bluuebunny/crossref_metadata_2025 huggingface dataset:
On the possible causes of recent increases in NH 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 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 (effective equivalent 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 the natural decadal atmospheric variability or will persist. If the latter is the case, it could be interpreted as a possible signature of climate change.
Conceptual study on nucleation burst evolution in the convective boundary layer – Part II: Meteorological characterization
Authors: Hellmuth O.
Published: April 2010

Abstract. While in part I of the present paper a revised columnar high-order modelling approach to investigate gas-aerosol interactions in the convective boundary layer (CBL) was deduced, in the present part the model capability to predict the evolution of meteorological CBL parameters is demonstrated. Based on a model setup to simulate typical CBL conditions, predicted first-, second- and third-order moments were shown to agree very well with those obtained from in situ and remote sensing turbulence measurements such as aircraft, SODAR and LIDAR measurements as well as with those derived from ensemble-averaged large-eddy simulations and wind tunnel experiments. The results show that the model is able to predict the meteorological CBL parameters, required to verify or falsify, respectively, previous hypothesis on the interaction between CBL turbulence and new particle formation.
2-D reconstruction of atmospheric concentration peaks from horizontal long path DOAS tomographic measurements: parametrisation and geometry within a discrete approach
Authors: Hartl A. , Song B. C. , Pundt I.
Published: April 2010

Abstract. In this study, we theoretically investigate the reconstruction of 2-D cross sections through Gaussian concentration distributions, e.g. emission plumes, from long path DOAS measurements along a limited number of light paths. This is done systematically with respect to the extension of the up to four peaks and for six different measurement setups with 2–4 telescopes and 36 light paths each. We distinguish between cases with and without additional background concentrations. Our approach parametrises the unknown distribution by local piecewise constant or linear functions on a regular grid and solves the resulting discrete, linear system by a least squares minimum norm principle. We show that the linear parametrisation not only allows better representation of the distributions in terms of discretisation errors, but also better inversion of the system. We calculate area integrals of the concentration field (i.e. total emissions rates for non-vanishing perpendicular wind speed components) and show that reconstruction errors and reconstructed area integrals within the peaks for narrow distributions crucially depend on the resolution of the reconstruction grid. A recently suggested grid translation method for the piecewise constant basis functions, combining reconstructions from several shifted grids, is modified for the linear basis functions and proven to reduce overall reconstruction errors, but not the uncertainty of concentration integrals. We suggest a procedure to subtract additional background concentration fields before inversion. We find large differences in reconstruction quality between the geometries and conclude that, in general, for a constant number of light paths increasing the number of telescopes leads to better reconstruction results. It appears that geometries that give better results for negligible measurement errors and parts of the geometry that are better resolved are also less sensitive to increasing measurement errors.
A study of dispersion in complex terrain under winter conditions using high-resolution mesoscale and Lagrangian particle models
Authors: Palau J. L. , Pérez-Landa G. , Meliá J. , Segarra D. , Millán M. M.
Published: April 2010

Abstract. A mesoscale model (MM5), a dispersive Langrangian particle model (FLEXPART), and intensive meteorological and COrrelation SPECtrometer (COSPEC) measurements from a field campaign are used to examine the advection and turbulent diffusion patterns associated with interactions and forcings between topography, synoptic atmospheric flows and thermally-driven circulations. This study describes the atmospheric dispersion of emissions from a power plant with a 343-meter-tall chimney, situated on very complex terrain in the North-East of Spain, under winter conditions. During the field campaign, the plume was transported with low transversal dispersion and deformed essentially due to the effect of mechanical turbulence. The main surface impacts appeared at long distances from the emission source (more than 30 km). The results show that the coupled models (MM5 and FLEXPART) are able to predict the plume integral advection from the power plant on very complex terrain. Integral advection and turbulent dispersion are derived from the dispersive Lagrangian model output for three consecutive days so that a direct quantitative comparison has been made between the temporal evolution of the predicted three-dimensional dispersive conditions and the COSPEC measurements. Comparison between experimental and simulated transversal dispersion shows an index of agreement between 80% and 90%, within distance ranges from 6 to 33 km from the stack. Linked to the orographic features, the simulated plume impacts on the ground more than 30 km away from the stack, because of the lee waves simulated by MM5.
Evidence for long-lived polar vortex air in the mid-latitude summer stratosphere from in situ laser diode CH4 and H2O measurements
Authors: Durry G. , Hauchecorne A.
Published: April 2010

Abstract. A balloon borne diode laser spectrometer was launched in southern France in June 2000 to yield in situ stratospheric CH4 and H2O measurements. In the altitude region ranging from 20 km to 25 km, striking large spatial structures were observed in the vertical concentration profiles of both species. We suggest these patterns are due to the presence of long-lived remnants of the wintertime polar vortex in the mid-latitude summer stratosphere. To support this interpretation, a high resolution advection model for potential vorticity is used to investigate the evolution of the Arctic vortex after its breakdown phase in spring 2000.
A scaling analysis of ozone photochemistry: II Investigation of the similarity relationship
Authors: Ainslie B. , Steyn D. G.
Published: April 2010

