Publications (43)4.88 Total impact
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Dataset: acpd-2007-0083-1-0-0 p
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Article: Case study of the diurnal variability of chemically active species with respect to boundary layer dynamics during DOMINO
Atmospheric Chemistry and Physics. 01/2012; 12(12):5329-5341. -
Article: Oxidation photochemistry in the Southern Atlantic boundary layer: unexpected deviations of photochemical steady state
Atmospheric Chemistry and Physics. 01/2011; 11(16):8497-8513. -
Article: Distribution of hydrogen peroxide and formaldehyde over Central Europe during the HOOVER project
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ABSTRACT: In this study we report measurements of hydrogen peroxide (H2O2), methyl hydroperoxide* (MHP* as a proxy of MHP based on an unspecific measurement of total organic peroxides) and formaldehyde (HCHO) from the HOx OVer EuRope (HOOVER) project (HOx = OH+HO2). HOOVER included two airborne field campaigns, in October 2006 and July 2007. Measurement flights were conducted from the base of operation Hohn (Germany, 54° N, 9° E) towards the Mediterranean and to the subpolar regions over Norway. We find negative concentration gradients with increasing latitude throughout the troposphere for H2O2 and CH3OOH*. In contrast, observed HCHO is almost homogeneously distributed over central and northern Europe and is elevated over the Mediterranean. In general, the measured gradients tend to be steepest entering the Mediterranean region, where we also find the highest abundances of the 3 species. Mixing ratios of these tracers generally decrease with altitude. H2O2 and CH3OOH* show maxima above the boundary layer at 2–5 km, being more distinct over southern than over northern Europe. We also present a comparison of our data with simulations by two global 3-D-models, MATCH-MPIC and EMAC, and with the box model CAABA. The models realistically represent altitude and latitude gradients for both HCHO and hydroperoxides (ROOH). In contrast, the models have problems reproducing the absolute mixing ratios, in particular of H2O2. Large uncertainties about retention coefficients and cloud microphysical parameters suggest that cloud scavenging might be a large source of error for the simulation of H2O2. A sensitivity study with EMAC shows a strong influence of cloud and precipitation scavenging on the budget of H2O2 as simulations improve significantly with this effect switched off.Atmospheric Chemistry and Physics. 01/2011; 11(2011-05-11):4391-4410. -
Article: Ozone over the Southern Oceans is exceptionally sensitive to ship exhausts
Environmental Chemistry. 01/2010; 7:171-182. -
Article: Halogens and their role in polar boundary-layer ozone depletion
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ABSTRACT: During springtime in the polar regions, unique photochemistry converts inert halide salt ions (e.g. Br−) into reactive halogen species (e.g. Br atoms and BrO) that deplete ozone in the boundary layer to near zero levels. Since their discovery in the late 1980s, research on ozone depletion events (ODEs) has made great advances; however many key processes remain poorly understood. In this article we review the history, chemistry, dependence on environmental conditions, and impacts of ODEs. This research has shown the central role of bromine photochemistry, but how salts are transported from the ocean and are oxidized to become reactive halogen species in the air is still not fully understood. Halogens other than bromine (chlorine and iodine) are also activated through incompletely understood mechanisms that are probably coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The different reactivity of halogens as compared to OH and ozone has broad impacts on atmospheric chemistry, including near complete removal and deposition of mercury, alteration of oxidation fates for organic gases, and export of bromine into the free troposphere. Recent changes in the climate of the Arctic and state of the Arctic sea ice cover are likely to have strong effects on halogen activation and ODEs; however, more research is needed to make meaningful predictions of these changes.Atmospheric Chemistry and Physics 08/2007; 7(16):4375-4418. · 4.88 Impact Factor -
Article: Consistent Simulation of Bromine Chemistry From the Marine Boundary Layer to the Stratopause
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ABSTRACT: Most model studies of bromine chemistry in the troposphere have been performed with box or column models. Only a few global model studies exist. To our knowledge all these global model studies were performed with CTMs and contain parameterised halogen sources. In our approach we avoid most of these assumptions. We use the chemistry climate model ECHAM5/MESSy to simulate bromine chemistry consistently from the surface up to the stratopause. Emissions of sea salt aerosol as the largest surface source and the chemistry in both the gas phase and the aerosol phase are explicitly calculated, leading to a fully prognostically determined bromine release from the aerosol into the gas phase. Furthermore the stratospheric halogen chemistry including the degradation of long-lived halons and CH3Br which are transported from the surface up to the stratosphere as well as all important halogen reactions cycles and reactions on polar stratospheric clouds and on stratospheric sulfate aerosol are part of our simulation. So far little is known about the origin of bromine in the free troposphere. The main source may be downward transport from the stratosphere, upward transport from the boundary layer, or local production by photolysis of bromocarbons. Due to the complex setup of our model simulation, we are able to assess the main sources of bromine in the free troposphere. Additionally, we investigate the influence of bromine chemistry on other gas phase species, e.g. ozone.AGU Fall Meeting Abstracts. 