scholarly journals Oxidative capacity of the Mexico City atmosphere – Part 2: A RO<sub>x</sub> radical cycling perspective

2008 ◽  
Vol 8 (2) ◽  
pp. 5359-5412 ◽  
Author(s):  
P. M. Sheehy ◽  
R. Volkamer ◽  
L. T. Molina ◽  
M. J. Molina
Keyword(s):  
Mexico City ◽  
Oxidative Capacity ◽  
Early Morning ◽  
Photochemical Activity ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Vapor Concentration ◽  
Photolysis Frequencies ◽  
Pressure Water ◽  
Major Chemical

Abstract. A box model using measurements from the Mexico City Metropolitan Area study in the spring of 2003 (MCMA-2003) is presented to study ROx (ROx=OH+HO2+RO2+RO) radical cycling in the troposphere. Model simulations were performed with the Master Chemical Mechanism (MCMv3.1) constrained with 10 min averaged measurements of major radical sources (i.e., HCHO, HONO, O3, CHOCHO, etc.), radical sink precursors (i.e., NO, NO2, SO2, CO, and 102 volatile organic compounds VOC), meteorological parameters (temperature, pressure, water vapor concentration, dilution), and photolysis frequencies. Modeled HOx concentrations compare favorably with measured concentrations for most of the day; however, the model under-predicts the concentrations of radicals in the early morning. This "missing reactivity" is highest during peak photochemical activity, and is least visible in a direct comparison of HOx radical concentrations. The true uncertainty due to "missing reactivity" is apparent in parameters like chain length, and ozone production (P(O3)). For example, the integral amount of ozone produced could be under-predicted by a factor of two. Our analysis highlights that apart from uncertainties in emissions, and meteorology, there is an additional major chemical uncertainty in current models.

scholarly journals Oxidative capacity of the Mexico City atmosphere – Part 2: A RO<sub>x</sub> radical cycling perspective

2010 ◽  
Vol 10 (14) ◽  
pp. 6993-7008 ◽  
Author(s):  
P. M. Sheehy ◽  
R. Volkamer ◽  
L. T. Molina ◽  
M. J. Molina
Keyword(s):  
Chain Length ◽  
Mexico City ◽  
Oxidative Capacity ◽  
Early Morning ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Vapor Concentration ◽  
Oh Radicals ◽  
Radical Initiation ◽  
Very High

Abstract. A box model using measurements from the Mexico City Metropolitan Area study in the spring of 2003 (MCMA-2003) is presented to study oxidative capacity (our ability to predict OH radicals) and ROx (ROx=OH+HO2+RO2+RO) radical cycling in a polluted (i.e., very high NOx=NO+NO2) atmosphere. Model simulations were performed using the Master Chemical Mechanism (MCMv3.1) constrained with 10 min averaged measurements of major radical sources (i.e., HCHO, HONO, O3, CHOCHO, etc.), radical sink precursors (i.e., NO, NO2, SO2, CO, and 102 volatile organic compounds (VOC)), meteorological parameters (temperature, pressure, water vapor concentration, dilution), and photolysis frequencies. Modeled HOx (=OH+HO2) concentrations compare favorably with measured concentrations for most of the day; however, the model under-predicts the concentrations of radicals in the early morning. This "missing reactivity" is highest during peak photochemical activity, and is least visible in a direct comparison of HOx radical concentrations. We conclude that the most likely scenario to reconcile model predictions with observations is the existence of a currently unidentified additional source for RO2 radicals, in combination with an additional sink for HO2 radicals that does not form OH. The true uncertainty due to "missing reactivity" is apparent in parameters like chain length. We present a first attempt to calculate chain length rigorously i.e., we define two parameters that account for atmospheric complexity, and are based on (1) radical initiation, n(OH), and (2) radical termination, ω. We find very high values of n(OH) in the early morning are incompatible with our current understanding of ROx termination routes. We also observe missing reactivity in the rate of ozone production (P(O3)). For example, the integral amount of ozone produced could be under-predicted by a factor of two. We argue that this uncertainty is partly accounted for in lumped chemical codes that are optimized to predict ozone concentrations; however, these codes do not reflect the true uncertainty in oxidative capacity that is relevant to other aspects of air quality management, such as the formation of secondary organic aerosol (SOA). Our analysis highlights that apart from uncertainties in emissions, and meteorology, there is an additional major uncertainty in chemical mechanisms that affects our ability to predict ozone and SOA formation with confidence.