Abstract. The similarity relationship for maximum ozone concentration as a function of initial precursor concentrations developed in the first article of this 2-part series exhibits a scale break, most easily seen after a Weibull transformation, which identifies a characteristic scale for ozone photochemistry. In this paper, we investigate the similarity relationship using simple semi-quantitative models and model output. From this investigation, we develop a set of properties characterizing ozone-precursor relationships. We find the scaling break is associated with a change in the temporal variability of ozone production. Finally, we examine a series of smog chamber experiments for evidence of a scaling break. We find the data support a slight break after suitable transformation. It is difficult to tell if the lack of distinct break is due to smog chamber experimental limitations, a bias in the test conditions or if the processes leading to the scaling break are overly enhanced by chemical mechanisms.
Water activity in polyol/water systems: new UNIFAC parameterization
Authors: Marcolli C. , Peter Th.
Published: April 2010

Abstract. Water activities of a series of polyol/water systems were measured with an AquaLab dew point water activity meter at 298 K. The investigated polyols with carbon numbers from n=2–7 are all in liquid state at room temperature and miscible at any molar ratio 5 with water. In aqueous solutions with the same mass concentration, the diols with lower molecular weight lead to lower water activities than those with higher molecular weights. For diols with four or more carbon atoms, the hygroscopicity shows considerable differences between isomers: The 1,2-isomers – consisting of a hydrophilic and a hydrophobic part – bind less strongly to water than isomers with a more balanced 10 distribution of the hydroxyl groups. The experimental water activities were compared with the predictions of the group contribution method UNIFAC: the model predictions overestimate the water activity of water/polyol systems of substances with two or more hydroxyl groups and can not describe the decreased binding to water of isomers with hydrophobic tails. To account for the differences between isomers, a modified UNIFAC 15 parameterization was developed, that allows to discriminate between three types of alkyl groups depending on their position in the molecule. These new group-interaction parameters were calculated using water activities of alcohol/water mixtures. This leads to a distinctly improved agreement of model predictions with experimental results while largely keeping the simplicity of the functional group approach.
Fall vortex ozone as a predictor of springtime total ozone at high northern latitudes
Authors: Kawa S. R. , Newman P. A. , Stolarski R. S. , Bevilacqua R. M.
Published: April 2010

Abstract. Understanding the impact of atmospheric dynamical variability on observed changes in stratospheric O3 is a key to understanding how O3 will change with future climate dynamics and trace gas abundances. In this paper we examine the linkage between interannual variability in total column O3 at northern high latitudes in March and lower-to-mid stratospheric vortex O3 in the prior November. We find that these two quantities are significantly correlated in the years available from TOMS, SBUV, and POAM data (1978–2004). Additionally, we find that the apparent decadal shift in March O3 variability from the 1980s to years post-1990 is also seen in the November vortex O3, so that interannual variability in both quantities is largely driven by the later years. The cause of this correlation is not clear, however. Interannual variations in March total O3 are known to correspond closely with variations in winter stratospheric wave driving consistent with the effects of varying residual circulation, temperature, and chemical loss. Variation in November vortex O3 may also depend on dynamical wave activity, however, the dynamics in fall are less variable than in winter and spring. We do not find significant correlations of dynamic indicators for November such as temperature, heat flux, or polar average total O3 with the November vortex O3, nor with dynamical indicators later in winter and spring that might lead to a connection to March. We discuss several potential hypotheses for the observed correlation but do not find strong evidence for any considered mechanism. We present the observations as a phenomenon whose understanding may improve our ability to predict the dependence of O3 on changing dynamics and chemistry.
Long-term changes and variability in a transient simulation with a chemistry-climate model employing realistic forcing
Authors: Dameris M. , Grewe V. , Ponater M. , Deckert R. , Eyring V. , Mager F. , Matthes S. , Schnadt C. , Stenke A. , Steil B. , Brühl C. , Giorgetta M. A.
Published: April 2010

