bluuebunny/crossref_metadata_2025_split huggingface dataset:
A discussion on the determination of atmospheric OH and its trends
Authors: Jöckel P. , Brenninkmeijer C. A. M. , Crutzen P. J. 
Published: April 2010

Abstract. The global hydroxyl radical distribution largely determines the oxidation efficiency of the atmosphere and, together with their sources and atmospheric transport, the distributions and lifetimes of most trace gases. Because of the great importance of several of these gases for climate, ozone budget and OH itself, it is of fundamental importance to acquire knowledge about atmospheric OH and possible trends in its concentrations. In the past, average concentrations of OH and trends were largely derived using industrially produced CH3CCl3 as a chemical tracer. The analyses have given valuable, but also rather uncertain results. In this paper we describe an idealized computer aided tracer experiment which has as one of its goals to derive tracer concentration weighted, global average <k(OH)>, where he temporal and spatial OH distribution is prescribed and k is the reaction rate coefficient of OH with a hitherto never produced (Gedanken) tracer, which is injected at a number of surface sites in the atmosphere in well known amounts over a given time period. Using a three-dimensional (3D) time-dependent chemistry/transport model <k(OH)> can be accurately determined from the calculated 3-D tracer distribution. It is next explored how well <k(OH)> can be retrieved solely from tracer measurements at a limited number of surface sites. The results from this analysis are encouraging enough to actually think about the feasibility to carry out a global dedicated tracer experiment to derive <k(OH)> and its temporal trends. However, before that, we propose to test the methods which are used to derive <k(OH)>, so far largely using CH3CCl3, with an idealized tracer experiment, in which a global model is used to calculate the "Gedanken" tracer distribution, representing the real 3-D world, from which we next derive <k(OH)>, using only the tracer information from a limited set of surface sites. We propose here that research groups which are, or will be, involved in global average OH studies to participate in such an inter-comparison of methods, organized and over-seen by a committee appointed by the International Global Atmospheric Chemistry (IGAC) program.
Global chemical weather forecasts for field campaign planning: predictions and observations of large-scale features during MINOS, CONTRACE, and INDOEX
Authors: Lawrence M. G. , Rasch P. J. , von Kuhlmann R. , Williams J. , Fischer H. , de Reus M. , Lelieveld J. , Crutzen P. J. , Schultz M. , Stier P. , Huntrieser H. , Heland J. , Stohl A. , Forster C. , Elbern H. , Jakobs H. , Dickerson R. R. 
Published: April 2010

Abstract. The first global tropospheric forecasts of O3 and its precursors have been used in the daily flight planning of field measurement campaigns. The 3-D chemistry-transport model MATCH-MPIC is driven by meteorological data from a weather center (NCEP) to produce daily 3-day forecasts of the global distributions of O3 and related gases, as well as regional CO tracers. This paper describes the forecast system and its use in three field campaigns, MINOS, CONTRACE and INDOEX. An overview is given of the forecasts by MATCH-MPIC and by three other chemical weather forecast models (EURAD, ECHAM, and FLEXPART), focusing on O3 and CO. Total CO and regional CO tracers were found to be the most valuable gases for flight planning, due to their relatively well-defined anthropogenic source regions and lifetimes of one to a few months. CO was in good agreement with the observations on nearly all the flights (generally r > 0.7, RMS < 20%). In every case in which the chemical weather forecasts were primarily responsible for the flight plans, the targeted features were observed. Two forecasted phenomena are discussed in detail: outflow from Asia observed in the Mediterranean upper troposphere during MINOS, and outflow from North America observed in the middle troposphere over northern Europe during CONTRACE. It is shown that although such pollution plumes occur repeatedly during the months around the campaigns, their frequency is sufficiently low (~10--30% of the time) that global chemical weather forecasts are important for enabling them to be observed during limited-duration field campaigns. The MATCH-MPIC chemical weather forecasts, including an interface for making customized figures from the output, are available for community use via http://www.mpch-mainz.mpg.de/~lawrence/forecasts.html .
Wavelength dependence of isotope fractionation in N2O photolysis
Authors: Kaiser J. , Röckmann T. , Brenninkmeijer C. A. M. , Crutzen P. J. 
Published: April 2010

