bluuebunny/crossref_metadata_2025 huggingface dataset:
Geophysical validation of temperature retrieved by the ESA processor from MIPAS/ENVISAT atmospheric limb-emission measurements
Authors: Ridolfi M. , Blum U. , Carli B. , Catoire V. , Ceccherini S. , Claude H. , De Clercq C. , Fricke K. H. , Friedl-Vallon F. , Iarlori M. , Keckhut P. , Kerridge B. , Lambert J.-C. , Meijer Y. J. , Mona L. , Oelhaf H. , Pappalardo G. , Pirre M. , Rizi V. , Robert C. , Swart D. , von Clarmann T. , Waterfall A. , Wetzel G.
Published: April 2010

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) has been operating since March 2002 onboard of the ENVIronmental SATellite of the European Space Agency (ESA). The high resolution (0.035 cm−1) limb-emission measurements acquired by MIPAS in the first two years of operation have very good geographical and temporal coverage and have been re-processed by ESA with the most recent versions (4.61 and 4.62) of the inversion algorithms. The products of this processing chain are geolocated profiles of temperature and of the volume mixing ratios of six key atmospheric constituents: H2O, O3, HNO3, CH4, N2O and NO2. As for all the measurements made with innovative instruments and techniques, this data set requires a thorough validation. In this paper we present a geophysical validation of the temperature profiles derived from MIPAS measurements by the ESA retrieval algorithm. The validation is carried-out by comparing MIPAS temperature with correlative measurements made by radiosondes, lidars, in-situ and remote sensors operated either from the ground or stratospheric balloons. The results of the intercomparison indicate that the bias of the MIPAS profiles is generally smaller than 1 or 2 K depending on altitude. Furthermore we find that, especially at the edges of the altitude range covered by the MIPAS scan, the random error estimated from the intercomparison is larger (typically by a factor of two to three) than the corresponding estimate derived on the basis of error propagation. In this work we also characterize the discrepancies between MIPAS temperature and the temperature fields resulting from the analyses of the European Centre for Medium-range Weather Forecasts (ECMWF). The bias and the standard deviation of these discrepancies are consistent with those obtained when comparing MIPAS to correlative measurements; however, in this case the detected bias has a peculiar behavior as a function of altitude. This behavior is very similar to that observed in previous studies and is suspected to be due to a problem in the ECMWF temperature.
Nitrate aerosols today and in 2030: importance relative to other aerosol species and tropospheric ozone
Authors: Bauer S. E. , Koch D. , Unger N. , Metzger S. M. , Shindell D. T. , Streets D. G.
Published: April 2010

Abstract. Ammonium-nitrate aerosols are expected to become more important in the future atmosphere due to the expected increase in nitrate precursor emissions and the decline of ammonium-sulphate aerosols in wide regions of this planet. The GISS climate model is used in this study, including atmospheric gas- and aerosol phase chemistry to investigate current and future (2030, following the SRES A1B emission scenario) atmospheric compositions. A set of sensitivity experiments was carried out to quantify the individual impact of emission- and physical climate change on nitrate aerosol formation. We found that future nitrate aerosol loads depend most strongly on changes that may occur in the ammonia sources. Furthermore, microphysical processes that lead to aerosol mixing play a very important role in sulphate and nitrate aerosol formation. The role of nitrate aerosols as climate change driver is analyzed and set in perspective to other aerosol and ozone forcings under pre-industrial, present day and future conditions. In the near future, year 2030, ammonium nitrate radiative forcing is about –0.14 W/m2 and contributes roughly 10% of the net aerosol and ozone forcing. The present day nitrate and pre-industrial nitrate forcings are –0.11 and –0.05 W/m2, respectively. The steady increase of nitrate aerosols since industrialization increases its role as a non greenhouse gas forcing agent. However, this impact is still small compared to greenhouse gas forcings, therefore the main role nitrate will play in the future atmosphere is as an air pollutant, with annual mean near surface air concentrations rising above 3 μg/m3 in China and therefore reaching pollution levels, like sulphate aerosols, in the fine particle mode.
Seeking for the rational basis of the median model: the optimal combination of multi-model ensemble results
Authors: Riccio A. , Giunta G. , Galmarini S.
Published: April 2010

Abstract. In this paper we present an approach for the statistical analysis of multi-model ensemble results. The models considered here are operational long-range transport and dispersion models, also used for the real-time simulation of pollutant dispersion or the accidental release of radioactive nuclides. We first introduce the theoretical basis (with its roots sinking into the Bayes theorem) and then apply this approach to the analysis of model results obtained during the ETEX-1 exercise. We recover some interesting results, supporting the heuristic approach called "median model", originally introduced in Galmarini et al. (2004a, b). This approach also provides a way to systematically reduce (and quantify) model uncertainties, thus supporting the decision-making process and/or regulatory-purpose activities in a very effective manner.
A study on the relationship between mass concentrations, chemistry and number size distribution of urban fine aerosols in Milan, Barcelona and London
Authors: Rodríguez S. , Van Dingenen R. , Putaud J.-P. , Dell'Acqua A. , Pey J. , Querol X. , Alastuey A. , Chenery S. , Ho K.-F. , Harrison R. M. , Tardivo R. , Scarnato B. , Gianelle V.
Published: April 2010