Abstract. A transient simulation with the interactively coupled chemistry-climate model (CCM) E39/C has been carried out which covers the 40-year period between 1960 and 1999. Forcing of natural and anthropogenic origin is prescribed where the characteristics are sufficiently well known and the typical timescales are slow compared to synoptic timescale so that the simulated atmospheric chemistry and climate evolves under a ''slowly'' varying external forcing. Based on observations, sea surface temperature (SST) and ice cover are prescribed. The increase of greenhouse gas and chloroflurocarbon concentrations, as well as nitrogen oxide emissions is taken into account. The 11-year solar cycle is considered in the calculation of heating rates and photolysis of chemical species. The three major volcanic eruptions during that time (Agung, 1963; El Chichon, 1982; Pinatubo, 1991) are considered. The quasi-biennial oscillation (QBO) is forced by linear relaxation, also known as nudging, of the equatorial zonal wind in the lower stratosphere towards observed zonal wind profiles. Beyond a reasonable reproduction of mean parameters and long-term variability characteristics there are many apparent features of episodic similarities between simulation and observation: In the years 1986 and 1988 the Antarctic ozone holes are smaller than in the other years of the respective decade. In mid-latitudes of the Southern Hemisphere ozone anomalies, especially in 1985, 1989, 1991/1992, and 1996, resemble the corresponding observations. In the Northern Hemisphere, the first half of the 1990s is dynamically quiet, no stratospheric warming is found for a period of at least 6 years. As observed, volcanic eruptions strongly influence dynamics and chemistry, though only for few years. Obviously, planetary wave activity is strongly driven by the prescribed SST and modulated by the QBO. Preliminary evidence of realistic cause and effect relationships strongly suggest that detailed process-oriented studies will be a worthwhile endeavour.
Commentary on ''Measurements of ice supersaturations exceeding 100% at the cold tropical tropopause'' by E. Jensen et al.
Authors: Murphy D. M.
Published: April 2010

Abstract. The paper by Jensen et al. (2005) provides an excellent use of a microphysical model to examine the logical consequences of high saturation ratios indicated by measurements during a high altitude flight of the NASA WB-57F. I would like to comment on a turn made by the aircraft that makes this particular event harder to interpret.
Mexico City basin wind circulation during the MCMA-2003 field campaign
Authors: de Foy B. , Caetano E. , Magaña V. , Zitácuaro A. , Cárdenas B. , Retama A. , Ramos R. , Molina L. T. , Molina M. J.
Published: April 2010

Abstract. MCMA-2003 was a major field campaign investigating the atmospheric chemistry of the Mexico City Metropolitan Area (MCMA) in April of 2003. This paper describes the wind circulation patterns during the campaign both within the Mexico City basin and on the regional scale. ''Time roses'' are introduced to concisely analyze the diurnal wind patterns. Three episode types were identified that explain the conditions encountered: ''O3-South'', ''Cold Surge'' and ''O3-North''. These can be diagnosed from a combination of synoptic and basin observations based on whether the day was predominantly cloudy, or whether the O3 peak was in the north or south of the basin. O3-South days have weak synoptic forcing due to an anti-cyclone over the eastern Pacific. Strong solar heating leads to northerly flows in the basin and an evening shift due to a gap flow from the south-east. Peak ozone concentrations are in the convergence zone in the south of the city. Cold Surge days are associated with ''El Norte'' events, with strong surface northerlies bringing cold moist air and rain. Stable conditions lead to high concentrations of primary pollutants and peak ozone in the city center. O3-North days occur when the sub-tropical jet is closer to Mexico City. With strong westerlies aloft, the circulation pattern is the same as O3-South days except for a wind shift in the mid-afternoon leading to ozone peaks in the north of the city. This classification is proposed as a means of understanding pollutant transport in the Mexico City basin and as a basis for future meteorological and chemical analysis. Furthermore, model evaluation and design of policy recommendations will need to take into account the three episode types.
Characterization of air ions in boreal forest air during BIOFOR III campaign
Authors: Hõrrak U. , Aalto P. P. , Salm J. , Mäkelä J. M. , Laakso L. , Laakso L. , Kulmala M.
Published: April 2010

Abstract. The behavior of the concentration of positive small (or cluster) air ions and naturally charged nanometer aerosol particles (aerosol ions) has been studied on the basis of measurements carried out in a boreal forest at the Hyytiälä SMEAR station, Finland, during the BIOFOR III campaign in spring 1999. Statistical characteristics of the concentrations of cluster ions, two classes of aerosol ions of the sizes of 2.5–8 nm and 8–ca 20 nm and the quantities that determine the balance of small ions in the atmosphere have been given for the nucleation event days and non-event days. The dependence of small ion concentration on the ion loss (sink) due to aerosol particles was investigated applying a model of bipolar diffusion charging of particles by small ions. The small ion concentration and the ion sink were closely correlated (correlation coefficient 87%) when the fog events and the hours of high relative humidity (above 97%), as well as nocturnal calms and weak wind (wind speed<0.6 m s-1 had been excluded. In the case of nucleation burst events, variations in the concentration of small positive ions were in accordance with the changes caused by the ion sink due to aerosols; no clear indication of positive ion depletion by ion-induced nucleation was found. The estimated average ionization rate of air at the Hyytiälä station in early spring, when the ground was partly covered with snow, was about 4.8 ion pairs cm-3 s-1. The study of the charging state of nanometer aerosol particles (2.5–8 nm) revealed a strong correlation (correlation coefficient 88%) between the concentrations of particles and their charged fraction (positive air ions) during nucleation bursts. The estimated charged fraction of particles, which varied from 3% to 6% considering various nucleation event days, confirms that these particles are almost quasi-steady state charged. Also the particles and air ions in the size range of 8–ca 20 nm showed a good qualitative consistency; the correlation coefficient was 92%.
Airborne measurements of trace gas and aerosol particle emissions from biomass burning in Amazonia
Authors: Guyon P. , Frank G. , Welling M. , Chand D. , Artaxo P. , Rizzo L. , Nishioka G. , Kolle O. , Fritsch H. , Silva Dias M. A. F. , Gatti L. V. , Cordova M. , Andreae M. O.
Published: April 2010

