Incorporation and evaluation of the CRI v2.2 chemical mechanism in UKESM1: An alternative mechanism with updated isoprene chemistry for investigating the influence of BVOCs on atmospheric composition and climate. 

2021 ◽  
Author(s):  
James Weber ◽  
Scott Archer-Nicholls ◽  
N. Luke Abraham ◽  
Youngsub M. Shin ◽  
Thomas Bannan ◽  
...  
Keyword(s):  
Peroxy Radical ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Atmospheric Composition ◽  
Radiation Budget ◽  
Alternative Mechanism ◽  
Mixing Ratios ◽  
The United Kingdom ◽  
Surface Mixing ◽  
Phase Chemistry

<p>We present the first incorporation and evaluation of the Common Representative Intermediates version 2.2 chemistry mechanism, CRI v2.2, for use in the United Kingdom Earth System Model (UKESM1). Tuned against the MCM v3.3.1, the CRI v2.2 mechanism builds on the previous CRI version, CRI v2.1, in UKESM1 (Archer-Nicholls et al., 2020) by updating isoprene chemistry and offers a more comprehensive description of tropospheric chemistry than the standard chemistry mechanism STRAT-TROP (ST).</p><p><span>CRI v2.2 adds state-of-the-art isoprene chemistry with the introduction of HO</span><sub><span>x</span></sub><span>-recycling via the isoprene peroxy radical isomerisation pathway, </span><span>making UKESM1 one of the first CMIP6 models to include this important chemistry. </span><span>HO</span><sub><span>x</span></sub><span>-recycling has noticeable effects on oxidants in regions with large emissions of biogenic volatile organic compounds (BVOCs). Low altitude OH in tropical forested regions increases by 75-150% relative to ST, reducing the existing model low bias compared to observations. Consequently, isoprene surface mixing ratios decrease considerably (25-40%), significantly improving the model high bias relative to ST. Methane lifetime decreases by 2% and tropospheric ozone burden increases by 4%. </span></p><p>Aerosol processes also differ between CRI v2.2 and ST, resulting in changes to the size and number distributions. Relative to ST, CRI v2.2 simulates an 8% decrease in the sulphate aerosol burden with 20% decreases in the nucleation and Aitken modes. By contrast, the secondary organic aerosol (SOA) nucleation mode burden increases by 11%. Globally, the average nucleation and Aitken mode aerosol number concentrations decrease by 20%.</p><p>The differences in aerosol and gas phase chemistry between CRI v2.2 and ST are likely to have impacts on the radiation budget. We plan to use CRI v2.2 and ST to investigate the influence that the chemical mechanism has on the simulated chemistry-climate feedbacks from BVOCs. In addition, CRI v2.2 will serve as the basis for the addition of a scheme describing the formation of highly oxygenated organic molecules (HOMs) from BVOCs, facilitating a semi-explicit mechanism for new particle formation from organic species.</p>

scholarly journals Assessment of Tropospheric Concentrations of NO2 from the TROPOMI/Sentinel-5 Precursor for the Estimation of Long-Term Exposure to Surface NO2 over South Korea

2021 ◽  
Vol 13 (10) ◽  
pp. 1877
Author(s):  
Ukkyo Jeong ◽  
Hyunkee Hong
Keyword(s):  
South Korea ◽  
Spatial Resolution ◽  
Atmospheric Composition ◽  
Mixing Ratio ◽  
Mean Values ◽  
Mixing Ratios ◽  
Tropospheric No2 ◽  
Korean Ministry ◽  
Surface Mixing ◽  
Rural Sites

Since April 2018, the TROPOspheric Monitoring Instrument (TROPOMI) has provided data on tropospheric NO2 column concentrations (CTROPOMI) with unprecedented spatial resolution. This study aims to assess the capability of TROPOMI to acquire high spatial resolution data regarding surface NO2 mixing ratios. In general, the instrument effectively detected major and moderate sources of NO2 over South Korea with a clear weekday–weekend distinction. We compared the CTROPOMI with surface NO2 mixing ratio measurements from an extensive ground-based network over South Korea operated by the Korean Ministry of Environment (SKME; more than 570 sites), for 2019. Spatiotemporally collocated CTROPOMI and SKME showed a moderate correlation (correlation coefficient, r = 0.67), whereas their annual mean values at each site showed a higher correlation (r = 0.84). The CTROPOMI and SKME were well correlated around the Seoul metropolitan area, where significant amounts of NO2 prevailed throughout the year, whereas they showed lower correlation at rural sites. We converted the tropospheric NO2 from TROPOMI to the surface mixing ratio (STROPOMI) using the EAC4 (ECMWF Atmospheric Composition Reanalysis 4) profile shape, for quantitative comparison with the SKME. The estimated STROPOMI generally underestimated the in-situ value obtained, SKME (slope = 0.64), as reported in previous studies.

