Oxidation Of Non-methane Hydrocarbons Research Articles

Molecular and isotopic signatures of oil-driven bacterial sulfate reduction at seeps in the southern Gulf of Mexico

Oil seepage is widespread in the Gulf of Mexico, which also applies to the Bay of Campeche in the southern Gulf. The ascension of crude oil and oil-derived hydrocarbons poses a challenge to most seep-dwelling organisms. On the other hand, short- and long-chain hydrocarbons have been shown to be potentially degraded by a range of heterotrophic sulfate-reducing bacteria. Here we present lipid biomarker and carbon isotope data from authigenic carbonates from the Campeche Knolls in the southern Gulf of Mexico and use methane-seep carbonates from the Makran convergent margin (southern Pakistan and Iran) for comparison. The Campeche Knolls and Makran were selected for such comparison as endmember types for oil versus methane seepage in an attempt to identify molecular signatures of oil seepage. The Campeche carbonates yielded on average higher δ13C values (−31.3‰ to −21.9‰) than the Makran methane-seep carbonates (−54.3‰ to −39.8‰) and revealed a particularly high content of ether lipids. The Campeche carbonates revealed a greater variety of alkyl chains in non-isoprenoidal dialkyl glycerol diether lipids (DAGE) and a higher relative proportion of long alkyl chains (DAGEs >C36) compared with the Makran methane-seep carbonates. Bacterial biomarkers showed an on average distinctively heavier δ13C signature than at the studied methane seeps, indicating bacterial oxidation of oil-derived hydrocarbons. Mixing calculations indicate that up to 73% of the local sulfate reduction is coupled to the oxidation of non-methane hydrocarbons at the oil seeps, contributing as much as 40% to carbonate precipitation. These data imply that oil-seep carbonates can be discriminated from methane-seep carbonates by their respective biomarker inventories in modern and, in cases of moderate to good biomarker preservation, ancient environments, setting the stage for the reconstruction of the influence of fluid composition on the compositions of chemosynthesis-based communities at seeps.

Lipid biomarker patterns reflect seepage activity and variable geochemical processes in sediments from the Haima cold seeps, South China Sea

The anaerobic oxidation of methane (AOM), aerobic methane oxidation and the oxidation of non-methane hydrocarbons have been demonstrated to occur in seepage ecosystems, but when they occur during seepage evolutionary is lack of constraints. Here, lipid biomarker patterns combined with total organic carbon (TOC), δ13Corg, δ13CTIC and δ18OTIC of a sediment core (~ 3 m long) from the active Haima cold seep were analyzed. The observed lipid inventories reflected the prevailing of anaerobic methane oxidizing archaea (ANME)/Desulfosarcina/Desulfococcus (DSS) and ANME-2/DSS dominated over the whole sediments. Seepage fluids originated from local gas hydrate dissociation as indicated by the pronounced δ13CTIC and δ18OTIC values, while a mixture of microbial and thermogenic methane (−65‰ to −55‰) was corroborated by back-calculation based on the predominant consortia and δ13C values of ANME-specific biomarkers. AOM occurred over the whole sediments and was strengthened between depths 40 cm and 120 cm as revealed by the extremely low δ13CTIC, δ13Corg values, and abundant lipid biomarkers of ANME such as crocetane, 2,6,10,15,19-pentamethylicosane (PMI), archaeol and sn2-OH-archaeol with strong 13C depletions (δ13C values as low as −118‰). For sediment below the depth of 120 cm, molecular fossils of aerobic methanotrophs 4α-methylcholesta-2,8(14),24-triene and C34-3β-methyl tetracyclic-ketone occurred and yielded their δ13C values of −64‰ to −61‰, indicating the prevailing of oxic condition and aerobic methane oxidation. Compared to the sediment between 40 cm and 120 cm, the abundant iso-/anteiso-C15:0 (i-/ai-C15:0) fatty acids with relatively enriched δ13C values in the bottom sediment were better explained by contribution of sulfate-reducing bacteria (SRB)-driven oxidation of non-methane hydrocarbons. The distinct biomarker patterns and the respective geochemical processes at various sediment depths revealed the microbial community succession sequence in seepage evolutionary, since the different growth rates may have led to a successive colonization of aerobic methanotrophs, SRB, and ANME in an emerging cold seep ecosystem.