Abstract. A physicochemical characterization of the urban fine aerosol (aerosol number size distribution, chemical composition and mass concentrations) in Milan, Barcelona and London is presented in this article. The objective is to obtain a comprehensive picture on the involvement of the microphysical processes of the aerosol dynamic in the: 1) regular evolution of the urban aerosol (daily, weekly and seasonal basis) and in the day-to-day variations (from clean-air to pollution-events), and 2) link between "aerosol chemistry and mass concentrations" with the "number size distribution". The mass concentrations of the fine PM2.5 aerosol exhibit a high correlation with the number concentration of particles >100 nm (which only accounts for <20% of the total number concentration N of fine aerosols) and do not correlate with the number of particles <100 nm ("ultrafine particles", which accounts for >80% of fine particles). Organic matter (OM) and black-carbon (BC) are the only aerosol components showing a significant correlation with ultrafine particles (attributed to vehicles emissions), whereas ammonium-nitrate, ammonium-sulphate and also OM and BC correlate with N>100(nm) (attributed to gas-to-particle transformation mechanisms and some primary emissions). Time series of the aerosol DpN diameter (dN/dlogD mode), mass PM2.5 concentrations and number N>100(nm) concentrations, exhibit correlated day-to-day variations which point to a significant involvement of condensation of semi-volatile compounds during urban pollution events. This agrees with the fact that ammonium-nitrate is the component exhibiting the highest increases from mid-to-high pollution episodes, when the highest DpN increases are observed. The results indicates that "fine PM2.5 particles urban pollution events" tend to occur when condensation processes have made particles grow enough to produce significant concentrations of N>100(nm). In contrast, because the low contribution of ultrafine particles to the fine aerosol mass concentrations, high "ultrafine particles N<100(nm) events" frequently occurs under low PM2.5 conditions. The data of this study point that vehicles emissions are strongly involved in this ultrafine particles aerosol pollution (for example, the "morning-rush-hours to nocturnal-background" concentrations ratio is 1.5–2.5 for "particles 10–100 nm" and <1.5 for both "particle >100 nm and PM2.5").
Climate impact of supersonic air traffic: an approach to optimize a potential future supersonic fleet – results from the EU-project SCENIC
Authors: Grewe V. , Stenke A. , Ponater M. , Sausen R. , Pitari G. , Iachetti D. , Rogers H. , Dessens O. , Pyle J. , Isaksen I.S.A. , Gulstad L. , Søvde O.A. , Marizy C. , Pascuillo E.
Published: April 2010

Abstract. The demand for intercontinental transportation is increasing and people are requesting short travel times, which supersonic air transportation would enable. However, besides noise and sonic boom issues, which we are not referring to in this investigation, emissions from supersonic aircraft are known to alter the atmospheric composition, in particular the ozone layer, and hence affect climate significantly more than subsonic aircraft. Here, we suggest a metric to quantitatively assess different options for supersonic transport with regard to the potential destruction of the ozone layer and climate impacts. Options for fleet size, engine technology (nitrogen oxide emission level), cruising speed, range, and cruising altitude, are analyzed, based on SCENIC emissions scenarios for 2050, which underlay the requirements to be as realistic as possible in terms of e.g. economic markets and profitable market penetration. This methodology is based on a number of atmosphere-chemistry and climate models to reduce model dependencies. The model results differ significantly in terms of the response to a replacement of subsonic aircraft by supersonic aircraft. However, model differences are smaller when comparing the different options for a supersonic fleet. The base scenario, where supersonic aircraft get in service in 2015, a first fleet fully operational in 2025 and a second in 2050, lead in our simulations to a near surface temperature increase in 2050 of around 7 mK and with constant emissions afterwards to around 21 mK in 2100. The related total radiative forcing amounts to 22 mWm²in 2050, with an uncertainty between 9 and 29 mWm². A reduced supersonic cruise altitude or speed (from March 2 to Mach 1.6) reduces both, climate impact and ozone destruction, by around 40%. An increase in the range of the supersonic aircraft leads to more emissions at lower latitudes since more routes to SE Asia are taken into account, which increases ozone depletion, but reduces climate impact compared to the base case.
Interannual variability of the stratospheric wave driving during northern winter
Authors: Haklander A. J. , Siegmund P. C. , Kelder H. M.
Published: April 2010

Abstract. The strength of the stratospheric wave driving during northern winter is often quantified by the January–February mean poleward eddy heat flux at 100 hPa, averaged over 40°–80° N (or a similar area and period). Despite the dynamical and chemical relevance of the wave driving, the causes for its variability are still not well understood. In this study, 45 years of ERA-40 reanalysis data are used to examine several factors that significantly affect the interannual variability of the wave driving. The total poleward heat flux at 100 hPa is poorly correlated with that in the troposphere, suggesting a decoupling between 100 hPa and the troposphere. However, the individual zonal wave-1 and wave-2 contributions to the wave driving at 100 hPa do exhibit a significant coupling with the troposphere, predominantly due to their stationary components. The stationary wave-1 contribution to the total wave driving significantly depends on the latitude of the stationary wave-1 source in the troposphere. The results suggest that this dependence is associated with the varying ability of stationary wave-1 activity to enter the tropospheric waveguide at mid- to subpolar latitudes. If composites of strong and weak wave-driving years are compared, we find significantly higher refractive index values in the midlatitude stratosphere for the strong composite than for the weak composite. Since wave activity tends to propagate towards higher refractive index values, this could explain part of the interannual variability of the wave driving. Finally, an alternative approach is taken, in which the wave driving anomalies are separated into three parts: one part due to anomalies in the zonal correlation between the eddy temperature and eddy meridional wind, another part due to anomalies in the zonal eddy temperature amplitude, and a third part due to anomalies in the zonal eddy meridional wind amplitude. It is found that year-to-year variability in the zonal correlation between the eddy temperature and the eddy meridional wind is the most dominant factor in explaining the year-to-year variability of the poleward eddy heat flux.
A case study on long-range transported aerosols of biomass burning: effects on aerosol optical properties and surface radiation levels
Authors: Arola A. , Lindfors A. , Natunen A. , Lehtinen K. E. J.
Published: April 2010

