Development and chamber evaluation of the MCM v3.2 degradation scheme for β-caryophyllene

Abstract. A degradation mechanism for β-caryophyllene has recently been released as part of version 3.2 of the Master Chemical Mechanism (MCM v3.2), describing the gas phase oxidation initiated by reaction with ozone, OH radicals and NO3 radicals. A detailed overview of the construction methodology is given, within the context of reported experimental and theoretical mechanistic appraisals. The performance of the mechanism has been evaluated in chamber simulations in which the gas phase chemistry was coupled to a representation of the gas-to-aerosol partitioning of 280 multi-functional oxidation products. This evaluation exercise considered data from a number of chamber studies of either the ozonolysis of β-caryophyllene, or the photo-oxidation of β-caryophyllene/NOx mixtures, in which detailed product distributions have been reported. This includes the results of a series of photo-oxidation experiments performed in the University of Manchester aerosol chamber, also reported here, in which a comprehensive characterization of the temporal evolution of the organic product distribution in the gas phase was carried out, using Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), in conjunction with measurements of NOx, O3 and SOA mass loading. The CIR-TOF-MS measurements allowed approximately 45 time-resolved product ion signals to be detected, which were assigned on the basis of the simulated temporal profiles of the more abundant MCM v3.2 species, and their probable fragmentation patterns. The evaluation studies demonstrate that the MCM v3.2 mechanism provides an acceptable description of β-caryophyllene degradation under the chamber conditions considered, with the temporal evolution of the observables identified above generally being recreated within the uncertainty bounds of key parameters within the mechanism. The studies have highlighted a number of areas of uncertainty or discrepancy, where further investigation would be valuable to help interpret the results of chamber studies and improve detailed mechanistic understanding. These particularly include: (i) quantification of the yield and stability of the secondary ozonide (denoted BCSOZ in MCM v3.2), formed from β-caryophyllene ozonolysis, and elucidation of the details of its further oxidation, including whether the products retain the "ozonide" functionality; (ii) investigation of the impact of NOx on the β-caryophyllene ozonolysis mechanism, in particular its effect on the formation of β-caryophyllinic acid (denoted C137CO2H in MCM v3.2), and elucidation of its formation mechanism; (iii) routine independent identification of β-caryophyllinic acid, and its potentially significant isomer β-nocaryophyllonic acid (denoted C131CO2H in MCM v3.2); (iv) more precise quantification of the primary yield of OH (and other radicals) from β-caryophyllene ozonolysis; (v) quantification of the yields of the first-generation hydroxy nitrates (denoted BCANO3, BCBNO3 and BCCNO3 in MCM v3.2) from the OH-initiated chemistry in the presence of NOx; and (vi) further studies in general to improve the identification and quantification of products formed from both ozonolysis and photo-oxidation, including confirmation of the simulated formation of multifunctional species containing hydroperoxide groups, and their important contribution to SOA under NOx-free conditions.

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Development and chamber evaluation of the MCM v3.2 degradation scheme for β-caryophyllene

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-2891-2012 ◽

2012 ◽

Vol 12 (1) ◽

pp. 2891-2974 ◽

Cited By ~ 1

Author(s):

M. E. Jenkin ◽

K. P. Wyche ◽

C. J. Evans ◽

T. Carr ◽

P. S. Monks ◽

...

Keyword(s):

