scholarly journals Rapid intercontinental air pollution transport associated with a meteorological bomb

2003 ◽  
Vol 3 (2) ◽  
pp. 2101-2141 ◽  
Author(s):  
A. Stohl ◽  
H. Huntrieser ◽  
A. Richter ◽  
S. Beirle ◽  
O. Cooper ◽  
...  
Keyword(s):  
Transport Model ◽  
Pollution Transport ◽  
Satellite Measurements ◽  
Model Calculations ◽  
Wind Speeds ◽  
Mixing Ratios ◽  
The North ◽  
Intercontinental Transport ◽  
Remote Troposphere ◽  
Rough Calculation

Abstract. Intercontinental transport (ICT) of trace substances normally occurs on timescales ranging from a few days to several weeks. In this paper an extraordinary episode in November 2001 is presented, where pollution transport across the North Atlantic took only about one day. The transport mechanism, termed here an intercontinental pollution express highway, was exceptional, as it involved an explosively generated cyclone, a so-called meteorological "bomb". To the authors' knowledge, this is the first study describing pollution transport in a bomb. The discovery of this event was based on transport model calculations and satellite measurements of NO2, a species with a relatively short lifetime in the atmosphere, which could be transported that far only because of the high wind speeds produced by the bomb. A 15-year transport climatology shows that intercontinental express highways are about four times more frequent in winter than in summer, in agreement with bomb climatologies. The climatology furthermore reveals that intercontinental express highways may be important for the budget of short-lived substances in the remote troposphere. For instance, for a substance with a lifetime of 1 day, express highways may be responsible for about two thirds of the total ICT. A rough calculation suggests that express highways connecting North America with Europe enhance the average NOx mixing ratios over Europe, due to North American emissions, by about 2–3 pptv in winter.

scholarly journals Rapid intercontinental air pollution transport associated with a meteorological bomb

2003 ◽  
Vol 3 (4) ◽  
pp. 969-985 ◽  
Author(s):  
A. Stohl ◽  
H. Huntrieser ◽  
A. Richter ◽  
S. Beirle ◽  
O. R. Cooper ◽  
...  
Keyword(s):  
Transport Model ◽  
Pollution Transport ◽  
Tracer Transport ◽  
High Wind ◽  
Model Calculations ◽  
Wind Speeds ◽  
Mixing Ratios ◽  
The North ◽  
Intercontinental Transport ◽  
Remote Troposphere

Abstract. Intercontinental transport (ICT) of trace substances normally occurs on timescales ranging from a few days to several weeks. In this paper an extraordinary episode in November 2001 is presented, where pollution transport across the North Atlantic took only about one day. The transport mechanism, termed here an intercontinental pollution express highway because of the high wind speeds, was exceptional, as it involved an explosively generated cyclone, a so-called meteorological "bomb''. To the authors' knowledge, this is the first study describing pollution transport in a bomb. The discovery of this event was based on tracer transport model calculations and satellite measurements of NO2, a species with a relatively short lifetime in the atmosphere, which could be transported that far only because of the high wind speeds produced by the bomb. A 15-year transport climatology shows that intercontinental express highways are about four times more frequent in winter than in summer, in agreement with bomb climatologies. The climatology furthermore suggests that intercontinental express highways may be important for the budget of short-lived substances in the remote troposphere. For instance, for a substance with a lifetime of 1 day, express highways may be responsible for about two thirds of the total ICT. We roughly estimate that express highways connecting North America with Europe enhance the average NOx mixing ratios over Europe, due to North American emissions, by about 2-3 pptv in winter.

scholarly journals Radical chemistry at a rural site (Wangdu) in the North China Plain: Observation and model calculations of OH, HO<sub>2</sub> and RO<sub>2</sub> radicals

2016 ◽  
Author(s):  
Zhaofeng Tan ◽  
Hendrik Fuchs ◽  
Keding Lu ◽  
Birger Bohn ◽  
Sebastian Broch ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Rural Site ◽  
Daily Maximum ◽  
Model Calculations ◽  
Mixing Ratios ◽  
The North ◽  
The North China Plain

