bluuebunny/crossref_metadata_2025 huggingface dataset:
Polar stratospheric cloud observations by MIPAS on ENVISAT: detection method, validation and analysis of the northern hemisphere winter 2002/2003
Authors: Spang R. , Remedios J. J. , Kramer L. J. , Poole L. R. , Fromm M. D. , Müller M. , Baumgarten G. , Konopka P.
Published: April 2010

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT has made extensive measurements of polar stratospheric clouds (PSCs) in the northern hemisphere winter 2002/2003. A PSC detection method based on a ratio of radiances (the cloud index) has been implemented for MIPAS and is validated in this study with respect to ground-based lidar and space borne occultation measurements. A very good correspondence in PSC sighting and cloud altitude between MIPAS detections and those of other instruments is found for cloud index values of less than four. Comparisons with data from the Stratospheric Aerosol and Gas Experiment (SAGE) III are used to further show that the sensitivity of the MIPAS detection method for this threshold value of cloud index is approximately equivalent to an extinction limit of 10-3km-1 at 1022nm, a wavelength used by solar occultation experiments. The MIPAS cloud index data are subsequently used to examine, for the first time with any technique, the evolution of PSCs throughout the Arctic polar vortex up to a latitude close to 90° north on a near-daily basis. We find that the winter of 2002/2003 is characterised by three phases of very different PSC activity. First, an unusual, extremely cold phase in the first three weeks of December resulted in high PSC occurrence rates. This was followed by a second phase of only moderate PSC activity from 5-13 January, separated from the first phase by a minor warming event. Finally there was a third phase from February to the end of March where only sporadic and mostly weak PSC events took place. The composition of PSCs during the winter period has also been examined, exploiting in particular an infra-red spectral signature which is probably characteristic of NAT. The MIPAS observations show the presence of these particles on a number of occasions in December but very rarely in January. The PSC type differentiation from MIPAS indicates that future comparisons of PSC observations with microphysical and denitrification models might be revealing about aspects of solid particle existence and location.
The role of organic aerosols in homogeneous ice formation
Authors: Kärcher B. , Koop T.
Published: April 2010

Abstract. Recent field observations suggest that the fraction of organic-containing aerosol particles in ice cloud particles is diminished when compared to the background aerosol prior to freezing. In this work, we use model calculations to investigate possible causes for the observed behavior. In particular, homogeneous freezing processes in cooling air parcels containing aqueous inorganic particles and organic particles are studied with a detailed microphysical model. A disparate water uptake and resulting size differences that occur between organic and inorganic particles prior to freezing are identified as the most likely reason for the poor partitioning of organic aerosols into the ice phase. The differences in water uptake can be caused by changes in the relationship between solute mass fraction and water activity of the supercooled liquid phase, by modifications of the accommodation coefficient for water molecules, or by a combination thereof. The behavior of peak ice saturation ratios and total ice crystal number concentrations is examined, and the dependence of the results on cooling rate is investigated. Finally, processes are discussed that could possibly modify the homogeneous freezing behavior of organic particles.
A review of biomass burning emissions part II: intensive physical properties of biomass burning particles
Authors: Reid J. S. , Koppmann R. , Eck T. F. , Eleuterio D. P.
Published: April 2010

Abstract. The last decade has seen tremendous advances in atmospheric aerosol particle research that is often performed in the context of climate and global change science. Biomass burning, one of the largest sources of accumulation mode particles globally, has been closely studied for its radiative, geochemical, and dynamic impacts. These studies have taken many forms including laboratory burns, in situ experiments, remote sensing, and modeling. While the differing perspectives of these studies have ultimately improved our qualitative understanding of biomass-burning issues, the varied nature of the work make inter-comparisons and resolutions of some specific issues difficult. In short, the literature base has become a milieu of small pieces of the biomass-burning puzzle. This manuscript, the second part of four, examines the properties of biomass-burning particle emissions. Here we review and discuss the literature concerning the measurement of smoke particle size, chemistry, thermodynamic properties, and emission factors. Where appropriate, critiques of measurement techniques are presented. We show that very large differences in measured particle properties have appeared in the literature, in particular with regards to particle carbon budgets. We investigate emissions uncertainties using scale analyses, which shows that while emission factors for grass and brush are relatively well known, very large uncertainties still exist in emission factors of boreal, temperate and some tropical forests. Based on an uncertainty analysis of the community data set of biomass burning measurements, we present simplified models for particle size and emission factors. We close this review paper with a discussion of the community experimental data, point to lapses in the data set, and prioritize future research topics.
Intercomparison between Lagrangian and Eulerian simulations of the development of mid-latitude streamers as observed by CRISTA
Authors: Khosrawi F. , Grooß J.-U. , Müller R. , Konopka P. , Kouker W. , Ruhnke R. , Reddmann T. , Riese M.
Published: April 2010