Synthesis of Mn-CeOx/cordierite catalysts using various coating materials and pore-forming agents for non-methane hydrocarbon oxidation in cooking oil fumes

Cooking oil fumes (COFs) as an important source of volatile organic compounds (VOCs) in metropolitan areas is poisonous to the environment and human health, and the removal rate of Non-methane Hydrocarbon (NMHC) in COFs was used to verify the activity of catalysts made to depurate COFs. The textural properties of cordierite are limitation to the catalyst's performance. Therefore, in this paper, coating the cordierite to improve its surface properties was investigated. The experiment results and characterization data revealed that TiO2 was a better coating material because of coating on TiO2 can improve the surface morphology better than that of Al2O3. The SEM and BET data of the materials synthesized with different content of CTAB showed that 10 wt% additive amount of pore-forming agent had a better textural properties than other additive amount of pore-forming agents. It is clear that the SBET and DV of the catalysts were significantly increased, and the catalyst exhibited smaller particle size and more developed pore structure after ultrasonic treatment which proving that ultrasound can enhance the catalyst's catalytic activity. It is obviously that the catalyst synthesized with CTAB had best pore structure and Mn4Ce1/Ti/NC-CTAB-U exhibited the best performance for catalytic combustion of NMHC with the removal rate was 93.6% at 400 °C.

Cordierite-supported metal oxide for non-methane hydrocarbon oxidation in cooking oil fumes

ABSTRACTCooking emission is an important reason for the air quality deterioration in the metropolitan area in China. Transition metal oxide and different loading of manganese oxide supported on cordierite were prepared by incipient wetness impregnation method and were used for non-methane hydrocarbon (NMHC) oxidation in cooking oil fumes (COFs). The effects of different calcination temperature and different Mn content were also studied. The SEM photographs and CO2 temperature-programmed desorption revealed 5 wt% Mn/cordierite had the best pore structure and the largest number of the weak and moderate basic sites so it showed the best performance for NMHC oxidation. XRD analysis exhibited 5 wt% Mn/cordierite had the best dispersion of active phase and the active phase was MnO2 when the calcination temperature was 400℃ which were good for the catalytic oxidation of NMHC.

Improving the Efficiency of Mn-CeOx/Cordierite Catalysts for Nonmethane Hydrocarbon Oxidation in Cooking Oil Fumes

Cooking oil fumes (COFs) are considered to be one of the important pollution sources in urban areas, and nonmethane hydrocarbon (NMHC) can be an index of volatile organic compounds (VOCs) from COFs. In this paper, cordierite supported Mn-CeOx catalysts were used for NMHC oxidation in COFs. The results showed that the catalytic oxidation activity of Mn-CeOx/cordierite was obviously improved by adding an appropriate proportion of Ce. The catalytic activity of Mn4Ce1/C was obviously better than catalysts with other molar ratios of Mn/Ce and Mn/C because of the extra adsorbed oxygen species and high ratio of Ce4+/Ce3+ according to the XPS analysis. The physisorption of N2 and SEM-EDS revealed that the structure of catalysts prepared by a sol–gel method presented a higher BET specific surface area, more abundant pore structure, and better dispersion of catalysts’ active components which were favorable for catalytic oxidation reaction of NMHC.

Benchmark study of the structural and spectroscopic parameters of the hydroxymethyl peroxy (HOCH2OO) radical and its decomposition reaction to HO2 and H2CO.

The hydroxymethyl peroxy (HMOO) radical is a product of the oxidation of non-methane hydrocarbons. The present study provides the first accurate computational determination of critical spectroscopic features of the title radical that should aid in its experimental characterization. Structure, energetics, vibrational frequencies, and rotational parameters are reported for the three stable isomers on the ground electronic state of HMOO. While preliminary computations have been carried out using density functional theory as well as second-order Møller-Plesset perturbation theory, for the accurate structural and spectroscopic characterization we made use of coupled-cluster techniques, herewith considering both standard and explicitly correlated methods. The "CCSD(T)/CBS + CV" composite scheme, a state-of-the-art composite approach based on the coupled-cluster theory including single and double excitations together with a perturbative treatment of triples that accounts for extrapolation to the complete basis-set limit as well as core-valence correlation effects, is used to obtain accurate structural and energetic data, in particular for the decomposition reaction to HO2 and H2CO.