Abstract. In previous reports on isotopic fractionation in the ultraviolet photolysis of nitrous oxide (N2O) only enrichments of heavy isotopes in the remaining N2O fraction have been found. However, most direct photolysis experiments have been performed at wavelengths far from the absorption maximum at 182 nm. Here we present high-precision measurements of the 15N and 18O fractionation constants (e) in photolysis at 185 nm. Small, but statistically robust depletions of heavy isotopes for the terminal atoms in the linear N2O molecule are found. This means that the absorption cross sections s(15N14N16O) and s(14N218O) are larger than s(14N216O) at this specific wavelength. In contrast, the central N atom becomes enriched in 15N. The corresponding fractionation constants (±1 standard deviation) are 15e1 = s(15N14N16O)/s(14N216O) - 1 = (3.7 ± 0.2)%o 18e = s(14N218O)/s(14N216O) - 1 = (4.5 ± 0.2)%o and 15e2 = s(\\chem{14N15N16O)/s(14N216O) - 1 = (-18.6 ± 0.5) %o To our knowledge, this is the first documented case of such a heavy isotope depletion in the photolysis of N2O which supports theoretical models and pioneering vacuum ultraviolet spectroscopic measurements of 15N substituted N2O species that predict fluctuations of e around zero in this spectral region (Selwyn and Johnston, 1981). Such a variability in isotopic fractionation could have consequences for atmospheric models of N2O isotopes since actinic flux varies also strongly over narrow wavelength regions between 175 and 200 nm due to the Schumann-Runge bands of oxygen. However, the spacing between maxima and minima of the fractionation constants and of the actinic flux differ by two orders of magnitude in the wavelength domain. The wavelength dependence of fractionation constants in N2O photolysis can thus be approximated by a linear fit with negligible consequences on the actual value of the spectrally averaged fractionation constant. In order to establish this linear fit, additional measurements at wavelengths other than 185 nm were made using broadband light sources, namely D2, Hg/Xe and Sb lamps. The latter lamp was used in conjunction with various interference filters to shift the peak photolysis rate to longer wavelengths. From these experiments and existing data in the literature, a comprehensive picture of the wavelength dependence of N2O photolysis is created.
The flux of carbonyl sulfide and carbon disulfide between the atmosphere and a spruce forest
Authors: Xu X. , Bingemer H. G. , Schmidt U. 
Published: April 2010

Abstract. Turbulent fluxes of carbonyl sulfide (COS) and carbon disulfide (CS2) were measured over a spruce forest in Central Germany using the relaxed eddy accumulation (REA) technique. A REA sampler was developed and validated using simultaneous measurements of CO2 fluxes by REA and by eddy correlation. REA measurements were conducted during six campaigns covering spring, summer, and fall between 1997 and 1999. Both uptake and emission of COS and CS2 by the forest were observed, with deposition occurring mainly during the sunlit period and emission mainly during the dark period. On the average, however, the forest acts as a sink for both gases. The average fluxes for COS and CS2 are -93 ± 11.7 pmol m -2 s -1 and -18 ± 7.6 pmol m -2 s -1, respectively. The fluxes of both gases appear to be correlated to photosynthetically active radiation and to the CO2 and H2O fluxes, supporting the idea that the air-vegetation exchange of both gases is controlled by stomata. An uptake ratio COS / CO2 of 10 ± 1.7 pmol mmol -1 has been derived from the regression line for the correlation between the COS and CO2 fluxes. This uptake ratio, if representative for the global terrestrial net primary production, would correspond to a sink of 2.3 ± 0.5 Tg COS yr-1.
Intercontinental transport of nitrogen oxide pollution plumes
Authors: Wenig M. , Spichtinger N. , Stohl A. , Held G. , Beirle S. , Wagner T. , Jähne B. , Platt U. 
Published: April 2010