Abstract. During the CRISTA-1 mission three pronounced fingerlike structures reaching from the lower latitudes to the mid-latitudes, so-called streamers, were observed in the measurements of several trace gases in early November 1994. A simulation of these streamers in previous studies employing the KASIMA (Karlsruhe Simulation Model of the Middle Atmosphere) and ROSE (Research on Ozone in the Stratosphere and its Evolution) model, both being Eulerian models, show that their formation is due to adiabatic transport processes. Here, the impact of mixing on the development of these streamers is investigated. These streamers were simulated with the CLaMS model (Chemical Lagrangian Model of the Stratosphere), a Lagrangian model, using N2O as long-lived tracer. Using several different initialisations the results were compared to the KASIMA simulations and CRISTA (Cryogenic Infrared Spectrometer and Telescope for the Atmosphere) observations. Further, since the KASIMA model was employed to derive a 9-year climatology, the quality of the reproduction of streamers from such a study was tested by the comparison of the KASIMA results with CLaMS and CRISTA. The streamers are reproduced well for the Northern Hemisphere in the simulations of CLaMS and KASIMA for the 6 November 1994. However, in the CLaMS simulation a stronger filamentation is found while larger discrepancies between KASIMA and CRISTA were found especially for the Southern Hemisphere. Further, compared to the CRISTA observations the mixing ratios of N2O are in general underestimated in the KASIMA simulations. An improvement of the simulations with KASIMA was obtained for a simulation time according to the length of the CLaMS simulation. To quantify the differences between the simulations with CLaMS and KASIMA, and the CRISTA observations, the probability density function technique (PDF) is used to interpret the tracer distributions. While in the PDF of the KASIMA simulation the small scale structures observed by CRISTA are smoothed out due to the numerical diffusion in the model, the PDFs derived from CRISTA observations can be reproduced by CLaMS by optimising the mixing parameterisation. Further, this procedure gives information on small-scale variabilities not resolved by the CRISTA observations.
Parameterization of the nitric acid effect on CCN activation
Authors: Romakkaniemi S. , Kokkola H. , Laaksonen A.
Published: April 2010

Abstract. In this paper we present a parameterization of the nitric acid effect on cloud droplet formation. The new parameterization is intended to be used in large scale models in order to obtain regional and global estimates of the effect of nitric acid on cloud drop concentrations and the radiative balance. The parameterization is based on numerical air parcel model simulations and can be applied for unimodal and bimodal lognormal aerosol particle size distributions in a large variety of different conditions. In addition to the aerosol particle distribution and gas-phase HNO3 concentration, the parameterization requires temperature, total pressure, updraft velocity, and the number concentration of cloud droplets formed at zero nitric acid concentration, as input parameters. The parameterization is also suitable for describing the effect of hydrochloric acid on the cloud drop concentrations, and in practice, the HNO3 and HCl concentrations can be summed up to yield the total effect. The comparison between the parameterization and the results from numerical air parcel model simulations show good consistency.
4-D comparison method to study the NOy partitioning in summer polar stratosphere – Influence of aerosol burden
Authors: Dufour G. , Payan S. , Lefèvre F. , Eremenko M. , Butz A. , Jeseck P. , Té Y. , Pfeilsticker K. , Camy-Peyret C.
Published: April 2010

Abstract. On 21–22 August 2001, NO, NO2 and HNO3 mixing ratio profiles were measured at high latitudes during sunset and sunrise using the Limb Profile Monitor of the Atmosphere (LPMA) and the DOAS experiments under stratospheric balloon. Photochemical simulations using the chemistry module of the Reprobus Chemistry Transport Model (CTM) that are constrained by ozone and total NOy balloon observations reproduce well the partitioning of NOx and NOy when model results are calculated at the exact time and location of the measurement for each tangent altitude. Taking the recently recommended reaction rate coefficients for the NOy partitioning (JPL-2003) and using realistic aerosol surface area in order to initialise the model leads to an agreement between calculations and measurements better than 10% all over the covered altitude range.
Mesoscale modeling of combined aerosol and photo-oxidant processes in the Eastern Mediterranean
Authors: Lazaridis M. , Spyridaki A. , Solberg S. , Smolík J. , Zdímal V. , Eleftheriadis K. , Aleksanropoulou V. , Hov O. , Georgopoulos P. G.
Published: April 2010

Abstract. Particulate matter and photo-oxidant processes in the Eastern Mediterranean have been studied using the UAM-AERO mesoscale air quality model in conjunction with the NILU-CTM regional model. Meteorological data were obtained from the RAMS prognostic meteorological model. The modeling domain includes the eastern Mediterranean area between the Greek mainland and the island of Crete. The modeling system is applied to study the atmospheric processes in three periods, i.e. 13–16 July 2000, 26–30 July 2000 and 7–14 January 2001. The spatial and temporal distributions of both gaseous and particulate matter pollutants have been extensively studied together with the identification of major emission sources in the area. The modeling results were compared with field data obtained in the same period. The objective of the current modeling work was mainly to apply the UAM-AERO mesoscale model in the eastern Mediterranean in order to assess the performed field campaigns and determine that the applied mesoscale model is fit for this purpose. Comparison of the modeling results with measured data was performed for a number of gaseous and aerosol species. The UAM-AERO model underestimates the PM10 measured concentrations during summer and winter campaigns. Discrepancies between modeled and measured data are attributed to unresolved particulate matter emissions. Particulate matter in the area is mainly composed by sulphate, sea salt and crustal materials, and with significant amounts of nitrate, ammonium and organics. During winter the particulate matter and oxidant concentrations were lower than the summer values.
Atmospheric methane and carbon dioxide from SCIAMACHY satellite data: initial comparison with chemistry and transport models
Authors: Buchwitz M. , de Beek R. , Burrows J. P. , Bovensmann H. , Warneke T. , Notholt J. , Meirink J. F. , Goede A. P. H. , Bergamaschi P. , Körner S. , Heimann M. , Schulz A.
Published: April 2010