Diverse sulfate-reducing bacteria of the Desulfosarcina/Desulfococcus clade are the key alkane degraders at marine seeps.

Biogeochemical and microbiological data indicate that the anaerobic oxidation of non-methane hydrocarbons by sulfate-reducing bacteria (SRB) has an important role in carbon and sulfur cycling at marine seeps. Yet, little is known about the bacterial hydrocarbon degraders active in situ. Here, we provide the link between previous biogeochemical measurements and the cultivation of degraders by direct identification of SRB responsible for butane and dodecane degradation in complex on-site microbiota. Two contrasting seep sediments from Mediterranean Amon mud volcano and Guaymas Basin (Gulf of California) were incubated with (13)C-labeled butane or dodecane under sulfate-reducing conditions and analyzed via complementary stable isotope probing (SIP) techniques. Using DNA- and rRNA-SIP, we identified four specialized clades of alkane oxidizers within Desulfobacteraceae to be distinctively active in oxidation of short- and long-chain alkanes. All clades belong to the Desulfosarcina/Desulfococcus (DSS) clade, substantiating the crucial role of these bacteria in anaerobic hydrocarbon degradation at marine seeps. The identification of key enzymes of anaerobic alkane degradation, subsequent β-oxidation and the reverse Wood-Ljungdahl pathway for complete substrate oxidation by protein-SIP further corroborated the importance of the DSS clade and indicated that biochemical pathways, analog to those discovered in the laboratory, are of great relevance for natural settings. The high diversity within identified subclades together with their capability to initiate alkane degradation and growth within days to weeks after substrate amendment suggest an overlooked potential of marine benthic microbiota to react to natural changes in seepage, as well as to massive hydrocarbon input, for example, as encountered during anthropogenic oil spills.

Communication: Theoretical prediction of the structure and spectroscopic properties of the $\tilde{\mathrm{X}}$X̃ and $\tilde{\mathrm{A}}$Ã states of hydroxymethyl peroxy (HOCH2OO) radical

The hydroxymethyl peroxy (HMOO) radical is a radical product from the oxidation of non-methane hydrocarbons. The present study provides theoretical prediction of critical spectroscopic features of this radical that should aid in its experimental characterization. Structure, rotational constants, and harmonic frequencies are presented for the ground and first excited electronic states of HMOO. The adiabatic transition energy for the Ã←X̃ process is 7360 cm(-1), suggesting that this transition, occurring in the mid to near infrared, is the most promising candidate for observing the radical spectroscopically. The band origin of the Ã←X̃ transition of HMOO is calibrated and benchmarked with the corresponding state of the HOO radical, which is experimentally and theoretically well characterized.

Satellite evidence for a large source of formic acid from boreal and tropical forests

Formic acid contributes significantly to acid rain in remote environments. Direct sources of formic acid include human activities, biomass burning and plant leaves. Aside from these direct sources, sunlight-induced oxidation of non-methane hydrocarbons (largely of biogenic origin) is probably the largest source. However, model simulations substantially underpredict atmospheric formic acid levels, indicating that not all sources have been included in the models. Here, we use satellite measurements of formic acid concentrations to constrain model simulations of the global formic acid budget. According to our simulations, 100- 120Tg of formic acid is produced annually, which is two to three times more than that estimated from known sources. We show that 90% of the formic acid produced is biogenic in origin, and largely sourced from tropical and boreal forests. We suggest that terpenoids- volatile organic compounds released by plants- are the predominant precursors. Model comparisons with independent observations of formic acid strengthen our conclusions, and provide indirect validation for the satellite measurements. Finally, we show that the larger formic acid emissions have a substantial impact on rainwater acidity, especially over boreal forests in the summer, where formic acid reduces pH by 0.25- 0.5.