scholarly journals Oxidative capacity of the Mexico City atmosphere – Part 1: A radical source perspective

2007 ◽  
Vol 7 (2) ◽  
pp. 5365-5412 ◽  
Author(s):  
R. Volkamer ◽  
P. M. Sheehy ◽  
L. T. Molina ◽  
M. J. Molina
Keyword(s):  
Mexico City ◽  
Near Field ◽  
Oxidative Capacity ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Time Resolved ◽  
Time Profiles ◽  
Concentration Time ◽  
Radical Production ◽  
Photolysis Frequencies

Abstract. A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area (MCMA). During spring of 2003 (MCMA-2003 field campaign) an extensive set of measurements was collected to quantify time resolved ROx (sum of OH, HO2, RO2) radical production rates from day- and nighttime radical sources. The Master Chemical Mechanism (MCMv3.1) was constrained by measurements of (1) concentration time-profiles of photosensitive radical precursors, i.e., nitrous acid (HONO), formaldehyde (HCHO), ozone (O3), glyoxal (CHOCHO), and other oxygenated volatile organic compounds (OVOCs); (2) respective photolysis-frequencies (J-values); (3) concentration time-profiles of alkanes, alkenes, and aromatic VOCs (103 compound are treated) and oxidants, i.e., OH- and NO3 radicals, O3; and (4) NO, NO2, meteorological and other parameters. The ROx production rate was calculated directly from these observations; MCM was used to estimate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e., taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals). Daytime radical production is found to be about 10-25 times higher than at night; it does not track the abundance of sunlight. 12-h average daytime contributions of individual sources are: HCHO and O3 photolysis, each about 20%; O3/alkene reactions and HONO photolysis, each about 15%; unmeasured sources about 30%. While the direct contribution of O3/alkene reactions appears to be moderately small, source-apportionment of ambient HCHO and HONO identifies O3/alkene reactions as being largely responsible for jump-starting photochemistry about one hour after sunrise. The peak radical production is found to be higher than in any other urban influenced environment studied to date; further, differences exist in the timing of radical production. Our measurements and analysis comprise a database that enables testing of the representation of radical sources in photochemical models. Since the photochemical processing of pollutants is radical-limited in the MCMA, our analysis identifies the drivers for such processing. Three pathways are identified by which reductions in VOC emissions induce reductions in peak concentrations of secondary pollutants, such as O3 and secondary organic aerosol (SOA).

scholarly journals Comparison of surface ozone simulation among selected regional models in MICS-Asia III – effects of chemistry and vertical transport for the causes of difference

2019 ◽  
Vol 19 (1) ◽  
pp. 603-615 ◽  
Author(s):  
Hajime Akimoto ◽  
Tatsuya Nagashima ◽  
Jie Li ◽  
Joshua S. Fu ◽  
Dongsheng Ji ◽  
...  
Keyword(s):  
Surface Ozone ◽  
Early Morning ◽  
Photochemical Activity ◽  
Vertical Transport ◽  
Ozone Production ◽  
Phase Iii ◽  
Regional Models ◽  
Mixing Ratios ◽  
The Difference ◽  
Intercomparison Study

