2003Co-Authors: Xinrong Ren, C A Cantrell, G. D. Edwards, R. Lesher, Andrew R. Metcalf, T. Shirley, William H. BruneAbstract:[1] Two different instruments were deployed to measure hydroPeroxy Radical (HO2) and total Peroxy Radicals during May and June 2002 at a rural site located at Rock Springs near State College, Pennsylvania. One instrument was the Penn State Ground-Based Tropospheric Hydrogen Oxides Sensor (GTHOS), which measured HO2 by laser-induced fluorescence (LIF) of OH following the chemical conversion of HO2 to OH by adding NO. The other was the Peroxy Radical Chemical Ionization Mass Spectrometer (PerCIMS) instrument that provided HO2 (HO2 mode) or total Peroxy Radicals (HOxROx mode) measurements. The two instruments were compared by exchanging calibration sources and by side-by-side ambient measurements. Excellent agreement was obtained in the calibration comparisons with the slope of a correlation plot close to 1.0 and a small intercept. Daily HO2 measurements from GTHOS and PerCIMS (in HO2 mode) on 4 days show that diurnal variations normally agreed to within about 40%. A comparison of HO2 measured by GTHOS and HOxROx measured by PerCIMS shows good correlation for both average diurnal variation and individual diurnal cycles. On average, HO2 from GTHOS was about 0.66 times the HOxROx from PerCIMS, meaning that organic Peroxy Radicals account for about one third of the total Peroxy Radicals in this environment.
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Peroxy Radical observations using chemical ionization mass spectrometry during topse
Journal of Geophysical Research, 2003Co-Authors: C A Cantrell, G. D. Edwards, S Stephens, Mark A Zondlo, E Kosciuch, L Mauldin, F L EiseleAbstract:[1] Peroxy Radicals (HO2 + RO2) were measured by chemical conversion-chemical ionization mass spectroscopy in the TOPSE (Tropospheric Ozone Production about the Spring Equinox) campaign that took place February through May 2000. Instrumentation for these measurements was deployed on the NCAR/NSF C-130 aircraft that flew at latitudes from 40 to 85°N, and altitudes from the surface to 7.5 km over the North American continent. The measurements demonstrate the evolution of photochemical activity as time progresses through the study period due to increases in free Radical source rates. The increase in average Peroxy Radical concentration moves northward as the maximum solar elevation and length of sunlit days increase. HOxROx (HO2 + RO2) concentrations are distributed lognormally with means of 11.5 and 7.8 pptv for the middle-latitude band (MLB) and high-latitude band (HLB), respectively. The observations agree well on average with steady state derived concentrations; measurement-model concentration ratios are 1.04 (MLB) and 0.94 (HLB). Concentrations within a given latitude band and altitude region sometimes appear to increase with NOx concentrations, but this correlation nearly disappears at low and moderate NOx levels when the data are parsed by Radical production rate; lower Radical levels are observed at the highest NOx levels measured (near 1 ppbv). These data are compared with results from other recent observations utilizing a variety of platforms.
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Peroxy Radical concentrations measured and calculated from trace gas measurements in the mauna loa observatory photochemistry experiment 2
Journal of Geophysical Research, 1996Co-Authors: C A Cantrell, Richard E. Shetter, Jack G. Calvert, Timothy M Gilpin, F L Eisele, D J TannerAbstract:Measurements of Peroxy Radical concentrations ([HO 2 ] + [RO 2 ]) were made by the chemical amplifier technique during the four intensives of the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) at the Mauna Loa Observatory in 1991-1992. In this study these data are compared with the theoretical values of the Peroxy Radical concentrations obtained from steady state analysis of the complete suite of trace gas measurements and other relevant parameters also measured during the experiment. The data from 33 days of the study contain time overlap of the concentration and physical data which allow a meaningful theoretical treatment. The experimental results for [HO 2 ] + [RO 2 ] agree well with theory for many of the days, but are significantly suppressed from the theoretical expectations on other days. Two hypotheses are presented and tested to explain the observed suppression. The first involves the reaction of the Peroxy Radicals at aerosol surfaces. The second proposes the loss of [OH] through its reaction with unknown and undetected species to develop Peroxy Radicals subsequently to which the chemical amplifier is insensitive. Evidence at hand does not allow a clear choice between these or possible alternative explanations. The data suggest that the net rate of O 3 generation in the free troposphere is about -1.5 parts per billion by volume per day (ppbv d -1 ; 24-hour average).
