Investigations of ROx Radical Photochemistry During the MCMA-2006 Field Campaign
Measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals were made during the Mexico City Met... more Measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals were made during the Mexico City Metropolitan Area (MCMA) field campaign, providing an opportunity to investigate the strong coupling between ROX radicals (HOX = OH + HO2 + RO2), nitrogen oxides (NOX = NO + NO2) and Volatile Organic Compounds (VOCs). A highly constrained zero-dimensional box model, based on the Regional Atmospheric
Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the gas-phase oxidation of o... more Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the gas-phase oxidation of organic trace gases that lead to the formation of ozone and secondary organic aerosols in the troposphere. Previous measurements of OH and HO2 radicals in forest environments have shown serious discrepancies with modeled concentrations of these radicals. These discrepancies bring into question our understanding of the
This supplement consists of a map of the study area (Fig. ), figures describing the characterizat... more This supplement consists of a map of the study area (Fig. ), figures describing the characterizations made on the MD-CRM and UL-FAGE instruments (Figs. ), details about the synthetic VOC mixtures described in Sect. 3.1 of the main paper (Tables ), and measurements of ambient formaldehyde (HCHO) mixing ratios (Fig. ).
Synoptic-scale meteorological conditions for the 4-5 August 2009 case period, time series of mete... more Synoptic-scale meteorological conditions for the 4-5 August 2009 case period, time series of meteorology used as input in CACHE, and modeled versus measured glyoxal.
Journal of Geophysical Research: Atmospheres, 2018
We analyze an expanded data set of oxygenated volatile organic compounds (OVOCs) in air measured ... more We analyze an expanded data set of oxygenated volatile organic compounds (OVOCs) in air measured by several instruments at a surface site in Pasadena near Los Angeles during the National Oceanic and Atmospheric Administration California Nexus study in 2010. The contributions of emissions, chemical formation, and removal are quantified for each OVOC using CO as a tracer of emissions and the OH exposure of the sampled air masses calculated from hydrocarbon ratios. The method for separating emissions from chemical formation is evaluated using output for Pasadena from the Weather Research and Forecasting-Chemistry model. The model is analyzed by the same method as the measurement data, and the emission ratios versus CO calculated from the model output agree for ketones with the inventory used in the model but overestimate aldehydes by~70%. In contrast with the measurements, nighttime formation of OVOCs is significant in the model and is attributed to overestimated precursor emissions and overestimated rate coefficients for the reactions of the precursors with ozone and NO 3. Most measured aldehydes correlated strongly with CO at night, suggesting a contribution from motor vehicle emissions. However, the emission ratios of most aldehydes versus CO are higher than those reported in motor vehicle emissions and the aldehyde sources remain unclear. Formation of several OVOCs is investigated in terms of the removal of specific precursors. Direct emissions of alcohols and aldehydes contribute significantly to OH reactivity throughout the day, and these emissions should be accurately represented in models describing ozone formation. Plain Language Summary We report new measurements of volatile organic compounds (VOCs) in ambient air in the Los Angeles basin. Chemical reactions between VOCs and nitrogen oxides form ozone and fine particles, two important pollutants in Los Angeles smog. It is therefore important to understand VOC emission sources. In this work, we derive the composition of VOC emissions using ambient measurements at Pasadena in 2010. The study is complicated due to rapid chemical reactions that can form and remove VOCs in between the time of emission and measurement. After correcting for this chemistry, it is shown that emissions of many oxygen-containing VOCs are important for the formation of ozone.