Abstract. A comprehensive field campaign was carried out in summer 2014 in Wangdu located in the North China Plain. A month of continuous OH, HO2 and RO2 measurements were achieved. Observations of radicals by laser induced fluorescence (LIF) technique gave daily maximum concentrations between (5–15) × 106 cm−3, (3–14) × 108 cm−3 and (3–15) × 108 cm−3 for OH, HO2 and RO2, respectively. Measured OH reactivities (inverse OH lifetimes) were 10 to 20 s−1 during daytime. A chemical box model constrained by trace-gas observations and based on a state-of-the-art chemical mechanism is used to interpret the observed radical concentrations. In general, the model can reasonably well reproduce measured radical concentrations during daytime. Like in previous field campaigns in China, modelled and measured OH concentrations agree for NO mixing ratios higher than 1 ppbv, but systematic discrepancies are observed in the afternoon for NO mixing ratios of less than 300 pptv (the model-measurement ratio is between 1.4 to 2 in this case). If additional OH recycling equivalent to 100 pptv NO is assumed, the model is also capable of reproducing the observed OH concentrations for conditions of high VOC and low NOx concentrations with good agreement in HO2 and RO2. Observed RO2 concentrations are underestimated in the morning hours by a factor of 3 to 5. This indicates that an additional chemical source of RO2 is missing in the model. The OH reactivity is also underpredicted in the early morning. Increasing VOC concentrations to match measured OH reactivity helps to reduce the discrepancy between modelled and measured RO2. The underprediction of RO2 coincides with high NO concentrations and therefore leads to a significant underestimation of the local ozone production rates determined from the peroxy radical (HO2 and RO2) reactions with NO. The underestimation corresponds to a daily integral ozone production of about 20 ppbv per day.

scholarly journals Global sensitivity analysis of the GEOS-Chem chemical transport model: Ozone and hydrogen oxides during ARCTAS (2008)

2016 ◽  
Author(s):  
Kenneth E. Christian ◽  
William H. Brune ◽  
Jingqiu Mao
Keyword(s):  
Aerosol Particle ◽  
Transport Model ◽  
Chemical Transport ◽  
Sensitivity Analyses ◽  
Chemical Transport Model ◽  
Global Sensitivity ◽  
Particle Uptake ◽  
Mixing Ratios ◽  
The North ◽  
Input Variables

Abstract. Developing predictive capability for future atmospheric oxidation capability requires a detailed analysis of model uncertainties and sensitivity of the modeled oxidation capacity to model input variables. Using oxidant mixing ratios modeled by the GEOS-Chem chemical transport model and measured on the NASA DC8 aircraft, uncertainty and global sensitivity analyses were performed on the GEOS-Chem chemical transport model for the modeled oxidants hydroxyl (OH), hydroperoxyl (HO2), and ozone (O3). The sensitivity of modeled OH, HO2, and ozone to modeled inputs perturbed simultaneously within their respective uncertainties were found for the period of NASA's Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) A &amp; B campaigns (2008) in the North American Arctic. For the spring deployment (ARCTAS-A), ozone is most sensitive to the photolysis rate of NO2, the NO2 + OH reaction rate, and various emissions, including methyl bromoform (CHBr3). OH and HO2 were overwhelmingly sensitive to aerosol particle uptake of HO2 with this one factor contributing upwards of 75 % of the uncertainty in HO2. For the summer deployment (ARCTAS-B), ozone was most sensitive to emissions factors, such as soil NOx and isoprene. OH and HO2 were most sensitive to biomass emissions and aerosol particle uptake of HO2. With modeled HO2 showing a factor of 2 underestimation compared to measurements in the lowest 2 kilometers of the troposphere, lower uptake rates (γHO2 < 0.04), regardless of whether or not the product of the uptake is H2O or H2O2, produced better agreement between modeled and measured HO2.

scholarly journals Free tropospheric peroxyacetyl nitrate (PAN) and ozone at Mount Bachelor: causes of variability and timescale for trend detection

2011 ◽  
Vol 11 (2) ◽  
pp. 4105-4139 ◽  
Author(s):  
E. V. Fischer ◽  
D. A. Jaffe ◽  
E. C. Weatherhead
Keyword(s):  
Pacific Northwest ◽  
Biomass Burning ◽  
Transport Model ◽  
Relative Increase ◽  
Trend Detection ◽  
Positive Trend ◽  
Chemical Transport Model ◽  
Mixing Ratios ◽  
The North ◽  
The Us