Authigenic carbonates at cold seeps in the Marmara Sea (Turkey): A lipid biomarker and stable carbon and oxygen isotope investigation

Cold seeps along the North Anatolian fault in the Marmara Sea (Turkey) have been recently explored during international expeditions through submersible surveys, seafloor mapping and extensive sampling of sediments, biota, carbonates and pore waters. In this study, we investigated the main mineralogy, carbon and oxygen isotopic compositions and lipid biomarkers in authigenic carbonates retrieved from active seepage areas in the Marmara Sea. Abundant microbial lipid biomarkers with light δ 13C values (as low as − 113‰), as well as light δ 13C–CaCO 3 values of bulk carbonate (− 34‰ to − 21‰), provided evidence that anaerobic oxidation of methane (AOM) mediated by methanotrophic archaea (ANME) and their bacterial partners, is the major process leading to sequestration of methane-derived carbon. Diagnostic lipid distributions indicated that ANME-2 archaea and associated sulphate-reducing bacteria (SRB) as the prevalent AOM-mediating microbes. Diverse non-isoprenoid dialkyl glycerol ethers (DAGEs), including tentatively identified novel compounds, were identified with similar δ 13C values as lipid biomarkers of SRB (− 105‰ to − 68‰). Though DAGEs are often assigned to SRB, other unknown bacteria closely involved in AOM are likely as source organisms as well. Despite dominant AOM-related lipid biomarker patterns, the stable carbon isotopic composition of bulk carbonates in two samples, from South Çinarcik Basin and Central High, in combination with higher hydrocarbon signatures and environmental parameters suggested that oxidation of non-methane hydrocarbons, including oil, may be a contributor to the dissolved inorganic carbon pool and may also be involved in carbonate authigenesis at hydrocarbon seepage settings as previously proposed in the Gulf of Mexico.

Degradation of Nonmethane Hydrocarbon Oxidation Efficiency of a Catalyzed Diesel Particulate Filter during Aging

Degradation of Nonmethane Hydrocarbon Oxidation Efficiency of a Catalyzed Diesel Particulate Filter during Aging

Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area

Abstract. The volatile organic compound (VOC) distribution in the Mexico City Metropolitan Area (MCMA) and its evolution as it is uplifted and transported out of the MCMA basin was studied during the 2006 MILAGRO/MIRAGE-Mex field campaign. The results show that in the morning hours in the city center, the VOC distribution is dominated by non-methane hydrocarbons (NMHCs) but with a substantial contribution from oxygenated volatile organic compounds (OVOCs), predominantly from primary emissions. Alkanes account for a large part of the NMHC distribution in terms of mixing ratios. In terms of reactivity, NMHCs also dominate overall, especially in the morning hours. However, in the afternoon, as the boundary layer lifts and air is mixed and aged within the basin, the distribution changes as secondary products are formed. The WRF-Chem (Weather Research and Forecasting with Chemistry) model and MOZART (Model for Ozone and Related chemical Tracers) were able to approximate the observed MCMA daytime patterns and absolute values of the VOC OH reactivity. The MOZART model is also in agreement with observations showing that NMHCs dominate the reactivity distribution except in the afternoon hours. The WRF-Chem and MOZART models showed higher reactivity than the experimental data during the nighttime cycle, perhaps indicating problems with the modeled nighttime boundary layer height. A northeast transport event was studied in which air originating in the MCMA was intercepted aloft with the Department of Energy (DOE) G1 on 18 March and downwind with the National Center for Atmospheric Research (NCAR) C130 one day later on 19 March. A number of identical species measured aboard each aircraft gave insight into the chemical evolution of the plume as it aged and was transported as far as 1000 km downwind; ozone was shown to be photochemically produced in the plume. The WRF-Chem and MOZART models were used to examine the spatial extent and temporal evolution of the plume and to help interpret the observed OH reactivity. The model results generally showed good agreement with experimental results for the total VOC OH reactivity downwind and gave insight into the distributions of VOC chemical classes. A box model with detailed gas phase chemistry (NCAR Master Mechanism), initialized with concentrations observed at one of the ground sites in the MCMA, was used to examine the expected evolution of specific VOCs over a 1–2 day period. The models clearly supported the experimental evidence for NMHC oxidation leading to the formation of OVOCs downwind, which then become the primary fuel for ozone production far away from the MCMA.