Abstract. The remote sensing of the atmospheric greenhouse gases methane (CH4) and carbon dioxide (CO2) in the troposphere from instrumentation aboard satellites is a new area of research. In this manuscript, results obtained from observations of the up-welling radiation in the near-infrared by SCIAMACHY on board ENVISAT are presented. Vertical columns of CH4, CO2 and oxygen (O2) have been retrieved and the (air or) O2-normalised CH4 and CO2 column amounts, the dry air column averaged mixing ratios XCH4 and XCO2 derived. In this manuscript the first results, obtained by using the version 0.4 of the Weighting Function Modified (WFM) DOAS retrieval algorithm applied to SCIAMACHY data, are described and compared with global models. For the set of individual cloud free measurements over land the standard deviation of the difference with respect to the models is in the range ~100–200 ppbv (5–10%) for XCH4 and ~14–32 ppmv (4–9%) for XCO2. The inter-hemispheric difference of the methane mixing ratio, as determined from single day data, is in the range 30–110 ppbv and in reasonable agreement with the corresponding model data (48–71 ppbv). The weak inter-hemispheric difference of the CO2 mixing ratio can also be detected with single day data. The spatiotemporal pattern of the measured and the modelled XCO2 are in reasonable agreement. However, the amplitude of the difference between the maximum and the minimum for SCIAMACHY XCO2 is about ±20 ppmv which is about a factor of four larger than the variability of the model data which is about ±5 ppmv. More studies are needed to explain the observed differences. The XCO2 model field shows low CO2 concentrations beginning of January 2003 over a spatially extended CO2 sink region located in southern tropical/sub-tropical Africa. The SCIAMACHY data also show low CO2 mixing ratios over this area. According to the model the sink region becomes a source region about six months later and exhibits higher mixing ratios. The SCIAMACHY and the model data over this region show a similar time dependence over the period from January to October 2003. These results indicate that for the first time a regional CO2 surface source/sink region has been detected by measurements from space. The interpretation of the SCIAMACHY CO2 and CH4 measurements is difficult, e.g., because the error analysis of the currently implemented retrieval algorithm indicates that the retrieval errors are on the same order as the small greenhouse gas mixing ratio changes that are to be detected.
Technical Note: Evaporation of polar stratospheric cloud particles, in situ, in a heated inlet
Authors: Eidhammer T. , Deshler T.
Published: April 2010

Abstract. In December 2001 and 2002 in situ aerosol measurements were made from balloon-borne platforms within polar stratospheric clouds (PSC) which contained particles of supercooled ternary solution (STS), nitric acid trihydrate (NAT) and ice. Particle size and number concentrations were measured with two optical particle counters. One of these included an ~80cm inlet heated to K to evaporate the PSC particles and thus to obtain measurements, within PSCs, of the size distribution of the particles upon which the PSCs condensed. These measurements are compared to models, described here, that calculate the evaporation of PSC particles at and for an inlet transition time of about 0.1s. The modeled evaporation for STS agrees well with the measurements. For NAT the modeled evaporation is less than the evaporation measured. The primary uncertainty concerns the phase and morphology of NAT particles as they are brought to temperatures >50K above equilibrium temperatures for NAT at stratospheric partial pressures. The slow evaporation of NAT in heated inlets could be used to identify a small NAT component within a mixed phase PSC dominated by STS.
Convective damping of buoyancy anomalies and its effect on lapse rates in the tropical lower troposphere
Authors: Folkins I.
Published: April 2010

Abstract. In regions of the tropics undergoing active deep convection, the variation of lower tropospheric lapse rates (2.0 km to 5.2 km) with height is inconsistent with both reversible moist adiabatic and pseudoadiabatic assumptions. It is argued that this anomalous behavior arises from the tendency for the divergence of a convective buoyancy anomaly to be primarily offset by the collective divergence of other updrafts and downdrafts within one Rossby radius of deformation. Ordinarily, convective mass flux divergences are at least partially offset by an induced radiative mass flux divergence in the background atmosphere. If mass flux divergences from lower tropospheric convection are balanced mainly by those of neighboring updrafts/downdrafts, it would force the vertical clear sky radiative mass flux of the background atmosphere to be weakly dependent on height. This is observed at several radiosonde locations in the Western Tropical Pacific between 2.0 and the 5.2 km melting level. At tropical locations where SST's exceed 27°C over a region whose horizontal extent exceeds the local Rossby radius, this condition on the vertical variation of the background radiative mass flux partially constrains the range of physically allowed mean temperature and moisture profiles in the lower troposphere.
Atmospheric number size distributions of soot particles and estimation of emission factors
Authors: Rose D. , Wehner B. , Ketzel M. , Engler C. , Voigtländer J. , Tuch T. , Wiedensohler A.
Published: April 2010

