bluuebunny/crossref_metadata_2025 huggingface dataset:
Elemental content of PM2.5 aerosol particles collected in Göteborg during the Göte-2005 campaign in February 2005
Authors: Boman J. , Gatari M. J. , Janhäll S. , Shannigrahi A. S. , Wagner A.
Published: April 2010

Abstract. The Göte–2005 measurement campaign aimed at studying the influence of the winter thermal inversions on urban air pollution. Elemental speciation of PM2.5 aerosol particles, collected on Teflon filters at three urban sites and one rural site in the Göteborg region, was a major part of the study. Trace element analysis was done by Energy Dispersive X-Ray Fluorescence (EDXRF) spectrometry and the concentrations of S, Cl, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, Br and Pb were determined. The elemental content of the particles, local wind speed and direction, and backward trajectories were used to investigate possible sources for the pollutants. We concluded that S, V, Ni, Br, and Pb had their main sources outside the central Göteborg area, since elevated concentrations of these elements were not observed during an inversion episode. Sea traffic and harbour activities were identified, primarily by the S and V content of the particles. This study showed that the elemental analysis by EDXRF presents valuable information for tracing the origin of air masses arriving at a measurement site.
Long-term behavior of the concentration of the minor constituents in the mesosphere – a model study
Authors: Grygalashvyly M. , Sonnemann G. R. , Hartogh P.
Published: April 2010

Abstract. We investigate the influence the rising concentrations of methane, nitrous oxide and carbon dioxide which have occurred since the pre-industrial era, have had on the chemistry of the mesosphere. For this investigation we use our global 3-D-model COMMA-IAP which was designed for the exploration of the MLT-region and in particular the extended mesopause region. Assumptions and approximations for the trends in the Lyman-α flux (needed for the water vapor dissociation rate), methane and the water vapor mixing ratio at the hygropause are necessary to accomplish this study. To approximate the solar Lyman-α flux back to the pre-industrial time, we derived a quadratic fit using the sunspot number record which extends back to 1749 and is the only solar proxy available for the Lyman-α flux prior to 1947. We assume that methane increases with a constant growth rate from the pre-industrial era to the present. An unsolved problem for the model calculations consists of how the water vapor mixing ratio at the hygropause should be specified during this period. We assume that the hygropause was dryer during pre-industrial times than the present. As a consequence of methane oxidation, the model simulation indicates that the middle atmosphere has become more humid as a result of the rising methane concentration, but with some dependence on height and with a small time delay of few years. The solar influence on the water vapor mixing ratio is insignificant below about 80 km in summer high latitudes, but becomes increasingly more important above this altitude. The enhanced water vapor concentration increases the hydrogen radical concentration and reduces the mesospheric ozone. A second region of stronger ozone decrease is located in the vicinity of the stratopause. Increases in CO2 concentration enhance slightly the concentration of CO in the mesosphere. However, its influence upon the chemistry is small and its main effect is connected with a cooling of the upper atmosphere. The long-term behavior of water vapor is discussed in particular with respect to its impact on the NLC region.
The Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CATT-BRAMS) – Part 1: Model description and evaluation
Authors: Freitas S. R. , Longo K. M. , Silva Dias M. A. F. , Chatfield R. , Silva Dias P. , Artaxo P. , Andreae M. O. , Grell G. , Rodrigues L. F. , Fazenda A. , Panetta J.
Published: April 2010

Abstract. We introduce the Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CATT-BRAMS). CATT-BRAMS is an on-line transport model fully consistent with the simulated atmospheric dynamics. Emission sources from biomass burning and urban-industrial-vehicular activities for trace gases and from biomass burning aerosol particles are obtained from several published datasets and remote sensing information. The tracer and aerosol mass concentration prognostics include the effects of sub-grid scale turbulence in the planetary boundary layer, convective transport by shallow and deep moist convection, wet and dry deposition, and plume rise associated with vegetation fires in addition to the grid scale transport. The radiation parameterization takes into account the interaction between the simulated biomass burning aerosol particles and short and long wave radiation. The atmospheric model BRAMS is based on the Regional Atmospheric Modeling System (RAMS), with several improvements associated with cumulus convection representation, soil moisture initialization and surface scheme tuned for the tropics, among others. In this paper the CATT-BRAMS model is used to simulate carbon monoxide and particulate material (PM2.5) surface fluxes and atmospheric transport during the 2002 LBA field campaigns, conducted during the transition from the dry to wet season in the southwest Amazon Basin. Model evaluation is addressed with comparisons between model results and near surface, radiosondes and airborne measurements performed during the field campaign, as well as remote sensing derived products. We show the matching of emissions strengths to observed carbon monoxide in the LBA campaign. A relatively good comparison to the MOPITT data, in spite of the fact that MOPITT a priori assumptions imply several difficulties, is also obtained.
Evaluation of recently-proposed secondary organic aerosol models for a case study in Mexico City
Authors: Dzepina K. , Volkamer R. M. , Madronich S. , Tulet P. , Ulbrich I. M. , Zhang Q. , Cappa C. D. , Ziemann P. J. , Jimenez J. L.
Published: April 2010