scholarly journals Mainz Isoprene Mechanism 2 (MIM2): an isoprene oxidation mechanism for regional and global atmospheric modelling

2008 ◽  
Vol 8 (4) ◽  
pp. 14033-14085 ◽  
Author(s):  
D. Taraborrelli ◽  
M. G. Lawrence ◽  
T. M. Butler ◽  
R. Sander ◽  
J. Lelieveld
Keyword(s):  
Atmospheric Chemistry ◽  
Oxidation Mechanism ◽  
Tropospheric Chemistry ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Good Representation ◽  
Chemical Production ◽  
Global Models ◽  
Mixing Ratios ◽  
Isoprene Oxidation

Abstract. We present an oxidation mechanism of intermediate size for isoprene (2-methyl-1,3-butadiene) suitable for simulations in regional and global atmospheric chemistry models, which we call MIM2. It is a reduction of the corresponding detailed mechanism in the Master Chemical Mechanism (MCM v3.1) and intended as the second version of the well-established Mainz Isoprene Mechanism (MIM). Our aim is to improve the representation of tropospheric chemistry in regional and global models under all NOx regimes. We evaluate MIM2 and re-evaluate MIM through comparisons with MCM v3.1. We find that MIM and MIM2 compute similar O3, OH and isoprene mixing ratios. Unlike MIM, MIM2 produces small relative biases for NOx and organic nitrogen-containing species due to a good representation of the alkyl and peroxy acyl nitrates (RONO2 and RC(O)OONO2). Moreover, MIM2 computes only small relative biases with respect to hydrogen peroxide (H2O2), methyl peroxide (CH3OOH), methanol (CH3OH), formaldehyde (HCHO), peroxy acetyl nitrate (PAN), and formic and acetic acids (HCOOH and CH3C(O)OH), being always below ≈6% in all NOx scenarios studied. Most of the isoprene oxidation products are represented explicitly, including methyl vinyl ketone (MVK), methacrolein (MACR), hydroxyacetone and methyl glyoxal. MIM2 is mass-conserving with respect to carbon, including CO2 as well. Therefore, it is suitable for studies assessing carbon monoxide (CO) from biogenic sources, as well as for studies focused on the carbon cycle. Compared to MIM, MIM2 considers new species like acetaldehyde (CH3CHO), propene (CH2=CHCH3) and glyoxal (CHOCHO) with global chemical production rates for the year 2005 of 7.3, 9.5 and 33.8 Tg/yr, respectively. Our new mechanism is expected to substantially improve the results of atmospheric chemistry models by more accurately representing the interplay between atmospheric chemistry, transport and deposition, especially of nitrogen reservoir species. MIM2 allows regional and global models to easily incorporate new experimental results on the chemistry of organic species.

scholarly journals Effect of different emission inventories on modeled ozone and carbon monoxide in Southeast Asia

2014 ◽  
Vol 14 (23) ◽  
pp. 12983-13012 ◽  
Author(s):  
T. Amnuaylojaroen ◽  
M. C. Barth ◽  
L. K. Emmons ◽  
G. R. Carmichael ◽  
J. Kreasuwun ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Southeast Asia ◽  
Biomass Burning ◽  
Atmospheric Composition ◽  
Anthropogenic Emissions ◽  
Emission Inventories ◽  
Anthropogenic Emission ◽  
Regional Study ◽  
Mixing Ratios ◽  
Surface Mixing