Abstract. As part of the LBA-SMOCC (Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke, Aerosols, Clouds, Rainfall, and Climate) 2002 campaign, we studied the emission of carbon monoxide (CO), carbon dioxide (CO2), and aerosol particles from Amazonian deforestation fires using an instrumented aircraft. Emission ratios for aerosol number (CN) relative to CO (ERCN/CO) fell in the range 14–32 cm-3 ppb-1 for most of the time, in agreement with values usually found from tropical savanna fires. The number of particles emitted per amount biomass burned was found to be dependant on the fire condition (combustion efficiency). Variability in the ERCN/CO between fires was similar to the variability caused by variations in combustion behavior within each individual fire. This was confirmed by observations of CO-to-CO2 emission ratios (ERCO/CO2), which stretched across the same wide range of values for individual fires as for all the fires observed during the sampling campaign, indicating that flaming and smoldering phases are present simultaneously in deforestation fires. Emission factors (EF) for CO and aerosol particles were computed and a correction was applied for the residual smoldering combustion (RSC) fraction of emissions that are not sampled by the aircraft. The correction, previously unpublished for tropical deforestation fires, suggested an EF about one and a half to twice as large for these species. Vertical transport of biomass-burning plumes from the boundary layer (BL) to the cloud detrainment layer (CDL) and the free troposphere (FT) was found to be a very common phenomenon. We observed a 20% loss in particle number as a result of this vertical transport and subsequent cloud processing, attributable to in-cloud coagulation. This small loss fraction suggests that this mode of transport is very efficient in terms of particle numbers and occurs mostly via non-precipitating clouds. The detrained aerosol particles released in the CDL and FT were larger due to coagulation and secondary growth, and therefore more efficient at scattering radiation and nucleating cloud droplets than the fresh particles. This process may have significant atmospheric implications on a regional and larger scale.
Statistical analysis of the precision of the Match method
Authors: Lehmann R. , von der Gathen P. , Rex M. , Streibel M.
Published: April 2010

Abstract. The Match method quantifies chemical ozone loss in the polar stratosphere. The basic idea consists in calculating the forward trajectory of an air parcel that has been probed by an ozone measurement (e.g., by an ozone sonde or satellite) and finding a second ozone measurement close to this trajectory. Such an event is called a ''match''. A rate of chemical ozone destruction can be obtained by a statistical analysis of several tens of such match events. Information on the uncertainty of the calculated rate can be inferred from the scatter of the ozone mixing ratio difference (second measurement minus first measurement) associated with individual matches. A standard analysis would assume that the errors of these differences are statistically independent. However, this assumption may be violated because different matches can share a common ozone measurement, so that the errors associated with these match events become statistically dependent. Taking this effect into account, we present an analysis of the uncertainty of the final Match result. It has been applied to Match data from the Arctic winters 1995, 1996, 2000, and 2003. For these ozone-sonde Match studies the effect of the error correlation on the uncertainty estimates is rather small: compared to a standard error analysis, the uncertainty estimates increase by 15% on average. However, the effect is more pronounced for typical satellite Match analyses: for an Antarctic satellite Match study (2003), the uncertainty estimates increase by 60% on average.
A global off-line model of size-resolved aerosol microphysics: II. Identification of key uncertainties
Authors: Spracklen D. V. , Pringle K. J. , Carslaw K. S. , Chipperfield M. P. , Mann G. W.
Published: April 2010