Abstract. We report on the first multi-year springtime measurements of PAN in the free troposphere over the US Pacific Northwest. The measurements were made at the summit of Mount Bachelor (43.979° N, 121.687° W; 2.7 km a.s.l.) by gas chromatography with electron capture detector during spring 2008, 2009, and 2010. This dataset provides an observational estimate of the month-to-month and springtime interannual variability of PAN mixing ratios in this region. Springtime seasonal mean (1 April–20 May) PAN mixing ratios at Mount Bachelor varied from 100 pptv to 152 pptv. The standard deviation of the three seasonal means was 28 pptv, 21% of the springtime mean. We focus on three factors that we expect to drive PAN variability: biomass burning, transport efficiency over the central and eastern Pacific, and transport temperature. There was an early and unusually strong fire source in southeastern Russia in spring 2008 due to early snow melt, and several fire plumes were observed at Mount Bachelor. Colder air mass transport from higher altitudes in April 2009 is consistent with the higher average PAN mixing ratios observed at MBO during this month. A trough located off the US Pacific Northwest coast in April 2010 caused reduced transport from the north in spring 2010 as compared to previous years. It also facilitated more frequent transport to Mount Bachelor during spring 2010 from the southwest and from lower elevations. Zhang et al. (2008) used the GEOS-Chem global chemical transport model to show that rising Asian NOx emissions from 2000 to 2006 resulted in a relatively larger positive trend in PAN than O3 over western North America. However the model results only considered monotonic changes in Asian emissions, whereas other factors, such as biomass burning, isoprene emissions or climate change can complicate the atmospheric concentrations. We combined the observed variability in PAN and O3 at Mount Bachelor with a range of possible trends in these species to determine the observational requirements to detect the trends. Though the relative increase in PAN is expected to be nearly four times larger than that of O3, PAN is more variable. If PAN mixing ratios are currently increasing at a rate of 4% per year due to rising Asian emissions, we would detect a trend with 13 yr of measurements at a site like Mount Bachelor. If the corresponding trend in O3 is 1% per year, the trends in O3 and PAN should be detected on approximately the same timescale.

scholarly journals Global sensitivity analysis of the GEOS-Chem chemical transport model: ozone and hydrogen oxides during ARCTAS (2008)

2017 ◽  
Vol 17 (5) ◽  
pp. 3769-3784 ◽  
Author(s):  
Kenneth E. Christian ◽  
William H. Brune ◽  
Jingqiu Mao
Keyword(s):  
Aerosol Particle ◽  
Transport Model ◽  
Chemical Transport ◽  
Sensitivity Analyses ◽  
Chemical Transport Model ◽  
Oxidation Capacity ◽  
Global Sensitivity ◽  
Particle Uptake ◽  
Mixing Ratios ◽  
The North

Abstract. Developing predictive capability for future atmospheric oxidation capacity requires a detailed analysis of model uncertainties and sensitivity of the modeled oxidation capacity to model input variables. Using oxidant mixing ratios modeled by the GEOS-Chem chemical transport model and measured on the NASA DC-8 aircraft, uncertainty and global sensitivity analyses were performed on the GEOS-Chem chemical transport model for the modeled oxidants hydroxyl (OH), hydroperoxyl (HO2), and ozone (O3). The sensitivity of modeled OH, HO2, and ozone to model inputs perturbed simultaneously within their respective uncertainties were found for the flight tracks of NASA's Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) A and B campaigns (2008) in the North American Arctic. For the spring deployment (ARCTAS-A), ozone was most sensitive to the photolysis rate of NO2, the NO2 + OH reaction rate, and various emissions, including methyl bromoform (CHBr3). OH and HO2 were overwhelmingly sensitive to aerosol particle uptake of HO2 with this one factor contributing upwards of 75 % of the uncertainty in HO2. For the summer deployment (ARCTAS-B), ozone was most sensitive to emission factors, such as soil NOx and isoprene. OH and HO2 were most sensitive to biomass emissions and aerosol particle uptake of HO2. With modeled HO2 showing a factor of 2 underestimation compared to measurements in the lowest 2 km of the troposphere, lower uptake rates (γHO2 < 0. 055), regardless of whether or not the product of the uptake is H2O or H2O2, produced better agreement between modeled and measured HO2.

scholarly journals Exploring Constraints on a Wetland Methane Emission Ensemble (WetCHARTs) using GOSAT Satellite Observations