Gas Phase ◽

Degradation Mechanism ◽

Oxidation Products ◽

Chemical Mechanism ◽

Oh Radicals ◽

Photo Oxidation ◽

Primary Yield ◽

Chamber Studies ◽

The Impact ◽

Tof Ms

Abstract. A degradation mechanism for β-caryophyllene has recently been released as part of version 3.2 of the Master Chemical Mechanism (MCM v3.2), describing the gas phase oxidation initiated by reaction with ozone, OH radicals and NO3 radicals. A detailed overview of the construction methodology is given, within the context of reported experimental and theoretical mechanistic appraisals. The performance of the mechanism has been evaluated in chamber simulations in which the gas phase chemistry was coupled to a representation of the gas-to-aerosol partitioning of 280 multi-functional oxidation products. This evaluation exercise considered data from a number of chamber studies of either the ozonolysis of β-caryophyllene, or the photo-oxidation of β-caryophyllene/NOx mixtures, in which detailed product distributions have been reported. This includes the results of a series of photo-oxidation experiments performed in the University of Manchester aerosol chamber, also reported here, in which a comprehensive characterization of the temporal evolution of the organic product distribution in the gas phase was carried out, using Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), in conjunction with measurements of NOx, O3 and SOA mass loading. The CIR-TOF-MS measurements allowed approximately 45 time-resolved product ion signals to be detected, which were assigned on the basis of the simulated temporal profiles of the more abundant MCM v3.2 species, and their probable fragmentation patterns. The evaluation studies demonstrate that the MCM v3.2 mechanism provides a generally acceptable description of β-caryophyllene degradation, under the chamber conditions considered, and a reliable basis for simulations where a representation of chemical detail is required. The studies have also highlighted a number of areas of uncertainty, where further investigation would be valuable to help interpret the results of chamber studies and improve detailed mechanistic understanding. These particularly include: (i) quantification of the yield and stability of the secondary ozonide (denoted BCSOZ in MCM v3.2), formed from β-caryophyllene ozonolysis, and elucidation of the details of its further oxidation, including whether the products retain the "ozonide" functionality; (ii) investigation of the impact of NOx on the β-caryophyllene ozonolysis mechanism, in particular its effect on the formation of β-caryophyllinic acid (denoted C137CO2H in MCM v3.2), and elucidation of its formation mechanism; (iii) routine independent identification of β-caryophyllinic acid, and its potentially significant isomer β-nocaryophyllonic acid (denoted C131CO2H in MCM v3.2); (iv) more precise quantification of the primary yield of OH (and other radicals) from β-caryophyllene ozonolysis; (v) quantification of the yields of the first-generation hydroxy nitrates (denoted BCANO3, BCBNO3 and BCCNO3 in MCM v3.2) from the OH-initiated chemistry in the presence of NOx; and (vi) further studies in general to improve the identification and quantification of products formed from both ozonolysis and photo-oxidation, including confirmation of the simulated formation of multifunctional species containing hydroperoxide groups, and their important contribution to SOA under NOx-free conditions.

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Evaluation of 1,3,5 trimethylbenzene degradation in the detailed tropospheric chemistry mechanism, MCMv3.1, using environmental chamber data

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-6453-2008 ◽

2008 ◽

Vol 8 (21) ◽

pp. 6453-6468 ◽

Cited By ~ 39

Author(s):

A. Metzger ◽

J. Dommen ◽

K. Gaeggeler ◽

J. Duplissy ◽

A. S. H. Prevot ◽

...

Keyword(s):

Degradation Mechanism ◽

Reactive Systems ◽

Tropospheric Chemistry ◽

Chemical Mechanism ◽

Oh Radicals ◽

Environmental Chamber ◽

Photo Oxidation ◽

Trimethyl Benzene ◽

Using Data ◽

Paul Scherrer

Abstract. The degradation mechanism of 1,3,5-trimethyl- benzene (TMB) as implemented in the Master Chemical Mechanism version 3.1 (MCM) was evaluated using data from the environmental chamber at the Paul Scherrer Institute. The results show that the MCM provides a consistent description of the photo-oxidation of TMB/NOx mixtures for a range of conditions. In all cases the agreement between the measurement and the simulation decreases with decreasing VOC-NOx ratio and in addition with increasing precursor concentration. A significant underestimation of the decay rate of TMB and thus underestimation of reactivity in the system, consistent with results from previous appraisals of the MCM, was observed. Much higher nitrous acid (HONO) concentrations compared to simulations and expected from chamber characterization experiments were measured during these smog chamber experiments. A light induced NO2 to HONO conversion at the chamber walls is suggested to occur. This photo-enhanced NO2 to HONO conversion with subsequent HONO photolysis enhances the reactivity of the system. After the implementation of this reaction in the model it describes the decay of TMB properly. Nevertheless, the model still over-predicts ozone at a later stage of the experiment. This can be attributed to a too slow removal of NO2. It is also shown that this photo-enhanced HONO formation is not restricted to TMB photo-oxidation but also occurs in other chemical systems (e.g. α-pinene). However, the influence of HONO as a source of OH radicals is less important in these more reactive systems and therefore the importance of the HONO chemistry is less obvious.