Abstract. In order to clarify the causes of variability among the model outputs for surface ozone in the Model Intercomparison Study Asia Phase III (MICS-Asia III), three regional models, CMAQ v.5.0.2, CMAQ v.4.7.1, and NAQPMS (abbreviated as NAQM in this paper), have been selected. Detailed analyses of monthly averaged diurnal variation have been performed for selected grids covering the metropolitan areas of Beijing and Tokyo and at a remote oceanic site, Oki. The chemical reaction mechanism, SAPRC99, used in the CMAQ models tended to give a higher net chemical ozone production than CBM-Z used in NAQM, agreeing with previous studies. Inclusion of the heterogeneous “renoxification” reaction of HNO3 (on soot surface)→NO+NO2 only in NAQM would give a higher NO concentration resulting in a better agreement with observational data for NO and nighttime O3 mixing ratios. In addition to chemical processes, the difference in the vertical transport of O3 was found to affect the simulated results significantly. Particularly, the increase in downward O3 flux from the upper layer to the surface after dawn was found to be substantially different among the models. Larger early morning vertical transport of O3 simulated by CMAQ 5.0.2 is thought to be the reason for higher daytime O3 in July in this model. All three models overestimated the daytime ozone by ca. 20 ppbv at the remote site Oki in July, where in situ photochemical activity is minimal.

scholarly journals Oxidative capacity of the Mexico City atmosphere – Part 1: A radical source perspective

2010 ◽  
Vol 10 (14) ◽  
pp. 6969-6991 ◽  
Author(s):  
R. Volkamer ◽  
P. Sheehy ◽  
L. T. Molina ◽  
M. J. Molina
Keyword(s):  
Mexico City ◽  
Oxidative Capacity ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Small Contribution ◽  
Radical Chain ◽  
Chain Reactions ◽  
Time Profiles ◽  
Concentration Time ◽  
Radical Production

Abstract. A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area (MCMA). During spring of 2003 (MCMA-2003 field campaign) an extensive set of measurements was collected to quantify time-resolved ROx (sum of OH, HO2, RO2) radical production rates from day- and nighttime radical sources. The Master Chemical Mechanism (MCMv3.1) was constrained by measurements of (1) concentration time-profiles of photosensitive radical precursors, i.e., nitrous acid (HONO), formaldehyde (HCHO), ozone (O3), glyoxal (CHOCHO), and other oxygenated volatile organic compounds (OVOCs); (2) respective photolysis-frequencies (J-values); (3) concentration time-profiles of alkanes, alkenes, and aromatic VOCs (103 compound are treated) and oxidants, i.e., OH- and NO3 radicals, O3; and (4) NO, NO2, meteorological and other parameters. The ROx production rate was calculated directly from these observations; the MCM was used to estimate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e., taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals). Daytime radical production is found to be about 10–25 times higher than at night; it does not track the abundance of sunlight. 12-h average daytime contributions of individual sources are: Oxygenated VOC other than HCHO about 33%; HCHO and O3 photolysis each about 20%; O3/alkene reactions and HONO photolysis each about 12%, other sources <3%. Nitryl chloride photolysis could potentially contribute ~15% additional radicals, while NO2* + water makes – if any – a very small contribution (~2%). The peak radical production of ~7.5 107 molec cm−3 s−1 is found already at 10:00 a.m., i.e., more than 2.5 h before solar noon. O3/alkene reactions are indirectly responsible for ~33% of these radicals. Our measurements and analysis comprise a database that enables testing of the representation of radical sources and radical chain reactions in photochemical models. Since the photochemical processing of pollutants in the MCMA is radical limited, our analysis identifies the drivers for ozone and SOA formation. We conclude that reductions in VOC emissions provide an efficient opportunity to reduce peak concentrations of these secondary pollutants, because (1) about 70% of radical production is linked to VOC precursors; (2) lowering the VOC/NOx ratio has the further benefit of reducing the radical re-cycling efficiency from radical chain reactions (chemical amplification of radical sources); (3) a positive feedback is identified: lowering the rate of radical production from organic precursors also reduces that from inorganic precursors, like ozone, as pollution export from the MCMA caps the amount of ozone that accumulates at a lower rate inside the MCMA. Continued VOC reductions will in the future result in decreasing peak concentrations of ozone and SOA in the MCMA.

scholarly journals Development of a chlorine chemistry module for the Master Chemical Mechanism

2015 ◽  
Vol 8 (6) ◽  
pp. 4823-4849
Author(s):  
L. K. Xue ◽  
S. M. Saunders ◽  
T. Wang ◽  
R. Gao ◽  
X. F. Wang ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Southern China ◽  
Oxidative Capacity ◽  
Early Morning ◽  
Chemical Mechanism ◽  
Atmospheric Photochemistry ◽  
Nitryl Chloride ◽  
Chemistry Research ◽  
Master Chemical Mechanism ◽  
Chemistry Module