Abstract. Recent field studies have found large discrepancies in the measured vs. modeled SOA mass loadings in both urban and regional polluted atmospheres. The reasons for these large differences are unclear. Here we revisit a case study of SOA formation in Mexico City described by Volkamer et al. (2006), during a photochemically active period when the impact of regional biomass burning is minor or negligible, and show that the observed increase in OA/ΔCO is consistent with results from several groups during MILAGRO 2006. Then we use the case study to evaluate three new SOA models: 1) the update of aromatic SOA yields from recent chamber experiments (Ng et al., 2007); 2) the formation of SOA from glyoxal (Volkamer et al., 2007a); and 3) the formation of SOA from primary semivolatile and intermediate volatility species (P-S/IVOC) (Robinson et al., 2007). We also evaluate the effect of reduced partitioning of SOA into POA (Song et al., 2007). Traditional SOA precursors (mainly aromatics) by themselves still fail to produce enough SOA to match the observations by a factor of ~7. The new low-NOx aromatic pathways with very high SOA yields make a very small contribution in this high-NOx urban environment as the RO2·+NO reaction dominates the fate of the RO2· radicals. Glyoxal contributes several μg m−3 to SOA formation, with similar timing as the measurements. P-S/IVOC are estimated from equilibrium with emitted POA, and introduce a large amount of gas-phase oxidizable carbon that was not in models before. With the formulation in Robinson et al. (2007) these species have a high SOA yield, and this mechanism can close the gap in SOA mass between measurements and models in our case study. However the volatility of SOA produced in the model is too high and the O/C ratio is somewhat lower than observations. Glyoxal SOA helps to bring the O/C ratio of predicted and observed SOA into better agreement. The sensitivities of the model to some key uncertain parameters are evaluated.
Variability of residence time in the Tropical Tropopause Layer during Northern Hemisphere winter
Authors: Krüger K. , Tegtmeier S. , Rex M.
Published: April 2010

Abstract. For the first time the long-term interannual and spatial variability of residence time (τ) is presented for the TTL between 360 K and 400 K potential temperature (~14 to 18 km altitude). The analysis is based on a Lagrangian approach using offline calculated diabatic heating rates as vertical velocities, covering Northern Hemisphere (NH) winters from 1962–2004. The residence time τLCP–400 K, being the duration time of air parcels in the layer between the Lagrangian Cold Point (LCP) and 400 K, varies spatially and is longer (>50 days) over the maritime continent as the LCP is lowest there (<370 K). Comparing three theta layers within the TTL reveals the vertical dependence of τ. We derive a mean duration time of 34 days for 360–380 K (lower TTL), 38 days for 380–400 K (upper TTL) and 70 days for 360–400 K theta layers for the 1962–2001 period. A case analysis reveals that τ is positively skewed for 360–380 K and 380–400 K during La Niña and El Niño Southern Oscillation (ENSO) neutral years. For these cases, ~60% of air parcels travel from 360 K to 380 K within 25 days. There is large interannual variability for τ varying up to ±20% from the long-term mean, with strongest variability seen in the lower part of the TTL. Statistical analysis reveals a significant anti-correlation between the residence time and the extratropical and subtropical wave driving in the lowermost stratosphere.
The basic mechanism behind the hurricane-free warm tropical ocean
Authors: Yuan Z. , Qian Y.-K. , Wu J. , Qi J.
Published: April 2010

Abstract. No hurricane is detected in the tropics off the Brazilian coast due to the lack of initial conditions (e.g., the weak vertical shear of horizontal wind) despite that high sea surface temperature is available. According to previous studies, the initial conditions (as the ingredients of hurricane's embryo) are related so that the thick warm-and-moist layer (due to the updraft vapour) below a cold-and-dry layer frames the convective instability which enhances diabatic processes accompanied by tropical cyclones with the weak vertical shear. So the basic question is how, starting with an internal-disturbance-free balance-situation, external forces create the rapidly-upward acceleration of moist air at the warm sea surface. The answer is revealed by the vertical-momentum equation which shows that boosted by the external-force-induced significant lower-layer equatorial westerly wind (LLEWW), the upward (unit-mass) acceleration could be as significant as the midlatitude Coriolis force. Besides creating cyclonic vortices through the upward acceleration and diabatic processes, the external-force-induced significant-LLEWW could directly create cyclonic wind shears along with easterly jets for the low-level cyclonic vorticity through reducing the peak value of zonally-homogeneous trade easterlies (centered at the Equator between the Northern and Southern Hemisphere subtropical high-belts). We emphasize external forces to avoid the ''chicken-and-egg'' problem accompanying nonlinear interactions of internal-forcing processes. The external-force-induced significant-LLEWW could result from the deflection of the cross-equatorial flow characterized by the seasonal shift coincident with that of locations of most embryos. This significant cross-equatorial flow is driven by the significant differential heating between the largest continent with the highest plateau and the largest ocean with the warm pool located to the east and on the equatorward side of the continent on the rotating Earth. Unfortunately, in the tropics off the Brazilian coast, the differential heating is weak between the relatively-small ocean and land mostly covered by tropical rainforest. No significant-LLEWW means no hurricane's embryo. A warm spawning ground without the embryo means no hurricane. Our investigation suggests that the external-force-induced significant-LLEWW embedded in the significant trade easterlies over the warm ocean be necessary and sufficient for making the embryo originate in an internal-disturbance-free balance-situation.
Estimating the maritime component of aerosol optical depth and its dependency on surface wind speed using MODIS and QuikSCAT data
Authors: Lehahn Y. , Koren I. , Boss E. , Ben-Ami Y. , Altaratz O.
Published: April 2010