2020 ◽  
Author(s):  
Robert J. Parker ◽  
Chris Wilson ◽  
A. Anthony Bloom ◽  
Edward Comyn-Platt ◽  
Garry Hayman ◽  
...  
Keyword(s):  
Land Surface ◽  
Seasonal Cycle ◽  
Transport Model ◽  
Global Scale ◽  
Data Driven ◽  
Emission Model ◽  
Chemical Transport Model ◽  
Mixing Ratios ◽  
The North ◽  
Gosat Satellite

Abstract. Wetland emissions contribute the largest uncertainties to the current global atmospheric CH4 budget and how these emissions will change under future climate scenarios is also still poorly understood. Bloom et al. (2017b) developed WetCHARTs, a simple, data-driven, ensemble-based model that produces estimates of CH4 wetland emissions constrained by observations of precipitation and temperature. This study performs the first detailed global and regional evaluation of the WetCHARTs CH4 emission model ensemble against 9 years of high-quality, validated atmospheric CH4 observations from the GOSAT satellite. A 3-D chemical transport model is used to estimate atmospheric CH4 mixing ratios based on the WetCHARTs emissions and other sources. Across all years and all ensemble members, the observed global seasonal cycle amplitude is typically underestimated by WetCHARTs by −7.4 ppb, but the correlation coefficient of 0.83 shows that the seasonality is well-produced at a global scale. The Southern Hemisphere has less of a bias (−1.9 ppb) than the Northern Hemisphere (−9.3 ppb) and our findings show that it is typically the North Tropics where this bias is worst (−11.9 ppb). We find that WetCHARTs generally performs well in reproducing the observed wetland CH4 seasonal cycle for the majority of wetland regions although, for some regions, regardless of the ensemble configuration, WetCHARTs does not well-reproduce the observed seasonal cycle. In order to investigate this, we performed detailed analysis of some of the more challenging exemplar regions (Parana River, Congo, Sudd and Yucatan). Our results show that certain ensemble members are more suited to specific regions, either due to deficiencies in the underlying data driving the model or complexities in representing the processes involved. In particular, incorrect definition of the wetland extent is found to be the most common reason for the discrepancy between the modelled and observed CH4 concentrations. The remaining driving data (i.e. heterotrophic respiration and temperature) are shown to also contribute to the mismatch to observations, with the details differing on a region-by-region basis but generally showing that some degree of temperature dependency is better than none. We conclude that the data-driven approach used by WetCHARTs is well-suited to produce a benchmark ensemble dataset against which to evaluate more complex process-based land surface models that explicitly model the hydrological behaviour of these complex wetland regions.

scholarly journals Exploring constraints on a wetland methane emission ensemble (WetCHARTs) using GOSAT observations

2020 ◽  
Vol 17 (22) ◽  
pp. 5669-5691
Author(s):  
Robert J. Parker ◽  
Chris Wilson ◽  
A. Anthony Bloom ◽  
Edward Comyn-Platt ◽  
Garry Hayman ◽  
...  
Keyword(s):  
Land Surface ◽  
Seasonal Cycle ◽  
Transport Model ◽  
Global Scale ◽  
Data Driven ◽  
Emission Model ◽  
Chemical Transport Model ◽  
Mixing Ratios ◽  
The North ◽  
Data Driven Approach