Abstract. In spring 2006, biomass burning aerosols from eastern Europe were transported extensively to Finland, and to other parts of northern Europe. They were observed as far as in the European Arctic. In the first part of this paper, temporal and spatial evolution and transport of these biomass burning aerosols are monitored with MODIS retrieved aerosol optical depth (AOD) imagery at visible wavelengths (0.55 μm). Comparison of MODIS and AERONET AOD is conducted at Tõravere, Estonia. Then trajectory analyses, as well as MODIS Fire Mapper products are used to better understand the type and origin of the air masses. During the studied four-week period AOD values ranged from near zero up to 1.2 at 0.55 μm and the linear correlation between MODIS and AERONET was very high (~0.97). Temporal variability observed within this four-week period was also rather well explained by the trajectory analysis in conjunction with the fire detections produced by the MODIS Rapid Response System. In the second part of our study, the surface measurements of global and UV radiation at Jokioinen, Finland are used to study the effect of this haze episode on the levels of surface radiation. We found reductions up to 35% in surface UV irradiance (at 340 nm) as compared to typical aerosol conditions. For global (total solar) radiation, the reduction was always smaller, in line with the expected wavelength dependence of the aerosol effect.
First direct observation of the atmospheric CO2 year-to-year increase from space
Authors: Buchwitz M. , Schneising O. , Burrows J. P. , Bovensmann H. , Notholt J.
Published: April 2010

Abstract. The reliable prediction of future atmospheric CO2 concentrations and associated global climate change requires an adequate understanding of the CO2 sources and sinks. The sparseness of the existing surface measurement network limits current knowledge about the global distribution of CO2 surface fluxes. The retrieval of the CO2 total vertical column from satellite observations is predicted to improve this situation. Such an application however requires very high accuracy and precision on the order of 1% (4 ppm) or better. We report on retrievals of the column-averaged CO2 dry air mole fraction, denoted XCO2, from the measurements of the SCIAMACHY satellite instrument between 2003 and 2005. We focus on northern hemispheric large scale CO2 features such as the CO2 seasonal cycle and show – for the first time – that the atmospheric annual increase of CO2 can be directly observed using satellite measurements of the CO2 total column. The satellite retrievals are compared with the global assimilation system CarbonTracker and with local surface CO2 measurements based on weekly flask sampling. We show that the year-to-year CO2 increase as determined from the satellite data agrees with the reference data within about 1 ppm/year. We also show that the CO2 seasonal cycle over northern hemispheric low and mid latitudes can be retrieved with a precision of about 2 ppm. The results presented here demonstrate that it is possible using satellite measurements to retrieved information on the atmospheric CO2 on the level of a few parts per million.
Kinetic modeling of Secondary Organic Aerosol formation: effects of particle- and gas-phase reactions of semivolatile products
Authors: Chan A. W. H. , Kroll J. H. , Ng N. L. , Seinfeld J. H.
Published: April 2010

Abstract. The distinguishing mechanism of formation of secondary organic aerosol (SOA) is the partitioning of semivolatile hydrocarbon oxidation products between the gas and aerosol phases. While SOA formation is typically described in terms of partitioning only, the rate of formation and ultimate yield of SOA can also depend on the kinetics of both gas- and aerosol-phase processes. We present a general equilibrium/kinetic model of SOA formation that provides a framework for evaluating the extent to which the controlling mechanisms of SOA formation can be inferred from laboratory chamber data. With this model we examine the effect on SOA formation of gas-phase oxidation of first-generation products to either more or less volatile species, of particle-phase reaction (both first- and second-order kinetics), of the rate of parent hydrocarbon oxidation, and of the extent of reaction of the parent hydrocarbon. The effect of pre-existing organic aerosol mass on SOA yield, an issue of direct relevance to the translation of laboratory data to atmospheric applications, is examined. The importance of direct chemical measurements of gas- and particle-phase species is underscored in identifying SOA formation mechanisms.
Concentrations and fluxes of aerosol particles during the LAPBIAT measurement campaign in Värriö field station
Authors: Ruuskanen T. M. , Kaasik M. , Aalto P. P. , Hõrrak U. , Vana M. , Mårtensson M. , Yoon Y. J. , Keronen P. , Mordas G. , Ceburnis D. , Nilsson E. D. , O'Dowd C. , Noppel M. , Alliksaar T. , Ivask J. , Sofiev M. , Prank M. , Kulmala M.
Published: April 2010