Abstract. Seven years (2002–2008) of satellite measurements from SeaWinds aboard Quick Scatterometer (QuikSCAT) and Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra are used for providing a global view on the link between surface wind speed and marine aerosol optical depth. This study shows that away form the continents the correlation time between the surface winds and the marine aerosol exceeds 4 h and therefore the two measurements can be linked. A systematic comparison between the satellite derived fields at different locations over the World Ocean allows to: (i) separate the relative contribution of wind-induced marine aerosol to the aerosol optical depth (ii) identify a threshold wind speed for triggering maritime contribution to aerosol optical depth; and (iii) extract an empirical linear equation linking marine aerosol optical depth and wind intensity. Wind induced marine aerosol contribution to aerosol optical depth is found to be dominated by the coarse mode elements. The threshold wind speed for triggering emission of coarse maritime aerosol is remarkably consistent with an average value of 4.1±0.1 m/s. When wind intensity exceeds the threshold value, coarse mode marine aerosol optical depth is linearly correlated to the surface wind speed, with a consistent slope of 0.0082±0.0004 s/m. The background aerosol optical depth, associated with aerosols that are not produced in-situ through wind driven processes, shows relatively large seasonal and geographical variability, and can be used for estimating the contribution of terrestrial aerosols to the aerosol optical depth over the ocean.
Volcanic ash as fertiliser for the surface ocean
Authors: Langmann B. , Zakšek K. , Hort M. , Duggen S.
Published: April 2010

Abstract. Iron is a key limiting micro-nutrient for marine primary productivity. It can be supplied to the ocean by atmospheric dust deposition. Volcanic ash deposition into the ocean represents another external and so far largely neglected source of iron. This study demonstrates strong evidence for natural fertilisation in the iron-limited oceanic area of the NE Pacific, induced by volcanic ash from the eruption of Kasatochi volcano in August 2008. Atmospheric and oceanic conditions were favourable to generate a massive phytoplankton bloom in the NE Pacific Ocean which for the first time establishes a causal connection between oceanic iron-fertilisation and volcanic ash supply.
Rapid growth of HFC-227ea (1,1,1,2,3,3,3-Heptafluoropropane) in the atmosphere
Authors: Laube J. C. , Martinerie P. , Witrant E. , Blunier T. , Schwander J. , Brenninkmeijer C. A. M. , Schuck T. J. , Bolder M. , Röckmann T. , van der Veen C. , Bönisch H. , Engel A. , Mills G. P. , Newland M. J. , Oram D. E. , Reeves C. E. , Sturges W. T.
Published: April 2010

Abstract. We report the first measurements of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), a substitute for ozone depleting compounds, in remote regions of the atmosphere and present evidence for its rapid growth. Observed mixing ratios ranged from below 0.01 ppt in deep firn air to 0.59 ppt in the northern mid-latitudinal upper troposphere. Firn air samples collected in Greenland were used to reconstruct a history of atmospheric abundance. Year-on-year increases were deduced, with acceleration in the growth rate from 0.026 ppt per year in 2000 to 0.057 ppt per year in 2007. Upper tropospheric air samples provide evidence for a continuing growth until late 2009. Furthermore we calculated a stratospheric lifetime of 370 years from measurements of air samples collected on board high altitude aircraft and balloons. Emission estimates were determined from the reconstructed atmospheric trend and suggest that current "bottom-up" estimates of global emissions for 2005 are too high by more than a factor of three.
Derivation of the stoichiometric coefficient of water (νw) to account for water uptake by atmospheric aerosols
Authors: Metzger S. , Steil B. , Penner J. E. , Xu L. , Lelieveld J.
Published: April 2010

Abstract. In this work we derive the effective stoichiometric coefficient of water (vw), introduced by Metzger and Lelieveld, 2007 (ML07), from first principles. We give examples of the application of vw in CPU efficient computations of the Deliquescence Relative Humidity (DRH) and the water uptake of atmospheric aerosols, being important parameters in atmospheric chemistry and climate modeling. We show that the application of vw in a gas/liquid/solid aerosol equilibrium partitioning model (EQSAM3) leads to results that are in excellent agreement with those of widely used thermodynamic (reference) models (E-AIM and ISORROPIA2) for various single salt solutions (NaCl, NH4NO3, (NH4)2SO4, NH4HSO4, NaHSO4) and the corresponding mixed solutions (including (NH4)3H(SO4)2 and Na3H(SO4)2), notwithstanding the distinct different theoretical and numerical concepts on which these models are based.
Aerosol dynamics in the Copenhagen urban plume during regional transport
Authors: Wang F. , Roldin P. , Massling A. , Kristensson A. , Swietlicki E. , Fang D. , Ketzel M.
Published: April 2010