Weijun Zhang - One of the best experts on this subject based on the ideXlab platform.
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Vacuum ultraviolet photodynamics of the methyl Peroxy Radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Krisztina Voronova, Balint Sztaray, Laurent NahonAbstract:The vacuum ultraviolet (VUV) photoionization of the methyl Peroxy Radical, CH3O2, and unimolecular dissociation of internal energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV energy range by synchrotron-based double imaging photoelectron photoion coincidence (i2PEPICO). A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl Radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum(SPES) of CH3O2 was obtained exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A′′ and a1A′overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization energy (AIE) of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracytheoretical data from the literature. The vertical ionization energy of the b1A' electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2fragments. The 0 K adiabatic appearance energy (AE0K) of the CH3+ fragment ion is determined to be 11.1548 ± 0.020 eV.
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vacuum ultraviolet photodynamics of the methyl Peroxy Radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Krisztina Voronova, Balint Sztaray, Laurent NahonAbstract:The vacuum ultraviolet photoionization of the methyl Peroxy Radical, CH3O2, and unimolecular dissociation of internal energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV energy range by synchrotron-based double imaging photoelectron photoion coincidence. A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl Radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum (SPES) of CH3O2 was obtained, exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A″ and a1A′ overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization energy of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracy theoretical data from the literature. The vertical ionization energy of the b1A′ electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2 fragments. The 0 K adiabatic appearance energy (AE0K) of the CH3+ fragment ion is determined to be 11.15 ± 0.02 eV.
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computational study on the mechanism and kinetics for the reaction between ho2 and n propyl Peroxy Radical
RSC Advances, 2019Co-Authors: Xiaoxiao Lin, Zhenli Yang, Yanbo Gai, Weijun Zhang, Weixiong Zhao, Jiacheng Zhou, Bo LongAbstract:The n-propyl Peroxy Radical (n-C3H7O2) is the key intermediate during atmospheric oxidation of propane (C3H8) which plays an important role in the carbon and nitrogen cycles in the troposphere. In this paper, a comprehensive theoretical study on the reaction mechanism and kinetics of the reaction between HO2 and n-C3H7O2 was performed at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311G(d,p) level of theory. Computational results show that the HO2 + n-C3H7O2 reaction proceeds on both singlet and triplet potential energy surfaces (PESs). From an energetic point of view, the formation of C3H7O2H and 3O2 via triplet hydrogen abstraction is the most favorable channel while other product channels are negligible. In addition, the calculated rate constants for the title reaction over the temperature range of 238–398 K were calculated by the multiconformer transition state theory (MC-TST), and the calculated rate constants show a negative temperature dependence. The contributions of the other four reaction channels to the total rate constant are negligible.
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Mechanism and kinetics of the atmospheric reaction of 1,3,5-trimethylbenzene bicyclic Peroxy Radical with OH
RSC Advances, 2019Co-Authors: Xiaoxiao Lin, Zhenli Yang, Yanbo Gai, Weijun ZhangAbstract:The bicyclic Peroxy Radical (BPR) is the key intermediate during atmospheric oxidation of aromatics. In this paper, the reaction mechanisms and kinetics of the atmospheric reaction of the 1,3,5-trimethylbenzene (1,3,5-TMB) BPR with the OH Radical were studied by density functional theory (DFT) and conventional transition-state theory (CTST) calculations. The product channels of formation of the 1,3,5-TMB trioxide (ROOOH), OH-adducts and Criegee intermediate (CI) have been identified, and the geometries and energies of all the stationary points were calculated at the M08-HX/6-311 + g(2df,2p) level of theory. In addition, the rate constants for the individual reaction pathway at 298 K were calculated. The results showed that OH addition reactions including the formation of ROOOH and OH-adducts are the main pathways, whereas Criegee intermediate formation is of minor importance.