Several physicochemical processes occurring within buildings are key drivers of indoor concentrat... more Several physicochemical processes occurring within buildings are key drivers of indoor concentrations of Volatile Organic compounds VOCs. Many models and experimental studies have been proposed to predict VOCs concentration indoors given these processes. However, there is a lack of representative data in literature to present gas-surface interaction in order to validate mathematical models. This work is divided in two parts and aims to develop and validate a method to perform fast measurements of VOC sorption parameters on the field by coupling a Field and Laboratory Emission Cell (FLEC) to a Proton Transfer Reaction-Mass Spectrometer (PTR-MS). In the part 1 of the work, sorption coefficients of aromatic compounds on a gypsum board and vinyl flooring were investigated at ppb levels to test and evaluate the proposed methodology. Sorption coefficients in the range of 0.03-1.88 m.h-1 for k a and 2.04-17.32 h-1 for k d were successfully measured within a (0.5-8 hours) for the two materials. Robustness tests highlight that the determination of sorption coefficients does not depend on operating conditions. While sorption coefficients for the gypsum board were measured with a PTR-MS time resolution of 20 seconds, the vinyl flooring material required measurements at a higher time resolution of 2 seconds due to its lower sorption properties. Limits of applicability assessed for this method indicate that sets of sorption parameters (k a , k d) of (0.01 m.h-1 ; 0.01 h-1) and (0.09 m.h-1 ; 0.09 h-1) can be measured with an accuracy better than 10% at time resolutions of 2 and 20 seconds respectively.
The hydroxyl (OH) radical is an important oxidant in the troposphere, which controls the lifetime... more The hydroxyl (OH) radical is an important oxidant in the troposphere, which controls the lifetime of most air quality-and climate-related trace gases. However, there are still uncertainties concerning its atmospheric budget, and integrated measurements of OH sinks have been valuable to improve this aspect. Among the analytical tools used for measuring total OH reactivity in ambient air, the comparative reactivity method (CRM) is spreading rapidly in the atmospheric community. However, measurement artifacts have been highlighted for this technique, and additional work is needed to fully characterize them. In this study, we present the new Mines Douai CRM instrument, with an emphasis on the corrections that need to be applied to ambient measurements of total OH reactivity. Measurement artifacts identified in the literature have been investigated, including (1) a correction for a change in relative humidity between the measurement steps leading to different OH levels, (2) the formation of spurious OH in the sampling reactor when hydroperoxy radicals (HO 2) react with nitrogen monoxide (NO), (3) not operating the CRM under pseudo-first-order kinetics, and (4) the dilution of ambient air inside the reactor. The dependences of these artifacts on various measurable parameters, such as the pyrrole-to-OH ratio and the bimolecular reaction rate constants of ambient trace gases with OH, have also been studied. Based on these observations, parameterizations are proposed to correct ambient OH reactivity measurements. On average, corrections of 5.2 ± 3.2, 9.2 ± 15.7, and 8.5 ± 5.8 s −1 were respectively observed for (1), (2) and (3) during a field campaign performed in Dunkirk, France (summer 2014). Numerical simulations have been performed using a box model to check whether experimental observations mentioned above are consistent with our understanding of the chemistry occurring in the CRM reactor. Two different chemical mechanisms have been shown to reproduce the magnitude of corrections (2) and (3). In addition, these simulations reproduce their dependences on the pyrrole-to-OH ratio and on bimolecular reaction rate constants of gases reacting with OH. The good agreement found between laboratory experiments and model simulations gives us confidence in the proposed parameterizations. However, it is worth noting that the numerical values given in this study are suitable for the Mines Douai instrument and may not be appropriate for other CRM instruments. It is recommended that each group characterize its own instrument following the recommendations given in this study. An assessment of performances for the Mines Douai instrument, including a propagation of errors from the different corrections, indicates a limit of detection of 3.0 s −1 and total uncertainties of 17-25 % for OH reactivity values higher than 15 s −1 and NO x mixing ratios lower than 30 ppbv.
The investigation of hydroxyl radical (OH) chemistry during intensive field campaigns has led to ... more The investigation of hydroxyl radical (OH) chemistry during intensive field campaigns has led to the development of several techniques dedicated to ambient measurements of total OH reactivity, which is the inverse of the OH lifetime. Three techniques are currently used during field campaigns, including the total OH loss rate method, the pump-probe method, and the comparative reactivity method. However, no formal intercomparison of these techniques has been published so far, and there is a need to ensure that measurements of total OH reactivity are consistent among the different techniques. <br><br> An intercomparison of two OH reactivity instruments, one based on the Comparative Reactivity Method (CRM) and the other based on the pump-probe method, was performed in October 2012 in a NO<sub><i>x</i></sub>-rich environment, which is known to be challenging for the CRM technique. This study presents an extensive description of the two instruments, the...