Abstract. Aerosol particles in the submicrometer size range (PM1) have serious impacts on human health and climate. This work aims at studying the processes relevant for physical particle properties in and downwind Copenhagen and evaluating the capability of a detailed aerosol dynamics and chemistry model (ADCHEM) to describe the submicrometer aerosol dynamics in a complex urbanized region, subjected to a variety of important anthropogenic sources. The study area is the Oresund Region with Copenhagen (about 1.8 million people) as the major city, including the strait separating Denmark and Sweden with intense ship traffic. Modeled aerosol particle number size distributions and NOx concentrations are evaluated against ground-based measurements from two stations in the Copenhagen area in Denmark and one station in southern Sweden. The measured and modeled increments in NOx concentrations from rural background to the urban area showed satisfactory agreement, indicating that the estimated NOx emissions and modeled atmospheric dispersion are reasonable. For three out of five case studies, the modeled particle number concentrations and size distributions are in satisfactory agreement with the measurements at all stations along the trajectories. For the remaining cases the model significantly underestimates the particle number concentration over Copenhagen, but reaches acceptable agreement with the measurements at the downwind background station in Sweden. The major causes for this were identified as being the lack of spatial resolution in the meteorological data in describing boundary layer mixing heights and the uncertainty in the exact air mass trajectory path over Copenhagen. In addition, particle emission factors may also have been too low. It was shown that aerosol dynamics play a minor role from upwind to urban background, but are important 1–2 h downwind the city. Real-world size-resolved traffic number emission factors which take into account the initial ageing in the street canyon can be used to model traffic emissions in urban plume studies.
Composition and sources of particulate matter in an industrialised Alpine valley
Authors: Perron N. , Sandradewi J. , Alfarra M. R. , Lienemann P. , Gehrig R. , Kasper-Giebl A. , Lanz V. A. , Szidat S. , Ruff M. , Fahrni S. , Wacker L. , Baltensperger U. , Prévôt A. S. H.
Published: April 2010

Abstract. A three-week long field campaign was carried out under autumnal meteorological conditions at four valley floor sites in the industrialised Swiss Rhone Valley. For one week of stable meteorological conditions, particulate matter with an aerodynamic diameter below 10 μm (PM10) was analysed from daily filters using ion chromatography, X-ray fluorescence, anhydrosugars and radiocarbon analysis of the organic and elemental matter (OM and EM, respectively). Furthermore, PM1 composition along the whole campaign was monitored in Massongex (a site near industries) by a seven-wavelength aethalometer and a quadrupole aerosol mass spectrometer (Q-AMS). At all sites, PM10 secondary inorganics and non-fossil EM and OM exhibited relatively stable concentrations over the selected days. On the contrary, PM10 fossil carbonaceous fractions, mineral dust components and several trace elements showed a significant decrease on Sunday, compared to the analysed working days. Their concentrations were also highly correlated. This evidenced the role of exhaust and resuspension emissions by heavy-duty vehicle traffic to the PM10 concentrations along the valley. In Massongex, organic matter and black carbon (BC) were the main contributors to PM1 over the campaign (accounting for 45% and 18% of PM1, respectively). An optical discrimination of BC highlighted the prevalence of fossil over wood-burning sources. Three types of PM1 organics could be identified by factor analysis: primary wood-burning organic aerosol (P-WBOA) dominated the PM1 carbonaceous fraction, followed by oxygenated organics (OOA) mostly representing secondary organics, and by traffic or possibly industry-related hydrocarbon-like organics (HOA) as the smallest carbonaceous contribution. Furthermore, unusually high contributions of fine chloride were detected at all sites. They were attributed to ammonium chloride (NH4Cl) in Massongex and represented the only significant component exclusively attributable to industrial emissions.
Rarity of upper-tropospheric low O3 concentration events during MOZAIC flights
Authors: Asman W. A. H. , Lawrence M. G. , Brenninkmeijer C. A. M. , Crutzen P. J. , Cuijpers J. W. M. , Nédélec P.
Published: April 2010

Abstract. Only a few previous observations of very low O3 concentrations in the upper troposphere are available. The aim of this study was to examine the rich MOZAIC data set for more. Flights with at least 25 4 s averaged concentrations less than 8 ppbv at pressures lower than 500 hPa measured using commercial aircraft within the MOZAIC project have been analysed. There are eleven flights that fulfill these conditions (excluding artefacts as discussed below), representing about 0.001% of all measurements during the analyzed period August 1994–December 1997. The low O3 events occurred over Southeast Asia, Africa, Brazil and the sea area 200 km east of Florida (US) and were all likely to be associated with transport of air masses from tropical sea areas. These low concentration events occur in the upper troposphere during periods with generally low concentrations. They are not only found over sea, but also over land at pressure levels as low as 179 hPa.
The Mt Cimone, Italy, free tropospheric campaign: principal characteristics of the gaseous and aerosol composition from European pollution, Mediterranean influences and during African dust events
Authors: Balkanski Y. , Bauer S. E. , van Dingenen R. , Bonasoni P. , Schulz M. , Fischer H. , Gobbi G. P. , Hanke M. , Hauglustaine D. , Putaud J. P. , Stohl A. , Raes F.
Published: April 2010