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removing water vapor interference in Peroxy Radical chemical amplification with a large diameter nafion dryer
Analytical Chemistry, 2018Co-Authors: Yanbo Gai, Weijun Zhang, Chengqiang Yang, Weixiong Zhao, Bo Fang, Yang Zhang, Dean S Venables, Weidong ChenAbstract:The chemical amplification (PERCA) method has been widely used for measuring Peroxy Radical concentrations in the troposphere. The accuracy and sensitivity of the method is critically dependent on the chain length (CL)—that is, the number of Radical amplification cycles. However, CL decreases strongly with higher relative humidity (RH). So far, there does not appear to be a method to overcome this impact. Here we report the development of a Nafion dryer based dual-channel PERCA instrument. The large diameter Nafion dryer efficiently removes water vapor in milliseconds and minimally affects the sample. The low losses of Peroxy Radicals on the Nafion membrane make it an attractive tool for raising the CL, and thereby the measurement accuracy and sensitivity of PERCA systems. The reported instrument demonstrates this promising and simple method to minimize water vapor interference.
G M Wolfe - One of the best experts on this subject based on the ideXlab platform.
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missing Peroxy Radical sources within a summertime ponderosa pine forest
Atmospheric Chemistry and Physics, 2014Co-Authors: G M Wolfe, C A Cantrell, R L Mauldin, T KarlAbstract:Organic Peroxy (RO2) and hydroPeroxy (HO2) Radicals are key intermediates in the photochemical pro- cesses that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of Peroxy Radical chemistry presents a sig- nificant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present Peroxy Radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro- atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen - Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total Peroxy Radical mixing ra- tios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the compre- hensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of Peroxy Radicals below the forest canopy. The base chem- ical mechanism underestimates total Peroxy Radicals by as much as a factor of 3. Since primary reaction partners for Peroxy Radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO 2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 inde- pendently of sun-driven photochemistry, such as ozonolysis
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Missing Peroxy Radical sources within a summertime ponderosa pine forest
Atmospheric Chemistry and Physics, 2014Co-Authors: G M Wolfe, Christopher A. Cantrell, R L Mauldin, T Karl, Peter Harley, A. Turnipseed, W. Zheng, Frank Flocke, S. Kim, Eric C. ApelAbstract:Abstract. Organic Peroxy (RO2) and hydroPeroxy (HO2) Radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of Peroxy Radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present Peroxy Radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total Peroxy Radical mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of Peroxy Radicals below the forest canopy. The base chemical mechanism underestimates total Peroxy Radicals by as much as a factor of 3. Since primary reaction partners for Peroxy Radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min−1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.
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Missing Peroxy Radical sources within a rural forest canopy
2013Co-Authors: G M Wolfe, Christopher A. Cantrell, R L Mauldin, T Karl, Si-wan Kim, Peter Harley, A. Turnipseed, W. Zheng, Frank Flocke, Eric C. ApelAbstract:Organic Peroxy (RO2) and hydroPeroxy (HO2) Radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of Peroxy Radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present Peroxy Radical observations acquired within a Ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen - Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total Peroxy Radical mixing ratios reach as high as 180 pptv and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of Peroxy Radicals below the forest canopy. The base chemical mechanism underestimates total Peroxy Radicals by as much as a factor of 3. Since primary reaction partners for Peroxy Radicals are either measured (NO) or under-predicted (HO2 and RO2, i.e. self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (approximately 120 and 50 pptv min1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.
T Karl - One of the best experts on this subject based on the ideXlab platform.
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missing Peroxy Radical sources within a summertime ponderosa pine forest
Atmospheric Chemistry and Physics, 2014Co-Authors: G M Wolfe, C A Cantrell, R L Mauldin, T KarlAbstract:Organic Peroxy (RO2) and hydroPeroxy (HO2) Radicals are key intermediates in the photochemical pro- cesses that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of Peroxy Radical chemistry presents a sig- nificant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present Peroxy Radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro- atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen - Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total Peroxy Radical mixing ra- tios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the compre- hensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of Peroxy Radicals below the forest canopy. The base chem- ical mechanism underestimates total Peroxy Radicals by as much as a factor of 3. Since primary reaction partners for Peroxy Radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO 2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 inde- pendently of sun-driven photochemistry, such as ozonolysis
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Missing Peroxy Radical sources within a summertime ponderosa pine forest
Atmospheric Chemistry and Physics, 2014Co-Authors: G M Wolfe, Christopher A. Cantrell, R L Mauldin, T Karl, Peter Harley, A. Turnipseed, W. Zheng, Frank Flocke, S. Kim, Eric C. ApelAbstract:Abstract. Organic Peroxy (RO2) and hydroPeroxy (HO2) Radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of Peroxy Radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present Peroxy Radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total Peroxy Radical mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of Peroxy Radicals below the forest canopy. The base chemical mechanism underestimates total Peroxy Radicals by as much as a factor of 3. Since primary reaction partners for Peroxy Radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min−1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.