Abstract. We use the new GLOMAP model of global aerosol microphysics to investigate the sensitivity of modelled sulfate and sea salt aerosol properties to uncertainties in the driving microphysical processes and compare these uncertainties with those associated with aerosol and precursor gas emissions. Overall, we conclude that uncertainties in microphysical processes have a larger effect on global condensation nuclei (CN) and cloud condensation nuclei (CCN) concentrations than uncertainties in present-day sulfur emissions. Our simulations suggest that uncertainties in predicted sulfate and sea salt CCN abundances due to poorly constrained microphysical processes are likely to be of a similar magnitude to long-term changes in CCN due to changes in anthropogenic emissions. A microphysical treatment of the global sulfate aerosol allows the uncertainty in climate-relevant aerosol properties to be attributed to specific processes in a way that has not been possible with simpler aerosol schemes. In particular we conclude that: (1) changes in the binary H2SO4-H2O nucleation rate and condensation rate of gaseous H2SO4 cause a shift in the vertical location of the upper tropospheric CN layer by as much as 3 km, while changes in absolute concentration are relatively small; (2) uncertainties in the binary H2SO4-H2O nucleation rate have a relatively insignificant effect on boundary layer aerosol properties; (3) production of sulfate particles in power plant plumes below the scale of the model grid (which is of the order of 300 km) has the potential to change the global mean sulfate-derived CN concentration by a factor 2 or more at the surface, and changes of up to a factor 20 can occur in polluted regions; (4) predicted global mean sulfate and sea salt CCN concentrations change by 10 to 40% at the surface when several microphysical processes are changed within reasonable uncertainty ranges; (5) CCN concentrations are particularly sensitive to primary sulfate particle emissions, with global mean CCN changing by up to 40% and local concentrations changing by more than 100% when the percentage of anthropogenic SO2 emitted as particulates in plumes is changed from 0 to 5%; (6) uncertainties in CCN due to the mode of sulfate emission (i.e., the fraction of sulfur emitted as primary particles) are larger than those (~15%) caused by a ±25% change in total sulfur emissions; (7) large changes in sea spray flux have insignificant effects on global sulfate aerosol except when the mass accommodation coefficient of sulfuric acid on the salt particles is set unrealistically low.
Spatial and temporal characterization of SCIAMACHY limb pointing errors during the first three years of the mission
Authors: von Savigny C. , Kaiser J. W. , Bovensmann H. , Burrows J. P. , McDermid I. S. , Leblanc T.
Published: April 2010

Abstract. Limb scattering retrievals of atmospheric minor constituent profiles require highly accurate knowledge of the tangent heights during the measurements. The limb scattering measurements of the Scanning Imaging Absorption spectrometer for Atmospheric CartograpHY (SCIAMACHY) on Envisat are affected by tangent height errors of up to 2 km. This contribution provides a summary of the temporal and spatial variation of the SCIAMACHY limb pointing errors during the first three years of the SCIAMACHY mission. The tangent height errors are retrieved from the limb measurements in the UV-B spectral range. A seasonal modulation of the monthly mean tangent height offsets is identified with amplitudes of 800 m (220 m) before (after) the improvement of the Envisat orbit propagator model in December 2003. Even after the December 2003 orbit model improvement a constant offset component of about 1 km is present. Furthermore, pointing discontinuities are identified that coincide with the daily updates of the on-board orbit propagator model. In order to reduce the errors in ozone profile retrievals caused by pointing errors to less than 5%, the tangent heights have to be known to within 250 m.
Indicators of Antarctic ozone depletion
Authors: Bodeker G. E. , Shiona H. , Eskes H.
Published: April 2010

Abstract. An assimilated data base of total column ozone measurements from satellites has been used to generate a set of indicators describing attributes of the Antarctic ozone hole for the period 1979 to 2003, including (i) daily measures of the area over Antarctica where ozone levels are below 150DU, below 220DU, more than 30% below 1979 to 1981 norms, and more than 50% below 1979 to 1981 norms, (ii) the date of disappearance of 150DU ozone values, 220DU ozone values, values 30% below 1979 to 1981 norms, and values 50% below 1979 to 1981 norms, for each year, (iii) daily minimum total column ozone values over Antarctica, and (iv) daily values of the ozone mass deficit based on a O3<220DU threshold. The assimilated data base combines satellite-based ozone measurements from 4 Total Ozone Mapping Spectrometer (TOMS) instruments, 3 different retrievals from the Global Ozone Monitoring Experiment (GOME), and data from 4 Solar Backscatter Ultra-Violet (SBUV) instruments. Comparisons with the global ground-based Dobson spectrophotometer network are used to remove offsets and drifts between the different data sets to produce a global homogeneous data set that combines the advantages of good spatial coverage of satellite data with good long-term stability of ground-based measurements. One potential use of the derived indices is detection of the expected recovery of the Antarctic ozone hole. The suitability of the derived indicators to this task is discussed in the context of their variability and their susceptibility to saturation effects which makes them less responsive to decreasing stratospheric halogen loading. It is also shown that if the corrections required to match recent Earth Probe TOMS measurements to Dobson measurements are not applied, some of the indictors are affected so as to obscure detection of the recovery of the Antarctic ozone hole.
Morphological, chemical and optical absorbing characterization of aerosols in the urban atmosphere of Valladolid
Authors: Mogo S. , Cachorro V. E. , de Frutos A. M.
Published: April 2010