Abstract. In order to improve our understanding of air quality in Southeast Asia, the anthropogenic emissions inventory must be well represented. In this work, we apply different anthropogenic emission inventories in the Weather Research and Forecasting Model with Chemistry (WRF-Chem) version 3.3 using Model for Ozone and Related Chemical Tracers (MOZART) gas-phase chemistry and Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) aerosols to examine the differences in predicted carbon monoxide (CO) and ozone (O3) surface mixing ratios for Southeast Asia in March and December 2008. The anthropogenic emission inventories include the Reanalysis of the TROpospheric chemical composition (RETRO), the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B), the MACCity emissions (adapted from the Monitoring Atmospheric Composition and Climate and megacity Zoom for the Environment projects), the Southeast Asia Composition, Cloud, Climate Coupling Regional Study (SEAC4RS) emissions, and a combination of MACCity and SEAC4RS emissions. Biomass-burning emissions are from the Fire Inventory from the National Center for Atmospheric Research (NCAR) (FINNv1) model. WRF-Chem reasonably predicts the 2 m temperature, 10 m wind, and precipitation. In general, surface CO is underpredicted by WRF-Chem while surface O3 is overpredicted. The NO2 tropospheric column predicted by WRF-Chem has the same magnitude as observations, but tends to underpredict the NO2 column over the equatorial ocean and near Indonesia. Simulations using different anthropogenic emissions produce only a slight variability of O3 and CO mixing ratios, while biomass-burning emissions add more variability. The different anthropogenic emissions differ by up to 30% in CO emissions, but O3 and CO mixing ratios averaged over the land areas of the model domain differ by ~4.5% and ~8%, respectively, among the simulations. Biomass-burning emissions create a substantial increase for both O3 and CO by ~29% and ~16%, respectively, when comparing the March biomass-burning period to the December period with low biomass-burning emissions. The simulations show that none of the anthropogenic emission inventories are better than the others for predicting O3 surface mixing ratios. However, the simulations with different anthropogenic emission inventories do differ in their predictions of CO surface mixing ratios producing variations of ~30% for March and 10–20% for December at Thai surface monitoring sites.

scholarly journals Description and evaluation of a detailed gas-phase chemistry scheme in the TM5-MP global chemistry transport model (r112)

2020 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Nikos Daskalakis ◽  
Angelos Gkouvousis ◽  
Andreas Hilboll ◽  
Twan van Noije ◽  
...  
Keyword(s):  
Gas Phase ◽  
Transport Model ◽  
Vertical Mixing ◽  
Three Dimensional ◽  
Chemical Mechanism ◽  
Aerosol Formation ◽  
Chemistry Transport Model ◽  
Mixing Ratios ◽  
Time Requirements ◽  
Phase Chemistry

Abstract. This work documents and evaluates the tropospheric gas-phase chemical mechanism MOGUNTIA in the three-dimensional chemistry transport model TM5-MP. Compared to the modified CB05 chemical mechanism previously used in the model, the MOGUNTIA includes a detailed representation of the light hydrocarbons (C1-C4) and isoprene, along with a simplified chemistry representation of terpenes and aromatics. Another feature implemented in TM5-MP for this work is the use of the Rosenbrock solver in the chemistry code, which can replace the classical Euler Backward Integration method of the model. Global budgets of ozone (O3), carbon monoxide (CO), hydroxyl radicals (OH), nitrogen oxides (NOX) and volatile organic compounds (VOCs) are here analyzed and their mixing ratios are compared with a series of surface, aircraft and satellite observations for the year 2006. Both mechanisms appear to be able to represent satisfactorily observed mixing ratios of important trace gases, with the MOGUNTIA chemistry configuration yielding lower biases compared to measurements in most of the cases. However, the two chemical mechanisms fail to reproduce the observed mixing ratios of light VOCs, indicating insufficient primary emission source strengths, too weak vertical mixing in the boundary layer, and/or a low bias in the secondary contribution of C2-C3 organics via VOC atmospheric oxidation. Relative computational memory and time requirements of the different model configurations are also compared and discussed. Overall, compared to other chemistry schemes in use in global CTMs, the MOGUNTIA scheme simulates a large suite of oxygenated VOCs that are observed in the atmosphere at significant levels and are involved in aerosol formation, expanding, thus, the applications of TM5-MP.

