bluuebunny/crossref_metadata_2025 huggingface dataset:
Do supersonic aircraft avoid contrails?
Authors: Stenke A. , Grewe V. , Pechtl S.
Published: April 2010

Abstract. The impact of a potential future fleet of supersonic aircraft on contrail coverage and contrail radiative forcing is investigated by means of simulations with the general circulation model ECHAM4.L39(DLR) including a contrail parameterization. The model simulations consider air traffic inventories of a subsonic fleet and of a combined fleet of sub- and supersonic aircraft for the years 2025 and 2050, respectively. In case of the combined fleet, part of the subsonic fleet is replaced by supersonic aircraft. Supersonic aircraft fly at higher cruise levels (18 to 20 km) than subsonic aircraft (10 to 12 km). The different ambient meteorological conditions in terms of temperature and humidity affect the formation of contrails. At subsonic cruise levels, the combined air traffic scenario reveals a reduction in contrail cover in northern extratropics, especially over the North Atlantic and Pacific. At supersonic flight levels, contrail formation is mainly restricted to tropical regions. The northern extratropical stratosphere is only in winter cold enough for the formation of contrails. Total contrail coverage is only marginally affected by the shift in flight altitude. The model simulations indicate a global annual mean contrail cover of 0.372% for the subsonic and 0.366% for the combined fleet in 2050, respectively. The simulated contrail radiative forcing is most closely correlated to the total contrail cover, although contrails in the tropical lower stratosphere are found to be optically thinner than contrails in the extratropical upper troposphere. The global annual mean contrail radiative forcing in 2050 (2025) amounts to 24.7 mW m−2 (9.4 mW m−2) for the subsonic fleet and 24.2 mW m−2 (9.3 mW m−2) for the combined fleet. A reduced supersonic cruise speed (Mach 1.6 instead of Mach 2.0) leads to a downward shift in contrail cover, but does not affect global mean total contrail cover and contrail radiative forcing. Hence the partial substitution of subsonic air traffic leads to a shift of contrail occurrence from mid to low latitudes, but the resulting change in contrail-induced climate impact is almost negligible.
Observations of iodine monoxide (IO) columns from satellite
Authors: Schönhardt A. , Richter A. , Wittrock F. , Kirk H. , Oetjen H. , Roscoe H. K. , Burrows J. P.
Published: April 2010

Abstract. Iodine species in the troposphere are linked to ozone depletion and new particle formation. In this study, a full year of iodine monoxide (IO) columns retrieved from measurements of the SCIAMACHY satellite instrument is presented, alongside a discussion of their uncertainties and the detection limit. The largest amounts of IO are found near springtime Antarctica, where ground-based measurements have positively detected iodine compounds before. A seasonal variation of iodine monoxide in Antarctica is revealed with high values in springtime, slightly less IO in the summer period and again larger amounts in autumn. In winter, no elevated IO levels are found in the areas accessible to satellite measurements. This seasonal cycle is in good agreement with recent ground-based measurements in Antarctica. In the Arctic region, no elevated IO levels were found in the whole time period analysed, arguing for different conditions existing in the two Polar Regions. To investigate possible release mechanisms such as inorganic release or biogenic precursors, comparisons of IO results with tropospheric BrO maps, measurements of chlorophyll concentration, and ice coverage are discussed. Some parallels and interesting differences between IO and BrO temporal and spatial distributions are pointed out. Although no full interpretation can be given at this point, the large spatial coverage of satellite measurements and the availability of a long-term dataset give some new indications and understandings of the abundances and distributions of iodine compounds in the troposphere.
Basin-scale wind transport during the MILAGRO field campaign and comparison to climatology using cluster analysis
Authors: de Foy B. , Fast J. D. , Paech S. J. , Phillips D. , Walters J. T. , Coulter R. L. , Martin T. J. , Pekour M. S. , Shaw W. J. , Kastendeuch P. P. , Marley N. A. , Retama A. , Molina L. T.
Published: April 2010