Technical Note: Determination of formaldehyde mixing ratios in air with PTR-MS: laboratory experiments and field measurements

Abstract. Formaldehyde (HCHO), the most abundant carbonyl compound in the atmosphere, is generated as an intermediate product in the oxidation of nonmethane hydrocarbons. Proton transfer reaction mass spectrometry (PTR-MS) has the capability to detect HCHO from ion signals at m/z 31 with high time-resolution. However, the detection sensitivity is low compared to other detectable species, and is considerably affected by humidity, due to back reactions between protonated HCHO and water vapor prior to analysis. We performed a laboratory calibration of PTR-MS for HCHO and examined the detection sensitivity and humidity dependence at various field strengths. Subsequently, we deployed the PTR-MS instrument in a field campaign at Mount Tai in China in June 2006 to measure HCHO in various meteorological and photochemical conditions; we also conducted intercomparison measurements by Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). Correction of interference in the m/z 31 signals by fragments from proton transfer reactions with methyl hydroperoxide, methanol, and ethanol greatly improves agreement between the two methods, giving the correlation [HCHO]MAX-DOAS=(0.99±0.16) [HCHO]PTR-MS+(0.02±0.38), where error limits represent 95% confidence levels.

Size distributions of dicarboxylic acids and inorganic ions in atmospheric aerosols collected during polar sunrise in the Canadian high Arctic

Size‐segregated atmospheric aerosols (11 stages separating particles from <0.04 to >14.2 μm) collected in the Arctic during the polar sunrise at Alert were analyzed for aerosol mass, dicarboxylic acids, and major inorganic ions. Oxalic, malonic, succinic, and glutaric acids were detected in all size ranges, with oxalic acid being dominant. Their concentrations maximized in the accumulation mode either at 0.24–0.40 or 0.40–0.8 μm aerodynamic diameters, suggesting that diacids were mainly formed by gas‐to‐particle conversion via photochemical oxidation of nonmethane hydrocarbons and oxygenated organics originated from continental pollution sources. The relative abundances of oxalic acid were higher in the 0.24‐ to 0.4‐μm size particles (73–78%) than in supermicrometer particles (40–60%), indicating that oxalic acid is produced by gas phase oxidation of precursors followed by accumulation on preexisting particles. Mass size distributions of NH4+ and SO42− peaked in the accumulation mode similar to those of small diacids. The sea‐salt enrichment factor of K+ (biomass burning tracer) relative to Na+ maximized in 0.1‐ to 0.8‐μm sizes, whereas those of Mg2+ and Ca2+ (dust tracers) in 0.4‐ to 7.8‐μm particles. Maximized chlorine loss and bromine enrichment were found at 0.4–0.8 and 0.24–0.4 μm sizes, respectively. Concentrations of Br−, which typically showed a submicrometer maximum, increased significantly during an O3 depletion event having a shift of size distribution to a supermicrometer mode. During this event, oxalic acid concentration relative to succinic acid increased in submicrometer mode (0.24–0.4 μm), adding to a growing body of evidence supporting the hypothesis that halogen chemistry is important in the production and loss of oxalic acid in the arctic atmosphere.

Quantifying carbon sources in the formation of authigenic carbonates at gas hydrate sites in the Gulf of Mexico

The northern slope of the Gulf of Mexico is known for extensive venting of methane and other hydrocarbons as related to active salt diapirism and associated fault conduits which link world-class subsurface reserves to seafloor seeps. These venting hydrocarbons fuel extensive micro- and macrofaunal cold seep communities. Of particular interest is the relationship between anaerobic methane-oxidizing archaea and sulfate-reducing bacteria. It has been suggested that sulfate-dependent anaerobic methane oxidation dominates carbon oxidation and attendant authigenic carbonate precipitation at these sites. To test this assumption, we have quantified the relative contributions of dissolved carbon dioxide (ΣCO 2) from a variety of sources—specifically seawater, organic matter, methane, and non-methane liquid and gaseous hydrocarbons—using the carbon isotope compositions of authigenic carbonates and a simple isotopic mass balance. Our model, and a small but representative suite of data from the Gulf, demonstrates that methane is a contributor but is not the dominant source of metabolic energy at the sites of active venting. Instead, oxidation of non-methane hydrocarbons appears to be the primary source of carbonate alkalinity. The secondary role played by methane oxidation has been independently recognized by other workers from organic biomarker relationships and from disparities observed between measured rates of sulfate reduction and methane oxidation. Despite the domination of the carbon reservoir by non-methane sources, oxygen isotope data for the authigenic carbonates bear the mark of appreciable gas hydrate dissociation. This study, rather than being an exhaustive survey of Gulf of Mexico seeps, is intended only to provide a template for the investigation of the abundant authigenic carbonate deposits distributed throughout the geologic record. As in the Gulf of Mexico, many modern and ancient cold seeps are characterized by a complex interplay of carbon sources readily preserved in the δ 13C values of carbonates.