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Evaluation of 1,3,5 trimethylbenzene degradation in the detailed tropospheric chemistry mechanism, MCMv3.1, using environmental chamber data

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-11567-2008 ◽

2008 ◽

Vol 8 (3) ◽

pp. 11567-11607 ◽

Cited By ~ 2

Author(s):

A. Metzger ◽

J. Dommen ◽

K. Gaeggeler ◽

J. Duplissy ◽

A. S. H. Prevot ◽

...

Keyword(s):

Degradation Mechanism ◽

Reactive Systems ◽

Tropospheric Chemistry ◽

Chemical Mechanism ◽

Oh Radicals ◽

Environmental Chamber ◽

Chemical Systems ◽

Photo Oxidation ◽

Using Data ◽

Paul Scherrer

Abstract. The degradation mechanism of 1,3,5-trimethylbenzene (TMB) as implemented in the Master Chemical Mechanism version 3.1 (MCM) was evaluated using data from the environmental chamber at the Paul Scherrer Institute. The results show that the MCM provides a consistent description of the photo-oxidation of TMB/NOx mixtures for a range of conditions. In all cases the agreement between the measurement and the simulation decreases with decreasing VOC-NOx ratio and in addition with increasing precursor concentration. A significant underestimation of the decay rate of TMB and thus underestimation of reactivity in the system, consistent with results from previous appraisals of the MCM, was observed. Much higher nitrous acid (HONO) concentrations compared to simulations and expected from chamber characterization experiments were measured during these smog chamber experiments. A light induced NO2 to HONO conversion at the chamber walls is suggested to occur. This photo-enhanced NO2 to HONO conversion with subsequent HONO photolysis enhances the reactivity of the system. After the implementation of this reaction in the model it describes the decay of TMB properly. Nevertheless, the model still over-predicts ozone at a later stage of the experiment. This can be attributed to a too slow removal of NO2. It is also shown that this photo-enhanced HONO formation is not restricted to TMB photo-oxidation but also occurs in other chemical systems (e.g. α-pinene). However, the influence of HONO as a source of OH radicals is less important in these more reactive systems and therefore the importance of the HONO chemistry is less obvious.

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Gaseous chemistry and aerosol mechanism developments for version 3.5.1 of the online regional model, WRF-Chem

Geoscientific Model Development ◽

10.5194/gmd-7-2557-2014 ◽

2014 ◽

Vol 7 (6) ◽

pp. 2557-2579 ◽

Cited By ~ 30

Author(s):

S. Archer-Nicholls ◽

D. Lowe ◽

S. Utembe ◽

J. Allan ◽

R. A. Zaveri ◽

...

Keyword(s):

Gas Phase ◽

Chemical Mechanism ◽

Reduced Form ◽

Sea Spray ◽

Wind Fields ◽

Aerosol Composition ◽

Aerosol Emission ◽

Sea Spray Aerosol ◽

The Impact ◽

Phase Chemical

Abstract. We have made a number of developments to the Weather, Research and Forecasting model coupled with Chemistry (WRF-Chem), with the aim of improving model prediction of trace atmospheric gas-phase chemical and aerosol composition, and of interactions between air quality and weather. A reduced form of the Common Reactive Intermediates gas-phase chemical mechanism (CRIv2-R5) has been added, using the Kinetic Pre-Processor (KPP) interface, to enable more explicit simulation of VOC degradation. N2O5 heterogeneous chemistry has been added to the existing sectional MOSAIC aerosol module, and coupled to both the CRIv2-R5 and existing CBM-Z gas-phase schemes. Modifications have also been made to the sea-spray aerosol emission representation, allowing the inclusion of primary organic material in sea-spray aerosol. We have worked on the European domain, with a particular focus on making the model suitable for the study of nighttime chemistry and oxidation by the nitrate radical in the UK atmosphere. Driven by appropriate emissions, wind fields and chemical boundary conditions, implementation of the different developments are illustrated, using a modified version of WRF-Chem 3.4.1, in order to demonstrate the impact that these changes have in the Northwest European domain. These developments are publicly available in WRF-Chem from version 3.5.1 onwards.