Abstract. Number fractions of externally mixed particles of four different sizes (30, 50, 80, and 150 nm in diameter) were measured using a Volatility Tandem DMA. The system was operated in a street canyon (Eisenbahnstrasse, EI) and at an urban background site (Institute for Tropospheric Research, IfT), both in the city of Leipzig, Germany as well as at a rural site (Melpitz (ME), a village near Leipzig). Intensive campaigns of 3–5 weeks each took place in summer 2003 as well as in winter 2003/04. The data set thus obtained provides mean number fractions of externally mixed soot particles of atmospheric aerosols in differently polluted areas and different seasons (e.g. at 80 nm on working days, 60% (EI), 22% (IfT), and 6% (ME) in summer and 26% (IfT), and 13% (ME) in winter). Furthermore, a new method is used to calculate the size distribution of these externally mixed soot particles from parallel number size distribution measurements. A decrease of the externally mixed soot fraction with decreasing urbanity and a diurnal variation linked to the daily traffic changes demonstrate, that the traffic emissions have a significant impact on the soot fraction in urban areas. This influence becomes less in rural areas, due to atmospheric mixing and transformation processes. For estimating the source strength of soot particles emitted by vehicles (veh), soot particle emission factors were calculated using the Operational Street Pollution Model (OSPM). The emission factor for an average vehicle was found to be (1.5±0.4)·1014 #(km·veh). The separation of the emission factor into passenger cars ((5.8±2)·1013} #(km·veh)) and trucks ((2.5±0.9)·1015 #(km·veh)) yielded in a 40-times higher emission factor for trucks compared to passenger cars.
Tropopause referenced ozone climatology and inter-annual variability (1994–2003) from the MOZAIC programme
Authors: Thouret V. , Cammas J.-P. , Sauvage B. , Athier G. , Zbinden R. , Nédélec P. , Simon P. , Karcher F.
Published: April 2010

Abstract. The MOZAIC programme collects ozone and water vapour data using automatic equipment installed on board five long-range Airbus A340 aircraft flying regularly all over the world since August 1994. Those measurements made between September 1994 and August 1996 allowed the first accurate ozone climatology at 9–12 km altitude to be generated. The seasonal variability of the tropopause height has always provided a problem when constructing climatologies in this region. To remove any signal from the seasonal and synoptic scale variability in tropopause height we have chosen in this further study of these and subsequent data to reference our climatology to the altitude of the tropopause. We define the tropopause as a mixing zone 30 hPa thick across the 2 pvu potential vorticity surface. A new ozone climatology is now available for levels characteristic of the upper troposphere (UT) and the lower stratosphere (LS) regardless of the seasonal variations of the tropopause over the period 1994–2003. Moreover, this new presentation has allowed an estimation of the monthly mean climatological ozone concentration at the tropopause showing a sine seasonal variation with a maximum in May (120 ppbv) and a minimum in November (65 ppbv). Besides, we present a first assessment of the inter-annual variability of ozone in this particular critical region. The overall increase in the UTLS is about 1%/yr for the 9 years sampled. However, enhanced concentrations about 10–15 % higher than the other years were recorded in 1998 and 1999 in both the UT and the LS. This so-called "1998–1999 anomaly" may be attributed to a combination of different processes involving large scale modes of atmospheric variability, circulation features and local or global pollution, but the most dominant one seems to involve the variability of the North Atlantic Oscillation (NAO) as we find a strong positive correlation (above 0.60) between ozone recorded in the upper troposphere and the NAO index. A strong anti-correlation is also found between ozone and the extremes of the Northern Annular Mode (NAM) index, attributing the lower stratospheric variability to dynamical anomalies. Finally this analysis highlights the coupling between the troposphere, at least the upper one, and the stratosphere, at least the lower one.
Mid-latitude tropospheric ozone columns from the MOZAIC program: climatology and interannual variability
Authors: Zbinden R. M. , Cammas J.-P. , Thouret V. , Nédélec P. , Karcher F. , Simon P.
Published: April 2010