Abstract. The LAPBIAT measurement campaign took place in the SMEAR I measurement station located in Eastern Lapland in the spring of 2003 between 26 April and 11 May. In this paper we describe the measurement campaign, concentrations and fluxes of aerosol particles, air ions and trace gases, paying special attention to an aerosol particle formation event broken by a polluted air mass approaching from industrial areas of Kola Peninsula, Russia. Aerosol particle number flux measurements show strong downward fluxes during that time. Concentrations of coarse aerosol particles were high for 1–2 days before the nucleation event (i.e. 28–29 April), very low immediately before and during the observed aerosol particle formation event (30 April) and increased moderately from the moment of sudden break of the event. In general particle deposition measurements based on snow samples show the same changes. Measurements of the mobility distribution of air ions showed elevated concentrations of intermediate air ions during the particle formation event. We estimated the growth rates in the nucleation mode size range. For particles <10 nm, the growth rate increases with size on 30 April. Dispersion modelling made with model SILAM support the conclusion that the nucleation event was interrupted by an outbreak of sulphate-rich air mass in the evening of 30 April that originated from the industry at Kola Peninsula, Russia. The results of this campaign highlight the need for detailed research in atmospheric transport of air constituents for understanding the aerosol dynamics.
A cloud filtering method for microwave upper tropospheric humidity measurements
Authors: Buehler S. A. , Kuvatov M. , Sreerekha T. R. , John V. O. , Rydberg B. , Eriksson P. , Notholt J.
Published: April 2010

Abstract. The paper presents a cloud filtering method for upper tropospheric humidity (UTH) measurements at 183.31±1.00 GHz. The method uses two criteria: The difference between the brightness temperatures at 183.31±7.00 and 183.31±1.00 GHz, and a threshold for the brightness temperature at 183.31±1.00 GHz. The robustness of this cloud filter is demonstrated by a mid-latitudes winter case-study. The paper then studies different biases on UTH climatologies. Clouds are associated with high humidity, therefore the dry bias introduced by cloud filtering is discussed and compared to the wet biases introduced by the clouds radiative effect if no filtering is done. This is done by means of a case study, and by means of a stochastic cloud database with representative statistics for midlatitude conditions. The consistent result is that both cloud wet bias (0.8% RH) and cloud filtering dry bias (–2.4% RH) are modest for microwave data, where the numbers given are for the stochastic cloud dataset. This indicates that for microwave data cloud-filtered UTH and unfiltered UTH can be taken as error bounds for errors due to clouds. This is not possible for the more traditional infrared data, since the radiative effect of clouds is much stronger there. The focus of the paper is on midlatitude data, since atmospheric data to test the filter for that case were readily available. The filter is expected to be applicable also to subtropical and tropical data, but should be further validated with case studies similar to the one presented here for those cases.
Global cloud and precipitation chemistry and wet deposition: tropospheric model simulations with ECHAM5/MESSy1
Authors: Tost H. , Jöckel P. , Kerkweg A. , Pozzer A. , Sander R. , Lelieveld J.
Published: April 2010

Abstract. The representation of cloud and precipitation chemistry and subsequent wet deposition of trace constituents in global atmospheric chemistry models is associated with large uncertainties. To improve the simulated trace gas distributions we apply the new submodel SCAV, which includes detailed cloud and precipitation chemistry and present results of the atmospheric chemistry general circulation model ECHAM5/MESSy1. A good agreement with observed wet deposition fluxes for species causing acid rain is obtained. The new scheme enables prognostic calculations of the pH of clouds and precipitation, and these results are also in accordance with observations. We address the influence of detailed cloud and precipitation chemistry on trace constituents based on sensitivity simulations. The results confirm previous results from regional scale and box models, and we extend the analysis to the role of aqueous phase chemistry on the global scale. Some species are directly affected through multiphase removal processes, and many also indirectly through changes in oxidant concentrations, which in turn have an impact on the species lifetime. While the overall effect on tropospheric ozone is relatively small (<10%), regional effects on O3 can reach ~20%, and several important compounds (e.g., H2O2, HCHO) are substantially depleted by clouds and precipitation.
Recipe for continuous monitoring of total ozone with a precision of around 1 DU applying mid-infrared solar absorption spectra
Authors: Schneider M. , Hase F.
Published: April 2010

Abstract. Mid-infrared solar absorption spectra recorded by a state-of-the-art ground-based FTIR system have the potential to provide precise total O3 amounts. The currently best-performing retrieval approaches use a combination of small and broad spectral O3 windows between 780 and 1015 cm−1. We show that for these approaches uncertainties in the temperature profile are by far the major error sources. We demonstrate that a joint optimal estimation of temperature and O3 profiles widely eliminates this error. The improvements are documented by an extensive theoretical error estimation. Our results suggest that mid-infrared FTIR measurements can provide total O3 amounts with a precision of around 1 DU, placing this method among the most precise ground-based O3 monitoring techniques. We recapitulate the requirements on instrumental hardware and retrieval necessary to achieve this high precision.
Data assimilation of stratospheric constituents: a review
Authors: Lahoz W. A. , Errera Q. , Swinbank R. , Fonteyn D.
Published: April 2010

