Closing the peroxy acetyl (PA) radical budget: observations of acyl peroxy nitrates (PAN, PPN, and MPAN) during BEARPEX 2007

Abstract. Acyl peroxy nitrates (APNs, also known as PANs) are formed from the oxidation of aldehydes and other oxygenated VOC (oVOC) in the presence of NO2. Formation of APNs suppresses NOx (NOx≡NO+NO2) in urban areas and enhances NOx downwind in urban plumes, increasing the rate of ozone production throughout an urban plume. APNs also redistribute NOx on global scales, enhancing NOx and thus ozone production. There are both anthropogenic and biogenic oVOC precursors to APNs, but a detailed evaluation of their chemistry against observations has proven elusive. Here we describe measurements of PAN, PPN, and MPAN along with the majority of chemicals that participate in their production and loss, including OH, HO2, numerous oVOC, and NO2. Observations were made during the Biosphere Effects on AeRosols and Photochemistry Experiment (BEARPEX 2007) in the outflow of the Sacramento urban plume. These observations are used to evaluate a detailed chemical model of APN ratios and concentrations. We find the ratios of APNs are nearly independent of the loss mechanisms and thus an especially good test of our understanding of their sources. We show that oxidation of methylvinyl ketone, methacrolein, methyl glyoxal, biacetyl and acetaldehyde are all significant sources of the PAN+peroxy acetyl (PA) radical reservoir, with methylvinyl ketone (MVK) often being the primary non-acetaldehyde source. At high temperatures, oxidation of non-acetaldehyde PA radical sources contributes over 60% to the total PA production rate. An analysis of absolute APN concentrations reveals a missing APN sink that can be resolved by increasing the PA+∑RO2 rate constant by a factor of 3.

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Closing the peroxy acetyl nitrate budget: observations of acyl peroxy nitrates (PAN, PPN, and MPAN) during BEARPEX 2007

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-7623-2009 ◽

2009 ◽

Vol 9 (19) ◽

pp. 7623-7641 ◽

Cited By ~ 80

Author(s):

B. W. LaFranchi ◽

G. M. Wolfe ◽

J. A. Thornton ◽

S. A. Harrold ◽

E. C. Browne ◽

...

Keyword(s):

Production Rate ◽

Rate Constant ◽

Methyl Glyoxal ◽

Good Test ◽

Peroxy Nitrates ◽

Detailed Evaluation ◽

Urban Plume ◽

Acetyl Nitrate ◽

Peroxy Acetyl Nitrate ◽

Detailed Chemical

Abstract. Acyl peroxy nitrates (APNs, also known as PANs) are formed from the oxidation of aldehydes and other oxygenated VOC (oVOC) in the presence of NO2. There are both anthropogenic and biogenic oVOC precursors to APNs, but a detailed evaluation of this chemistry against observations has proven elusive. Here we describe measurements of PAN, PPN, and MPAN along with the majority of chemicals that participate in their production and loss, including OH, HO2, numerous oVOC, and NO2. Observations were made during the Biosphere Effects on AeRosols and Photochemistry Experiment (BEARPEX 2007) in the outflow of the Sacramento urban plume. These observations are used to evaluate a detailed chemical model of APN ratios and concentrations. We find that the ratios of APNs are nearly independent of the loss mechanisms and thus an especially good test of our understanding of their sources. We show that oxidation of methylvinyl ketone, methacrolein, methyl glyoxal, biacetyl and acetaldehyde are all significant sources of the PAN+peroxy acetyl (PA) radical reservoir, accounting for 26%, 2%, 7%, 20%, and 45%, of the production rate on average during the campaign, respectively. At high temperatures, when upwind isoprene emissions are highest, oxidation of non-acetaldehyde PA radical sources contributes over 60% to the total PA production rate, with methylvinyl ketone being the most important of the isoprene-derived sources. An analysis of absolute APN concentrations reveals a missing APN sink that can be resolved by increasing the PA+∑RO2 rate constant by a factor of 3.

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Ozone production chemistry in the presence of urban plumes

Faraday Discussions ◽

10.1039/c5fd00204d ◽

2016 ◽

Vol 189 ◽

pp. 169-189 ◽

Cited By ~ 27

Author(s):

W. H. Brune ◽

B. C. Baier ◽

J. Thomas ◽

X. Ren ◽

R. C. Cohen ◽

...