Impacts of monocyclic aromatics on regional and global tropospheric gas-phase chemistry

2020 ◽  
Author(s):  
Rolf Sander ◽  
David Cabrera-Perez ◽  
Sara Bacer ◽  
Sergey Gromov ◽  
Jos Lelieveld ◽  
...  
Keyword(s):  
East Asia ◽  
Gas Phase ◽  
Aromatic Compounds ◽  
General Circulation ◽  
Regional Scale ◽  
Circulation Model ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

<p>Aromatic compounds in the troposphere are reactive towards ozone<br>(O<sub>3</sub>), hydroxyl (OH) and other radicals. Here we present an<br>assessment of their impacts on the gas-phase chemistry, using the<br>general circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry). The<br>monocyclic aromatics considered in this study comprise benzene, toluene,<br>xylenes, phenol, styrene, ethylbenzene, trimethylbenzenes, benzaldehyde<br>and lumped higher aromatics bearing more than 9 C atoms. On a global<br>scale, the estimated net changes are minor when aromatic compounds are<br>included in the chemical mechanism of our model. For instance, the<br>tropospheric burden of CO increases by about 6 %, and those of OH,<br>O<sub>3</sub>, and NO<sub>x</sub> (NO + NO<sub>2</sub>) decrease between<br>2 % and 14 %. The global mean changes are small partially because of<br>compensating effects between high- and low-NO<sub>x</sub> regions. The<br>largest change is predicted for glyoxal, which increases globally by 36<br>%. Significant regional changes are identified for several species. For<br>instance, glyoxal increases by 130 % in Europe and 260 % in East Asia,<br>respectively. Large increases in HCHO are also predicted in these<br>regions. In general, the influence of aromatics is particularly evident<br>in areas with high concentrations of NO<sub>x</sub>, with increases up<br>to 12 % in O<sub>3</sub> and 17 % in OH. Although the global impact of<br>aromatics is limited, our results indicate that aromatics can strongly<br>influence tropospheric chemistry on a regional scale, most significantly<br>in East Asia.</p>

scholarly journals Missing peroxy radical sources within a summertime ponderosa pine forest

2014 ◽  
Vol 14 (9) ◽  
pp. 4715-4732 ◽  
Author(s):  
G. M. Wolfe ◽  
C. Cantrell ◽  
S. Kim ◽  
R. L. Mauldin III ◽  
T. Karl ◽  
...  
Keyword(s):  
Ponderosa Pine ◽  
Forest Canopy ◽  
Strong Dependence ◽  
Rocky Mountain ◽  
Peroxy Radical ◽  
Pine Forest ◽  
Chemical Mechanism ◽  
Peroxy Radicals ◽  
Mixing Ratios ◽  
Ponderosa Pine Forest

Abstract. Organic peroxy (RO2) and hydroperoxy (HO2) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Since primary reaction partners for peroxy radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min−1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.

scholarly journals Sensitivity of tropospheric chemical composition to halogen-radical chemistry using a fully coupled size-resolved multiphase chemistry–global climate system: halogen distributions, aerosol composition, and sensitivity of climate-relevant gases

2014 ◽  
Vol 14 (7) ◽  
pp. 3397-3425 ◽  
Author(s):  
M. S. Long ◽  
W. C. Keene ◽  
R. C. Easter ◽  
R. Sander ◽  
X. Liu ◽  
...  
Keyword(s):  
Global Climate ◽  
Global Climate Model ◽  
Sea Salt ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Marine Aerosol ◽  
Aerosol Composition ◽  
Model Calculations ◽  
Mixing Ratios ◽  
Halogen Chemistry

Abstract. Observations and model calculations indicate that highly non-linear multiphase atmospheric processes involving inorganic Cl and Br significantly impact tropospheric chemistry and composition, aerosol evolution, and radiative transfer. The sensitivity of global atmospheric chemistry to the production of marine aerosol and the associated activation and cycling of inorganic Cl and Br was investigated using a size-resolved multiphase coupled chemistry–global climate model (National Center for Atmospheric Research's Community Atmosphere Model (CAM) v3.6.33). Simulated results revealed strong meridional and vertical gradients in Cl and Br species. They also point to possible physicochemical mechanisms that may account for several previously unexplained phenomena, including the enrichment of Br- in submicron aerosol and the presence of a BrO maximum in the polar free troposphere. However, simulated total volatile inorganic Br mixing ratios in the troposphere were generally higher than observed, due in part to the overly efficient net production of BrCl. In addition, the emission scheme for marine aerosol and associated Br−, which is the only source for Br in the model, overestimates emission fluxes from the high-latitude Southern Ocean. Br in the stratosphere was lower than observed due to the lack of long-lived precursor organobromine species in the simulation. Comparing simulations using chemical mechanisms with and without reactive Cl and Br species demonstrates a significant temporal and spatial sensitivity of primary atmospheric oxidants (O3, HOx, NOx), CH4, non-methane hydrocarbons (NMHCs), and dimethyl sulfide (DMS) to halogen cycling. Globally, halogen chemistry had relatively less impact on SO2 and non-sea-salt (nss) SO42− although significant regional differences were evident. Although variable geographically, much of this sensitivity is attributable to either over-vigorous activation of Br (primarily BrCl) via the chemical mechanism or overproduction of sea-salt aerosol simulated under higher-wind regimes. In regions where simulated mixing ratios of reactive Br and Cl fell within observed ranges, though, halogen chemistry drove large changes in oxidant fields and associated chemical processes relative to simulations with no halogens. However, the overall simulated impacts of Br chemistry globally are overestimated and thus caution is warranted in their interpretation.