Abstract. The MILAGRO field campaign was a multi-agency international collaborative project to evaluate the regional impacts of the Mexico City air pollution plume as a means of understanding urban impacts on the global climate. Mexico City lies on an elevated plateau with mountains on three sides and has complex mountain and surface-driven wind flows. This paper asks what the wind transport was in the basin during the field campaign and how representative it was of the climatology. Surface meteorology and air quality data, radiosoundings and radar wind profiler data were collected at sites in the basin and its vicinity. Cluster analysis is used to identify the dominant wind patterns both during the campaign and within the past 10 years of operational data from the warm dry season. Our analysis shows that March 2006 was representative of typical flow patterns experienced in the basin. Six episode types were identified for the basin scale circulation providing a way of interpreting atmospheric chemistry and particulate data collected during the campaign. Decoupling between surface winds and those aloft had a strong influence in leading to convection and poor air quality episodes. Hourly characterisation of wind circulation during the MILAGRO, MCMA-2003 and IMADA field campaigns will enable the comparisons of similar air pollution episodes and the evaluation of the impact of wind transport on measurements of the atmospheric chemistry taking place in the basin.
Alignment of atmospheric mineral dust due to electric field
Authors: Ulanowski Z. , Bailey J. , Lucas P. W. , Hough J. H. , Hirst E.
Published: April 2010

Abstract. Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction consistent with the presence of vertically aligned particles in the atmosphere. Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling also indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here.
Attenuation of global ultraviolet and visible irradiance over Greece during the total solar eclipse of 29 March 2006
Authors: Kazantzidis A. , Bais A. F. , Emde C. , Kazadzis S. , Zerefos C. S.
Published: April 2010

Abstract. The variability of ultraviolet and photosynthetically active radiation during the total solar eclipse of 29 March 2006 was examined in this study. The measurements from NILU-UV multichannel actinometers at 7 stations of the Greek UV Network were used, where the maximum eclipse percentage ranged from 73.1% to 94.8%. In addition, an extra instrument was established at a remote Greek island, Kastelorizo, which was within the Moon's umbral shadow. The measured changes in UV and visible irradiance were compared with 1-D model calculations (accounting for the limb darkening effect) and differences up 30% were observed for the lower UV wavelengths at high eclipse percentages. The spectral ratios between wavelengths was generally reproduced by the 1-D model, expect for 305 nm, where the irradiance at eclipse percentages of more than 85% decreased with slower rates than for longer wavelengths. As a result, the total ozone, derived from the 305/320 nm ratio, apparently decreased significantly for high eclipse percentages. Comparison results with 3-D model calculations approaching and during totality revealed an agreement with measurements in the UV-A region.
Validation of ACE-FTS satellite data in the upper troposphere/lower stratosphere (UTLS) using non-coincident measurements
Authors: Hegglin M. I. , Bernath P. F. , Boone C. D. , Daffer W. H. , Hoor P. , Manney G. L. , Schiller C. , Strong K. , Walker K. A.
Published: April 2010

Abstract. CO, O3, and H2O data in the upper troposphere/lower stratosphere (UTLS) measured by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on Canada's SCISAT-1 satellite are validated using aircraft measurements. In the UTLS, validation of chemical trace gas measurements is a challenging task due to small-scale variability in the tracer fields, strong gradients of the tracers across the tropopause, and scarcity of measurements suitable for validation purposes. Two alternative methods for the validation of the satellite data are introduced, which avoid the usual need for coincident measurements: tracer-tracer correlations, and vertical profiles relative to the tropopause height. Both largely reduce geophysical variability and thereby provide an "instantaneous climatology", allowing measurement comparison with non-coincident data which yields information about the precision, and a statistically meaningful error-assessment of the ACE-FTS satellite data. We found that the ACE-FTS CO and lower stratospheric O3 agree with the aircraft measurements within ±10% and ±5%, respectively. The ACE-FTS O3 in the UT exhibits a high bias of up to 40%. H2O indicates a low bias with relative differences of around 20% in the LS and 40% in the UT, respectively. When taking into account the smearing effect of the vertically limited spacing between measurements of the ACE-FTS instrument, the errors decrease by 5–15% around the tropopause. The ACE-FTS instrument hence offers unprecedented precision and vertical resolution in the UTLS, that will allow a new global perspective on UTLS tracer distributions.
Global peroxyacetyl nitrate (PAN) retrieval in the upper troposphere from limb emission spectra of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)
Authors: Glatthor N. , von Clarmann T. , Fischer H. , Funke B. , Grabowski U. , Höpfner M. , Kellmann S. , Kiefer M. , Linden A. , Milz M. , Steck T. , Stiller G. P.
Published: April 2010