Abstract. A 5 weeks experiment (1 June to 5 July 2000) took place at a mountain site, Mt Cimone (44°11' N, 10°42' E, 2165 m a.s.l.), that is representative of Southern Europe background conditions. During this field campaign, a comprehensive characterisation of trace gases and radicals, involved in the production and destruction of O3, as well as of chemical, physical and optical properties of the aerosol was done. Atmospheric gases and aerosols were measured continuously over the 5 weeks period, in order to characterize their background concentrations in the free troposphere and their respective differences in air containing dust aerosols advected from Africa. Due to its location and elevation, Mt Cimone gets free tropospheric air both from the Mediterranean and from the Po Valley, which makes it an invaluable place to study gas/aerosol interactions. A global chemical model coupled to a GCM was used to simulate based upon ECMWF reanalysis the ozone over the region during the period of the field study. The heterogeneous reactions of O3, N2O5, HNO3 and NO3 were accounted for. We estimate that during the field campaign, the effect of heterogeous reactions was to reduce by 8 to 10% the ozone concentration at MTC in cases when air had passed over the Mediterranean Sea. When air was coming from the Atlantic or continental Europe, the reduction of ozone is still 4%. This reduction is mostly due to the large uptake of HNO3 and is the the topic of ongoing work to assess how it affects the global cycle of O3 and the global nitrogen budget.
Aircraft measurements of nitrogen oxides, ozone, and carbon monoxide during MINOS 2001: distributions and correlation analyses
Authors: Heland J. , Ziereis H. , Schlager H. , de Reus M. , Traub M. , Lelieveld J. , Roelofs G.-J. , Stock P. , Roiger A.
Published: April 2010

Abstract. We present mean altitude profiles of NOx, NOy, O3, and CO as measured by the DLR Falcon aircraft during the MINOS 2001 campaign over the Mediterranean in August 2001 and compare the data with results from other aircraft campaigns, namely the SIL 1996 (North Atlantic flight corridor), the POLINAT-2 (North Atlantic flight corridor), and the EXPORT 2000 (central Europe) campaigns. The MINOS NOy, O3, and CO mixing ratios in the free troposphere, especially between 4–8 km, are very similar to those measured during the EXPORT 2000 campaign. However, compared to the other campaigns the MINOS O3 and CO were significantly higher in the boundary layer, by about 20 ppbV and 50 ppbV, respectively. In the second part of the paper the D[O3]/D[NOy], D[O3]/D[CO], D[CO]/D[NOy], and D[NOx]/D[NOy] trace gas correlations were calculated for the MINOS 2001 campaign. It was found that, within the scatter of the data, the overall average altitude profiles of the correlations compared well with data from a literature survey. The analysis of the mean vertical correlation profiles as measured during MINOS 2001 does therefore not single out special meteorological conditions and air mass origins over the Mediterranean in summer but reflects a more general condition of the free troposphere in the northern hemisphere. Correlation analyses for single flights at different altitudes, however, unambiguously identify air masses influenced by the stratosphere, whereas pollution plumes could only be identified with the help of back trajectories.
Trace gas transport in the 1999/2000 Arctic winter: comparison of nudged GCM runs with observations
Authors: van Aalst M. K. , van den Broek M. M. P. , Bregman A. , Brühl C. , Steil B. , Toon G. C. , Garcelon S. , Hansford G. M. , Jones R. L. , Gardiner T. D. , Roelofs G. J. , Lelieveld J. , Crutzen P. J.
Published: April 2010

Abstract. We have compared satellite and balloon observations of methane (CH4) and hydrogen fluoride (HF) during the Arctic winter 1999/2000 with results from the MA-ECHAM4 middle atmospheric general circulation model (GCM). For this purpose, the meteorology in the model was nudged towards ECMWF analyses. This nudging technique is shown to work well for this middle atmospheric model, and offers good opportunities for the simulation of realistic chemistry and transport processes. The current study focuses on transport of HF and CH4, initialized with satellite measurements from the HALOE instrument aboard the UARS satellite. We have compared the model results with HALOE data and balloon measurements throughout the winter, and analyzed the uncertainties associated with tracer initialization, boundary conditions and the passive tracer assumption. This comparison shows that the model represents the Arctic vortex well, including relatively small-scale features. However, while profiles outside the vortex match well, the model underestimates HF and overestimates CH4 concentrations inside the vortex, particularly in the middle stratosphere. This problem is also evident in a comparison of vortex descent rates based upon vortex average tracer profiles from MA-ECHAM4, and various observations, respectively. This could be due to an underestimate of diabatic subsidence in the model, or due to too much mixing between vortex and non-vortex air.
One year boundary layer aerosol size distribution data from five Nordic background stations
Authors: Tunved P. , Hansson H.-C. , Kulmala M. , Aalto P. , Viisanen Y. , Karlsson H. , Kristensson A. , Swietlicki E. , Dal Maso M. , Ström J. , Komppula M.
Published: April 2010