Abstract. Wetland emissions contribute the largest uncertainties to the current global atmospheric CH4 budget, and how these emissions will change under future climate scenarios is also still poorly understood. Bloom et al. (2017b) developed WetCHARTs, a simple, data-driven, ensemble-based model that produces estimates of CH4 wetland emissions constrained by observations of precipitation and temperature. This study performs the first detailed global and regional evaluation of the WetCHARTs CH4 emission model ensemble against 9 years of high-quality, validated atmospheric CH4 observations from GOSAT (the Greenhouse Gases Observing Satellite). A 3-D chemical transport model is used to estimate atmospheric CH4 mixing ratios based on the WetCHARTs emissions and other sources. Across all years and all ensemble members, the observed global seasonal-cycle amplitude is typically underestimated by WetCHARTs by −7.4 ppb, but the correlation coefficient of 0.83 shows that the seasonality is well-produced at a global scale. The Southern Hemisphere has less of a bias (−1.9 ppb) than the Northern Hemisphere (−9.3 ppb), and our findings show that it is typically the North Tropics where this bias is the worst (−11.9 ppb). We find that WetCHARTs generally performs well in reproducing the observed wetland CH4 seasonal cycle for the majority of wetland regions although, for some regions, regardless of the ensemble configuration, WetCHARTs does not reproduce the observed seasonal cycle well. In order to investigate this, we performed detailed analysis of some of the more challenging exemplar regions (Paraná River, Congo, Sudd and Yucatán). Our results show that certain ensemble members are more suited to specific regions, due to either deficiencies in the underlying data driving the model or complexities in representing the processes involved. In particular, incorrect definition of the wetland extent is found to be the most common reason for the discrepancy between the modelled and observed CH4 concentrations. The remaining driving data (i.e. heterotrophic respiration and temperature) are shown to also contribute to the mismatch with observations, with the details differing on a region-by-region basis but generally showing that some degree of temperature dependency is better than none. We conclude that the data-driven approach used by WetCHARTs is well-suited to producing a benchmark ensemble dataset against which to evaluate more complex process-based land surface models that explicitly model the hydrological behaviour of these complex wetland regions.

scholarly journals New approach to evaluate satellite derived XCO<sub>2</sub> over oceans by integrating ship and aircraft observations

2020 ◽  
Author(s):  
Astrid Müller ◽  
Hiroshi Tanimoto ◽  
Takafumi Sugita ◽  
Toshinobu Machida ◽  
Shin-ichiro Nakaoka ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Atmospheric Chemistry ◽  
Transport Model ◽  
Satellite Observations ◽  
Reference Dataset ◽  
Model Calculations ◽  
New Approach ◽  
Mixing Ratios ◽  
In Situ Data

Abstract. Satellite observations provide spatially-resolved global estimates of column-averaged mixing ratios of CO2 (XCO2) over the Earth's surface. The accuracy of these datasets can be validated against reliable standards in some areas, but other areas remain inaccessible. To date, limited reference data over oceans hinders successful uncertainty quantification or bias correction efforts, and precludes reliable conclusions about changes in the carbon cycle in some regions. Here, we propose a new approach to analyze and evaluate seasonal, interannual and latitudinal variations of XCO2 over oceans by integrating cargo-ship (SOOP, Ship Of Opportunity) and commercial aircraft (CONTRAIL, Comprehensive Observation Network for Trace gases by Airliner) observations with the aid of state-of-the art atmospheric chemistry-transport model calculations. The consistency of the in situ based column-averaged CO2 dataset (in situ XCO2) with satellite estimates was analyzed over the Western Pacific between 2014 and 2017, and its utility as reference dataset evaluated. Our results demonstrate that the new dataset accurately captures seasonal and interannual variations of CO2. Retrievals of XCO2 over the ocean from GOSAT (Greenhouse gases observing satellite: NIES v02.75, National Institute for Environmental Studies; ACOS v7.3, Atmospheric CO2 Observation from Space) and OCO-2 (Orbiting Carbon Observatory, v9r) observations show a negative bias of about 1 parts per million (ppm) in northern midlatitudes, which was attributed to measurement uncertainties of the satellite observations. The NIES retrieval had higher consistency with in situ XCO2 at midlatitudes as compared to the other retrievals. At low latitudes, it shows many fewer valid data and high scatter, such that ACOS and OCO-2 appear to provide a better representation of the carbon cycle. At different times, the seasonal cycles of all three retrievals show positive phase shifts of one month relative to the in situ data. The study indicates that even if the retrievals complement each other, remaining uncertainties limit the accurate interpretation of spatiotemporal changes in CO2 fluxes. A continuous long-term XCO2 dataset with wide latitudinal coverage based on the new approach has a great potential as a robust reference dataset for XCO2 and can help to better understand changes in the carbon cycle in response to climate change using satellite observations.

scholarly journals Winter observations of ClNO<sub>2</sub> in northern China: Spatiotemporal variability and insights into daytime peaks

2021 ◽  
Author(s):  
Men Xia ◽  
Xiang Peng ◽  
Weihao Wang ◽  
Chuan Yu ◽  
Zhe Wang ◽  
...  
Keyword(s):  
Northern China ◽  
Spatiotemporal Variability ◽  
Model Calculations ◽  
Dinitrogen Pentoxide ◽  
Mixing Ratios ◽  
The North ◽  
Urban Rural ◽  
Rural Sites ◽  
Related Compounds ◽  
Cl Atoms