11/2006; -1:07. -
Article: Consistent simulation of bromine chemistry from the marine boundary layer to the stratosphere, Part I: model description, sea salt aerosols and pH
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ABSTRACT: This is the first article of a series presenting a detailed analysis of bromine chemistry simulated with the atmospheric chemistry general circulation model ECHAM5/MESSy. Release from sea salt is an important bromine source, hence the model explicitly calculates aerosol chemistry and phase partitioning for coarse mode aerosol particles. Many processes including chemical reaction rates are influenced by the particle size distribution, and aerosol associated water strongly affects the aerosol pH. Knowledge of the aerosol pH is important as it determines the aerosol chemistry, e.g., the efficiency of sulphur oxidation and bromine release. Here, we focus on the simulated sea salt aerosol size distribution and the coarse mode aerosol pH. A comparison with available field data shows that the simulated aerosol distributions agree reasonably well within the range of measurements. In spite of the small number of aerosol pH measurements and the uncertainty in its experimental determination, the simulated aerosol pH compares well with the observations. The aerosol pH ranges from alkaline aerosol in areas of strong production down to pH values of 1 over regions of medium sea salt production and high levels of gas phase acids, mostly polluted regions over the oceans in the northern hemisphere. -
Article: Carbonate precipitation in brine ? a potential trigger for tropospheric ozone depletion events
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ABSTRACT: Tropospheric ozone depletion events (ODEs) at high latitudes were discovered 20 years ago and are attributed to bromine explosions. However, an unresolved issue is the explanation of how the acid-catalyzed reaction cycle is triggered in atmospheric particles derived from alkaline sea water. By simulating the chemistry occuring in polar regions over recently formed sea ice, we can model successfully the transformation of inert sea-salt bromide to reactive bromine monoxide (BrO) and the subsequent ODE when precipitation of calcium carbonate from freezing sea water is taken into account. In addition, we found the temperature dependence of the equilibrium BrCl+Br<sup>?</sup>?Br<sub>2</sub>Cl<sup>?</sup> to be important. -
Article: Carbonate precipitation in brine ? the trigger for tropospheric ozone depletion events
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ABSTRACT: Tropospheric ozone depletion events (ODEs) at high latitudes were discovered 20 years ago and are attributed to bromine explosions. However, an outstanding and unresolved issue is the explanation of how the acid-catalyzed reaction cycle is triggered in atmospheric particles derived from alkaline sea water. By simulating the chemistry occuring in polar regions over recently formed sea ice, we can model successfully the transformation of inert sea-salt bromide to reactive bromine monoxide (BrO) and the subsequent ODE when precipitation of calcium carbonate from freezing sea water is taken into account. In addition, we found the temperature dependence of the equilibrium BrCl+Br?Br<sub>2</sub>Cl<sup>?</sup> to be important. -
Article: Technical Note: The new comprehensive atmospheric chemistry module MECCA
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ABSTRACT: In this technical note we present the multi-purpose atmospheric chemistry model MECCA. Owing to its versatility and modular structure, it can be used for tropospheric as well as stratospheric chemistry calculations. Extending the code to other domains (e.g. mesospheric or oceanic chemistry) is easily possible. MECCA contains a comprehensive atmospheric reaction mechanism that currently includes: 1) the basic O<sub>3</sub>, CH<sub>4</sub>, HO<sub>x</sub>, and NO<sub>x</sub>, chemistry, 2) non-methane hydrocarbon (NMHC) chemistry, 3) halogen (Cl, Br, I) chemistry, and 4) sulfur chemistry. Not only gas-phase chemistry but also aqueous-phase and heterogeneous reactions are considered. Arbitrary subsets of the comprehensive mechanism can be selected according to the research objectives. The program code resulting from the chemical mechanism can easily be used in any kind of model, from a simple box model to a sophisticated global general circulation model. -