Abstract. The data assimilation of stratospheric constituents is reviewed. The data assimilation method is introduced, with particular consideration to its application to stratospheric constituent measurements. Differences from meteorological data assimilation are outlined. Historically, two approaches have been used to carry out constituent assimilation. One approach has carried constituent assimilation out as part of a numerical weather prediction system; the other has carried it out in a standalone chemical model, often with a more sophisticated representation of chemical processes. Whereas the aim of the numerical weather prediction approach has been to improve weather forecasts, the aims of the chemical model approach have included providing chemical forecasts and analyses of chemical constituents. A range of constituent assimilation systems developed in these two areas is presented and strengths and weaknesses discussed. The use of stratospheric constituent data assimilation to evaluate models, observations and analyses, and to provide analyses of constituents, monitor ozone, and make ozone forecasts is discussed. Finally, the current state of affairs is assessed, future directions are discussed, and potential key drivers identified.
Evaluating model performance of an ensemble-based chemical data assimilation system during INTEX-B field mission
Authors:   A. F. Arellano Jr., Raeder K. , Anderson J. L. , Hess P. G. , Emmons L. K. , Edwards D. P. , Pfister G. G. , Campos T. L. , Sachse G. W.
Published: April 2010

Abstract. We present a global chemical data assimilation system using a global atmosphere model, the Community Atmosphere Model (CAM3) with simplified chemistry and the Data Assimilation Research Testbed (DART) assimilation package. DART is a community software facility for assimilation studies using the ensemble Kalman filter approach. Here, we apply the assimilation system to constrain global tropospheric carbon monoxide (CO) by assimilating meteorological observations of temperature and horizontal wind velocity and satellite CO retrievals from the Measurement of Pollution in the Troposphere (MOPITT) satellite instrument. We verify the system performance using independent CO observations taken on board the NSF/NCAR C-130 and NASA DC-8 aircrafts during the April 2006 part of the Intercontinental Chemical Transport Experiment (INTEX-B). Our evaluations show that MOPITT data assimilation provides significant improvements in terms of capturing the observed CO variability relative to no MOPITT assimilation (i.e. the correlation improves from 0.62 to 0.71, significant at 99% confidence). The assimilation provides evidence of median CO loading of about 150 ppbv at 700 hPa over the NE Pacific during April 2006. This is marginally higher than the modeled CO with no MOPITT assimilation (~140 ppbv). Our ensemble-based estimates of model uncertainty also show model overprediction over the source region (i.e. China) and underprediction over the NE Pacific, suggesting model errors that cannot be readily explained by emissions alone. These results have important implications for improving regional chemical forecasts and for inverse modeling of CO sources and further demonstrates the utility of the assimilation system in comparing non-coincident measurements, e.g. comparing satellite retrievals of CO with in-situ aircraft measurements.
Introducing the concept of Potential Aerosol Mass (PAM)
Authors: Kang E. , Root M. J. , Brune W. H.
Published: April 2010

Abstract. Potential Aerosol Mass (PAM) can be defined as the maximum aerosol mass that the oxidation of precursor gases produces. In the measurement, all precursor gases are rapidly oxidized with extreme amounts of oxidants to low volatility compounds, resulting in the aerosol formation. Oxidation occurs in a small, simple, flow-through chamber that has a short residence time and is irradiated with ultraviolet light. The amount of the oxidants ozone (O3), hydroxyl (OH), and hydroperoxyl (HO2) were measured directly and can be controlled by varying the UV light and the relative humidity. Maximum values were 40 ppmv for O3, 500 pptv for OH, and 4 ppbv for HO2. The oxidant amounts are 100 to 1000 times troposphere values, but the ratios OH/O3 and HO2/OH are similar to troposphere values. The aerosol production mechanism and the aerosol mass yield were studied for several controlling variables, such as temperature, relative humidity, oxidant concentration, presence of nitrogen oxides (NOx), precursor gas composition and amount, and the presence of acidic seed aerosol. The measured secondary organic aerosol (SOA) yield of several natural and anthropogenic volatile organic compounds and a mixture of hydrocarbons in the PAM chamber were similar to those obtained in large, batch-style environmental chambers. This PAM method is being developed for measuring potential aerosol mass in the atmosphere, but is also useful for examining SOA processes in the laboratory and in environmental chambers.
Estimated UV doses to psoriasis patients during climate therapy at Gran Canaria in March 2006
Authors: Nilsen L. T. N. , Søyland E. , Krogstad A. L.
Published: April 2010

Abstract. Psoriasis is a chronic inflammatory disease involving about 2–3% of the Norwegian population. Sun exposure has a positive effect on most psoriasis lesions, but ultraviolet (UV) radiation also causes a direct DNA damage in the skin cells and comprises a carcinogenic potential. UV exposure on the skin causes a local as well as a systemic immune suppressive effect, but the relation between sun exposure and these biological effects is not well known. In March 2006 a study was carried out to investigate possible therapeutic outcome mechanisms in 20 psoriasis patients receiving climate therapy at Gran Canaria. This paper presents estimates of their individual skin UV-doses based on UV measurements and the patients' diaries with information on time spent in the sun. On the first day of exposure the patients received on average 5.1 Standard Erythema Doses (SED: median=4.0 SED, range 2.6–10.3 SED) estimated to the skin. During the 15 days study they received 165.8 SED (range 104.3–210.1 SED). The reduction in PASI score was 72.8% on average, but there was no obvious relation between the improvement and the UV dose. The UV doses were higher than those found from climate therapy studies at other locations. It seems beneficial to use more strict exposure schedules that consider the available UV irradiance, depending on time of the day, time of the year and weather conditions.
Increase of the aerosol hygroscopicity by aqueous mixing in a mesoscale convective system: a case study from the AMMA campaign
Authors: Crumeyrolle S. , Gomes L. , Tulet P. , Matsuki A. , Schwarzenboeck A. , Crahan K.
Published: April 2010