Hohenpeissenberg Photochemical Experiment (HOPE 2000): Measurements and photostationary state calculations of OH and peroxy radicals

Abstract. Measurements of OH, total peroxy radicals, non-methane hydrocarbons (NMHCs) and various other trace gases were made at the Meteorological Observatory Hohenpeissenberg in June 2000. The data from an intensive measurement period characterised by high solar insolation (18-21 June) are analysed. The maximum midday OH concentration ranged between 4.5x106 molecules cm-3 and 7.4x106 molecules cm-3. The maximum total ROx (ROx =OH+RO+HO2+RO2) mixing ratio increased from about 55 pptv on 18 June to nearly 70 pptv on 20 and 21 June. A total of 64 NMHCs, including isoprene and monoterpenes, were measured every 1 to 6 hours. The oxidation rate of the NMHCs by OH was calculated and reached a total of over 14x106 molecules cm-3 s-1 on two days. A simple photostationary state balance model was used to simulate the ambient OH and peroxy radical concentrations with the measured data as input. This approach was able to reproduce the main features of the diurnal profiles of both OH and peroxy radicals. The balance equations were used to test the effect of the assumptions made in this model. The results proved to be most sensitive to assumptions about the impact of unmeasured volatile organic compounds (VOC), e.g. formaldehyde (HCHO), and about the partitioning between HO2 and RO2. The measured OH concentration and peroxy radical mixing ratios were reproduced well by assuming the presence of 3 ppbv HCHO as a proxy for oxygenated hydrocarbons, and a HO2/ RO2 ratio between 1:1 and 1:2. The most important source of OH, and conversely the greatest sink for peroxy radicals, was the recycling of HO2 radicals to OH. This reaction was responsible for the recycling of more than 45x106 molecules cm-3 s-1 on two days. The most important sink for OH, and the largest source of peroxy radicals, was the oxidation of NMHCs, in particular, of isoprene and the monoterpenes.

CHASER: A global chemical model of the troposphere 2. Model results and evaluation

We present results from a global three‐dimensional chemical model for the troposphere, named Chemical AGCM for Study of Atmospheric Environment and Radiative Forcing (CHASER). This model has been developed to simulate the tropospheric photochemistry involving the O3‐HOx‐NOx‐CH4‐CO photochemical system and oxidation of nonmethane hydrocarbons (NMHCs), based on an atmospheric general circulation model (AGCM). In this paper, we present results from a climatological run of the model, and evaluate them with observational data. The simulation was conducted at the model horizontal resolution of T21 (5.6° × 5.6°) with 32 vertical layers from the surface to about 40 km altitude. The model reproduces well the observed vertical profiles of CO and NMHCs as ethane, propane, and acetone in almost all cases. The simulated seasonal cycle of surface CO in the biomass‐burning region (South America) shows a good agreement with observation. In the case of nitric oxide (NO), the model generally reproduces the observed vertical profiles well, though it appears to somewhat underestimate NO in the upper troposphere in the low latitudes. Although the model overestimates nitric acid (HNO3) in some cases like other model studies, the calculated HNO3 is generally within the range of observations. Peroxyacetyl nitrate (PAN) appears to be generally simulated well, but overestimated by the model in some remote regions. In the simulation of O3, the vertical profiles and seasonal variations observed in polluted and remote sites are well reproduced. The ozone distributions calculated in the biomass‐burning‐related regions as South America, Africa, and the South Atlantic show good agreements with observations. However, in the midlatitudes, the model tends to overestimate O3 in the upper troposphere in winter‐springtime, maybe indicating the need of improving the model's horizontal resolution. The model calculates a net chemical ozone production of 397 TgO3/yr in the global troposphere (4895 TgO3/yr production and 4498 TgO3/yr destruction). The estimated net O3 flux from the stratosphere is 593 TgO3/yr, well within the range suggested by recent studies. The calculated global OH concentration leads to a global mean CH4 lifetime of 7.9 years in this simulation.