Abstract. We use limb emission spectra of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard the ENVIronmental SATellite (ENVISAT) to derive the first global distribution of peroxyacetyl nitrate (PAN) in the upper troposphere. PAN is generated in tropospheric air masses polluted by fuel combustion or biomass burning and acts as a reservoir and carrier of NOx in the cold free troposphere. Since PAN exhibits continuum-like broadband structures in the mid-infrared region, we have applied a contiguous analysis window covering the wavenumber region 775–800 cm−1 for retrieval. The interfering species CCl4, HCFC-22, H2O, ClONO2, CH3CCl3 and C2H2 were fitted along with PAN, whereas pre-fitted profiles were used to model the contribution of other contaminants like ozone. Sensitivity tests consisting in retrieval without consideration of PAN have demonstrated the existence of PAN signatures in MIPAS spectra obtained from polluted air masses. The analysed dataset consists of 10 days between 4 October and 1 December 2003. This period covers the end of the biomass burning season in South America and South and East Africa, in which generally large amounts of pollutants are produced and distributed over wide areas in the southern hemispheric free troposphere. Elevated PAN amounts of 200–700 pptv were measured in a large plume extending from Brasil over the Southern Atlantic, Central and South Africa, the South Indian Ocean as far as Australia at altitudes between 8 and 16 km. Enhanced PAN values were also found in a much more restricted area between northern subtropical Africa and India. The most significant northern midlatitude PAN signal in MIPAS data is an area extending at 8 km altitude from China into the Chinese Sea. The average mid and high latitude PAN amounts found at 8 km were around 125 pptv in the northern, but only between 75 and 50 pptv in the southern hemisphere. The PAN distribution found in the southern hemispheric tropics and subtropics is highly correlated with the jointly fitted acetylene (C2H2), which is another pollutant produced by biomass burning, and agrees reasonably well with the CO plume detected during end of September 2003 at the 275 hPa level (~10 km) by the Measurement of Pollution in the Troposphere (MOPITT) instrument on the Terra satellite. Similar southern hemispheric PAN amounts were also observed by previous airborne measurements performed in September/October 1992 and 1996 above the South Atlantic and the South Pacific, respectively.
An improvement on the dust emission scheme in the global aerosol-climate model ECHAM5-HAM
Authors: Cheng T. , Peng Y. , Feichter J. , Tegen I.
Published: April 2010

Abstract. Formulation of the dust emission scheme in the global aerosol-climate modeling system ECHAM5-HAM has been improved. Modifications on the surface aerodynamic roughness length, soil moisture and East-Asian soil properties are included in the parameterization, which result in a large impact on the threshold wind friction velocity for aeolian erosion and thus influence the simulated dust emission amount. The annual global mean of dust emission in the year 2000 is reduced by 76.5% and 2.2%, respectively, due to changes in the aerodynamic roughness length and the soil moisture. An inclusion of detailed East-Asian soil properties leads to an increase of 16.6% in the annual global mean of dust emission, which exhibits mainly in the arid and semi-arid areas of northern China and southern Mongolia. Reasonable values of annual global mean of dust emission, dust burden and total aerosol optical thickness can be obtained in the improved model. In addition, measurements of the surface dust concentrations are collected in dust source regions of East Asia, and verify a more realistic spatial distribution of dust emission in the improved model.
Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter
Authors: Krüger K. , Tegtmeier S. , Rex M.
Published: April 2010

Abstract. A long-term climatology of air mass transport through the tropical tropopause layer (TTL) is presented, covering the period from 1962–2005. The transport through the TTL is calculated with a Lagrangian approach using radiative heating rates as vertical velocities in an isentropic trajectory model. We demonstrate the improved performance of such an approach compared to previous studies using vertical winds from meteorological analyses. Within the TTL, the averaged diabatic ascent is 0.5 K/day during Northern Hemisphere (NH) winters 1992–2001, close to observations from the tape recorder. Climatological maps show a cooling and strengthening of this part of the residual circulation during the late 1990s and early 2000s compared to the long-term mean. Lagrangian cold point (LCP) fields show systematic differences for varying time periods and natural forcing components. The interannual variability of LCP temperature and density fields are found to be influenced by volcanic eruptions, ENSO, QBO and the solar cycle. The coldest and driest TTL is reached during QBOE and La Niña over the western Pacific, whereas during volcanic eruptions, El Niño and QBOW it is warmer and less dry.
Comparison of measurements of peroxyacyl nitrates and primary carbonaceous aerosol concentrations in Mexico City determined in 1997 and 2003
Authors: Marley N. A. , Gaffney J. S. , Ramos-Villegas R. , Cárdenas González B.
Published: April 2010