Article: Technical Note: The Modular Earth Submodel System (MESSy) ? a new approach towards Earth System Modeling
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ABSTRACT: Generally, the typical approach towards Earth System Modeling has been to couple existing models of different domains (land, ocean, atmosphere, ...) offline, using output files of one model to provide input for the other. However, for a detailed study of the interactions and feedbacks between chemical, physical, and biological processes, it is necessary to perform the coupling online. One strategy is to link the existing domain-specific models with a universal coupler. In many cases, however, a much simpler approach is more feasible. To achieve the online coupling, we have developed the Modular Earth Submodel System (MESSy). Data are exchanged between a and several within one comprehensive model system. MESSy includes a generalized interface structure for the standardized control of the and their interconnections. The internal complexity of the is controllable in a transparent and user friendly way. This provides remarkable new possibilities to study feedback mechanisms (by two-way coupling), e.g., by applying MESSy to a general circulation model (GCM). -
Article: Technical Note: Implementation of prescribed (OFFLEM), calculated (ONLEM), and pseudo-emissions (TNUDGE) of chemical species in the Modular Earth Submodel System (MESSy)
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ABSTRACT: We present the submodels OFFLEM, ONLEM, and TNUDGE for the Modular Earth Submodel System (MESSy). Prescribed emissions from input files are handled by OFFLEM. ONLEM deals with online-calculated emissions, i.e., emissions that are calculated during the simulation. The submodel TNUDGE uses the ''tracer nudging'' technique for pseudo-sources and -sinks. For species with highly uncertain emission fluxes and/or with sufficiently long lifetimes, e.g., CH<sub>4</sub>, it is common to create such pseudo-fluxes by prescribing the observed mixing ratio of the species at a given boundary (e.g., the mixing ratio of methane at the surface, or the ozone mixing ratio at the tropopause). All three submodels substantially simplify the inclusion of emissions into a model. Specific emissions can easily be switched on or off. New prescribed emissions can be included without rewriting any code. New online emissions only require one additional subroutine containing the new parameterization. A major advantage is that input fields at arbitrary resolution can be used. The problem of incompatible grids between emission data and model is overcome by utilizing the MESSy data import interface. To further simplify the creation of new offline emission data, the preprocessing program EDGAR2NC is provided. EDGAR2NC transforms files from the EDGAR format into the netCDF format which is required by OFFLEM. The presented routines are a part of the community modeling project MESSy and can be made available for use to the atmospheric modeling community. -
Article: Global cloud and precipitation chemistry and wet deposition: tropospheric model simulations with ECHAM5/MESSy1
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ABSTRACT: The representation of cloud and precipitation chemistry and subsequent wet deposition of trace constituents in global atmospheric chemistry models is associated with large uncertainties. To improve the simulated trace gas distributions we apply the new submodel SCAV, which includes detailed cloud and precipitation chemistry and present results of the atmospheric chemistry general circulation model ECHAM5/MESSy1. A good agreement with observed wet deposition fluxes for species causing acid rain is obtained. The new scheme enables prognostic calculations of the pH of clouds and precipitation, and these results are also in accordance with observations. We address the influence of detailed cloud and precipitation chemistry on trace constituents based on sensitivity simulations. The results confirm previous results from regional scale and box models, and we extend the analysis to the role of aqueous phase chemistry on the global scale. Some species are directly affected through multiphase removal processes, and many also indirectly through changes in oxidant concentrations, which in turn have an impact on the species lifetime. While the overall effect on tropospheric ozone is relatively small (<10%), regional effects on O<sub>3</sub> can reach ~20%, and several important compounds (e.g., H<sub>2</sub>O<sub>2</sub>, HCHO) are substantially depleted by clouds and precipitation. -
Article: Variation of marine aerosol acidity with particle size
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ABSTRACT: [1] pHs were measured in minimally diluted extracts of size- segregated aerosols sampled under moderately polluted conditions at Bermuda during spring 1997. Extrapolation to aerosol liquid water contents yielded ambient pHs for most super-mum mdiameter size fractions in the upper 3s to upper 4s. Aerosols within this size range of each sample approached similar pH. These results are consistent with recent estimates of sea-salt aerosol pHs based on thermodynamic considerations and model calculations. Most pHs for finer aerosol size fractions were in the 1s and 2s. The H+ +SO42- <-> HSO4- equilibrium strongly buffered aerosol pH in all size fractions.Geophysical Research Letters, v.29 (2002). -