CHASER: A global chemical model of the troposphere 1. Model description

We present a new global three‐dimensional chemical model for the troposphere, named chemical atmospheric general circulation model (AGCM) for study of atmospheric environment and radiative forcing (CHASER). This model, developed in the framework of the Center for Climate System Research/National Institute for Environment Studies (CCSR/NIES) AGCM, is aimed to study tropospheric photochemistry and its influences on climate. The chemical component of the model simulates the O3‐HOx‐NOx‐CH4‐CO photochemical system and oxidation of nonmethane hydrocarbons through 88 chemical and 25 photolytic reactions with 47 chemical species in its present configuration. The model includes emission sources, dry and wet deposition, as well as chemical transformations. Meteorological processes such as transport due to advection, convection, and other subgrid‐scale mixing are simulated “on‐line” by the dynamical component of the CCSR/NIES AGCM. A detailed evaluation of the model results is presented in a companion paper [Sudo et al., 2002]. An evaluation of the transport scheme adopted in the model suggests that the model is capable of simulating transport associated with convection and boundary layer mixing as well as large‐scale advection. The model capability to simulate dry and wet deposition was also evaluated by conducting a simulation of atmospheric lead. The simulated lead distributions are consistent with those observed at the surface, showing the validity of the deposition parameterization adopted in the model.

Eastern Atlantic Spring Experiment 1997 (EASE97) 2. Comparisons of model concentrations of OH, HO2, and RO2 with measurements

An observationally constrained box model has been used to investigate the chemistry of the marine boundary layer at the Mace Head Atmospheric Research Station, a remote site on the west coast of Ireland. The model aims to simulate concentrations of the hydroxyl (OH) and hydroperoxy (HO2) radicals measured by an in situ fluorescence assay by gas expansion instrument, and the sum of peroxy radicals ([HO2] + Σ[RO2]) as determined by a peroxy radical chemical amplification instrument. The model has been constructed based on observed concentrations of nonmethane hydrocarbons, measured in situ during the campaign by gas chromatography. The chemical mechanism for the model is a subset of a comprehensive master chemical mechanism. This paper details comparisons of the concentrations of modeled and measured radical species from a field campaign held at Mace Head during spring 1997. The air masses arriving at the site have been split into three categories depending on their origin and chemical characteristics and model‐measurement comparisons carried out for each air mass. The average model‐measurement ratios are 2.4 for [OH], 3.6 for [HO2], and 0.9 for ([HO2] + Σ[RO2]), respectively, between 1100 and 1500 hours: the level of agreement is better for all three sets of radicals in the cleanest air mass. Possible reasons for the observed discrepancies are discussed. In addition, a rate of production analysis is used to identify key OH and HO2 reactions in the three air masses. The rate of OH production from HO2 with NO exceeds that from ozone photolysis by factors of 2–6 in the polluted air masses studied. In cleaner air from the northern polar region, primary production from ozone photolysis exceeds that from HO2 + NO by a factor of 2.5. HO2 and CH3O2 dominate the peroxy radical composition in all air masses, but peroxy radicals derived from the oxidation of nonmethane hydrocarbons are more important in polluted air masses.

Simulation of carbon monoxide transport during April 1994

The Multiscale Air Quality Simulation Platform (MAQSIP) is used to simulate transport of carbon monoxide (CO) as a passive tracer over North America, Europe, and the North Atlantic during the April 1994 Measurement of Air Pollution from Satellites (MAPS) mission. MAQSIP is driven by meteorological fields generated by the Pennsylvania State University/National Center for Atmospheric Research fifth‐generation mesoscale model. Model CO surface emissions from biomass burning, fossil fuel combustion, nonmethane hydrocarbon oxidation, oceans, and soils are based on inventories from the Belgian Institute for Space Aeronomy and the Global Emissions Inventory Activity. Predicted CO mixing ratios are vertically weighted for comparison with MAPS observations. The spread in the mission‐averaged vertically weighted simulated CO mixing ratios (∼38 ppbv, compared to 60 ppbv in the MAPS data) suggests that CO surface emissions significantly affect MAPS observations on a weekly timescale. Good qualitative agreement is found between MAPS observations and model predictions on several temporal and spatial scales. Possible reasons for discrepancies are examined. A simulation without cumulus convection increases CO mixing ratios in the lower model layers and depletes CO above, resulting in a complex pattern of increases and decreases upon vertical weighted integration. Another simulation, which included a diurnal emissions variation, produced significant changes in instantaneous local CO mixing ratios, but had a minimal effect on the mission‐averaged MAPS comparisons.