Abstract. Peroxyacetyl nitrate (PAN) concentrations in ambient air can be a good indicator of air quality and the effectiveness of control strategies for reducing ozone levels in urban areas. As PAN is formed by the oxidation of reactive hydrocarbons in the presence of nitrogen dioxide (NO2), it is a direct measure of the peroxyacyl radical levels produced from reactive organic emissions in the urban air shed. Carbon soot, known as black carbon or elemental carbon, is a primary atmospheric aerosol species and is a good indicator of the levels of combustion emissions, particularly from diesel engines, in major cities. Mexico City is the second largest megacity in the world and has long suffered from poor air quality. Reported here are atmospheric measurements of PAN and black carbon obtained in Mexico City during the Mexico Megacity 2003 field study. These results are compared with measurements obtained earlier during the Investigación sobre Materia Particulada y Deterioro Atmosférico – Aerosol and Visibility Research (IMADA-AVER) campaign in 1997 to obtain an estimate of the changes in emissions in Mexico City and the effectiveness of control strategies adopted during that time. Concentrations of PAN in 1997 reached a maximum of 34 ppb with an average daily maximum of 15 ppb. The PAN levels recorded in 2003 were quite different, with an average daily maximum of 3 ppb. This dramatic reduction in PAN levels observed in 2003 indicate that reactive hydrocarbon emissions have been reduced in the city due to controls on olefins in liquefied petroleum gas (LPG) and also due to the significant number of newer vehicles with catalytic converters that have replaced older higher emission vehicles. In contrast, black/elemental carbon levels were similar in 1997 and 2003 indicating little improvement likely due to the lack of controls on diesel vehicles in the city. Thus, while air quality and ozone production has improved, Mexico City and other megacities continue to be a major source of black carbon aerosols, which can be an important species in determining regional radiative balance and climate.
Black carbon concentration trends in Helsinki during 1996–2005
Authors: Järvi L. , Junninen H. , Karppinen A. , Hillamo R. , Virkkula A. , Mäkelä T. , Pakkanen T. , Kulmala M.
Published: April 2010

Abstract. The black carbon (BC) concentration trends were studied during ten years in Helsinki, Finland. Measurements were made in three campaigns between 1996 and 2005 at an urban area locating two kilometres from the centre of Helsinki. The first campaign was from November 1996 to June 1997, the second from September 2000 to May 2001 and the third from March 2004 to October 2005. In this study, only data from winter and spring months was analysed. The effect of traffic and meteorological variables on the measured BC concentrations was studied by means of a multiple regression analysis, where the meteorological data was obtained from a meteorological pre-processing model (MPP-FMI). During the ten years, the campaign median BC concentrations were found to decrease slightly from 1.11 to 1.00 μg m−3. The lowest campaign median concentration (0.93 μg m−3) was measured during the second campaign in 2000–2001, when also the lowest traffic rates were measured. The strongest decrease between campaigns 1 and 3 was observed during weekday daytimes, when the traffic rates are highest. The variables affecting the measured BC concentrations most were traffic, wind speed and mixing height. On weekdays, traffic had clearly the most important influence and on weekends the effect of wind speed diluted the effect of traffic. The affecting variables and their influence on the BC concentration were similar in winter and spring. The separate examination of the three campaigns showed that the effect of traffic on the BC concentrations had decreased during the studied years. This reduction was caused by cleaner emissions from vehicles, since between years 1996 and 2005 the traffic rates had increased. A rough estimate gave that vehicle number-scaled BC mass concentrations have decreased from 0.0028 to 0.0020 μg m−3 between campaigns 1 and 3.
Trends and variability of midlatitude stratospheric water vapour deduced from the re-evaluated Boulder balloon series and HALOE
Authors: Scherer M. , Vömel H. , Fueglistaler S. , Oltmans S. J. , Staehelin J.
Published: April 2010

Abstract. This paper presents an updated trend analysis of water vapour in the lower midlatitude stratosphere from the Boulder balloon-borne NOAA frostpoint hygrometer measurements and from the Halogen Occulation Experiment (HALOE). Two corrections for instrumental bias are applied to homogenise the frostpoint data series, and a quality assessment of all soundings after 1991 is presented. Linear trend estimates based on the corrected data for the period 1980–2000 are up to 40% lower than previously reported. Vertically resolved trends and variability are calculated with a multi regression analysis including the quasi-biennal oscillation and equivalent latitude as explanatory variables. In the range of 380 to 640 K potential temperature (≈14 to 25 km), the frostpoint data from 1981 to 2006 show positive linear trends between 0.3± 0.3 and 0.7±0.1%/yr. The same dataset shows trends between −0.2±0.3 and 1.0±0.3%/yr for the period 1992 to 2005. HALOE data over the same time period suggest negative trends ranging from −1.1±0.2 to −0.1±0.1%/yr. In the lower stratosphere, a rapid drop of water vapour is observed in 2000/2001 with little change since. At higher altitudes, the transition is more gradual, with slowly decreasing concentrations between 2001 and 2007. This pattern is consistent with a change induced by a drop of water concentrations at entry into the stratosphere. Previously noted differences in trends and variability between frostpoint and HALOE remain for the homogenised data. Due to uncertainties in reanalysis temperatures and stratospheric transport combined with uncertainties in observations, no quantitative inference about changes of water entering the stratosphere in the tropics could be made with the mid latitude measurements analysed here.
Introduction of prognostic rain in ECHAM5: design and Single Column Model simulations
Authors: Posselt R. , Lohmann U.
Published: April 2010