Abstract. Aerosol properties were measured during an airborne campaign experiment that took place in July 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to determine the main microphysical processes that affect the aerosols during the passage of a mesoscale convective system (MCS) over the region of Niamey in Niger. A main difference in the aerosol profiles measured before and after the passage of the MCS was found for a layer located between 1300 and 3000 m where the aerosol concentration has drastically decreased after the passage of the MCS. Concurrently, a significant increase of the cloud condensation nuclei fraction was also observed during the post-MCS period in the same layer. Moreover, the results of the elemental composition analyses of individual particles collected in this layer after the MCS passage have shown higher contributions of sulfate, nitrate and chloride to the total aerosol. A mesoscale atmospheric model with on-line dust parameterization and Lagrangian backtrajectories was used to interpret the impact of the MCS on the aerosol properties. The results of the simulation show that the MCS 1) generates dust particles at the surface in front of the system and washout particles behind, 2) modifies the aerosol mixing state through cloud processing, and 3) enhances CCN activity of particles through the coating of soluble material.
High spatial resolution measurements of NO2 applying Topographic Target Light scattering-Differential Optical Absorption Spectroscopy (ToTaL-DOAS)
Authors: Frins E. , Platt U. , Wagner T.
Published: April 2010

Abstract. Tomographic Target Light scattering – Differential Optical Absorption Spectroscopy (ToTaL-DOAS), also called Target-DOAS, is a novel experimental procedure to retrieve trace gas concentrations present in the low atmosphere. Scattered sunlight (partially or totally) reflected from natural or artificial targets of similar albedo located at different distances is analyzed to retrieve the concentration of different trace gases like NO2, SO2 and others. We report high spatial resolution measurements of NO2 mixing ratios in the city of Montevideo (Uruguay) observing three buildings as targets with a Mini-DOAS instrument. Our instrument was 146 m apart from the first building, 196 m from the second and 286 m from the third one. All three buildings are located along a main Avenue. We obtain temporal variation of NO2 mixing ratios between 30 ppb and 65 ppb (±2 ppb). Our measurements demonstrate that ToTaL-DOAS measurements can be made over very short distances. In polluted air masses, the retrieved absorption signal was found to be strong enough to allow measurements over distances in the range of several ten meters, and achieve a spatial resolution of 50 m approximately.
Photolysis frequency measurement techniques: results of a comparison within the ACCENT project
Authors: Bohn B. , Corlett G. K. , Gillmann M. , Sanghavi S. , Stange G. , Tensing E. , Vrekoussis M. , Bloss W. J. , Clapp L. J. , Kortner M. , Dorn H.-P. , Monks P. S. , Platt U. , Plass-Dülmer C. , Mihalopoulos N. , Heard D. E. , Clemitshaw K. C. , Meixner F. X. , Prevot A. S. H. , Schmitt R.
Published: April 2010

Abstract. An intercomparison of different radiometric techniques measuring atmospheric photolysis frequencies j(NO2), j(HCHO) and j(O1D) was carried out in a two-week field campaign in June 2005 at Jülich, Germany. Three double-monochromator based spectroradiometers (DM-SR), three single-monochromator based spectroradiometers with diode-array detectors (SM-SR) and seventeen filter radiometers (FR) (ten j(NO2)-FR, seven j(O1D)-FR) took part in this comparison. For j(NO2), all spectroradiometer results agreed within ±3%. For j(HCHO), agreement was slightly poorer between −8% and +4% of the DM-SR reference result. For the SM-SR deviations were explained by poorer spectral resolutions and lower accuracies caused by decreased sensitivities of the photodiode arrays in a wavelength range below 350 nm. For j(O1D), the results were more complex within +8% and −4% with increasing deviations towards larger solar zenith angles for the SM-SR. The direction and the magnitude of the deviations were dependent on the technique of background determination. All j(NO2)-FR showed good linearity with single calibration factors being sufficient to convert from output voltages to j(NO2). Measurements were feasible until sunset and comparison with previous calibrations showed good long-term stability. For the j(O1D)-FR, conversion from output voltages to j(O1D) needed calibration factors and correction functions considering the influences of total ozone column and altitude of the sun. All instruments showed good linearity at photolysis frequencies exceeding about 10% of maximum values. At larger solar zenith angles, the agreement was non-uniform with deviations explainable by insufficient correction functions. Comparison with previous calibrations for some j(O1D)-FR indicated drifts of calibration factors.
First airborne water vapor lidar measurements in the tropical upper troposphere and mid-latitudes lower stratosphere: accuracy evaluation and intercomparisons with other instruments
Authors: Kiemle C. , Wirth M. , Fix A. , Ehret G. , Schumann U. , Gardiner T. , Schiller C. , Sitnikov N. , Stiller G.
Published: April 2010