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The MCM v3.3 degradation scheme for isoprene

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-9709-2015 ◽

2015 ◽

Vol 15 (6) ◽

pp. 9709-9766 ◽

Cited By ~ 18

Author(s):

M. E. Jenkin ◽

J. C. Young ◽

A. R. Rickard

Keyword(s):

Boundary Layer ◽

Free Radical ◽

Degradation Mechanism ◽

Closed Shell ◽

Chemical Mechanism ◽

Formation Mechanisms ◽

Oh Radicals ◽

Atmospheric Conditions ◽

Radical Species ◽

Master Chemical Mechanism

Abstract. The chemistry of isoprene degradation in the Master Chemical Mechanism (MCM) has been systematically refined and updated to reflect recent advances in understanding, with these updates appearing in the latest version, MCM v3.3. The complete isoprene degradation mechanism in MCM v3.3 consists of 1935 reactions of 605 closed shell and free radical species, which treat the chemistry initiated by reaction with OH radicals, NO3 radicals and ozone (O3). A detailed overview of the updates is provided, within the context of reported kinetic and mechanistic information. The revisions mainly relate to the OH-initiated chemistry, which tends to dominate under atmospheric conditions, although these include updates to the chemistry of some products that are also generated from the O3 - and NO3-initiated oxidation. The revisions have impacts in a number of key areas, including HOx recycling, NOx recycling and the formation of species reported to play a role in SOA-formation mechanisms. The performance of the MCM v3.3 isoprene mechanism has been compared with those of earlier versions (MCM v3.1 and MCM v3.2) over a range of relevant conditions, using a box model of the tropical forested boundary layer. The results of these calculations are presented and discussed, and are used to illustrate the impacts of the mechanistic updates in MCM v3.3.

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Influence of relative humidity and temperature on the production of pinonaldehyde and OH radicals from the ozonolysis of α-pinene

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-7057-2010 ◽

2010 ◽

Vol 10 (15) ◽

pp. 7057-7072 ◽

Cited By ~ 40

Author(s):

R. Tillmann ◽

M. Hallquist ◽

Å. M. Jonsson ◽

A. Kiendler-Scharr ◽

H. Saathoff ◽

...

Keyword(s):

Gas Phase ◽

Degradation Mechanism ◽

Product Distribution ◽

Major Product ◽

Radical Formation ◽

Oh Radicals ◽

Oh Radical ◽

Significant Difference ◽

Dry Conditions

Abstract. The ozonolysis of α-pinene has been investigated under dry and humid conditions in the temperature range of 243–303 K. The results provided new insight into the role of water and temperature in the degradation mechanism of α-pinene and in the formation of secondary organic aerosols (SOA). The SOA yields were higher at humid conditions than at dry conditions. The water induced gain was largest for the lowest temperatures investigated (243 and 253 K). The increase in the SOA yields was dominated by water (and temperature) effects on the organic product distribution, whilst physical uptake of water was negligible. This will be demonstrated for the example of pinonaldehyde (PA) which was formed as a major product in the humid experiments with total molar yields of 0.30±0.06 at 303 K and 0.15±0.03 at 243 K. In the dry experiments the molar yields of PA were only 0.07±0.02 at 303 K and 0.02±0.02 at 253 K. The observed partitioning of PA as a function of the SOA mass present at 303 K limited the effective vapour pressure of pure PA pPA0 to the range of 0.01–0.001 Pa, 3–4 orders of magnitude lower than literature values. The corresponding mass partitioning coefficient was determined to KPA=0.005±0.004 m3 μg−1 and the total mass yield αPAtotal=0.37±0.08. At 303 K PA preferably stayed in the gas-phase, whereas at 253 K and 243 K it exclusively partitioned into the particulate phase. PA could thus account at least for half of the water induced gain in SOA mass at 253 K. The corresponding effect was negligible at 303 K because the PA preferably remained in the gas-phase. The yield of OH radicals, which were produced in the ozonolysis, was indirectly determined by means of the yield of cyclohexanone formed in the reaction of OH radicals with cyclohexane. OH yields of the α-pinene ozonolysis were determined to 0.67±0.17 for humid and 0.54±0.13 for dry conditions at 303 K, indicating a water dependent path of OH radical formation. For 253 and 243 K OH yields could be estimated to 0.5 with no significant difference between the dry and humid experiments. This is the first clear indication for OH radical formation by α-pinene ozonolysis at such low temperatures.