Abstract. Aerosol samples were collected from the Valladolid (Spain) atmosphere during 2003–2004 winter using a Dekati PM10 cascade impactor which allows to discriminate four level of particle sizes: greater than 10 µm, between 10 and 2.5, from 2.5 to 1 and less than 1 µm. The size and shape of the aerosol deposits were analyzed by means of individual particles through scanning electron microscope (SEM) technique. Additionally an energy dispersive X-ray analysis (EDX) was performed enabling elemental analysis of a large number of individual particles in a relatively short time. We present a classification in size, shape and composition of the major particulate species present in the Valladolid urban atmosphere. The aerosol concentration is very variable during winter, ranging from 39.86 µg·m−3 to 184.88 µg·m−3 with coarse particle as dominant fraction. Emphasize was given to fine particles, behind 1 µm, for which the visible (from 400 nm to 650 nm) light absorption coefficients were measured using the integrating plate technique. We have made some enhancements relative to the illumination system in the well known integrating plate method, for the absorption coefficients determination. The absorption coefficient ranges from 7.33×10−6 m−1 to 1.01×10−4 m−1 for the 550 nm wavelength. Its visible spectrum decreases with wavelength with greater slope for greater σ values.
Tropospheric distribution of sulphate aerosol mass and number concentration during INDOEX-IFP and its transport over the Indian Ocean: a GCM study
Authors: Verma S. , Boucher O. , Reddy M. S. , Deb S. K. , Upadhyaya H. C. , Le Van P. , Binkowski F. S. , Sharma O. P.
Published: April 2010

Abstract. An interactive sulphate aerosol chemistry module has been incorporated in the Laboratoire de Météorologie Dynamique General Circulation Model (LMD-GCM) to simulate the sulphur chemistry during the Indian Ocean Experiment (INDOEX) Intensive Field Phase-1999 (INDOEX-IFP). The originality of this module is its ability to predict particle mass and number concentration for the Aitken and accumulation modes. The model qualitatively reproduces the spatial patterns of observations on sulphate aerosol during INDOEX. On the basis of size distribution retrieved from the observations made along the cruise route during 1998 and 1999, the model successfully simulates the order of magnitude and the general north-south gradient in aerosol number concentration. The result shows the southward migration of minimum concentrations, which follows ITCZ (Inter Tropical Convergence Zone) migration. Sulphate surface concentration during INDOEX-IFP at Kaashidhoo (73.46° E, 4.96° N) gives an agreement within a factor of 2 to 3. Predicted sulphate aerosol optical depth (AOD) matches reasonably with measured values, indicating the capability of this model to predict the vertically integrated column sulphate burden. The Indian contribution to estimated sulphate burden over India is more than 60% with values upto 40% over the Arabian Sea.
Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry – Part II: overview of the results at the CENICA supersite and comparison to previous studies
Authors: Salcedo D. , Dzepina K. , Onasch T. B. , Canagaratna M. R. , Jayne J. T. , Worsnop D. R. , Gaffney J S. , Marley N. A. , Johnson K. S. , Zuberi B. , Molina L. T. , Molina M. J. , Shutthanandan V. , Xie Y. , Jimenez J. L.
Published: April 2010

Abstract. An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at the CENICA Supersite during the Mexico City Metropolitan Area field study from 31 March–4 May 2003. The AMS provides real time information on mass concentration and composition of the non-refractory species in particulate matter less than 1 µm (NR-PM1) with high time and size-resolution. Measurements of Black Carbon (BC) using an aethalometer, and estimated soil concentrations from Proton-Induced X-Ray Emission (PIXE) analysis of impactor substrates are also presented and combined with the AMS in order to include refractory material and estimate the total PM2.5 mass concentration at CENICA during this campaign. In Mexico City, the organic fraction of the estimated PM2.5 at CENICA represents 54.6% of the mass, with the rest consisting of inorganic compounds (mainly ammonium nitrate and sulfate/ammonium salts), BC, and soil. Inorganic compounds represent 27.5% of PM2.5; BC mass concentration is about 11%; while soil represents about 6.9%. The NR species and BC have diurnal cycles that can be qualitatively interpreted as the interplay of direct emissions, photochemical production in the atmosphere followed by condensation and gas-to-particle partitioning, boundary layer dynamics, and/or advection. Bi- and trimodal size distributions are observed for the AMS species, with a small combustion (likely traffic) organic particle mode and an accumulation mode that contains mainly organic and secondary inorganic compounds. The AMS and BC mass concentrations, size distributions, and diurnal cycles are found to be qualitatively similar to those from most previous field measurements in Mexico City.
Retrieval and validation of ozone columns derived from measurements of SCIAMACHY on Envisat
Authors: Eskes H. J. , van der A R. J. , Brinksma E. J. , Veefkind J. P. , de Haan J. F. , Valks P. J. M.
Published: April 2010