Abstract. In the tropics, deep convection is the major source of uncertainty in water vapor transport to the upper troposphere and into the stratosphere. Although accurate measurements in this region would be of first order importance to better understand the processes that govern stratospheric water vapor concentrations and trends in the context of a changing climate, they are sparse because of instrumental shortcomings and observational challenges. Therefore, the Falcon research aircraft of the Deutsches Zentrum für Luft- und Raumfahrt (DLR) flew a zenith-viewing water vapor differential absorption lidar (DIAL) during the Tropical Convection, Cirrus and Nitrogen Oxides Experiment (TROCCINOX) in 2004 and 2005 in Brazil. The measurements were performed alternatively on three water vapor absorption lines of different strength around 940 nm. These are the first aircraft DIAL measurements in the tropical upper troposphere and in the mid-latitudes lower stratosphere. A sensitivity analysis reveals that the DIAL profiles have an accuracy of ~5% between altitudes of 8 and 16 km. This is confirmed by intercomparisons with the Fast In-situ Stratospheric Hygrometer (FISH) and the Fluorescent Advanced Stratospheric Hygrometer (FLASH) onboard the Russian M-55 Geophysica research aircraft during five coordinated flights. The average relative differences between FISH and DIAL amount to –3%±8% and between FLASH and DIAL to –8%±14%, negative meaning DIAL is more humid. The average distance between the probed air masses was 129 km. The DIAL is found to have no altitude- or latitude-dependent bias. A comparison with the balloon ascent of a laser absorption spectrometer gives an average difference of 0%±19% at a distance of 75 km. Six tropical DIAL under-flights of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT show a mean difference of –8%±49% at an average distance of 315 km. While the comparison with MIPAS is somewhat less significant due to poorer comparison conditions, the agreement with the in-situ hygrometers provides evidence of the excellent quality of FISH, FLASH and DIAL. Most DIAL profiles exhibit a smooth exponential decrease of water vapor mixing ratio in the tropical upper troposphere to lower stratosphere transition. The hygropause with a minimum mixing ratio of ~2.5 μmol/mol is found between 15 and 16 km, 1 to 2 km beneath the local tropopause. A high-resolution (2 km horizontal, ~200 m vertical) DIAL cross section through the anvil outflow of tropical convection shows that the ambient humidity is increased by a factor of three across 100 km.
Variations of O3 and CO in summertime at a rural site near Beijing
Authors: Wang Y. , McElroy M. B. , Munger J. W. , Hao J. , Ma H. , Nielsen C. P. , Chen Y.
Published: April 2010

Abstract. Large intra-season differences in concentrations of CO and O3 ([CO], [O3]) were detected at Miyun, a rural site north of Beijing, in summer 2006. Despite an increase in mean daytime [CO] from 500 ppbv in June to 700 ppbv in July, mean daytime [O3] dropped from 67 ppbv in June to 50 ppbv in July and August. The observed changes in CO and O3 are attributed to the influence of the summer monsoonal circulation that develops over the North China Plain in July. Photochemical production of O3 is reduced as a consequence of increased cloudiness during July and August, as indicated by the strong negative correlation observed between [O3] and satellite observations of cloud optical depth, with cloudiness having little effect on CO. The analysis suggests a strategy for emission controls that could be implemented in an economically efficient manner to minimize the frequency of high levels of O3 during summer in Beijing.
Sensitivity of aerosol concentrations and cloud properties to nucleation and secondary organic distribution in ECHAM5-HAM global circulation model
Authors: Makkonen R. , Asmi A. , Korhonen H. , Kokkola H. , Järvenoja S. , Räisänen P. , Lehtinen K. E. J. , Laaksonen A. , Kerminen V.-M. , Järvinen H. , Lohmann U. , Feichter J. , Kulmala M.
Published: April 2010

Abstract. The global aerosol-climate model ECHAM5-HAM was modified to improve the representation of new particle formation in the boundary layer. Activation-type nucleation mechanism was introduced to produce observed nucleation rates in lower troposphere. A simple and computationally efficient model for biogenic secondary organic aerosol (BSOA) formation was implemented. We studied the sensitivity of aerosol and cloud droplet number concentrations (CDNC) to these additions. Activation-type nucleation significantly increases aerosol number concentrations in the boundary layer. Increased particle number concentrations have a significant effect also on cloud droplet number concentrations and therefore on cloud properties. We performed calculations with activation nucleation coefficient values of 2×10-7 s−1, 2×10-6 s-1 and 2×10-5 s−1 to evaluate the sensitivity to this parameter. For BSOA we have used yields of 0.025, 0.07 and 0.15 to estimate the amount of monoterpene oxidation products available for condensation. The dynamic SOA scheme induces large regional changes to size distribution of organic carbon, and therefore affects particle optical properties and cloud droplet number concentrations locally. Comparison with satellite observation shows that activation-type nucleation significantly decreases the differences between observed and modeled values of cloud top CDNC.
Tropospheric ozone climatology at two southern subtropical sites, (Reunion Island and Irene, South Africa) from ozone sondes, LIDAR, aircraft and in situ measurements
Authors: Clain G. , Baray J. L. , Delmas R. , Diab R. , Leclair de Bellevue J. , Keckhut P. , Posny F. , Metzger J. M. , Cammas J. P.
Published: April 2010