The Hydroxyl radical (OH) is an important oxidant in the daytime troposphere that controls the li... more The Hydroxyl radical (OH) is an important oxidant in the daytime troposphere that controls the lifetime of most trace gases, whose oxidation leads to the formation of harmful secondary pollutants such as ozone (O<sub>3</sub>) and Secondary Organic Aerosols (SOA). In spite of the importance of OH, uncertainties remain concerning its atmospheric budget and integrated measurements of the total sink of OH can help reducing these uncertainties. In this context, several methods have been developed to measure the first-order loss rate of ambient OH, called total OH reactivity. Among these techniques, the Comparative Reactivity Method (CRM) is promising and has already been widely used in the field and in atmospheric simulation chambers. This technique relies on monitoring competitive OH reactions between a reference molecule (pyrrole) and compounds present in ambient air inside a sampling reactor. However, artefacts and interferences exist for this method and a thorough charact...
Recent developments of passive samplers for measuring material emission rates: toward simple tool... more Recent developments of passive samplers for measuring material emission rates: toward simple tools to help improving indoor air quality, Building and Environment (2015),
Quantitative Analysis of Isomeric Volatile Organic Compounds in a Northern Hardwood Forest by Proton Transfer Reaction Linear Ion Trap (PTR-LIT) Mass Spectrometry
Several low molecular weight, isomeric volatile organic compounds (VOCs) occur in the atmosphere ... more Several low molecular weight, isomeric volatile organic compounds (VOCs) occur in the atmosphere in the low ppb to ppt range, including methyl vinyl ketone (MVK) and (MACR) from isoprene oxidation, and aerosol precursor monoterpenes and sesquiterpenes. Although proton transfer reaction mass spectrometry (PTR- MS) quantifies VOCs with low ppt limits of detection (LOD), it cannot differentiate isomers or isobaric molecules.
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as
Above canopy OH and HO2 during PROPHET 2008 and CABINEX 2009: Measurement and theory
Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the oxidation of organic tra... more Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the oxidation of organic trace gases leading to the production of ozone and secondary organic aerosols. Previous measurements of these radicals in forest environments have shown serious discrepancies with modeled concentrations, bringing into question the current understanding of isoprene oxidation chemistry in these environments. During the summers of 2008 and
Journal of Geophysical Research: Atmospheres, 2011
Recent laboratory and field studies have indicated that glyoxal is a potentially large contributo... more Recent laboratory and field studies have indicated that glyoxal is a potentially large contributor to secondary organic aerosol mass. We present in situ glyoxal measurements acquired with a recently developed, high sensitivity spectroscopic instrument during the CalNex 2010 field campaign in Pasadena, California. We use three methods to quantify the production and loss of glyoxal in Los Angeles and its contribution to organic aerosol. First, we calculate the difference between steady state sources and sinks of glyoxal at the Pasadena site, assuming that the remainder is available for aerosol uptake. Second, we use the Master Chemical Mechanism to construct a two-dimensional model for gas-phase glyoxal chemistry in Los Angeles, assuming that the difference between the modeled and measured glyoxal concentration is available for aerosol uptake. Third, we examine the nighttime loss of glyoxal in the absence of its photochemical sources and sinks. Using these methods we constrain the glyoxal loss to aerosol to be 0-5 × 10 −5 s −1 during clear days and (1 ± 0.3) × 10 −5 s −1 at night. Between 07:00-15:00 local time, the diurnally averaged secondary organic aerosol mass increases from 3.2 mg m −3 to a maximum of 8.8 mg m −3. The constraints on the glyoxal budget from this analysis indicate that it contributes 0-0.2 mg m −3 or 0-4% of the secondary organic aerosol mass.