Abstract. Several thousands of ozone vertical profiles collected in the course of the MOZAIC programme (Measurements of Ozone, Water Vapour, Carbon Monoxide and Nitrogen Oxides by In-Service Airbus Aircraft) from August 1994 to February 2002 are investigated to bring out climatological and interannual variability aspects. The study is centred on the most frequently visited MOZAIC airports, i.e. Frankfurt (Germany), Paris (France), New York (USA) and the cluster of Tokyo, Nagoya and Osaka (Japan). The analysis focuses on the vertical integration of ozone from the ground to the dynamical tropopause and the vertical integration of stratospheric-origin ozone throughout the troposphere. The characteristics of the MOZAIC profiles: frequency of flights, accuracy, precision, and depth of the troposphere observed, are presented. The climatological analysis shows that the Tropospheric Ozone Column (TOC) seasonal cycle ranges from a wintertime minimum at all four stations to a spring-summer maximum in Frankfurt, Paris, and New York. Over Japan, the maximum occurs in spring presumably because of the earlier springtime sun. The incursion of monsoon air masses into the boundary layer and into the mid troposphere then steeply diminishes the summertime value. Boundary layer contributions to the TOC are 10% higher in New York than in Frankfurt and Paris during spring and summer, and are 10% higher in Japan than in New York, Frankfurt and Paris during autumn and early spring. Local and remote anthropogenic emissions, and biomass burning over upstream regions of Asia may be responsible for the larger low- and mid-tropospheric contributions to the tropospheric ozone column over Japan throughout the year except during the summer-monsoon season. A simple Lagrangian analysis has shown that a minimum of 10% of the TOC is of stratospheric-origin throughout the year. Investigation of the short-term trends of the TOC over the period 1995–2001 shows a linear increase 0.7%/year in Frankfurt, 0.8%/year in Japan, 1.1%/year in New York and 1.6%/year in Paris for the reduced 1995–1999 period. Dominant ingredients of these positive short-term trends are the continuous increase of wintertime tropospheric ozone columns from 1996 to 1999 and the positive contributions of the mid troposphere whatever the season.
Seasonal cycles and variability of O3 and H2O in the UT/LMS during SPURT
Authors: Krebsbach M. , Schiller C. , Brunner D. , Günther G. , Hegglin M. I. , Mottaghy D. , Riese M. , Spelten N. , Wernli H.
Published: April 2010

Abstract. Airborne high resolution in situ measurements of a large set of trace gases including ozone (O3) and total water (H2O) in the upper troposphere and the lowermost stratosphere (UT/LMS) have been performed above Europe within the SPURT project. SPURT provides an extensive data coverage of the UT/LMS in each season within the time period between November 2001 and July 2003. In the LMS a distinct spring maximum and autumn minimum is observed in O3, whereas its annual cycle in the UT is shifted by 2–3 months later towards the end of the year. The more variable H2O measurements reveal a maximum during summer and a minimum during autumn/winter with no phase shift between the two atmospheric compartments. For a comprehensive insight into trace gas composition and variability in the UT/LMS several statistical methods are applied using chemical, thermal and dynamical vertical coordinates. In particular, 2-dimensional probability distribution functions serve as a tool to transform localised aircraft data to a more comprehensive view of the probed atmospheric region. It appears that both trace gases, O3 and H2O, reveal the most compact arrangement and are best correlated in the view of potential vorticity (PV) and distance to the local tropopause, indicating an advanced mixing state on these surfaces. Thus, strong gradients of PV seem to act as a transport barrier both in the vertical and the horizontal direction. The alignment of trace gas isopleths reflects the existence of a year-round extra-tropical tropopause transition layer. The SPURT measurements reveal that this layer is mainly affected by stratospheric air during winter/spring and by tropospheric air during autumn/summer. Normalised mixing entropy values for O3 and H2O in the LMS appear to be maximal during spring and summer, respectively, indicating highest variability of these trace gases during the respective seasons.
On the possible causes of recent increases in northern hemispheric total ozone from a statistical analysis of satellite data from 1979 to 2003
Authors: Dhomse S. , Weber M. , Wohltmann I. , Rex M. , Burrows J. P.
Published: April 2010

Abstract. Global total ozone measurements from various satellite instruments such as SBUV, TOMS, and GOME show an increase in zonal mean total ozone at northern hemispheric (NH) mid to high latitudes since the mid-nineties. This increase could be expected from the peaking and start of decline in the effective stratospheric halogen loading, but the rather rapid increase observed in NH zonal mean total ozone suggests that another physical mechanism such as winter planetary wave activity has increased which has led to higher stratospheric Arctic temperatures. This has enhanced ozone transport into higher latitudes in recent years as part of the residual circulation and at the same time reduced the frequency of cold Arctic winters with enhanced polar ozone loss. Results from various multi-variate linear regression analyses using SBUV V8 total ozone with explanatory variables such as a linear trend or, alternatively, EESC (equivalent effective stratospheric chlorine) and on the other hand planetary wave driving (eddy heat flux) or, alternatively, polar ozone loss (PSC volume) in addition to proxies for stratospheric aerosol loading, QBO, and solar cycle, all considered to be main drivers for ozone variability, are presented. It is shown that the main contribution to the recent increase in NH total ozone is from the combined effect of rising tropospheric driven planetary wave activity associated with reduced polar ozone loss at high latitudes as well as increasing solar activity. This conclusion can be drawn regardless of the use of linear trend or EESC terms in our statistical model. It is also clear that more years of data will be needed to further improve our estimates of the relative contributions of the individual processes to decadal ozone variability. The question remains if the observed increase in planetary wave driving is part of natural decadal atmospheric variability or will persist. If the latter is the case, it could be interpreted as a possible signature of climate change.
Measurements of NO, NOy, N2O, and O3 during SPURT: implications for transport and chemistry in the lowermost stratosphere
Authors: Hegglin M. I. , Brunner D. , Peter T. , Hoor P. , Fischer H. , Staehelin J. , Krebsbach M. , Schiller C. , Parchatka U. , Weers U.
Published: April 2010