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Missing Peroxy Radical sources within a rural forest canopy
2013Co-Authors: G M Wolfe, Christopher A. Cantrell, R L Mauldin, T Karl, Si-wan Kim, Peter Harley, A. Turnipseed, W. Zheng, Frank Flocke, Eric C. ApelAbstract:Organic Peroxy (RO2) and hydroPeroxy (HO2) Radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of Peroxy Radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present Peroxy Radical observations acquired within a Ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen - Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total Peroxy Radical mixing ratios reach as high as 180 pptv and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of Peroxy Radicals below the forest canopy. The base chemical mechanism underestimates total Peroxy Radicals by as much as a factor of 3. Since primary reaction partners for Peroxy Radicals are either measured (NO) or under-predicted (HO2 and RO2, i.e. self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (approximately 120 and 50 pptv min1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.
S. A. Penkett - One of the best experts on this subject based on the ideXlab platform.
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Seasonal dependence of Peroxy Radical concentrations at a Northern hemisphere marine boundary layer site during summer and winter: evidence for Radical activity in winter
Atmospheric Chemistry and Physics, 2006Co-Authors: Z. L. Fleming, A. R. Rickard, P S Monks, B. J. Bandy, N. Brough, T. J. Green, C. E. Reeves, S. A. PenkettAbstract:Peroxy Radicals (HO2+? RO2) were measured at the Weybourne Atmospheric Observatory (52° N, 1° E), Norfolk using a Peroxy Radical Chemical Amplifier (PERCA) during the winter and summer of 2002. The Peroxy Radical diurnal cycles showed a marked difference between the winter and summer campaigns with maximum concentrations of 12 pptv at midday in the summer and maximum concentrations as high as 30 pptv (10 min averages) in winter at night. The corresponding nighttime Peroxy Radical concentrations were not as high in summer (3 pptv). The Peroxy Radical concentration shows a distinct anti-correlation with increasing NOx during the daylight hours. At night, Peroxy Radicals increase with increasing NOx indicative of the role of NO3 chemistry. The average diurnal cycles for net ozone production, N(O3) show a large variability in ozone production, P(O3), and a large ozone loss, L(O3) in summer relative to winter. For a daylight average, net ozone production in summer was higher than winter (1.51±0.5 ppbv h?1 and 1.11±0.47 ppbv h?1, respectively). The variability in NO concentration has a much larger effect on N(O3) than the Peroxy Radical concentrations. Photostationary state (PSS) calculations show an NO2 lifetime of 5 min in summer and 21 minutes in the winter, implying that steady-state NO-NO2 ratios are not always attained during the winter months. The results show an active Peroxy Radical chemistry at night and that significant oxidant levels are sustained in winter. The net effect of this with respect to production of ozone in winter is unclear owing to the breakdown in the photostationary state.
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Seasonal dependence of Peroxy Radical concentrations at a northern hemisphere marine boundary layer site during summer and winter: evidence for photochemical activity in winter
Atmospheric Chemistry and Physics Discussions, 2006Co-Authors: Z. L. Fleming, A. R. Rickard, P S Monks, B. J. Bandy, N. Brough, T. J. Green, C. E. Reeves, S. A. PenkettAbstract:Peroxy Radicals (HO2+?RO2) were measured at the Weybourne Atmospheric Observatory (52° N, 1° E), Norfolk using a Peroxy Radical Chemical Amplifier (PERCA) during the winter and summer of 2002. The Peroxy Radical diurnal cycles showed a marked difference between the winter and summer campaigns with maximum concentrations of 12 pptv at midday in the summer and maximum concentrations as high as 30 pptv (10 min averages) in winter at night. The corresponding nighttime Peroxy Radical concentrations were not as high in summer (3 pptv). The Peroxy Radical concentration shows a distinct anti-correlation with increasing NOx during the daylight hours. At night, Peroxy Radicals increase with increasing NOx indicative of the role of NO3 chemistry. The average diurnal cycles for net ozone production, N(O3) show a large variability in ozone production, P(O3), and a large ozone loss, L(O3) in summer relative to winter. For a daylight average, net ozone production in summer than winter (1.51±0.5 ppbv h?1 and 1.11±0.47 ppbv h?1 respectively) but summer shows more variability of (meteorological) conditions than winter. The variability in NO concentration has a much larger effect on N(O3) than the Peroxy Radical concentrations. Photostationary state (PSS) calculations show an NO2 lifetime of 5 min in summer and 21 min in the winter, implying that steady-state NO-NO2 ratios are not always attained during the winter months. The results show an active Peroxy Radical chemistry at night and the ability of winter to make oxidant. The net effect of this with respect to production of ozone in winter is unclear owing to the breakdown in the photostationary state.