Abstract. This paper describes a new ozone column retrieval algorithm and its application to SCIAMACHY measurements. The TOSOMI algorithm is based on the Differential Optical Absorption Spectroscopy (DOAS) technique and implements several improvements over older algorithms. These improvements include aspects like (i) the explicit treatment of rotational Raman scattering, (ii) an improved air-mass factor formulation which is based on a simulation of the reflectivity spectrum and a subsequent DOAS fit of this simulated spectrum, (iii) the use of an improved ozone climatology and a column dependent air-mass factor, (iv) the use of daily varying ECMWF temperature profile analyses. The results of three validation exercises are reported. The TOSOMI columns are compared with an extensive set of ground-based observations (Brewer, Dobson) for the years 2003 and 2004. Secondly, a direct comparison for January–June 2003 with two new GOME retrievals, GDP Version 4 and TOGOMI, is presented. Third, data assimilation is used to study the dependence of the TOSOMI columns with retrieval parameters such as the viewing angle, cloud fraction and geographical location. These comparisons show a good consistency on the percent level between the GOME and SCIAMACHY algorithms. The present TOSOMI implementation (v0.32) shows an offset of about −1.5% with respect to ground-based observations and the GOME retrievals.
Analysis of the decrease in the tropical mean outgoing shortwave radiation at the top of atmosphere for the period 1984-2000
Authors: Fotiadi A. , Hatzianastassiou N. , Matsoukas C. , Pavlakis K. G. , Drakakis E. , Hatzidimitriou D. , Vardavas I.
Published: April 2010

Abstract. A decadal-scale trend in the tropical radiative energy budget has been observed recently by satellites, which however is not reproduced by climate models. In the present study, we have computed the outgoing shortwave radiation (OSR) at the top of atmosphere (TOA) at 2.5° longitude-latitude resolution and on a mean monthly basis for the 17-year period 1984–2000, by using a deterministic solar radiative transfer model and cloud climatological data from the International Satellite Cloud Climatology Project (ISCCP) D2 database. Atmospheric temperature and humidity vertical profiles, as well as other supplementary data, were taken from the National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP/NCAR) and the European Center for Medium-Range Weather Forecasts (ECMWF) Global Reanalysis Projects, while other global databases, such as the Global Aerosol Data Set (GADS) for aerosol data, were also used. Anomaly time series for the mean monthly pixel-level OSR fluxes, as well as for the key physical parameters, were constructed. A significant decreasing trend in OSR anomalies, starting mainly from the late 1980s, was found in tropical and subtropical regions (30° S–30° N), indicating an increase in solar planetary heating equal to 3.2±0.5 Wm-2 over the 17-year time period from 1984 to 2000 or 1.9±0.3 Wm-2/decade, reproducing well the features recorded by satellite observations, in contrast to climate model results. The model computed trend is in good agreement with the corresponding linear decrease of 3.7±0.5 Wm-2 (or 2.5±0.4 Wm-2/decade) in tropical mean OSR anomalies derived from ERBE S-10N non-scanner data. An attempt was made to identify the physical processes responsible for the decreasing trend in tropical mean OSR. A detailed correlation analysis using pixel-level anomalies of OSR flux and ISCCP cloud cover over the entire tropical and subtropical region (30° S–30° N), gave a correlation coefficient of 0.79, indicating that decreasing cloud cover is the main reason for the tropical OSR trend. According to the ISCCP-D2 data derived from the combined visible/infrared (VIS/IR) analysis, the tropical cloud cover has decreased by 6.6±0.2% per decade, in relative terms. A detailed analysis of the inter-annual and long-term variability of the various parameters determining the OSR at TOA, has shown that the most important contribution to the observed OSR trend comes from a decrease in low-level cloud cover over the period 1984–2000, followed by decreases in middle and high-level cloud cover. Opposite but small trends are introduced by increases in cloud scattering optical depth of low and middle clouds.
The importance of meteorological scales to forecast air pollution scenarios on a complex-terrain coastal site of the Iberian Peninsula
Authors: Palau J. L. , Pérez-Landa G. , Diéguez J. J. , Monter C. , Millán M. M.
Published: April 2010

Abstract. Some of the meteorological approaches commonly considered in urban air pollution models do not take into account the importance of the smaller scales in the meteorology of complex-terrain coastal sites. The aim of this work is to estimate the impact of using the proper meteorological scales when simulating the behaviour of the pollutant concentrations emitted in the lower layers over coastal complex terrain areas. The availability of experimental measurements of a power plant plume near the Castellón conurbation (on the Spanish Mediterranean coast) has allowed us to use this plume as a tracer of opportunity of the lower atmosphere to check the results of a simulation exercise using the RAMS mesoscale model coupled to the HYPACT particle model. The results obtained show that in a complex-terrain coastal site, because of the strong effect of the meteorological interactions between the different scales on the integral advection and the turbulent dispersion of pollutants, using an inadequate scale to solve the meteorology can result in a very big gap in the simulation of lower-layer pollutant behaviour at urban scales.
Observations of total alkyl nitrates within the Sacramento Urban Plume
Authors: Cleary P. A. , Murphy J. G. , Wooldridge P. J. , Day D. A. , Millet D. B. , McKay M. , Goldstein A. H. , Cohen R. C.
Published: April 2010