Abstract. Nitryl chloride (ClNO2) is an important chlorine reservoir in the atmosphere that affects the oxidation of volatile organic compounds (VOCs) and the production of ROx radicals and ozone (O3). This study presents measurements of ClNO2 and related compounds at urban, rural, and mountain sites in the winter of 2017–2018 over the North China Plain (NCP). The nocturnal concentrations of ClNO2 were lower at the urban and rural sites but higher at the mountain site. The winter concentrations of ClNO2 were generally lower than the summer concentrations that were previously observed at these sites, which was due to the lower nitrate radical (NO3) production rate (P(NO3) and the smaller N2O5 uptake coefficients (γ(N2O5)) in winter, despite the higher dinitrogen pentoxide (N2O5) to NO3 ratios in winter. Significant daytime peaks of ClNO2 were observed at all the sites during the winter campaigns, with ClNO2 mixing ratios of up to 1.3 ppbv. Vertical transport of ClNO2 from the residual layers and prolonged photochemical lifetime of ClNO2 in winter may explain the elevated daytime concentrations. The daytime-averaged chlorine radical (Cl) production rates (P(Cl)) from the daytime ClNO2 were 0.17, 0.11, and 0.12 ppbv h−1 at the rural, urban, and mountain sites, respectively, which were approximately 3–4 times higher than the campaign-averaged conditions. Box model calculations showed that the Cl atoms liberated during the daytime peaks of ClNO2 increased the ROx levels by up to 27–37 % and increased the daily O3 productions by up to 13–18 %.

scholarly journals Radical chemistry at a rural site (Wangdu) in the North China Plain: observation and model calculations of OH, HO<sub>2</sub> and RO<sub>2</sub> radicals

2017 ◽  
Vol 17 (1) ◽  
pp. 663-690 ◽  
Author(s):  
Zhaofeng Tan ◽  
Hendrik Fuchs ◽  
Keding Lu ◽  
Andreas Hofzumahaus ◽  
Birger Bohn ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Ozone Production ◽  
Rural Site ◽  
Model Calculations ◽  
Radical Chemistry ◽  
Mixing Ratios ◽  
The North ◽  
The North China Plain ◽  
Field Campaigns

Abstract. A comprehensive field campaign was carried out in summer 2014 in Wangdu, located in the North China Plain. A month of continuous OH, HO2 and RO2 measurements was achieved. Observations of radicals by the laser-induced fluorescence (LIF) technique revealed daily maximum concentrations between (5–15)  × 106 cm−3, (3–14)  × 108 cm−3 and (3–15)  × 108 cm−3 for OH, HO2 and RO2, respectively. Measured OH reactivities (inverse OH lifetime) were 10 to 20 s−1 during daytime. The chemical box model RACM 2, including the Leuven isoprene mechanism (LIM), was used to interpret the observed radical concentrations. As in previous field campaigns in China, modeled and measured OH concentrations agree for NO mixing ratios higher than 1 ppbv, but systematic discrepancies are observed in the afternoon for NO mixing ratios of less than 300 pptv (the model–measurement ratio is between 1.4 and 2 in this case). If additional OH recycling equivalent to 100 pptv NO is assumed, the model is capable of reproducing the observed OH, HO2 and RO2 concentrations for conditions of high volatile organic compound (VOC) and low NOx concentrations. For HO2, good agreement is found between modeled and observed concentrations during day and night. In the case of RO2, the agreement between model calculations and measurements is good in the late afternoon when NO concentrations are below 0.3 ppbv. A significant model underprediction of RO2 by a factor of 3 to 5 is found in the morning at NO concentrations higher than 1 ppbv, which can be explained by a missing RO2 source of 2 ppbv h−1. As a consequence, the model underpredicts the photochemical net ozone production by 20 ppbv per day, which is a significant portion of the daily integrated ozone production (110 ppbv) derived from the measured HO2 and RO2. The additional RO2 production from the photolysis of ClNO2 and missing reactivity can explain about 10 % and 20 % of the discrepancy, respectively. The underprediction of the photochemical ozone production at high NOx found in this study is consistent with the results from other field campaigns in urban environments, which underlines the need for better understanding of the peroxy radical chemistry for high NOx conditions.

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