Investigations of ROx Radical Photochemistry During the MCMA-2006 Field Campaign
Measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals were made during the Mexico City Met... more Measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals were made during the Mexico City Metropolitan Area (MCMA) field campaign, providing an opportunity to investigate the strong coupling between ROX radicals (HOX = OH + HO2 + RO2), nitrogen oxides (NOX = NO + NO2) and Volatile Organic Compounds (VOCs). A highly constrained zero-dimensional box model, based on the Regional Atmospheric
Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the gas-phase oxidation of o... more Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the gas-phase oxidation of organic trace gases that lead to the formation of ozone and secondary organic aerosols in the troposphere. Previous measurements of OH and HO2 radicals in forest environments have shown serious discrepancies with modeled concentrations of these radicals. These discrepancies bring into question our understanding of the
This supplement consists of a map of the study area (Fig. ), figures describing the characterizat... more This supplement consists of a map of the study area (Fig. ), figures describing the characterizations made on the MD-CRM and UL-FAGE instruments (Figs. ), details about the synthetic VOC mixtures described in Sect. 3.1 of the main paper (Tables ), and measurements of ambient formaldehyde (HCHO) mixing ratios (Fig. ).
Synoptic-scale meteorological conditions for the 4-5 August 2009 case period, time series of mete... more Synoptic-scale meteorological conditions for the 4-5 August 2009 case period, time series of meteorology used as input in CACHE, and modeled versus measured glyoxal.
Journal of Geophysical Research: Atmospheres, 2018
We analyze an expanded data set of oxygenated volatile organic compounds (OVOCs) in air measured ... more We analyze an expanded data set of oxygenated volatile organic compounds (OVOCs) in air measured by several instruments at a surface site in Pasadena near Los Angeles during the National Oceanic and Atmospheric Administration California Nexus study in 2010. The contributions of emissions, chemical formation, and removal are quantified for each OVOC using CO as a tracer of emissions and the OH exposure of the sampled air masses calculated from hydrocarbon ratios. The method for separating emissions from chemical formation is evaluated using output for Pasadena from the Weather Research and Forecasting-Chemistry model. The model is analyzed by the same method as the measurement data, and the emission ratios versus CO calculated from the model output agree for ketones with the inventory used in the model but overestimate aldehydes by~70%. In contrast with the measurements, nighttime formation of OVOCs is significant in the model and is attributed to overestimated precursor emissions and overestimated rate coefficients for the reactions of the precursors with ozone and NO 3. Most measured aldehydes correlated strongly with CO at night, suggesting a contribution from motor vehicle emissions. However, the emission ratios of most aldehydes versus CO are higher than those reported in motor vehicle emissions and the aldehyde sources remain unclear. Formation of several OVOCs is investigated in terms of the removal of specific precursors. Direct emissions of alcohols and aldehydes contribute significantly to OH reactivity throughout the day, and these emissions should be accurately represented in models describing ozone formation. Plain Language Summary We report new measurements of volatile organic compounds (VOCs) in ambient air in the Los Angeles basin. Chemical reactions between VOCs and nitrogen oxides form ozone and fine particles, two important pollutants in Los Angeles smog. It is therefore important to understand VOC emission sources. In this work, we derive the composition of VOC emissions using ambient measurements at Pasadena in 2010. The study is complicated due to rapid chemical reactions that can form and remove VOCs in between the time of emission and measurement. After correcting for this chemistry, it is shown that emissions of many oxygen-containing VOCs are important for the formation of ozone.