Keyword(s):

Urban Areas ◽

Ozone Production ◽

Ozone Pollution ◽

Minimal Impact ◽

Organic Species ◽

Important Discrepancy ◽

Measurement Suite ◽

Ozone Photochemistry ◽

Urban Plumes ◽

No Emissions

Ozone pollution affects human health, especially in urban areas on hot sunny days. Its basic photochemistry has been known for decades and yet it is still not possible to correctly predict the high ozone levels that are the greatest threat. The CalNex_SJV study in Bakersfield CA in May/June 2010 provided an opportunity to examine ozone photochemistry in an urban area surrounded by agriculture. The measurement suite included hydroxyl (OH), hydroperoxyl (HO2), and OH reactivity, which are compared with the output of a photochemical box model. While the agreement is generally within combined uncertainties, measured HO2 far exceeds modeled HO2 in NOx-rich plumes. OH production and loss do not balance as they should in the morning, and the ozone production calculated with measured HO2 is a decade greater than that calculated with modeled HO2 when NO levels are high. Calculated ozone production using measured HO2 is twice that using modeled HO2, but this difference in calculated ozone production has minimal impact on the assessment of NOx-sensitivity or VOC-sensitivity for midday ozone production. Evidence from this study indicates that this important discrepancy is not due to the HO2 measurement or to the sampling of transported plumes but instead to either emissions of unknown organic species that accompany the NO emissions or unknown photochemistry involving nitrogen oxides and hydrogen oxides, possibly the hypothesized reaction OH + NO + O2 → HO2 + NO2.

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Modelling the impact of megacities on local, regional and global tropospheric ozone and the deposition of nitrogen species

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-12215-2013 ◽

2013 ◽

Vol 13 (24) ◽

pp. 12215-12231 ◽

Cited By ~ 14

Author(s):

Z. S. Stock ◽

M. R. Russo ◽

T. M. Butler ◽

A. T. Archibald ◽

M. G. Lawrence ◽

...

Keyword(s):

Air Quality ◽

Urban Areas ◽

Climate Model ◽

Surface Ozone ◽

Global Scale ◽

Chemical Environment ◽

Ozone Production ◽

The Uk ◽

The Impact ◽

Local Emissions

Abstract. We examine the effects of ozone precursor emissions from megacities on present-day air quality using the global chemistry–climate model UM-UKCA (UK Met Office Unified Model coupled to the UK Chemistry and Aerosols model). The sensitivity of megacity and regional ozone to local emissions, both from within the megacity and from surrounding regions, is important for determining air quality across many scales, which in turn is key for reducing human exposure to high levels of pollutants. We use two methods, perturbation and tagging, to quantify the impact of megacity emissions on global ozone. We also completely redistribute the anthropogenic emissions from megacities, to compare changes in local air quality going from centralised, densely populated megacities to decentralised, lower density urban areas. Focus is placed not only on how changes to megacity emissions affect regional and global NOx and O3, but also on changes to NOy deposition and to local chemical environments which are perturbed by the emission changes. The perturbation and tagging methods show broadly similar megacity impacts on total ozone, with the perturbation method underestimating the contribution partially because it perturbs the background chemical environment. The total redistribution of megacity emissions locally shifts the chemical environment towards more NOx-limited conditions in the megacities, which is more conducive to ozone production, and monthly mean surface ozone is found to increase up to 30% in megacities, depending on latitude and season. However, the displacement of emissions has little effect on the global annual ozone burden (0.12% change). Globally, megacity emissions are shown to contribute ~3% of total NOy deposition. The changes in O3, NOx and NOy deposition described here are useful for quantifying megacity impacts and for understanding the sensitivity of megacity regions to local emissions. The small global effects of the 100% redistribution carried out in this study suggest that the distribution of emissions on the local scale is unlikely to have large implications for chemistry–climate processes on the global scale.

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Observations of the temperature dependent response of ozone to NO<sub>x</sub> reductions in the Sacramento, CA urban plume

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-6945-2011 ◽

2011 ◽

Vol 11 (14) ◽

pp. 6945-6960 ◽

Cited By ~ 27

Author(s):

B. W. LaFranchi ◽

A. H. Goldstein ◽

R. C. Cohen

Keyword(s):

Ozone Production ◽

Metropolitan Region ◽

Temperature Dependent ◽

Strongly Coupled ◽

Detailed Chemistry ◽

Mixing Ratios ◽

Current Trends ◽

Biogenic Voc ◽

Steady State Model ◽

Urban Plume

Abstract. Observations of NOx in the Sacramento, CA region show that mixing ratios decreased by 30 % between 2001 and 2008. Here we use an observation-based method to quantify net ozone (O3) production rates in the outflow from the Sacramento metropolitan region and examine the O3 decrease resulting from reductions in NOx emissions. This observational method does not rely on assumptions about detailed chemistry of ozone production, rather it is an independent means to verify and test these assumptions. We use an instantaneous steady-state model as well as a detailed 1-D plume model to aid in interpretation of the ozone production inferred from observations. In agreement with the models, the observations show that early in the plume, the NOx dependence for Ox (Ox = O3 + NO2) production is strongly coupled with temperature, suggesting that temperature-dependent biogenic VOC emissions and other temperature-related effects can drive Ox production between NOx-limited and NOx-suppressed regimes. As a result, NOx reductions were found to be most effective at higher temperatures over the 7 year period. We show that violations of the California 1-h O3 standard (90 ppb) in the region have been decreasing linearly with decreases in NOx (at a given temperature) and predict that reductions of NOx concentrations (and presumably emissions) by an additional 30 % (relative to 2007 levels) will eliminate violations of the state 1 h standard in the region. If current trends continue, a 30 % decrease in NOx is expected by 2012, and an end to violations of the 1 h standard in the Sacramento region appears to be imminent.