Abstract. Size distribution measurements performed at five different stations have been investigated during a one-year period between 01 June 2000 and 31 May 2001 with focus on diurnal, seasonal and geographical differences of size distribution properties. The stations involved cover a large geographical area ranging from the Finnish Lapland (67° N) down to southern Sweden (56° N) in the order Värriö, Pallas, Hyytiälä, Aspvreten and Vavihill. The shape of the size distribution is typically bimodal during winter with a larger fraction of accumulation mode particles compared to the other seasons. Highest Aitken mode concentration is found during summer and spring. The maximum of nucleation events occur during spring months. Nucleation events occur during other seasons as well, although not as frequently. Large differences were found between different categories of stations. Northerly located stations such as Pallas and Värriö presented well-separated Aitken and accumulation modes, while the two modes often overlap significantly at the two southernmost stations Vavihill and Aspvreten. A method to cluster trajectories was used to analyse the impact of long-range transport on the observed aerosol properties. Clusters of trajectories arriving from the continent were clearly associated with size distributions shifted towards the accumulation mode. This feature was more pronounced the further south the station was located. Marine- or Arctic-type clusters were associated with large variability in the nuclei size ranges. A quasi-lagrangian approach was used to investigate transport related changes in the aerosol properties. Typically, an increase in especially Aitken mode concentrations was observed when advection from the north occurs, i.e. allowing more continental influence on the aerosol when comparing the different measurement sites. When trajectory clusters arrive to the stations from SW, a gradual decrease in number concentration is experienced in all modes as latitude of measurement site increases.
Radiative effects of tropospheric ionisation
Authors: Aplin K. L.
Published: April 2010

Abstract. Despite the increasing evidence that cosmic ray variations may influence clouds and climate, there has been little discussion of the direct radiative effects of atmospheric ionisation. Laboratory experiments show that hydrated molecular cluster-ions, formed in the atmosphere by cosmic rays, absorb in the infra-red continuum at wavelengths of 9–12 μm. The tropospheric magnitude of this effect is estimated: transmittance anomalies from clear sky ion concentrations peak at ~2% at 10 km in the mid-latitudes. A simple isothermal clear sky atmospheric model suggests the integrated effect of the absorption is ~2 Wm−2. The effect appears detectable in existing surface data sets; surface micrometeorological data shows a significant anticorrelation between downwelling infra-red radiation and atmospheric cosmic ray ionisation. This is consistent with the infra-red attenuation observed in laboratory studies of cluster-ion absorption. If atmospheric ionisation from cosmic rays has universally direct radiative effects, then reinterpretation of satellite cloud data may be necessary.
Köhler theory for a polydisperse droplet population in the presence of a soluble trace gas, and an application to stratospheric STS droplet growth
Authors: Kokkola H. , Romakkaniemi S. , Laaksonen A.
Published: April 2010

Abstract. We consider the equilibrium behavior of a polydisperse aqueous droplet population as a function of relative humidity (RH) when a soluble trace gas, such as nitric acid, is present in the system. The droplet population experiences a splitting when the RH is increased sufficiently. This splitting is not related to the traditional Köhler activation of cloud droplets, as it may occur at relative humidities below 100%. Remarkably, the splitting always takes place in such a way that the largest size class of the (discretized) droplet population starts taking up the soluble trace gas efficiently, growing steeply as a function of RH, and forcing the smaller droplets to shrink. We consider this behavior in terms of open and closed system Köhler curves (open system referring to one in which the trace gas concentration remains constant and closed system to one in which the gas concentration decreases as a result of uptake of the trace gas). We show how the open and closed system Köhler curves are related, and that the splitting of the population can be explained in terms of closed system curves crossing the Köhler maxima of the open system curves. We then go on to consider time-dependent situations, and show that due to gas-phase mass transfer limitations, the splitting of the size distributions moves toward smaller sizes as the rate of RH increase becomes more rapid. Finally, we consider stratospheric supercooled ternary solution droplet populations, and show that the splitting described using the new theory may explain observed bimodal size distributions.
Small scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes
Authors: Rapp M. , Lübken F.-J. , Blix T. A.
Published: April 2010

Abstract. We present small scale variations of electron number densities and particle charge number densities measured in situ in the presence of polar mesosphere summer echoes. It turns out that the small scale fluctuations of electrons and negatively charged particles show a strong anticorrelation down to the smallest scales observed. Comparing these small scale structures with the simultaneously measured radar signal to noise profile, we find that the radar profile is well described by the power spectral density of both electrons and charged particles at the radar half wavelength (= the Bragg scale). Finally, we consider the shape of the power spectra of the observed plasma fluctuations and find that both charged particles and electrons show spectra that can be explained in terms of either neutral air turbulence acting on the distribution of a low diffusivity tracer or the fossil remnants of a formerly active turbulent region. All these results are consistent with the theoretical ideas by Rapp and Lübken (2003) suggesting that PMSE can be explained by a combination of active and fossil neutral air turbulence acting on the large and heavy charged aerosol particles which are subsequently mirrored in the electron number density distribution that becomes visible to a VHF radar when small scale fluctuations are present.
Intercomparison of aircraft instruments on board the C-130 and Falcon 20 over southern Germany during EXPORT 2000
Authors: Brough N. , Reeves C. E. , Penkett S. A. , Dewey K. , Kent J. , Barjat H. , Monks P. S. , Ziereis H. , Stock P. , Huntrieser H. , Schlager H.
Published: April 2010