Abstract. The chlorine atom (Cl·) has a high potential to perturb atmospheric photochemistry by oxidizing volatile organic compounds (VOCs), but the exact role it plays in the polluted troposphere remains unclear. The Master Chemical Mechanism (MCM) is a near explicit mechanism that has been widely applied in the atmospheric chemistry research. While it addresses comprehensively the chemistry initiated by the OH, O3 and NO3 radicals, its representation of the Cl· chemistry is incomplete as it only considers the reactions for alkanes. In this paper, we develop a more comprehensive Cl· chemistry module that can be directly incorporated within the MCM framework. A suite of 199 chemical reactions describes the Cl·-initiated degradation of alkenes, aromatics, aldehydes, ketones, alcohols, and some organic acids and nitrates, along with the inorganic chemistry involving Cl· and its precursors. To demonstrate the potential influence of the new chemistry module, it was incorporated into a MCM box model to evaluate the impacts of nitryl chloride (ClNO2), a product of nocturnal halogen activation by nitrogen oxides (NOx), on the following-day's atmospheric photochemistry. With constraints of recent observations collected at a coastal site in Hong Kong, southern China, the modeling analyses suggest that the Cl· produced from ClNO2 photolysis may substantially enhance the atmospheric oxidative capacity, VOC oxidation, and O3 formation, particularly in the early morning period. The results demonstrate the critical need for photochemical models to include more fully chlorine chemistry in order to better understand the atmospheric photochemistry in polluted environments subject to intense emissions of NOx, VOCs and chlorine-containing constituents.

scholarly journals Comparison of Surface Ozone Simulation among Selected Regional Models in MICS-Asia III – Effect of Chemistry and Vertical Transport for the Causes of Difference –

2018 ◽  
Author(s):  
Hajime Akimoto ◽  
Tatsuya Nagashima ◽  
Jie Li ◽  
Joshua Fu ◽  
Dongsheng Ji ◽  
...  
Keyword(s):  
Surface Ozone ◽  
Early Morning ◽  
Photochemical Activity ◽  
Vertical Transport ◽  
Ozone Production ◽  
Phase Iii ◽  
Regional Models ◽  
Mixing Ratios ◽  
The Difference ◽  
Intercomparison Study

Abstract. In order to clarify the cause of variability among the model outputs for surface ozone in the Model Intercomparison Study Asia Phase III (MICS-Asia III), three regional models, CMAQ v.5.0.2, CMAQ v.4.7.1 and NAQPMS (abbreviated as NAQM in this paper) have been selected. The detailed analyses have been made for monthly averaged diurnal variation for select grids covering metropolitan area of Beijing and Tokyo, and at a remote oceanic site, Oki. The chemical reaction mechanism, SAPRC99 used in the CMAQ models tends to give higher net chemical ozone production than CBM-Z used in NAQM agreeing with previous studies. Inclusion of heterogeneous “renoxification” reaction of HNO3 (on soot) → NO + NO2 only in NAQM is supposed to give higher NO concentration to give better agreement with observational data for NO and nighttime O3 mixing ratios. In addition to chemistry, the difference in vertical transport of O3 was found to affect the simulated results significantly. Particularly, the increase in downward flux of O3 from upper layer to the surface after the dawn is found to be substantially different among the models. Larger early morning vertical transport of O3 by CMAQ 5.0.2 would be the reason for higher daytime O3 by this model in July. All the three models overestimate the daytime ozone by ca. 20 ppbv at the remote site Oki in July, where in situ photochemical activity is minimal.

scholarly journals How does the OH reactivity affect the ozone production efficiency: case studies in Beijing and Heshan

2016 ◽  
Author(s):  
Yudong Yang ◽  
Min Shao ◽  
Stephan Keβel ◽  
Yue Li ◽  
Keding Lu ◽  
...  
Keyword(s):  
Production Efficiency ◽  
Ambient Air ◽  
Early Morning ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
University Campus ◽  
Oxygenated Volatile Organic Compounds ◽  
Volatile Organic ◽  
Peking University ◽  
Significant Diurnal Variation