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Twenty years of ambient observations of nitrogen oxides and specified hydrocarbons in air masses dominated by traffic emissions in Germany

Faraday Discussions ◽

10.1039/c5fd00180c ◽

2016 ◽

Vol 189 ◽

pp. 407-437 ◽

Cited By ~ 18

Author(s):

Christian Ehlers ◽

Dieter Klemp ◽

Franz Rohrer ◽

Djuro Mihelcic ◽

Robert Wegener ◽

...

Keyword(s):

Nitrogen Oxides ◽

Urban Areas ◽

Road Traffic ◽

Traffic Emissions ◽

Ozone Production ◽

Hydrocarbon Mixture ◽

Oh Radicals ◽

Time Period ◽

Oxide Removal ◽

German Cities

The analysis of the individual composition of hydrocarbon (VOC) mixtures enables us to transform observed VOC-concentrations into their respective total VOC-reactivity versus OH radicals (RVOC = Σ(kOH+VOCi × [VOCi])). This is particularly useful because local ozone production essentially depends on this single parameter rather than on the details of the underlying hydrocarbon mixture (Klemp et al., Schriften des Forschungszentrums Jülich, Energy & Environment, 2012, 21). The VOC composition also enables us to pin down the major emission source of hydrocarbons in urban areas to be petrol cars with temporarily reduced catalyst efficiency (the so-called cold-start situation) whereas the source of nitrogen oxides (NOx = NO + NO2) is expected to be nowadays dominated by diesel cars. The observations in the vicinity of main roads in German cities show a decrease in the ratio of OH reactivities of VOC and NO2 (RVOC/RNO2) by a factor of 7.5 over the time period 1994–2014. This is larger than the expected decrease of a factor of 2.9 taking estimated trends of VOC and NOx traffic emissions in Germany (Umweltbundesamt Deutschland, National Trend Tables for the German Atmospheric Emission Reporting, 2015), during this time period. The observed reduction in the RVOC/RNO2 ratio leads to a drastic decrease in local ozone production driven by the reduction in hydrocarbons. The analysis reveals that the overall reduction of ozone production benefits from the low decrease of NOx emissions from road traffic which is a consequence of the eventual absence of catalytic converters for nitrogen oxide removal in diesel cars up to now.

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Impact of model resolution on chemical ozone formation in Mexico City: application of the WRF-Chem model

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-8983-2010 ◽

2010 ◽

Vol 10 (18) ◽

pp. 8983-8995 ◽

Cited By ~ 64

Author(s):

X. Tie ◽

G. Brasseur ◽

Z. Ying

Keyword(s):

Mexico City ◽

Urban Areas ◽

Air Pollutants ◽

Emission Inventory ◽

Meteorological Conditions ◽

Transport Processes ◽

Ozone Production ◽

Model Resolution ◽

Coarse Resolution ◽

Photochemical Ozone

Abstract. The resolution of regional chemical/dynamical models has important effects on the calculation of the distributions of air pollutants in urban areas. In this study, the sensitivity of air pollutants and photochemical ozone production to different model resolutions is assessed by applying a regional chemical/dynamical model (version 3 of Weather Research and Forecasting Chemical model – WRF-Chemv3) to the case of Mexico City. The model results with 3, 6, 12, and 24 km resolutions are compared to local surface measurements of CO, NOx, and O3. The study shows that the model resolutions of 3 and 6 km provide reasonable simulations of surface CO, NOx, and O3 concentrations and of diurnal variations. The model tends to underestimate the measurements when the resolution is reduced to 12 km or less. The calculated surface CO, NOx, and O3 concentrations at 24 km resolution are significantly lower than measured values. This study suggests that the ratio of the city size to the threshold resolution is 6 to 1, and that this ratio can be considered as a test value in other urban areas for model resolution setting. There are three major factors related to the effects of model resolution on the calculations of O3 and O3 precursors, including; (1) the calculated meteorological conditions, (2) the spatial distribution for the emissions of ozone precursors, and (3) the non-linearity in the photochemical ozone production. Model studies suggest that, for the calculations of O3 and O3 precursors, spatial resolutions (resulting from different meteorological condition and transport processes) have larger impacts than the effect of the resolution associated with emission inventories. The model shows that, with coarse resolution of emission inventory (24 km) and high resolution for meteorological conditions (6 km), the calculated CO and O3 are considerably improved compared to the results obtained with coarse resolution for both emission inventory and meteorological conditions (24 km). The resolution of the surface emissions has important effects on the calculated concentration fields, but the effects are smaller than those resulting from the model resolution. This study also suggests that the effect of model resolution on O3 precursors leads to important impacts on the photochemical formation of ozone. This results directly from the non-linear relationship between O3 formation and O3 precursor concentrations. Finally, this study suggests that, considering the balance between model performance and required computation time on current computers, the 6 km resolution is an optimal resolution for the calculation of ozone and its precursors in urban areas like Mexico City.

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