Article: Modeling halogen chemistry in the marine boundary layer - 1. Cloud-free MBL
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ABSTRACT: A numerical one-dimensional model of the marine boundary layer (MBL) is presented. It includes chemical reactions in the gas phase and aerosol particles, focusing on the reaction cycles of halogen compounds. Results of earlier box model studies were confirmed. They showed the acid-catalyzed activation of bromine from sea salt aerosol, and the role of halogen radicals in the destruction of O-3. A distinct diurnal variation in BrO mixing ratios with maxima at sunrise and sunset was found which might be the cause of the recently published "sunrise ozone destruction.'' Maxima of BrO and sea salt acidity are predicted at the top of the MBL and not close to the sea surface where sea salt spray is produced. The presence of sulfate aerosol was found to be important for the recycling of less reactive to photolyzable bromine species. Day/night and seasonal differences in halogen chemistry are shown.Journal of Geophysical Research, v.107 (2002). -
Article: Modeling halogen chemistry in the marine boundary layer - 2. Interactions with sulfur and the cloud-covered MBL
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ABSTRACT: A companion paper presented a numerical one-dimensional model of the marine boundary layer (MBL) including chemical reactions in the gas and aqueous phase, focusing on the reaction cycles of halogen compounds. In this paper we study interactions between halogen and sulfur chemistry. HOCl and HOBr were found to be generally more important than H(2)O(2)or O-3 in the oxidation of S(IV) in sea salt aerosols in the cloud-free MBL. The inclusion of halogen chemistry lead to an increase in the oxidation of DMS of roughly 63%. This additional oxidation is caused by BrO. The model was also expanded for the study of the cloudy MBL. We found that the effects of stratiform clouds on the evolution and diurnal cycle of halogen species are widespread; they are not restricted to cloud layers. The diurnal variation of gas and aqueous phase bromine was the opposite of that in cloud-free runs. Oxidation of S(IV) by HOBr and HOCl was important for cloud droplets, too. However, the relative importance of these oxidants changed compared to the cloud-free runs.Journal of Geophysical Research, v.107 (2002). -
Article: Bromide content of sea-salt aerosol particles collected over the Indian Ocean during INDOEX 1999
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ABSTRACT: [1] Bromide can be depleted from sea-salt aerosol particles in the marine boundary layer (MBL) and converted to reactive gas- phase species like Br, BrO, and HOBr, which affect ozone chemistry. Air pollution can enhance the bromine release from sea-salt aerosols and thus inject additional bromine into the MBL. During the winter monsoon the northern Indian Ocean is strongly affected by air pollution from the Indian subcontinent and Asia. As part of the Indian Ocean Experiment (INDOEX), aerosol particles were sampled with stacked filter units (SFU) on the NCAR Hercules C-130 aircraft during February-March 1999. We determined the vertical and latitudinal distribution of the major inorganic aerosol components (NH4+, Na+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42-) and the Br content of the coarse aerosol to examine the role of the bromine release on the gas-phase chemistry in the marine boundary layer over the tropical Indian Ocean. The aerosol mass and composition varied significantly with air mass origin and sampling location. In the northern part of the Indian Ocean (5degrees-15degreesN, 66degrees- 73degreesE), high concentrations of pollution-derived inorganic species were found in the marine boundary layer extending from the sea surface to about 1.2 km above sea level. In this layer, the average mass concentration of all aerosol species detected by our technique was comparable to pollution levels observed in industrialized regions. In the Southern Hemisphere (1degrees- 9degreesS, 66degrees-73degreesE), the aerosol concentrations rapidly declined to remote background levels. A chloride loss from the coarse aerosol particles was observed in parallel to the latitudinal gradient of the non sea salt SO42- burden. In most of the samples, Br was depleted from the sea-salt aerosols. However, we found an enrichment in bromide in aerosols affected by air masses originating over strong pollution sources in India (Bombay, Calcutta). In these cases the additional pollution-derived Br from organo-halogen additives in petrol outweighs the release of sea-salt bromine.Journal of Geophysical Research, v.107 (2002). -
Article: Study of the diurnal variability of atmospheric chemistry with respect to boundary layer dynamics during DOMINO
Atmos. Chem. Phys. Discuss. 12(3):6519-6550. -
Article: Comment on "Reactions at interfaces as a source of sulfate formation in sea-salt particles" (II)
Science, v.303, 628-628 (2004).