Abstract. We present measurements of NO, NOy, O3, and N2O within the lowermost stratosphere (LMS) over Europe obtained during the SPURT project. The measurements cover all seasons between November 2001 and July 2003. They span a broad band of latitudes from 30° N to 75° N and a potential temperature range from 290 to 380 K. The measurements represent a comprehensive data set of these tracers and reveal atmospheric transport processes that influence tracer distributions in the LMS. Median mixing ratios of stratospheric tracers in equivalent latitude-potential temperature coordinates show a clear seasonal cycle related to the Brewer-Dobson circulation, with highest values in spring and lowest values in autumn. Vertical tracer profiles show strong gradients at the extratropical tropopause, suggesting that vertical (cross-isentropic) mixing is reduced above the tropopause. Pronounced meridional gradients in the tracer mixing ratios are found on potential temperature surfaces in the LMS. This suggests strongly reduced mixing along isentropes. Concurrent large gradients in static stability in the vertical direction, and of PV in the meridional direction, suggest the presence of a mixing barrier. Seasonal cycles were found in the correlation slopes ΔO3/ΔN2O and ΔNOy/ΔN2O well above the tropopause. Absolute slope values are smallest in spring indicating chemically aged stratospheric air originating from high altitudes and latitudes. Larger values were measured in summer and autumn suggesting that a substantial fraction of air takes a "short-cut" from the tropical tropopause region into the extratropical LMS. The seasonal change in the composition of the LMS has direct implications for the ozone chemistry in this region. Comparisons of measured NO with the critical NO value at which net ozone production changes from negative to positive, imply ozone production up to 20 K above the local tropopause in spring, up to 30 K in summer, and up to 40 K in autumn. Above these heights, and in winter, net ozone production is negative.
A modelling study of the impact of cirrus clouds on the moisture budget of the upper troposphere
Authors: Fueglistaler S. , Baker M. B.
Published: April 2010

Abstract. We present a modelling study of the effect of cirrus clouds on the moisture budget of the layer wherein the cloud formed. Our framework simplifies many aspects of cloud microphysics and collapses the problem of sedimentation onto a 0-dimensional box model, but retains essential feedbacks between saturation mixing ratio, particle growth, and water removal through particle sedimentation. The water budget is described by two coupled first-order differential equations for dimensionless particle number density and saturation point temperature, where the parameters defining the system (layer depth, reference temperature, amplitude and time scale of temperature perturbation and inital particle number density, which may or may not be a function of reference temperature and cooling rate) are encapsulated in a single coefficient. This allows us to scale the results to a broad range of atmospheric conditions, and to test sensitivities. Results of the moisture budget calculations are presented for a range of atmospheric conditions (T: 238–205 K; p: 325–180 hPa) and a range of time scales τT of the temperature perturbation that induces the cloud formation. The cirrus clouds are found to efficiently remove water for τT longer than a few hours, with longer perturbations (τT≳10 h) required at lower temperatures (T≲210 K). Conversely, we find that temperature perturbations of duration order 1 h and less (a typical timescale for e.g., gravity waves) do not efficiently dehydrate over most of the upper troposphere. A consequence is that (for particle densities typical of current cirrus clouds) the assumption of complete dehydration to the saturation mixing ratio may yield valid predictions for upper tropospheric moisture distributions if it is based on the large scale temperature field, but this assumption is not necessarily valid if it is based on smaller scale temperature fields.
A group contribution method for estimating the vapour pressures of α-pinene oxidation products
Authors: Capouet M. , Müller J.-F.
Published: April 2010

Abstract. A prediction method based on group contribution principles is proposed for estimating the vapour pressure of α-pinene oxidation products. Temperature dependent contributions are provided for the following chemical groups: carbonyl, nitrate, hydroxy, hydroperoxy, acyl peroxy nitrate and carboxy. On the basis of observed vapour pressure differences between isomers of diols and dinitrates, a simple refinement is introduced in the method to account for the influence of substitutions on the vapour pressure for alcohols and nitrates. The vapour pressures predicted with this new method have been compared with the predictions from UNIFAC (Asher et al., 2002). Given the large uncertainties of the vapour pressure data for the least volatile compounds, further experimental studies of subcooled vapour pressures of multifunctional compounds at ambient temperatures are required for better parameterizations. Among the α-pinene products identified to date, pinic acid and hydroxy pinonic acid are predicted to be the least volatile compounds, with estimated vapour pressures of 3×10−6 torr and 6×10−7 torr, respectively. The vapour pressure of the other primary products range from 10−5 to 10−3 torr, with hydroxy hydroperoxides presenting the lowest values. Noting that multifunctional carboxylic acids, in particular pinic acid, are believed to be mostly present as dimers in laboratory conditions, we suggest that the partial vapour pressure of the pinic acid dimer should be close to the experimental subcooled vapour pressure for pinic acid (estimated at ~10−6 torr) due to its large contribution to the total concentration (dimer+monomer) in experimental conditions.
Evaluation of MIPAS ozone fields assimilated using a new algorithm constrained by isentropic tracer advection
Authors: Juckes M. N.
Published: April 2010