Abstract. During the summer of 2001, NO2, total peroxy nitrates (ΣPNs), total alkyl nitrates (ΣANs), HNO3, volatile organic compounds (VOC), CO2, O3, and meteorological variables were measured at Granite Bay, CA. The diurnal variation in ΣPNs, ΣANs and HNO3 were all strongly correlated with sunlight, indicating both that they are photochemically produced and that they have a lifetime of a few hours at this site. The mixing ratios of ΣANs ranged as high as 2 ppbv. Mixing ratios at night averaged 0.4 ppbv. Odd-oxygen (Ox=O3+NO2) and ΣANs were strongly correlated reflecting both the common chemical source terms and the similar lifetimes of both species. Several approaches to interpreting the simultaneous variations of Ox and ΣANs are described, and used to derive a best estimate of the ΣAN yield from the VOC mixture at this site of 4.2% and an estimate of the range that is consistent with the observations of 3.9–5.8%. A yield of 4.2% implies termination of the HOx catalytic cycle by ΣAN formation once every 24 cycles. Analysis of the HNO3 observations in combination with the ΣAN and O3 measurements suggests that NOx terminations limit the HOx chain length to between 4.7 and 6.3.
Aerosol effect on the distribution of solar radiation over the clear-sky global oceans derived from four years of MODIS retrievals
Authors: Remer L. A. , Kaufman Y. J.
Published: April 2010

Abstract. A four year record of MODIS spaceborne data provides a new measurement tool to assess the aerosol direct radiative effect at the top of the atmosphere. MODIS derives the aerosol optical thickness and microphysical properties from the scattered sunlight at 0.55–2.1 μm. The monthly MODIS data used here are accumulated measurements across a wide range of view and scattering angles and represent the aerosol's spectrally resolved angular properties. We use these data consistently to compute with estimated accuracy of ±0.3 Wm−2 the reflected sunlight by the aerosol over global oceans in cloud free conditions. The MODIS high spatial resolution (0.5 km) allows observation of the aerosol impact between clouds that can be missed by other sensors with larger footprints. We found that over the clear-sky global ocean the aerosol reflected 5.0±0.3Wm−2 with an average radiative efficiency of 46±2 Wm−2 per unit optical thickness. The seasonal and regional distribution of the aerosol radiative effects are discussed. The analysis adds a new measurement perspective to a climate change problem dominated so far by models.
Chemistry-climate model SOCOL: a validation of the present-day climatology
Authors: Egorova T. , Rozanov E. , Zubov V. , Manzini E. , Schmutz W. , Peter T.
Published: April 2010

Abstract. In this paper we document ''SOCOL'', a new chemistry-climate model, which has been ported for regular PCs and shows good wall-clock performance. An extensive validation of the model results against present-day climate obtained from observations and assimilation data sets shows that the model describes the climatological state of the atmosphere for the late 1990s with reasonable accuracy. The model has a significant temperature bias only in the upper stratosphere and near the tropopause in the tropics and high latitudes. The latter is the result of the rather low vertical resolution of the model near the tropopause. The former can be attributed to a crude representation of the radiation heating in the middle atmosphere. A comparison of the simulated and observed link between the tropical stratospheric structure and the strength of the polar vortex shows that in general, both observations and simulations reveal a higher temperature and ozone mixing ratio in the lower tropical stratosphere for the case with stronger Polar night jet (PNJ) as predicted by theoretical studies.
Transport and mixing zone of desert dust and sulphate over Tropical Africa and the Atlantic Ocean region
Authors: Desboeufs K. V. , Cautenet G.
Published: April 2010

Abstract. The potentiality of dust particles to mix with sulphate over Tropical Africa and the Atlantic Ocean is investigated by combining a meso-scale meteorological model with a dust production model and an SO2 emission database. This mixing process study is based on a qualitative approach where the reactivity of dust is estimated from its calcite content, which is the main mineral known to be reactive with sulphur species. We are presenting a 1-month simulation (January 1993). Our results show that the regions Northern Egypt and Libya (NEL), Western Sahara (WS) and Sahel (S) are the major sources of dust plumes. The simulated dust loading is in agreement with the measured data close to the African coasts. The Mediterranean and Maghreb regions are highly influenced by European sources of sulphate, for which the simulated concentrations are consistent with the observed trends. This simplified study identifies two zones that favour the mixing process between dust and sulphate: 1. the Eastern Mediterranean basin due to the concomitance of high concentrations of dust and sulphate and 2. the North-Eastern Atlantic Ocean due to the high amount of calcite in the ejected dust which is very reactive. Thus, we assume that the coating process takes place mainly in these regions and the sulphate-coated dust found on the other side of the Atlantic Ocean (Caribbean and American coasts) is principally due to this phenomenon.