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Evaluation of the daytime tropospheric loss of 2-methylbutanal

10.5194/acp-2021-758 ◽

2021 ◽

Author(s):

María Asensio ◽

María Antiñolo ◽

Sergio Blázquez ◽

José Albaladejo ◽

Elena Jiménez

Keyword(s):

Mass Spectrometry ◽

Gas Phase ◽

Degradation Products ◽

Rate Coefficients ◽

Oh Radicals ◽

Phase Reaction ◽

Gaseous Products ◽

Flight Mass Spectrometry ◽

Atmospheric Degradation ◽

The Impact

Abstract. Saturated aldehydes, e.g. 2-methylbutanal (2MB, CH3CH2CH(CH3)C(O)H), are emitted into the atmosphere by several biogenic sources. The first step in the daytime atmospheric degradation of 2MB involves gas-phase reactions initiated by hydroxyl (OH) radicals, chlorine (Cl) atoms and/or sunlight. In this work, we report the rate coefficients for the gas-phase reaction of 2MB with OH (kOH) and Cl (kCl) together with the photolysis rate coefficient (J) in the ultraviolet solar actinic region in Valencia (Spain) at different times of the day. The temperature dependence of kOH was described in the 263–353 K range by the following Arrhenius expression: kOH(T)=(8.88±0.41)×10-12 exp[(331±14)/T] cm3 molecule-1 s-1. At 298 K, the reported kOH and kCl are (2.68±0.07)×10-11 cm3 molecule-1 s-1 and (2.16±0.16)×10-11 cm3 molecule-1 s-1. Identification and quantification of the gaseous products of the Cl-reaction and those from the photodissociation of 2MB were carried out in a smog chamber by different techniques (Fourier transform infrared spectroscopy, proton transfer time-of-flight mass spectrometry, and gas chromatography coupled to mass spectrometry). The formation and size distribution of secondary organic aerosols formed in the Cl-reaction was monitored by a fast mobility particle sizer spectrometer. A discussion on the relative importance of the first step in the daytime atmospheric degradation of 2MB is presented together with the impact of the degradation products in marine atmospheres.

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Gas-phase O3 reaction of dimethyl phthalate and diethylphthalate: a kinetic and product study

10.5194/egusphere-egu21-10814 ◽

2021 ◽

Author(s):

María Antiñolo ◽

María Teresa Baeza ◽

Elena Jiménez ◽

José Albaladejo

Keyword(s):

Gas Phase ◽

Indoor Air ◽

Chemical Species ◽

Decay Rates ◽

Phase Reaction ◽

Dimethyl Phthalate ◽

Living Organisms ◽

Particle Sizer ◽

The Impact ◽

Tof Ms

Phthalates are chemical species widely used as plasticisers that are known to be absorbed by living organisms and negatively affect their health. Phthalates have been detected mostly indoors. For example, they have been measured in the gas phase, as part of particulate matter and on different surfaces in the form of dust.1-4 Although their presence in this kind of environments is well known and widely documented, there are scarce studies on their behaviour when they are in contact with tropospheric oxidants such as ozone (O3) or hydroxyl radicals.5-7The aim of this work is to measure, for the first time, the kinetics of the gas-phase reaction of O3 with two phthalates: dimethyl phthalate (DMP) and diethyl phthalate (DEP). In a smog chamber at room temperature and atmospheric pressure, decay rates of DMF or DEF are measured by a Proton Transfer-Time of Flight-Mass Spectrometer (PTR-ToF-MS), while the O3 concentration is determined by Fourier Transform Infrared (FTIR) spectroscopy. Gas-phase products are also monitored by PTR-ToF-MS and secondary organic aerosol (SOA) formation is also evaluated by a Fast Mobility Particle Sizer. The impact on the indoor air quality of DMP and DEP will be discussed considering their atmospheric lifetime and the generated products.REFERENCES: 1. Bornehag, C.G.; Lundgren, B.; Weschler, C. J.; Sigsgaard, T.; Hagerhed-Engman, L.; Sundell, J. Environ. Health Perspect. 2005, 113, 1399-404; 2. Rudel, R. A.; Perovich, L. J. Atmos. Environ. 2009, 43, 170&#8209;181; 3. Fromme, H.; Lahrz, T.; Piloty, M.; Gebhart, H.; Oddoy, A.; R&#252;den, H. Indoor Air 2004, 14, 188-195; 4. Larsson, K.; Lindh, C. H.; J&#246;nsson, B.A.; Giovanoulis, G.; Bibi, M.; Bottai, M.; Bergstr&#246;m, A.; Berglung, M. Environ. Int. 2017, 102, 114-124; 5. Mansouri, L.; Mohammed, H.; Tizaoui, C.; Bousselmi, L. Desalination Water Treat. 2013, 51, 6698-6710; 6. Mohan, S.; Mamane, H.; Avisar, D.; Gozlan, I.; Kaplan, A.; Dayalan, G. Materials 2019, 12, 4119 (3); 7. Due&#241;as Moreno, J.; Rodr&#237;guez S, J.L.; Poznyak, T.; Chairez, I.; Dorantes-Rosales, H.J. J. Environ. Manage. 2020, 270, 110863 (7).