Abstract. In the summer 2000 Export aircraft campaign (European eXport of Precursors and Ozone by long-Range Transport), two comprehensively instrumented research aircraft measuring a variety of chemical species flew wing tip to wing tip for a period of one and a quarter hours. During this interval a comparison was undertaken of the measurements of nitrogen oxide (NO), odd nitrogen species (NOy), carbon monoxide (CO) and ozone (O3). The comparison was performed at two different flight levels, which provided a 10-fold variation in the concentrations of both NO (10 to 1000 parts per trillion by volume (pptv)) and NOy (200 to over 2500 pptv). Large peaks of NO and NOy observed from the Falcon 20, which were at first thought to be from the exhaust of the C-130, were also detected on the 4 channel NOx,y instrument aboard the C-130. These peaks were a good indication that both aircraft were in the same air mass and that the Falcon 20 was not in the exhaust plume of the C-130. Correlations and statistical analysis are presented between the instruments used on the two separate aircraft platforms. These were found to be in good agreement giving a high degree of correlation for the ambient air studied. Any deviations from the correlations are accounted for in the estimated inaccuracies of the instruments. These results help to establish that the instruments aboard the separate aircraft are reliably able to measure the corresponding chemical species in the range of conditions sampled and that data collected by both aircraft can be co-ordinated for purposes of interpretation.
Simulation of ozone production in a complex circulation region using nested grids
Authors: Taghavi M. , Cautenet S. , Foret G.
Published: April 2010

Abstract. During ESCOMPTE precampaign (15 June to 10 July 2000), three days of intensive pollution (IOP0) have been observed and simulated. The comprehensive RAMS model, version 4.3, coupled online with a chemical module including 29 species, has been used to follow the chemistry of the zone polluted over southern France. This online method can be used because the code is paralleled and the SGI 3800 computer is very powerful. Two runs have been performed: run1 with one grid and run2 with two nested grids. The redistribution of simulated chemical species (ozone, carbon monoxide, sulphur dioxide and nitrogen oxides) was compared to aircraft measurements and surface stations. The 2-grid run has given substantially better results than the one-grid run only because the former takes the outer pollutants into account. This online method helps to explain dynamics and to retrieve the chemical species redistribution with a good agreement.
The isotope composition of water vapour: A powerful tool to study transport and chemistry of middle atmospheric water vapour
Authors: Bechtel C. , Zahn A.
Published: April 2010

Abstract. A one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. The stable isotope ratios of tropospheric H2O are determined by "physical'' fractionation effects, i.e. phase changes, diffusion processes, and mixing of air masses. Due to these processes water vapour entering the stratosphere (i) is mass-dependently fractionated (MDF), i.e. shifts in the isotope ratio 17O/16O are ~0.52 times of those of 18O/16O and (ii) shows isotope shifts in D/H, which are ~5 times of those in 18O/16O. In stratosphere and mesosphere "chemical'' fractionation, that are the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions are shown to considerably enhance the isotope ratios in the imported tropospheric H2O. Enrichments relative to the isotope ratios at the tropopause are used to derive the partitioning of tropospheric (unmodified), re-cycled and in situ generated H2O. The model reasonably predicts overall increases of the stable isotope ratios in H2O by ~23% for D/H, ~8.5% for 17O/16O, and ~14% for 18O/16O. The17O/16O and 18O/16O ratios in H2O are shown to be a measure of the partitioning of HOx that receives its O atom either from the reservoirs O2 or O3. In the entire middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. It is demonstrated that in the stratosphere mass-independent fractionation (MIF) in O3 in a first step is transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from the many badly quantified isotope exchange reactions and kinetic isotope fractionation factors.
Simulating gas-aerosol-cirrus interactions: Process-oriented microphysical model and applications
Authors: Kärcher B.
Published: April 2010

Abstract. This work describes a process-oriented, microphysical-chemical model to simulate the formation and evolution of aerosols and ice crystals under the conditions prevailing in the upper troposphere and lower stratosphere. The model can be run as a box model or along atmospheric trajectories, and considers mixing, gas phase chemistry of aerosol precursors, binary homogeneous aerosol nucleation, homogeneous and heterogeneous ice nucleation, coagulation, condensation and dissolution, gas retention during particle freezing, gas trapping in growing ice crystals, and reverse processes. Chemical equations are solved iteratively using a second order implicit integration method. Gas-particle interactions and coagulation are treated over various size structures, with fully mass conserving and non-iterative numerical solution schemes. Particle types include quinternary aqueous solutions composed of H2SO4, HNO3, HCl, and HBr with and without insoluble components, insoluble aerosol particles, and spherical or columnar ice crystals deriving from each aerosol type separately. Three case studies are discussed in detail to demonstrate the potential of the model to simulate real atmospheric processes and to highlight current research topics concerning aerosol and cirrus formation near the tropopause. Emphasis is placed on how the formation of cirrus clouds and the scavenging on nitric acid in cirrus depends on small-scale temperature fluctuations and the presence of efficient ice nuclei in the tropopause region, corroborating and partly extending the findings of previous studies.
Nitric acid partitioning in cirrus clouds: a synopsis based on field, laboratory and model studies
Authors: Krämer M. , Beuermann J. , Schiller C. , Grimm F. , Arnold F. , Peter T. , Meilinger S. , Meier A. , Hendricks J. , Petzold A. , Schlager H.
Published: April 2010