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a calibrated Peroxy Radical chemical amplifier for ground based tropospheric measurements
Journal of Geophysical Research, 1997Co-Authors: K C Clemitshaw, Lucy J Carpenter, S. A. Penkett, M E JenkinAbstract:A calibrated Peroxy Radical chemical amplifier (PERCA) instrument has been developed at the University of East Anglia (UEA) and deployed in several recent field measurement campaigns. The UEA PERCA utilizes modulated chemical amplification of NO 2 by HO 2 and RO 2 Radicals in the presence of 3.0 ppmv NO and 7.0% vol/vol CO, with the amplification factor or chain length approximately equal to ΔNO 2 /([HO 2 ] + [RO 2 ]). NO 2 measurements and calibrations are made in the linear response regime of an improved Scintrex LMA-3 NO 2 -luminol chemiluminescence detector with an estimated systematic uncertainty of ± 10% and a precision of 5%. A novel calibration source of CH 3 O 2 Radicals has been developed. It is used routinely during field campaigns to measure chain lengths of 175 ± 15 for a new inlet system. The source is based upon 253.7 nm photolysis of CH 3 I in air and is capable of producing between 25 and 100 pptv CH 3 O 2 Radicals. The detection limit of the PERCA varies from 0.2 to 2 pptv for a 30 min averaging time and is largely dependent upon the stability of the sum of the concentrations of ambient NO 2 and O 3 (O x ) which contribute to a background signal. The estimated systematic uncertainty in the measurements of HO 2 and RO 2 is ±30%. Observations of Peroxy Radicals made during the recent WAOWE'94 and WAOSE'95 field measurement campaign on the north Norfolk coast of England are presented to demonstrate the performance of the PERCA and are discussed briefly in terms of nighttime Radical chemistry and net photochemical production of O 3 and Peroxyacetyl nitrate (PAN).
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relationships between ozone photolysis rates and Peroxy Radical concentrations in clean marine air over the southern ocean
Journal of Geophysical Research, 1997Co-Authors: S. A. Penkett, Lucy J Carpenter, G P Ayers, Paul S. Monks, K C Clemitshaw, R W Gillett, I E Galbally, C P MeyerAbstract:Measurements of the sum of inorganic and organic Peroxy Radicals (RO2) and photolysis rate coefficients J(NO2) and J(O1D) have been made at Cape Grim, Tasmania in the course of a comprehensive experiment which studied photochemistry in the unpolluted marine boundary layer. The SOAPEX (Southern Ocean Atmospheric Photochemistry Experiment) campaign included measurements of ozone, peroxides, nitrogen oxides, water vapor, and many other parameters. This first full length paper concerned with the experiment focuses on the types of relationships observed between Peroxy Radicals and J(NO2), J(O1D) and √[J(O1D)] in different air masses in which ozone is either produced or destroyed by photochemistry. It was found that in baseline air with ozone loss, RO2 was proportional to √[J(O1D)], whereas in more polluted air RO2 was proportional to J(O1D). Simple algorithms were derived to explain these relationships and also to calculate the concentrations of OH Radicals in baseline air from the instantaneous RO2 concentrations. The signal to noise ratio of the Peroxy Radical measurements was up to 10 for 1-min values and much higher than in other previous deployments of the instrument in the northern hemisphere, leading to the confident determination of the relationships between RO2 and J(O1D) in different conditions. The absolute concentration Of RO2 determined in these experiments is in some doubt, but this does not affect our conclusions concerned either with the behavior of Peroxy Radicals with changing light levels or with the concentrations of OH calculated from RO2. The results provide confidence that the level of understanding of the photochemistry of ozone leading to the production of peroxide via recombination of Peroxy Radicals in clean air environments is well advanced.