Abstract. Prognostic equations for the rain mass mixing ratio and the rain drop number concentration are introduced into the large-scale cloud microphysics parameterization of the ECHAM5 general circulation model (ECHAM5-RAIN). For this a rain flux from one level to the next with the appropriate fall speed is introduced. This maintains rain water in the atmosphere to be available for the next time step. Rain formation in ECHAM5-RAIN is, therefore, less dependent on the autoconversion rate than the standard ECHAM5 but shifts the emphasis towards the accretion rates in accordance with observations. ECHAM5-RAIN is tested and evaluated with two cases: the continental mid-latitude ARM Cloud IOP (shallow frontal cloud case – March 2000) and EPIC (a marine stratocumulus study – October 2001). The prognostic equations for rain hardly affect the amount and timing of precipitation at the surface in different Single Column Model (SCM) simulations for heavy precipitating clouds because heavy rain depends mainly on the large-scale forcing. In case of thin, drizzling clouds (i.e., stratocumulus), an increase in surface precipitation is caused by more sub-time steps used in the prognostic rain scheme until convergence is reached. Cloud microphysical quantities, such as liquid and rain water, are more sensitive to the number of sub-time steps for light precipitation. This results from the decreasing autoconversion rate and increasing accretion rate.
Volatile Organic Compound (VOC) measurements in the Pearl River Delta (PRD) region, China
Authors: Liu Y. , Shao M. , Lu S. H. , Chang C.-C. , Wang J.-L. , Chen G.
Published: April 2010

Abstract. We measured levels of ambient volatile organic compounds (VOCs) at seven sites in the Pearl River Delta (PRD) region of China during the Air Quality Monitoring Campaign spanning 4 October to 3 November 2004. Two of the sites, Guangzhou (GZ) and Xinken (XK), were intensive sites at which we collected multiple daily canister samples. The observations reported here provide a look at the VOC distribution, speciation, and photochemical implications in the PRD region. Alkanes constituted the largest percentage (>40%) in mixing ratios of the quantified VOCs at six sites; the exception was one major industrial site that was dominated by aromatics (about 52%). Highly elevated VOC levels occurred at GZ during two pollution episodes; however, the chemical composition of the VOCs did not exhibit noticeable changes during these episodes, except that the fraction of aromatics was about 10% higher. We calculated the OH loss rate to estimate the chemical reactivity of all VOCs. Of the anthropogenic VOCs, alkenes played a predominant role in VOC reactivity at GZ, whereas the contributions of reactive aromatics were more important at XK. Our preliminary analysis of the VOC correlations suggests that the ambient VOCs at GZ came directly from local sources (i.e., automobiles); those at XK were influenced by both local emissions and transportation of air mass from upwind areas.
The wintertime two-day wave in the Polar Stratosphere, Mesosphere and lower Thermosphere
Authors: Sandford D. J. , Schwartz M. J. , Mitchell N. J.
Published: April 2010

Abstract. Recent observations of the polar mesosphere have revealed that waves with periods near two days reach significant amplitudes in both summer and winter. This is in striking contrast to mid-latitude observations where two-day waves maximise in summer only. Here, we use data from a meteor radar at Esrange (68° N, 21° E) in the Arctic and data from the MLS instrument aboard the EOS Aura satellite to investigate the wintertime polar two-day wave in the stratosphere, mesosphere and lower thermosphere. The radar data reveal that mesospheric two-day wave activity measured by horizontal-wind variance has a semi-annual cycle with maxima in winter and summer and equinoctial minima. The MLS data reveal that the summertime wave in the mesosphere is dominated by a westward-travelling zonal wavenumber three wave with significant westward wavenumber four present. It reaches largest amplitudes at mid-latitudes in the southern hemisphere. In the winter polar mesosphere, however, the wave appears to be an eastward-travelling zonal wavenumber two, which is not seen during the summer. At the latitude of Esrange, the eastward-two wave reaches maximum amplitudes near the stratopause and appears related to similar waves previously observed in the polar stratosphere. We conclude that the wintertime polar two-day wave is the mesospheric manifestation of an eastward-propagating, zonal-wavenumber-two wave originating in the stratosphere, maximising at the stratopause and likely to be generated by instabilities in the polar night jet.
Experimental studies on particle emissions from cruising ship, their characteristic properties, transformation and atmospheric lifetime in the marine boundary layer
Authors: Petzold A. , Hasselbach J. , Lauer P. , Baumann R. , Franke K. , Gurk C. , Schlager H. , Weingartner E.
Published: April 2010