Several physicochemical processes occurring within buildings are key drivers of indoor concentrat... more Several physicochemical processes occurring within buildings are key drivers of indoor concentrations of Volatile Organic compounds VOCs. Many models and experimental studies have been proposed to predict VOCs concentration indoors given these processes. However, there is a lack of representative data in literature to present gas-surface interaction in order to validate mathematical models. This work is divided in two parts and aims to develop and validate a method to perform fast measurements of VOC sorption parameters on the field by coupling a Field and Laboratory Emission Cell (FLEC) to a Proton Transfer Reaction-Mass Spectrometer (PTR-MS). In the part 1 of the work, sorption coefficients of aromatic compounds on a gypsum board and vinyl flooring were investigated at ppb levels to test and evaluate the proposed methodology. Sorption coefficients in the range of 0.03-1.88 m.h-1 for k a and 2.04-17.32 h-1 for k d were successfully measured within a (0.5-8 hours) for the two materials. Robustness tests highlight that the determination of sorption coefficients does not depend on operating conditions. While sorption coefficients for the gypsum board were measured with a PTR-MS time resolution of 20 seconds, the vinyl flooring material required measurements at a higher time resolution of 2 seconds due to its lower sorption properties. Limits of applicability assessed for this method indicate that sets of sorption parameters (k a , k d) of (0.01 m.h-1 ; 0.01 h-1) and (0.09 m.h-1 ; 0.09 h-1) can be measured with an accuracy better than 10% at time resolutions of 2 and 20 seconds respectively.
The hydroxyl (OH) radical is an important oxidant in the troposphere, which controls the lifetime... more The hydroxyl (OH) radical is an important oxidant in the troposphere, which controls the lifetime of most air quality-and climate-related trace gases. However, there are still uncertainties concerning its atmospheric budget, and integrated measurements of OH sinks have been valuable to improve this aspect. Among the analytical tools used for measuring total OH reactivity in ambient air, the comparative reactivity method (CRM) is spreading rapidly in the atmospheric community. However, measurement artifacts have been highlighted for this technique, and additional work is needed to fully characterize them. In this study, we present the new Mines Douai CRM instrument, with an emphasis on the corrections that need to be applied to ambient measurements of total OH reactivity. Measurement artifacts identified in the literature have been investigated, including (1) a correction for a change in relative humidity between the measurement steps leading to different OH levels, (2) the formation of spurious OH in the sampling reactor when hydroperoxy radicals (HO 2) react with nitrogen monoxide (NO), (3) not operating the CRM under pseudo-first-order kinetics, and (4) the dilution of ambient air inside the reactor. The dependences of these artifacts on various measurable parameters, such as the pyrrole-to-OH ratio and the bimolecular reaction rate constants of ambient trace gases with OH, have also been studied. Based on these observations, parameterizations are proposed to correct ambient OH reactivity measurements. On average, corrections of 5.2 ± 3.2, 9.2 ± 15.7, and 8.5 ± 5.8 s −1 were respectively observed for (1), (2) and (3) during a field campaign performed in Dunkirk, France (summer 2014). Numerical simulations have been performed using a box model to check whether experimental observations mentioned above are consistent with our understanding of the chemistry occurring in the CRM reactor. Two different chemical mechanisms have been shown to reproduce the magnitude of corrections (2) and (3). In addition, these simulations reproduce their dependences on the pyrrole-to-OH ratio and on bimolecular reaction rate constants of gases reacting with OH. The good agreement found between laboratory experiments and model simulations gives us confidence in the proposed parameterizations. However, it is worth noting that the numerical values given in this study are suitable for the Mines Douai instrument and may not be appropriate for other CRM instruments. It is recommended that each group characterize its own instrument following the recommendations given in this study. An assessment of performances for the Mines Douai instrument, including a propagation of errors from the different corrections, indicates a limit of detection of 3.0 s −1 and total uncertainties of 17-25 % for OH reactivity values higher than 15 s −1 and NO x mixing ratios lower than 30 ppbv.
The investigation of hydroxyl radical (OH) chemistry during intensive field campaigns has led to ... more The investigation of hydroxyl radical (OH) chemistry during intensive field campaigns has led to the development of several techniques dedicated to ambient measurements of total OH reactivity, which is the inverse of the OH lifetime. Three techniques are currently used during field campaigns, including the total OH loss rate method, the pump-probe method, and the comparative reactivity method. However, no formal intercomparison of these techniques has been published so far, and there is a need to ensure that measurements of total OH reactivity are consistent among the different techniques. <br><br> An intercomparison of two OH reactivity instruments, one based on the Comparative Reactivity Method (CRM) and the other based on the pump-probe method, was performed in October 2012 in a NO<sub><i>x</i></sub>-rich environment, which is known to be challenging for the CRM technique. This study presents an extensive description of the two instruments, the...