scholarly journals Improvements to the representation of BVOC chemistry–climate interactions in UKCA (v11.5) with the CRI-Strat 2 mechanism: incorporation and evaluation

2021 ◽  
Vol 14 (8) ◽  
pp. 5239-5268
Author(s):  
James Weber ◽  
Scott Archer-Nicholls ◽  
Nathan Luke Abraham ◽  
Youngsub M. Shin ◽  
Thomas J. Bannan ◽  
...  
Keyword(s):  
United Kingdom ◽  
Rate Constants ◽  
Inorganic Nitrogen ◽  
Peroxy Radical ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Aerosol Formation ◽  
Reaction Rate Constants ◽  
Climate Interactions ◽  
The Impact

Abstract. We present the first incorporation of the Common Representative Intermediates version 2.2 tropospheric chemistry mechanism, CRI v2.2, combined with stratospheric chemistry, into the global chemistry–climate United Kingdom Chemistry and Aerosols (UKCA) model to give the CRI-Strat 2 mechanism. A rigorous comparison of CRI-Strat 2 with the earlier version, CRI-Strat, is performed in UKCA in addition to an evaluation of three mechanisms, CRI-Strat 2, CRI-Strat and the standard UKCA chemical mechanism, StratTrop v1.0, against a wide array of surface and airborne chemical data. CRI-Strat 2 comprises a state-of-the-art isoprene scheme, optimized against the Master Chemical Mechanism v3.3.1, which includes isoprene peroxy radical isomerization, HOx recycling through the addition of photolabile hydroperoxy aldehydes (HPALDs), and isoprene epoxy diol (IEPOX) formation. CRI-Strat 2 also features updates to several rate constants for the inorganic chemistry, including the reactions of inorganic nitrogen and O(1D). The update to the isoprene chemistry in CRI-Strat 2 increases OH over the lowest 500 m in tropical forested regions by 30 %–50 % relative to CRI-Strat, leading to an improvement in model–observation comparisons for surface OH and isoprene relative to CRI-Strat and StratTrop. Enhanced oxidants also cause a 25 % reduction in isoprene burden and an increase in oxidation fluxes of isoprene and other biogenic volatile organic compounds (BVOCs) at low altitudes with likely impacts on subsequent aerosol formation, atmospheric lifetime, and climate. By contrast, updates to the rate constants of O(1D) with its main reactants relative to CRI-Strat reduces OH in much of the free troposphere, producing a 2 % increase in the methane lifetime, and increases the tropospheric ozone burden by 8 %, primarily from reduced loss via O(1D)+H2O. The changes to inorganic nitrogen reaction rate constants increase the NOx burden by 4 % and shift the distribution of nitrated species closer to that simulated by StratTrop. CRI-Strat 2 is suitable for multi-decadal model integrations and the improved representation of isoprene chemistry provides an opportunity to explore the consequences of HOx recycling in the United Kingdom Earth System Model (UKESM1). This new mechanism will enable a re-evaluation of the impact of BVOCs on the chemical composition of the atmosphere and further probe the feedback between the biosphere and the climate.

scholarly journals Investigation of the <i>α</i>-pinene photooxidation by OH in the atmospheric simulation chamber SAPHIR

2019 ◽  
Vol 19 (18) ◽  
pp. 11635-11649
Author(s):  
Michael Rolletter ◽  
Martin Kaminski ◽  
Ismail-Hakki Acir ◽  
Birger Bohn ◽  
Hans-Peter Dorn ◽  
...  
Keyword(s):  
Time Series ◽  
Oxidation Mechanism ◽  
Peroxy Radical ◽  
Chemical Oxidation ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Model Calculations ◽  
Mixing Ratios ◽  
Measured Time ◽  
Simulation Chamber