Abstract. We describe the first satellite observation of intercontinental transport of nitrogen oxides emitted by power plants, verified by simulations with a particle tracer model. The analysis of such episodes shows that anthropogenic NOx plumes may influence the atmospheric chemistry thousands of kilometers away from its origin, as well as the ocean they traverse due to nitrogen fertilization. This kind of monitoring became possible by applying an improved algorithm to extract the tropospheric fraction of NO2 from the spectral data coming from the GOME instrument. As an example we show the observation of NO2 in the time period 4--14 May, 1998, from the South African Plateau to Australia which was possible due to favourable weather conditions during that time period which availed the satellite measurement. This episode was also simulated with the Lagrangian particle dispersion model FLEXPART which uses NOx emissions taken from an inventory for industrial emissions in South Africa and is driven with analyses from the European Centre for Medium-Range Weather Forecasts. Additionally lightning emissions were added by utilizing Lightning Imaging Sensor data. Lightning NOx was found to amount to around 10% of the resulting concentrations. Both, the measured and simulated emission plume show matching patterns while traversing the Indian Ocean to Australia and show great resemblance to the aerosol and CO2 transport observed by Piketh et al. (2000)
Hohenpeissenberg Photochemical Experiment (HOPE 2000): Measurements and photostationary state calculations of OH and peroxy radicals
Authors: Handisides G. M. , Plass-Dülmer C. , Gilge S. , Bingemer H. , Berresheim H. 
Published: April 2010

Abstract. Measurements of OH, the sum of peroxy radicals (ROx), 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 4.5 x 106 molecules cm-3 and 7.4 x 106 molecules cm-3. The maximum total ROx 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 14 x 106 molecules cm-3 s-1 on two days. A simple photostationary state balance model was used to simulate the ambient OH and ROx concentrations with the measured data as input. The model was able to reproduce the main features of the diurnal profiles of both OH and ROx. The model results proved to be most sensitive to assumptions about the mixing ratio of formaldehyde (HCHO), which was included as a proxy for carbonyl compounds, and about the partitioning between HO2 and RO2. The measured OH concentration and ROx mixing ratios were reproduced well by assuming the presence of 3 ppbv HCHO and a ratio HO2/RO2 between 1:1 and 1:2. The most important source of OH, and conversely the greatest sink for ROx, was the recycling of HO2 radicals to OH. This reaction was responsible for the recycling of more than 45 x 106 molecules cm-3 s-1 on two days. The most important sink for OH, and the largest source of ROx, was the oxidation of NMHCs, in particular, of isoprene and the monoterpenes.
Three years of routine Raman lidar measurements of tropospheric aerosols: Planetary boundary layer heights, extinction and backscatter coefficients
Authors: Schneider J. , Eixmann R. 
Published: April 2010

Abstract. We have performed a three-year series of routine lidar measurements on a climatological base. To obtain an unbiased data set, the measurements were taken at preselected times. The measurements were performed between 1 December 1997, and 30 November 2000, at Kühlungsborn, Germany (54°07' N, 11°46' E). Using a Rayleigh/Mie/Raman lidar system, we measured the aerosol backscatter coefficients at three wavelengths in and above the planetary boundary layer. The aerosol extinction coefficient has been determined at 532 nm, but here the majority of the measurements has been restricted to heights above the boundary layer. Only after-sunset measurements are included in this data set since the Raman measurements were restricted to darkness. For the climatological analysis, we selected the cloud-free days out of a fixed measurement schedule. The annual cycle of the boundary layer height has been found to have a phase shift of about 25 days with respect to the summer/winter solstices. The mean values of the extinction and backscatter coefficients do not show significant annual differences. The backscatter coefficients in the planetary boundary layer were found to be about 10 times higher than above. The mean aerosol optical depth above the boundary layer and below 5 km is 0.26 (±1.0) x 10-2 in summer, and 1.5 (±0.95) x 10-2 in winter, which almost negligible compared to values measured in the boundary layer. A cluster analysis of the backward trajectories yielded two major directions of air mass origin above the planetary boundary layer and 4 major directions inside. A marked difference between the total aerosol load dependent on the air mass origin could be found for air masses originating from the west and travelling at high wind speeds. Comparing the measured spectral dependence of the backscatter coefficients with data from the Global Aerosol Data Set, we found a general agreement, but only a few conclusions with respect to the aerosol type could be draws due to the high variability of the measured backscatter coefficients.
On the origin of tropospheric O3 over the Indian Ocean during the winter monsoon: African biomass burning vs. stratosphere-troposphere exchange
Authors: de Laat A. T. J. 
Published: April 2010