Abstract. Total OH reactivity measurements have been conducted in August 2013 on the Peking University campus, Beijing and from October to November 2014 in Heshan, Guangdong Province. The daily median result for OH reactivity was 19.98 ± 11.03 s−1 in Beijing and 30.62 ± 19.76 s−1 in Heshan. Beijing presented a significant diurnal variation with maxima over 27 s−1 in the early morning and minima below 16 s−1 in the afternoon. Measurements in Heshan gave a much flatter diurnal pattern. Missing reactivity was observed at both sites, with 21 % missing in Beijing and 32 % missing in Heshan. Unmeasured primary species, such as branched-alkenes could contribute to missing reactivity in Beijing, especially in morning rush hour. An observation-based model with the Regional Atmospheric Chemical Mechanism 2 was used to understand the daytime missing reactivity in Beijing by adding unmeasured oxygenated volatile organic compounds and simulated intermediates of primary VOCs degradation. However, the model failed to explain the missing reactivity in Heshan, where the ambient air was found to be more aged, and the missing reactivity was presumably to attribute to oxidized species, such as aldehydes, acids and di-carbonyls. The ozone production efficiency was 27 % higher in Beijing and 35 % higher in Heshan when constrained by the measured reactivity, compared to the calculation with measured and modeled species included, indicating the importance of quantifying the OH reactivity for better understanding ozone chemistry.

scholarly journals Development of a chlorine chemistry module for the Master Chemical Mechanism

2015 ◽  
Vol 8 (10) ◽  
pp. 3151-3162 ◽  
Author(s):  
L. K. Xue ◽  
S. M. Saunders ◽  
T. Wang ◽  
R. Gao ◽  
X. F. Wang ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Southern China ◽  
Oxidative Capacity ◽  
Early Morning ◽  
Chemical Mechanism ◽  
Atmospheric Photochemistry ◽  
Nitryl Chloride ◽  
Chemistry Research ◽  
Master Chemical Mechanism ◽  
Chemistry Module

Abstract. The chlorine atom (Cl·) has a high potential to perturb atmospheric photochemistry by oxidizing volatile organic compounds (VOCs), but the exact role it plays in the polluted troposphere remains unclear. The Master Chemical Mechanism (MCM) is a near-explicit mechanism that has been widely applied in the atmospheric chemistry research. While it addresses comprehensively the chemistry initiated by the OH, O3 and NO3 radicals, its representation of the Cl· chemistry is incomplete as it only considers the reactions for alkanes. In this paper, we develop a more comprehensive Cl· chemistry module that can be directly incorporated within the MCM framework. A suite of 205 chemical reactions describes the Cl·-initiated degradation of alkenes, aromatics, alkynes, aldehydes, ketones, alcohols, and some organic acids and nitrates, along with the inorganic chemistry involving Cl· and its precursors. To demonstrate the potential influence of the new chemistry module, it was incorporated into a MCM box model to evaluate the impacts of nitryl chloride (ClNO2), a product of nocturnal halogen activation by nitrogen oxides (NOX), on the following day's atmospheric photochemistry. With constraints of recent observations collected at a coastal site in Hong Kong, southern China, the modeling analyses suggest that the Cl· produced from ClNO2 photolysis may substantially enhance the atmospheric oxidative capacity, VOC oxidation and O3 formation, particularly in the early morning period. The results demonstrate the critical need for photochemical models to include more detailed chlorine chemistry in order to better understand the atmospheric photochemistry in polluted environments subject to intense emissions of NOX, VOCs and chlorine-containing constituents.

scholarly journals Higher measured than modeled ozone production at increased NO<sub><i>x</i></sub> levels in the Colorado Front Range