Abstract. Particle emissions from ship engines and their atmospheric transformation in the marine boundary layer (MBL) were investigated in engine test bed studies and in airborne measurements of expanding ship plumes. During the test rig studies, detailed aerosol microphysical and chemical properties were measured in the exhaust gas of a serial MAN B{&}W seven-cylinder four-stroke marine diesel engine under various load conditions. The emission studies were complemented by airborne aerosol transformation studies in the plume of a large container ship in the English Channel using the DLR aircraft Falcon 20 E-5. Observations from emission studies and plume studies combined with a Gaussian plume dispersion model yield a consistent picture of particle transformation processes from emission to atmospheric processing during plume expansion. Particulate matter emission indices obtained from plume measurements are 8.8±1.0×1015(kg fuel)−1 by number for non-volatile particles and 174±43 mg (kg fuel)−1 by mass for Black Carbon (BC). Values determined for test rig conditions between 85 and 110% engine load are of similar magnitude. For the total particle number including volatile compounds no emission index can be derived since the volatile aerosol fraction is subject to rapid transformation processes in the plume. Ship exhaust particles occur in the size range Dp<0.3 μm, showing a bi-modal structure. The combustion particle mode is centred at modal diameters of 0.05 μm for raw emissions to 0.10 μm at a plume age of 1 h. The smaller-sized volatile particle mode is centred at Dp≤0.02 μm. From the decay of ship exhaust particle number concentrations in an expanding plume, a maximum plume life time of approx. 24 h is estimated for a well-mixed marine boundary layer.
The atmospheric chemistry of sulphuryl fluoride, SO2F2
Authors: Dillon T. J. , Horowitz A. , Crowley J. N.
Published: April 2010

Abstract. The atmospheric chemistry of sulphuryl fluoride, SO2F2, was investigated in a series of laboratory studies. A competitive rate method, using pulsed laser photolysis (PLP) to generate O(1D) coupled to detection of OH by laser induced fluorescence (LIF), was used to determine the overall rate coefficient for the reaction O(1D)+SO2F2 → products (R1) of k1 (220–300 K)=(1.3±0.2)×10−10 cm³ molecule−1 s−1. Monitoring the O(³P) product (R1a) enabled the contribution (α) of the physical quenching process (in which SO2F2 is not consumed) to be determined as α1 (225–296 K)=(0.55±0.04). Separate, relative rate measurements at 298 K provided a rate coefficient for reactive loss of O(1D), k1b, of (5.8±0.8)×10−11 cm³ molecule−1 s−1 in good agreement with the value calculated from (1−α)×k1=(5.9±1.0)×10−11 cm³ molecule−1 s−1. Upper limits for the rate coefficients for reaction of SO2F2 with OH (R2, using PLP-LIF), and with O3 (R3, static reactor) were determined as k2 (294 K)<1×10−15 cm³ molecule−1 s−1 and k3 (294 K)<1×10−23 cm³ molecule−1 s−1. In experiments using the wetted-wall flow tube technique, no loss of SO2F2 onto aqueous surfaces was observed, allowing an upper limit for the uptake coefficient of γ(pH 2–12)<1×10−7 to be determined. These results indicate that SO2F2 has no significant loss processes in the troposphere, and a very long stratospheric lifetime. Integrated band intensities for SO2F2 infrared absorption features between 6 and 19 μm were obtained, and indicate a significant global warming potential for this molecule. In the course of this work, ambient temperature rate coefficients for the reactions O(1D) with several important atmospheric species were determined. The results (in units of 10−10 cm³ molecule−1 s−1), k(O1D+N2)=(0.33±0.06); k(O1D+N2O)=(1.47±0.2) and k(O1D+H2O)=(1.94±0.5) were in good agreement with other recent determinations.
Long-term trends of the concentration of the minor constituents in the mesosphere – a model study
Authors: Grygalashvyly M. , Sonnemann G. R. , Hartogh P.
Published: April 2010