Abstract. A comparison and analysis of modeled and measured O3 profiles from the INDOEX campaign is presented. European Centre for Medium-Range Weather Forecast (ECMWF) meteorological analyses have been assimilated into the model to represent actual meteorology. The focus of this study is on two commonly observed features in the O3 profiles: mid tropospheric O3 maxima (300--500 hPa) over the tropical Indian Ocean, and the upper-tropospheric O3 laminae that occur above approximately 14 km (>150 hPa) altitude. A comparison of model simulated O3 profiles with measured O3 profiles indicates that the model realistically simulates the observed mid-tropospheric O3 maxima. An analysis of the model simulations shows that the major source of the mid-tropospheric O3 maxima is advection of polluted air masses from continental biomass burning areas over Africa, with generally only a small contribution of stratospheric O3. Previous studies hinted at Stratosphere-Troposphere exchange (STE) along the subtropical jet (STJ) as the primary source of the mid-tropospheric O3 maxima over the Indian Ocean. Analysis of the model simulations shows that the mechanism causing the mid-tropospheric transport of African biomass burning pollution and stratospheric air masses are frontal zones or waves passing along the subtropical jets, causing advection of tropical air masses in the prefrontal zone. Furthermore, these frontal zones or waves also cause STE at the mid-latitudinal side of the STJ. The model simulations also indicate that the contribution of STE in general is minor compared to advection and in situ tropospheric production of O3 for the mid-tropospheric O3 budget over the Indian Ocean region. An analysis of the model simulations shows that the model cannot exactly reproduce the measured upper-tropospheric O3 maxima. However, modeled O3 mixing ratios at 14 and 16 km altitude are significantly higher than at 8 to 12 km altitude, indicating that the model does simulate an upper-tropospheric layer. According to the model simulations, the sources of O3 at 14 and 16 km altitude are advection of both tropospheric and stratospheric O3 as well as in situ O3 formation.
A revised parameterization for gaseous dry deposition in air-quality models
Authors: Zhang L. , Brook J. R. , Vet R. 
Published: April 2010

Abstract. A parameterization scheme for calculating gaseous dry deposition velocities in air-quality models is revised based on recent study results on non-stomatal uptake of O3 and SO2 over 5 different vegetation types. Non-stomatal resistance, which includes in-canopy aerodynamic resistance, soil resistance and cuticle resistance, for SO2 and O3 is parameterized as a function of friction velocity, relative humidity, leaf area index, and canopy wetness. Non-stomatal resistance for all other species is scaled to those of SO2 and O3 based on their chemical and physical characteristics. Stomatal resistance is calculated using a leaf-stomatal-resistance model for all gaseous species of interest. The improvements in the present model compared to its earlier version include a newly developed non-stomatal resistance formulation, a realistic treatment of cuticle and ground resistance in winter and the handling of seasonally-dependent input parameters. Model evaluation shows that the revised parameterization can provide more realistic deposition velocities for both O3 and SO2, especially for wet canopies. Example model output shows that the parameterization provides reasonable estimates of dry deposition velocities for different gaseous species, land types and diurnal and seasonal variations. Maximum deposition velocities from model output are close to reported measurement values for different land types. The current parameterization can be easily adopted into different air-quality models that require inclusion of dry deposition processes.
Sensitivity studies of oxidative changes in the troposphere in 2100 using the GISS GCM
Authors: Grenfell J. L. , Shindell D. T. , Grewe V. 
Published: April 2010