Abstract. A new data assimilation algorithm, using the isentropic advection equation, is applied to MIPAS and SBUV measurements of stratospheric ozone. The system is solved separately on each isentropic level, with neither vertical advection nor chemical reactions represented. The results are validated against HALOE, POAM III, SAGE II & III, OSIRIS and ozone sonde data. The new assimilation algorithm has the accuracy of the Kalman smoother but is, for the systems studied here with up to 200 000 variables per time step and 61 million control variables in total, many orders of magnitude less computationally expensive. The analysis produced minimises a single penalty function evaluated over an analysis window of over one month. The cost of the analysis is found to increase nearly linearly with the number of control variables. Compared with over 800 profiles from Electrochemical Concentration Cell sondes at 29 sites the analysis is found to be merely 0.1% high at 420 K, rising to 0.4% at 650 K. Comparison against the other satellites imply that the bias remains small up to 1250 K (38 km) and then increases to around −10% at 1650 K (44 km). Between 20 and 35 km the root-mean-square difference relative to HALOE, SAGE II & III, and POAM is in the 5 to 10% range, with larger discrepancies relative to other instruments. Outside this height range rms differences are generally larger, though agreement with HALOE remains good up to 50 km. The assimilation has closer agreement to independent observations than found in direct near-neighbour comparisons between profiles, demonstrating that the assimilation can add value to the observations.
The overwhelming role of soils in the global atmospheric hydrogen cycle
Authors: Rhee T. S. , Brenninkmeijer C. A. M. , Röckmann T.
Published: April 2010

Abstract. The removal of molecular hydrogen (H2) from the atmosphere is dominated by the uptake in soils. Notwithstanding, estimates of the magnitude of this important process on a global scale are highly uncertain. The CARIBIC aircraft observations of the seasonal variations of H2 and its D/H isotopic ratio in the Northern Hemisphere allow an independent, better constrained estimate. We derive that 82% of the annual turnover of tropospheric H2 is due to soil uptake, equaling 88 (±11)Tg a-1, of which the Northern Hemisphere alone accounts for 62 (±10)Tg a-1. Our calculations further show that tropospheric H2 has a lifetime of only 1.4 (±0.2) years – significantly shorter than the recent estimate of ~2 years – which is expected to decrease in the future. In addition, our independent top-down approach, confined by the global and hemispheric sinks of H2, indicates 64 (±12)Tg a-1 emissions from various sources of volatile organic compounds by photochemical oxidation in the atmosphere. This estimate is as much as up to 60% larger than the previous estimates. This large airborne production of H2 helps to explain the fairly homogeneous distribution of H2 in the troposphere.
The influence of nitric acid on the cloud processing of aerosol particles
Authors: Romakkaniemi S. , Kokkola H. , Lehtinen K. E. J. , Laaksonen A.
Published: April 2010

Abstract. In this paper we present simulations of the effect of nitric acid (HNO3) on cloud processing of aerosol particles. Sulfuric acid (H2SO4) production and incloud coagulation are both affected by condensed nitric acid as nitric acid increases the number of cloud droplets, which will lead to smaller mean size and higher total surface area of droplets. As a result of increased cloud droplet number concentration (CDNC), the incloud coagulation rate is enhanced by a factor of 1–1.3, so that the number of interstitial particles reduces faster. In addition, sulfuric acid production occurs in smaller particles and so the cloud processed aerosol size distribution is dependent on the HNO3 concentration. This affects both radiative properties of aerosol particles and the formation of cloud droplets during a sequence of cloud formation-evaporation events. It is shown that although the condensation of HNO3 increases the number of cloud droplets during the single updraft, it is possible that presence of HNO3 can actually decrease the cloud droplet number concentration after several cloud cycles when also H2SO4 production is taken into account.
The effect of varying levels of surfactant on the reactive uptake of N2O5 to aqueous aerosol
Authors: McNeill V. F. , Patterson J. , Wolfe G. M. , Thornton J. A.
Published: April 2010

Abstract. Recent observations have detected surface active organics in atmospheric aerosols. We have studied the reaction of N2O5 on aqueous natural seawater and NaCl aerosols as a function of sodium dodecyl sulfate (SDS) concentration to test the effect of varying levels of surfactant on gas-aerosol reaction rates. SDS was chosen as a proxy for naturally occurring long chain monocarboxylic acid molecules, such as palmitic or stearic acid, because of its solubility in water and well-characterized surface properties. Experiments were performed using a newly constructed aerosol flow tube coupled to a chemical ionization mass spectrometer for monitoring the gas phase, and a differential mobility analyzer/condensation particle counter for determining aerosol surface area. We find that the presence of ~3.5wt% SDS in the aerosol, which corresponds to a monolayer surface coverage of ~2×1014 molecules cm-2, suppresses the N2O5 reaction probability, γN2O5, by approximately a factor of ten, independent of relative humidity. Consistent with this observation is a similar reduction in the rate of ClNO2 product generation measured simultaneously. However, the product yield remains nearly constant under all conditions. The degree of suppression is strongly dependent on SDS content in the aerosol, with no discernable effect at 0.1wt% SDS, but significant suppression at what we predict to be submonolayer coverages with 0.3–0.6wt% SDS on NaCl and natural seawater aerosols, respectively.
Effect of smoke and clouds on the transmissivity of photosynthetically active radiation inside the canopy
Authors: Yamasoe M. A. , von Randow C. , Manzi A. O. , Schafer J. S. , Eck T. F. , Holben B. N.
Published: April 2010