Abstract. We investigate the influence of the rising concentrations of methane, dinitrogen oxide and carbon dioxide since the pre-industrial era upon the chemistry of the mesosphere. We use for calculations our global 3D-model COMMA-IAP designed for the exploration of the MLT-region and particularly the extended mesopause region. In order to get approximated data of the solar Lyman-α flux back to the pre-industrial time, we derived a quadratic fit using the sunspot number available since 1749 as the only solar proxy for the Lyman-α flux before 1947. The Lyman-α flux values are employed to determine the water vapor dissociation rate. The water vapor trend analysis utilizes estimated methane trends since the pre-industrial era. An unsolved problem for the model calculations consists of the water vapor mixing ratio at the hygropause during the time range of trend calculation. We assume that the hygropause was dryer at the pre-industrial time than currently. As a consequence of the methane oxidation, the middle atmosphere became more humid according to the rising methane concentration, but depending on height and with a small time delay of few years. The solar influence on the water vapor mixing ratio is insignificant below about 80 km within summery high latitudes, but it becomes increasingly more important above this altitude. The growing water vapor concentration increases the hydrogen radical concentration and reduces the mesospheric ozone. A second region of stronger ozone decrease is located in the vicinity of the stratopause. Increasing CO2 concentration enhances slightly the concentration of CO in the mesosphere, but its influence upon the chemistry is small and its main effect is connected with a cooling of the upper atmosphere. We discuss the trends particularly in view of the impact on the NLC region.
Changes of fatty acid aerosol hygroscopicity induced by ozonolysis under humid conditions
Authors: Vesna O. , Sjogren S. , Weingartner E. , Samburova V. , Kalberer M. , Gäggeler H. W. , Ammann M.
Published: April 2010

Abstract. Unsaturated fatty acids are important constituents of the organic fraction of atmospheric aerosols originating from biogenic or combustion sources. Oxidative processing of these may change their interaction with water and thus affect their effect on climate. The ozonolysis of oleic and arachidonic acid aerosol particles was studied under humid conditions in a flow reactor at ozone exposures close to atmospheric levels, at concentrations between 0.5 and 2 ppm. While oleic acid is a widely used proxy for such studies, arachidonic acid represents polyunsaturated fatty acids, which may decompose into hygroscopic products. The hygroscopic (diameter) growth factor at 93% relative humidity (RH) of the oxidized arachidonic particles increased up to 1.09 with increasing RH during the ozonolysis. In contrast, the growth factor of oleic acid was very low (1.03 at 93% RH) and was almost invariant to the ozonolysis conditions, so that oleic acid is not a good model to observe oxidation induced changes of hygroscopicity under atmospheric conditions. We show for arachidonic particles that the hygroscopic changes induced by humidity during ozonolysis are accompanied by about a doubling of the ratio of carboxylic acid to aliphatic functional groups. We suggest that, under humid conditions, the reaction of water with the Criegee intermediates might open a pathway for the formation of smaller acids that lead to more significant changes in hygroscopicity. Thus the effect of water to provide a competing pathway during ozonolysis observed in this study should be motivation to include water, which is ubiquitously present in and around atmospheric particles, in future studies related to aerosol particle aging.
Air pollution during the 2003 European heat wave as seen by MOZAIC airliners
Authors: Tressol M. , Ordonez C. , Zbinden R. , Thouret V. , Mari C. , Nedelec P. , Cammas J.-P. , Smit H. , Patz H.-W. , Volz-Thomas A.
Published: April 2010

Abstract. This study presents an analysis of both MOZAIC profiles above Frankfurt and Lagrangian dispersion model simulations for the 2003 European heat wave. The comparison of MOZAIC measurements in summer 2003 with the 11-year MOZAIC climatology reflects strong temperature anomalies (exceeding 4°C) throughout the lower troposphere. Higher positive anomalies of temperature and negative anomalies of both wind speed and relative humidity are found for the period defined here as the heat wave (2–14 August 2003), compared to the periods before (16–31 July 2003) and after (16–31 August 2003) the heat wave. In addition, Lagrangian model simulations in backward mode indicate the suppressed long-range transport in the mid- to lower troposphere and the enhanced southern origin of air masses for all tropospheric levels during the heat wave. Ozone and carbon monoxide also present strong anomalies (both ~ +40 ppbv) during the heat wave, with a maximum vertical extension reaching 6 km altitude around 11 August 2003. Pollution in the planetary boundary layer (PBL) is enhanced during the day, with ozone mixing ratios two times higher than climatological values. This is due to a combination of factors, such as high temperature and radiation, stagnation of air masses and weak dry deposition, which favour the accumulation of ozone precursors and the build-up of ozone. A negligible role of a stratospheric-origin ozone tracer has been found for the lower troposphere in this study. From 29 July to 15 August 2003 forest fires burned around 0.3×106 ha) in Portugal and added to atmospheric pollution in Europe. Layers with enhanced CO and NOy mixing ratios, probably advected from Portugal, were crossed by the MOZAIC aircraft in the free troposphere over Frankfurt. A series of forward and backward Lagrangian model simulations have been performed to investigate the origin of these anomalies. During the whole heat wave, European anthropogenic emissions present the strongest contribution to the measured CO levels in the lower troposphere (near 30%). This source is followed by Portuguese forest fires which affect the lower troposphere after 6 August 2003 and even the PBL around 10 August 2003. The averaged biomass burning contribution reaches 35% during the affected period. Anthropogenic CO of North American origin only marginally influences CO levels over Europe during that period.
Intercomparison between aerosol optical properties by a PREDE skyradiometer and CIMEL sunphotometer over Beijing, China
Authors: Che H. , Shi G. , Uchiyama A. , Yamazaki A. , Chen H. , Goloub P. , Zhang X.
Published: April 2010