The Hydroxyl radical (OH) is an important oxidant in the daytime troposphere that controls the li... more The Hydroxyl radical (OH) is an important oxidant in the daytime troposphere that controls the lifetime of most trace gases, whose oxidation leads to the formation of harmful secondary pollutants such as ozone (O<sub>3</sub>) and Secondary Organic Aerosols (SOA). In spite of the importance of OH, uncertainties remain concerning its atmospheric budget and integrated measurements of the total sink of OH can help reducing these uncertainties. In this context, several methods have been developed to measure the first-order loss rate of ambient OH, called total OH reactivity. Among these techniques, the Comparative Reactivity Method (CRM) is promising and has already been widely used in the field and in atmospheric simulation chambers. This technique relies on monitoring competitive OH reactions between a reference molecule (pyrrole) and compounds present in ambient air inside a sampling reactor. However, artefacts and interferences exist for this method and a thorough charact...
Recent developments of passive samplers for measuring material emission rates: toward simple tool... more Recent developments of passive samplers for measuring material emission rates: toward simple tools to help improving indoor air quality, Building and Environment (2015),
Quantitative Analysis of Isomeric Volatile Organic Compounds in a Northern Hardwood Forest by Proton Transfer Reaction Linear Ion Trap (PTR-LIT) Mass Spectrometry
Several low molecular weight, isomeric volatile organic compounds (VOCs) occur in the atmosphere ... more Several low molecular weight, isomeric volatile organic compounds (VOCs) occur in the atmosphere in the low ppb to ppt range, including methyl vinyl ketone (MVK) and (MACR) from isoprene oxidation, and aerosol precursor monoterpenes and sesquiterpenes. Although proton transfer reaction mass spectrometry (PTR- MS) quantifies VOCs with low ppt limits of detection (LOD), it cannot differentiate isomers or isobaric molecules.
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as
Above canopy OH and HO2 during PROPHET 2008 and CABINEX 2009: Measurement and theory
Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the oxidation of organic tra... more Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the oxidation of organic trace gases leading to the production of ozone and secondary organic aerosols. Previous measurements of these radicals in forest environments have shown serious discrepancies with modeled concentrations, bringing into question the current understanding of isoprene oxidation chemistry in these environments. During the summers of 2008 and
Journal of Geophysical Research: Atmospheres, 2011
Recent laboratory and field studies have indicated that glyoxal is a potentially large contributo... more Recent laboratory and field studies have indicated that glyoxal is a potentially large contributor to secondary organic aerosol mass. We present in situ glyoxal measurements acquired with a recently developed, high sensitivity spectroscopic instrument during the CalNex 2010 field campaign in Pasadena, California. We use three methods to quantify the production and loss of glyoxal in Los Angeles and its contribution to organic aerosol. First, we calculate the difference between steady state sources and sinks of glyoxal at the Pasadena site, assuming that the remainder is available for aerosol uptake. Second, we use the Master Chemical Mechanism to construct a two-dimensional model for gas-phase glyoxal chemistry in Los Angeles, assuming that the difference between the modeled and measured glyoxal concentration is available for aerosol uptake. Third, we examine the nighttime loss of glyoxal in the absence of its photochemical sources and sinks. Using these methods we constrain the glyoxal loss to aerosol to be 0-5 × 10 −5 s −1 during clear days and (1 ± 0.3) × 10 −5 s −1 at night. Between 07:00-15:00 local time, the diurnally averaged secondary organic aerosol mass increases from 3.2 mg m −3 to a maximum of 8.8 mg m −3. The constraints on the glyoxal budget from this analysis indicate that it contributes 0-0.2 mg m −3 or 0-4% of the secondary organic aerosol mass.
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