Abstract. The photooxidation of the most abundant monoterpene, α-pinene, by the hydroxyl radical (OH) was investigated at atmospheric concentrations in the atmospheric simulation chamber SAPHIR. Concentrations of nitric oxide (NO) were below 120 pptv. Yields of organic oxidation products are determined from measured time series giving values of 0.11±0.05, 0.19±0.06, and 0.05±0.03 for formaldehyde, acetone, and pinonaldehyde, respectively. The pinonaldehyde yield is at the low side of yields measured in previous laboratory studies, ranging from 0.06 to 0.87. These studies were mostly performed at reactant concentrations much higher than observed in the atmosphere. Time series of measured radical and trace-gas concentrations are compared to results from model calculations applying the Master Chemical Mechanism (MCM) 3.3.1. The model predicts pinonaldehyde mixing ratios that are at least a factor of 4 higher than measured values. At the same time, modeled hydroxyl and hydroperoxy (HO2) radical concentrations are approximately 25 % lower than measured values. Vereecken et al. (2007) suggested a shift of the initial organic peroxy radical (RO2) distribution towards RO2 species that do not yield pinonaldehyde but produce other organic products. Implementing these modifications reduces the model–measurement gap of pinonaldehyde by 20 % and also improves the agreement in modeled and measured radical concentrations by 10 %. However, the chemical oxidation mechanism needs further adjustment to explain observed radical and pinonaldehyde concentrations. This could be achieved by adjusting the initial RO2 distribution, but could also be done by implementing alternative reaction channels of RO2 species that currently lead to the formation of pinonaldehyde in the model.

scholarly journals Elevated levels of OH observed in haze events during wintertime in central Beijing

2020 ◽  
Author(s):  
Eloise J. Slater ◽  
Lisa K. Whalley ◽  
Robert Woodward-Massey ◽  
Chunxiang Ye ◽  
James D. Lee ◽  
...  
Keyword(s):  
Gas Phase ◽  
Chemical Mechanism ◽  
Daily Maximum ◽  
Mixing Ratios ◽  
Gas Phase Chemistry ◽  
Photolysis Rates ◽  
Secondary Pollutants ◽  
High Pollution ◽  
Phase Chemistry

Abstract. Wintertime in situ measurements of OH, HO2 and RO2 radicals and OH reactivity were made in central Beijing during November and December 2016. Exceptionally elevated NO was observed on occasions, up to ~ 250 ppbv, believed to be the highest mole fraction for which there have then co-located radical observations. The daily maximum mixing ratios for radical species varied significantly day-to-day over the range 1–8 × 106 cm−3 (OH), 0.2–1.5 × 108 cm−3 (HO2) and 0.3–2.5 × 108 cm−3 (RO2). Averaged over the full observation period, the mean daytime peak in radicals was 2.7 × 106 cm−3, 0.39 × 108 cm−3 and 0.88 × 108 cm−3 for OH, HO2 and total RO2, respectively. The main daytime source of new radicals via initiation processes (primary production) was the photolysis of HONO (~ 83 %), and the dominant termination pathways were the reactions of OH with NO and NO2, particularly under polluted, haze conditions. The Master Chemical Mechanism (MCM) v3.3.1 operating within a box model was used to simulate the concentrations of OH, HO2 and RO2. The model underpredicted OH, HO2 and RO2, especially when NO mixing ratios were high (above 6 ppbv). The observation-to-model ratio of OH, HO2 and RO2 increased from ~ 1 (for all radicals) at 3 ppbv of NO to a factor of ~ 3, ~ 20 and ~ 91 for OH, HO2 and RO2, respectively, at ~ 200 ppbv of NO. The significant underprediction of radical concentrations by the MCM suggests a deficiency in the representation of gas-phase chemistry at high NOx. The OH concentrations were surprisingly similar (within 20 % during the day) inside and outside of haze events, despite j(O1D) decreasing by 50 % during haze periods. These observations provide strong evidence that gas-phase oxidation by OH can continue to generate secondary pollutants even under high pollution episodes, despite the reduction in photolysis rates within haze.

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