2017 ◽  
Vol 17 (18) ◽  
pp. 11273-11292 ◽  
Author(s):  
Bianca C. Baier ◽  
William H. Brune ◽  
David O. Miller ◽  
Donald Blake ◽  
Russell Long ◽  
...  
Keyword(s):  
Formation Rate ◽  
Chemical Species ◽  
Peroxy Radical ◽  
Early Morning ◽  
Mitigation Strategies ◽  
Chemical Mechanism ◽  
Colorado Front Range ◽  
Ozone Production ◽  
Front Range ◽  
Reduction Strategies

Abstract. Chemical models must correctly calculate the ozone formation rate, P(O3), to accurately predict ozone levels and to test mitigation strategies. However, air quality models can have large uncertainties in P(O3) calculations, which can create uncertainties in ozone forecasts, especially during the summertime when P(O3) is high. One way to test mechanisms is to compare modeled P(O3) to direct measurements. During summer 2014, the Measurement of Ozone Production Sensor (MOPS) directly measured net P(O3) in Golden, CO, approximately 25 km west of Denver along the Colorado Front Range. Net P(O3) was compared to rates calculated by a photochemical box model that was constrained by measurements of other chemical species and that used a lumped chemical mechanism and a more explicit one. Median observed P(O3) was up to a factor of 2 higher than that modeled during early morning hours when nitric oxide (NO) levels were high and was similar to modeled P(O3) for the rest of the day. While all interferences and offsets in this new method are not fully understood, simulations of these possible uncertainties cannot explain the observed P(O3) behavior. Modeled and measured P(O3) and peroxy radical (HO2 and RO2) discrepancies observed here are similar to those presented in prior studies. While a missing atmospheric organic peroxy radical source from volatile organic compounds co-emitted with NO could be one plausible solution to the P(O3) discrepancy, such a source has not been identified and does not fully explain the peroxy radical model–data mismatch. If the MOPS accurately depicts atmospheric P(O3), then these results would imply that P(O3) in Golden, CO, would be NOx-sensitive for more of the day than what is calculated by models, extending the NOx-sensitive P(O3) regime from the afternoon further into the morning. These results could affect ozone reduction strategies for the region surrounding Golden and possibly other areas that do not comply with national ozone regulations. Thus, it is important to continue the development of this direct ozone measurement technique to understand P(O3), especially under high-NOx regimes.

scholarly journals How the OH reactivity affects the ozone production efficiency: case studies in Beijing and Heshan, China

2017 ◽  
Vol 17 (11) ◽  
pp. 7127-7142 ◽  
Author(s):  
Yudong Yang ◽  
Min Shao ◽  
Stephan Keßel ◽  
Yue Li ◽  
Keding Lu ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Production Efficiency ◽  
Ambient Air ◽  
Early Morning ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Diurnal Pattern ◽  
Volatile Organic ◽  
The Difference

Abstract. Total OH reactivity measurements were conducted on the Peking University campus (Beijing) in August 2013 and in Heshan (Guangdong province) from October to November 2014. The daily median OH reactivity was 20 ± 11 s−1 in Beijing and 31 ± 20 s−1 in Heshan, respectively. The data in Beijing showed a distinct diurnal pattern with the maxima over 27 s−1 in the early morning and minima below 16 s−1 in the afternoon. The diurnal pattern in Heshan was not as evident as in Beijing. Missing reactivity, defined as the difference between measured and calculated OH reactivity, was observed at both sites, with 21 % missing reactivity in Beijing and 32 % missing reactivity in Heshan. Unmeasured primary species, such as branched alkenes, could contribute to missing reactivity in Beijing, especially during morning rush hours. An observation-based model with the RACM2 (Regional Atmospheric Chemical Mechanism version 2) was used to understand the daytime missing reactivity in Beijing by adding unmeasured oxygenated volatile organic compounds and simulated intermediates of the degradation from primary volatile organic compounds (VOCs). However, the model could not find a convincing explanation for the missing reactivity in Heshan, where the ambient air was found to be more aged, and the missing reactivity was presumably attributed to oxidized species, such as unmeasured aldehydes, acids and dicarbonyls. The ozone production efficiency was 21 % higher in Beijing and 30 % higher in Heshan when the model was constrained by the measured reactivity, compared to the calculations with measured and modeled species included, indicating the importance of quantifying the OH reactivity for better understanding ozone chemistry.

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