Abstract. This paper presents a climatology and trends of tropospheric ozone in the southwestern part of Indian Ocean (Reunion Island) and South Africa (Irene and Johannesburg). This study is based on a multi-instrumental dataset: PTU-O3 radiosoundings, DIAL LIDAR, MOZAIC airborne instrumentation and Dasibi UV ground based measurements. The seasonal profiles of tropospheric ozone at Reunion Island have been calculated from two different data sets: radiosondes and LIDAR. The two climatological profiles are similar, except in austral summer when smaller values for the LIDAR profiles in the free troposphere, and in the upper troposphere for all seasons occur. These results show that the LIDAR profiles are at times not representative of the true ozone climatological value as measurements can be taken only under clear sky conditions, and the upper limit reached depends on the signal. In the lower troposphere, climatological ozone values from radiosondes have been compared to a one year campaign of ground based measurements from a Dasibi instrument located at high altitude site (2150 m) at Reunion Island. The seasonal cycle is comparable for the two datasets, with Dasibi UV values displaying slightly higher values. This suggests that if local dynamical and possibly physico-chemical effects may influence the ozone level, the seasonal cycle can be followed with ground level measurements. Average ground level concentrations measured on the summits of the island seem to be representative of the lower free troposphere ozone concentration at the same altitude (~2000 m) whereas night time data would be representative of tropospheric concentration at a higher altitude (~3000 m) due to the subsidence effect. Finally, linear trends have been calculated from radiosondes data at Reunion and Irene. Considering the whole tropospheric column, the trend is slightly positive for Reunion, and more clearly positive for Irene. Trend calculations have also been made separating the troposphere into three layers, and separating the dataset into seasons. Results shows that the positive trend for Irene is governed by the lower layer most probably by industrial pollution and biomass burning. On the contrary, for Reunion Island, the strongest trends are observed in the upper troposphere, and in winter when stratospheric-tropospheric exchange is more frequently expected.
Aerosol dynamics simulations on the connection of sulphuric acid and new particle formation
Authors: Sihto S.-L. , Vuollekoski H. , Leppä J. , Riipinen I. , Kerminen V.-M. , Korhonen H. , Lehtinen K. E. J. , Boy M. , Kulmala M.
Published: April 2010

Abstract. We have performed a series of simulations with an aerosol dynamics box model to study the connection between new particle formation and sulphuric acid concentration. For nucleation either activation mechanism with a linear dependence on the sulphuric acid concentration or ternary H2O-H2SO4-NH3 nucleation was assumed. We investigated the factors that affect the sulphuric acid dependence during the early stages of particle growth, and tried to find conditions which would yield the linear dependence between the particle number concentration at 3–6 nm and sulphuric acid, as observed in field experiments. The simulations showed that the correlation with sulphuric acid may change during the growth from nucleation size to 3–6 nm size range, the main reason being the size dependent growth rate between 1 and 3 nm. In addition, the assumed size for the nucleated clusters had a crucial impact on the sulphuric acid dependence at 3 nm. The simulations yielded a linear dependence between the particle number concentration at 3 nm and sulphuric acid, when a low saturation vapour pressure for the condensable organic vapour was assumed, or when nucleation took place at ~2 nm instead of ~1 nm. Comparison of results with activation and ternary nucleation showed that ternary nucleation cannot explain the experimentally observed linear or square dependence on sulphuric acid.
Summertime PM2.5 ionic species in four major cities of China: nitrate formation in an ammonia-deficient atmosphere
Authors:   Ravi Kant Pathak,   Wai Shing Wu,   Tao Wang
Published: April 2010

Abstract. Strong atmospheric photochemistry in summer can produce a significant amount of secondary aerosols, which may have a large impact on regional air quality and visibility. In the study reported herein, we analyzed sulfate, nitrate, and ammonium in PM2.5 samples collected using a 24-h filter system at suburban and rural sites near four major cities in China (Beijing, Shanghai, Guangzhou, and Lanzhou). Overall, the PM2.5 mass concentrations were high (with a mean value of 55–68 µg m−3), which reflects the long-known particulate pollution in China's large urban centers. We observed very high concentrations of sulfate and nitrate at the Beijing and Shanghai sites, and, in particular, abnormally high levels of nitrate (24-h average concentration up to 42 µg m−3 and contributing up to 25% of the PM2.5 mass) in the ammonium-poor samples. The Beijing and Shanghai aerosols were characterized by high levels of aerosol acidity (~220–390 nmol m−3) and low levels of in-situ pH (−0.77 to −0.52). In these samples, the formation of the observed high concentrations of particulate nitrate cannot be explained by homogeneous gas-phase reaction between ammonia and nitric acid. Examination of the relation of nitrate to relative humidity and aerosol loading suggests that the nitrate was most probably formed via the heterogeneous hydrolysis of N2O5 on the surface of the moist and acidic aerosols in Beijing and Shanghai. In comparison, the samples collected in Lanzhou and Guangzhou were ammonium-rich with low levels of aerosol acidity (~65–70 nmol m−3), and the formation of ammonium nitrate via the homogeneous gas-phase reaction was favored, which is similar to many previous studies. An empirical fit has been derived to relate fine nitrate to aerosol acidity, aerosol water content, aerosol surface area, and the precursor of nitrate for the data from Beijing and Shanghai.