Abstract. From a synopsis of field, laboratory and model studies at T>205 K as well as from the field experiments POLSTAR at T<205 K we derive a general picture of the partitioning of nitric acid (HNO3) in cirrus clouds and a new hypothesis on the uptake of HNO3 on ice particles: A substantial part of nitric acid remains in the gas phase under cirrus cloud conditions. The HNO3 removed from the gas phase is distributed between interstitial aerosol and ice particles in dependence on the temperature and ice surface, respectively. In cold cirrus clouds with small ice surface areas (T <205 K) the partitioning is strongly in favour of interstitial ternary solution particles while in warmer cirrus clouds with large ice surface areas the uptake on ice dominates. Consequently, denitrification via sedimenting ice particles may occur only in the -more frequently occurring- warm cirrus clouds The HNO3 coverage on ice is found to be different for ice particles and ice films. On ice films the coverage can increase with decreasing temperature from about 0.1 to 0.8 monolayer, while that on ice particles is found to decrease with temperature and PHNO3 from 0.1 to 0.001 monolayer. An HNO3 uptake behaviour following dissociative Langmuir isotherms where the coverage decreases for descending temperatures may explain the observations for ice particles From a comparison of the HNO3 measurements with model calculations it is found that (i) the global model of Lawrence and Crutzen (1998) overestimates the HNO3 partitioning in favour of the ice particles (ii) the Langmuir surface chemistry model of Tabazadeh et al. (1999) overestimates HNO3 coverages for temperatures ≤210 K More appropriate coverages are calculated when implementing in that model a temperature dependent function for the adsorption free energy (ΔGads (T)), which is empirically derived from the coverage measurements.
A model of HDO in the tropical tropopause layer
Authors: Dessler A. E. , Sherwood S. C.
Published: April 2010

Abstract. Any theory of water vapor in the tropical tropopause layer (TTL) must explain both the abundance and isotopic composition of water there. In a previous paper, we presented a model of the TTL that simulated the abundance of water vapor as well as the details of the vertical profile. That model included the effects of  "overshooting" convection, which injects dry air directly into the TTL. Here, we present results for the model after modifying it to include water's stable isotopologue HDO (where D represents deuterium, 2H). We find that the model predicts a nearly uniform HDO depletion throughout the TTL, in agreement with recent measurements. This occurs because the model dehydrates by dilution, which does not fractionate, instead of by condensation. Our model shows that this dehydration by dilution is consistent with other physical constraints on the system. We also show the key role that lofted ice plays in determining the abundance of HDO in the TTL. Such lofted ice requires a complementary source of dry air in the TTL; without that, the TTL will rapidly saturate and the lofted ice will not evaporate.
Assessment of possible airborne impact from nuclear risk sites – Part II: probabilistic analysis of atmospheric transport patterns in Euro-Arctic region
Authors: Mahura A. G. , Baklanov A. A.
Published: April 2010

Abstract. The probabilistic analysis of atmospheric transport patterns from most important nuclear risk sites in the Euro-Arctic region is performed employing the methodology developed within the "Arctic Risk" Project of the NARP Programme (Baklanov and Mahura, 2003). The risk sites are the nuclear power plants in the Northwest Russia, Finland, Sweden, Lithuania, United Kingdom, and Germany as well as the Novaya Zemlya test site of Russia. The geographical regions of interest are the Northern and Central European countries and Northwest Russia. In this study, the employed research tools are the trajectory model to calculate a multiyear dataset of forward trajectories that originated over the risk site locations, and a set of statistical methods (including exploratory, cluster, and probability fields analyses) for analysis of trajectory modelling results. The probabilistic analyses of trajectory modelling results for eleven sites are presented as a set of various indicators of the risk sites possible impact on geographical regions and countries of interest. The nuclear risk site possible impact (on a particular geographical region, territory, country, site, etc.) due to atmospheric transport from the site after hypothetical accidental release of radioactivity can be properly estimated based on a combined interpretation of the indicators (simple characteristics, atmospheric transport pathways, airflow and fast transport probability fields, maximum reaching distance and maximum possible impact zone, typical transport time and precipitation factor fields) for different time periods (annual, seasonal, and monthly) for any selected site (both separately for each site or grouped for several sites) in the Euro-Arctic region. Such estimation could be the useful input information for the decision-making process, risk assessment, and planning of emergency response systems for sites of nuclear, chemical, and biological danger.