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The MCM v3.3.1 degradation scheme for isoprene

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-11433-2015 ◽

2015 ◽

Vol 15 (20) ◽

pp. 11433-11459 ◽

Cited By ~ 143

Author(s):

M. E. Jenkin ◽

J. C. Young ◽

A. R. Rickard

Keyword(s):

Degradation Mechanism ◽

Closed Shell ◽

Organic Aerosol ◽

Chemical Mechanism ◽

Formation Mechanisms ◽

Oh Radicals ◽

Atmospheric Conditions ◽

Aerosol Formation ◽

Radical Species ◽

Master Chemical Mechanism

Abstract. The chemistry of isoprene degradation in the Master Chemical Mechanism (MCM) has been systematically refined and updated to reflect recent advances in understanding, with these updates appearing in the latest version, MCM v3.3.1. The complete isoprene degradation mechanism in MCM v3.3.1 consists of 1926 reactions of 602 closed shell and free radical species, which treat the chemistry initiated by reaction with OH radicals, NO3 radicals and ozone (O3). A detailed overview of the updates is provided, within the context of reported kinetic and mechanistic information. The revisions mainly relate to the OH-initiated chemistry, which tends to dominate under atmospheric conditions, although these include updates to the chemistry of some products that are also generated from the O3- and NO3-initiated oxidation. The revisions have impacts in a number of key areas, including HOx recycling, NOx recycling and the formation of species reported to play a role in SOA (secondary organic aerosol)-formation mechanisms. The performance of the MCM v3.3.1 isoprene mechanism has been compared with those of earlier versions (MCM v3.1 and MCM v3.2) over a range of relevant conditions, using a box model of the tropical forested boundary layer. The results of these calculations are presented and discussed and are used to illustrate the impacts of the mechanistic updates in MCM v3.3.1.

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Comparison of tropospheric gas-phase chemistry schemes for use within global models

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-1831-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 1831-1845 ◽

Cited By ~ 108

Author(s):

K. M. Emmerson ◽

M. J. Evans

Keyword(s):

Gas Phase ◽

Transport Model ◽

Regional Scale ◽

Tropospheric Chemistry ◽

Chemical Mechanism ◽

Model Framework ◽

Transport Models ◽

Global Models ◽

Calculated Concentration ◽

The Impact

Abstract. Methane and ozone are two important climate gases with significant tropospheric chemistry. Within chemistry-climate and transport models this chemistry is simplified for computational expediency. We compare the state of the art Master Chemical Mechanism (MCM) with six tropospheric chemistry schemes (CRI-reduced, GEOS-CHEM and a GEOS-CHEM adduct, MOZART-2, TOMCAT and CBM-IV) that could be used within composition transport models. We test the schemes within a box model framework under conditions derived from a composition transport model and from field observations from a regional scale pollution event. We find that CRI-reduced provides much skill in simulating the full chemistry, yet with greatly reduced complexity. We find significant variations between the other chemical schemes, and reach the following conclusions. 1) The inclusion of a gas phase N2O5+H2O reaction in one scheme and not others is a large source of uncertainty in the inorganic chemistry. 2) There are significant variations in the calculated concentration of PAN between the schemes, which will affect the long range transport of reactive nitrogen in global models. 3) The representation of isoprene chemistry differs hugely between the schemes, leading to significant uncertainties on the impact of isoprene on composition. 4) Differences are found in NO3 concentrations in the nighttime chemistry. Resolving these four issues through further investigative laboratory studies will reduce the uncertainties within the chemical schemes of global tropospheric models.

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