Abstract. We examine the relative importance of chemical precursor emissions affecting ozone (O3) and hydroxyl (OH) for the year 2100. Runs were developed from the Comparison of Tropospheric Oxidants (Ox_Comp) modeling workshop year 2100 A2p emissions scenario, part of the Intergovernmental Panel on Climate Change (IPCC) third assessment report (TAR). While TAR examined only cumulative change, we examine individual components (NOx, CH4, CO, etc.). Also, since there will be climate changes in 2100 (not accounted for by TAR), we investigate the effect of changing our fixed SSTs/ocean ice from present day to 2100 conditions, as projected by a coupled ocean-atmosphere model with doubled CO2. Largest changes arose from the run with 2100 industrial NOx O3= +16.9%, OH= +29.4% in July) and the run with 2100 methane (O3= +17.4%, OH= −19.1% in July). In the latter run, large ozone increases in the NH upper troposphere appeared to repartition HO2 into OH to such an extent that the lowering in OH associated with increased methane was overwhelmed in that region. Incorporating all changes collectively led to the July tropospheric ozone burden increasing from 426 to 601 Tg (+41.1%) and the July OH concentration increasing from 13.6 to 15.2×105 molecules/cm3 (+11.8%).
On the formation of radiation fogs under heavily polluted conditions
Authors: Kokkola H. , Romakkaniemi S. , Laaksonen A 
Published: April 2010

Abstract. We have studied the effect of gaseous pollutants on fog droplet growth in heavily polluted air using a model that describes time-dependent sulfate production in the liquid phase and thermodynamical equilibrium between the droplets and the gas phase. Our research indicates that the oxidation of SO2 to sulfate has a significant effect on fog droplet growth especially when hygroscopic trace gases, for example HNO3 andNH3 are present. The increased sulfate production by dissolution of hygroscopic gases results from increased pH (caused by absorption of ammonia) and from the increased size of the fog/smog droplets. As a result of the enhancement of the droplet growth the optical thickness of the fog will increase.
Model study of multiphase DMS oxidation with a focus on halogens
Authors: von Glasow R. , Crutzen P. J. 
Published: April 2010

Abstract. We studied the oxidation of dimethylsulfide (DMS) in the marine boundary layer (MBL) with a one-dimensional numerical model and focused on the influence of halogens. Our model runs show that there is still significant uncertainty about the end products of the DMS addition pathway, which is especially caused by uncertainty in the product yield of the reaction MSIA + OH. Under cloud-free conditions a MSA yield of only 5% in this reaction could make the addition pathway in the gas phase dominant for MSA formation whereas a yield of 0% would make the gas phase unimportant. Under cloudy conditions the uptake of DMSO and MSIA to droplets results in a contribution of the gas phase of only about 2% to the total formation rate of MSA. The aqueous phase reaction MSIA + OH is the main source for total MSA when gas phase production of MSA is unimportant. BrO strongly increases the importance of the addition branch in the oxidation of DMS even when present at mixing ratios smaller than 0.5 pmol mol−1. The inclusion of halogen chemistry leads to higher DMS oxidation rates and smaller DMS to SO2 conversion efficiencies. The DMS to SO2 conversion efficiency is also drastically reduced under cloudy conditions. In clouds especially during winter the aqueous phase reaction DMS + O3 contributes 4–18% to total DMS oxidation. In cloud-free model runs between 5 and 15% of the oxidized DMS reacts further to particulate sulfur, in cloudy runs this fraction is almost 100%. In general, more particulate sulfur is formed when halogen chemistry is included. A possible enrichment of HCO3 in fresh sea salt aerosol would increase pH values enough to make the reaction of S(IV)* with O3 dominant for sulfate production. It leads to a shift from MSA to nss-SO4−2 production but increases the total nss-SO4−2 only somewhat because almost all available sulfur is already oxidized to particulate sulfur in the base scenario. We discuss how realistic this is for the MBL. We found the reaction MSAaq + OH to contribute about 10\\% to the production of nss-SO4−2 in clouds. It is unimportant for cloud-free model runs. Sulfate production by HOClaq and HOBraq is important in cloud droplets even for small Br− deficits and related small gas phase halogen concentrations. We found differences in the diurnal variation of the Br− in sea salt aerosol with a peak in the morning when the loss of Br− from the sea salt is small and a peak during day when the loss is almost complete. Overall we find that the presence of halogens lead to processes that decrease the albedo of stratiform clouds in the MBL.