Abstract. Biomass burning activities emit high concentrations of aerosol particles to the atmosphere. Such particles can interact with solar radiation, decreasing the amount of light reaching the surface and increasing the fraction of diffuse radiation through scattering processes, and thus has implications for photosynthesis within plant canopies. This work reports results from photosynthetically active radiation (PAR) and aerosol optical depth (AOD) measurements conducted simultaneously at Reserva Biológica do Jaru (Rondonia State, Brazil) during LBA/SMOCC (Large-Scale Biosphere-Atmosphere Experiment in Amazonia/ Smoke, Aerosols, Clouds, Rainfall, and Climate) and RaCCI (Radiation, Cloud, and Climate Interactions in the Amazon during the Dry-to-Wet Transition Season) field experiments from 15 September to 15 November 2002. AOD values were retrieved from an AERONET (Aerosol Robotic Network) radiometer, MODIS (Moderate Resolution Spectroradiometer) and a portable sunphotometer from the United States Department of Agriculture – Forest Service. Significant reduction of PAR irradiance at the top of the canopy was observed due to the smoke aerosol particles layer. This radiation reduction affected turbulent fluxes of sensible and latent heats. The increase of AOD also enhanced the transmission of PAR inside the canopy. As a consequence, the availability of diffuse radiation was enhanced due to light scattering by the aerosol particles. A complex relationship was identified between light availability inside the canopy and net ecosystem exchange (NEE). The results showed that the increase of aerosol optical depth corresponded to an increase of CO2 uptake by the vegetation. However, for even higher AOD values, the corresponding NEE was lower than for intermediate values. As expected, water vapor pressure deficit (VPD), retrieved at 28m height inside the canopy, can also affect photosynthesis. A decrease in NEE was observed as VPD increased. Further studies are needed to better understand these findings, which were reported for the first time for the Amazon region under smoky conditions.
Inverse modelling of the spatial distribution of NOx emissions on a continental scale using satellite data
Authors: Konovalov I. B. , Beekmann M. , Richter A. , Burrows J. P.
Published: April 2010

Abstract. The recent important developments in satellite measurements of the composition of the lower atmosphere open the challenging perspective to use such measurements as independent information on sources and sinks of atmospheric pollutants. This study explores the possibility to improve estimates of gridded NOx emissions used in a continental scale chemistry transport model (CTM), CHIMERE, by employing measurements performed by the GOME and SCIAMACHY instruments. We set-up an original inverse modelling scheme that not only enables a computationally efficient optimisation of the spatial distribution of seasonally averaged NOx emissions (during summertime), but also allows estimating uncertainties in input data and a priori emissions. The key features of our method are (i) replacement of the CTM by a set of empirical models describing the relationships between tropospheric NO2 columns and NOx emissions with sufficient accuracy, (ii) combination of satellite data for tropospheric NO2 columns with ground based measurements of near surface NO2 concentrations, and (iii) evaluation of uncertainties in a posteriori emissions by means of a special Bayesian Monte-Carlo experiment which is based on random sampling of errors of both NO2 columns and emission rates. We have estimated the uncertainty in a priori emissions based on the EMEP emission inventory to be about 1.9 (in terms of geometric standard deviation) and found the uncertainty in a posteriori emissions obtained from our inverse modelling scheme to be significantly lower (about 1.4). It is found also that a priori NOx emission estimates are probable to be persistently biased in many regions of Western Europe, and that the use of a posteriori emissions in the CTM improves the agreement between the modelled and measured data.
Episode of unusual high solar ultraviolet radiation over central Europe due to dynamical reduced total ozone in May 2005
Authors: Stick C. , Krüger K. , Schade N. H. , Sandmann H. , Macke A.
Published: April 2010

Abstract. In late May 2005 unusual high levels of solar ultraviolet radiation were observed over central Europe. In Northern Germany the measured irradiance of erythemally effective radiation exceeded the climatological mean by more than about 20%. An extreme low ozone event for the season coincided with high solar elevation angles and high pressure induced clear sky conditions leading to the highest value of erythemal UV-radiation ever observed over this location in May since 1994. This hereafter called "ozone mini-hole" was caused by an elevation of tropopause height accompanied with a poleward advection of ozone-poor air from the tropics. The resultant increase in UV-radiation is of particular significance for human health. Dynamically induced low ozone episodes that happen in late spring can considerably enhance the solar UV-radiation in mid latitudes and therefore contribute to the UV-burden of people living in these regions.