Abstract. This study compares the aerosol optical and physical properties simultaneously measured by a SKYNET PREDE skyradiometer and AERONET/PHOTONS CIMEL sunphotometer at a location in Beijing, China. Aerosol optical properties (AOP) including the Aerosol Optical Depth (AOD), Angstrom exponent (α), volume size distribution, single scattering albedo (ω) and the complex refractive index were compared. The difference between the two types of instruments was less than 1.3% for the AOD and less than 4% for the single scattering albedo below the wavelength of 670 nm. There is a difference between the volume size distribution patterns derived from two instruments, which is probablely due to difference of measurement protocols and inversion algorithms for the respective instruments. AOP under three distinct weather conditions (background, haze, and dust days) over Beijing were compared by using the retrieved skyradiometer and sunphotometer data combined with MODIS satellite results, pyranometer measurements, PM10 measurements, and backtrajectory analysis. The results show that the significant difference of AOP under background, haze, and dust days over Beijing is probablely due to different aerosol components under distinct weather conditions.
Parameterization of N2O5 reaction probabilities on the surface of particles containing ammonium, sulfate, and nitrate
Authors: Davis J. M. , Bhave P. V. , Foley K. M.
Published: April 2010

Abstract. A comprehensive parameterization was developed for the heterogeneous reaction probability (γ) of N2O5 as a function of temperature, relative humidity, particle composition, and phase state, for use in advanced air quality models. The reaction probabilities on aqueous NH4HSO4, (NH4)2SO4, and NH4NO3 were modeled statistically using data and uncertainty values compiled from seven different laboratory studies. A separate regression model was fit to laboratory data for dry NH4HSO4 and (NH4)2SO4 particles, yielding lower γ values than the corresponding aqueous parameterizations. The regression equations reproduced 79% of the laboratory data within a factor of two and 53% within a factor of 1.25. A fixed value was selected for γ on ice-containing particles based on a review of the literature. The combined parameterization was applied under atmospheric conditions representative of the eastern United States using 3-dimensional fields of temperature, relative humidity, sulfate, nitrate, and ammonium, obtained from a recent Community Multiscale Air Quality model simulation. The resulting spatial distributions of γ were contrasted with three other parameterizations that have been applied in air quality models in the past and with atmospheric observational determinations of γ. Our results highlight a critical need for more laboratory measurements of γ at low temperature and high relative humidity to improve model simulations of N2O5 hydrolysis during wintertime conditions.
Aerosol effects on clouds and precipitation during the 1997 smoke episode in Indonesia
Authors: Graf H.-F. , Yang J. , Wagner T. M.
Published: April 2010

Abstract. In 1997/98 a severe smoke episode due to extensive biomass burning, especially of peat, was observed over Indonesia. September 1997 was the month with the highest aerosol burden. This month was simulated using the limited area model REMOTE driven at its lateral boundaries by ERA40 reanalysis data. REMOTE was extended by a new convective cloud parameterization mimicking individual clouds competing for instability energy. This allows for the interaction of aerosols and convective clouds and precipitation. Results show that convective precipitation is diminished at all places with high aerosol loading, but at some areas with high background humidity precipitation from large-scale clouds may over-compensate the loss in convective rainfall. At individual time steps, very few cases were found when polluted convective clouds produced intensified rainfall via mixed phase microphysics. However, these cases are not unequivocal and opposite results were also simulated, indicating that other than aerosol-microphysics effects have important impact on the results. Overall, the introduction of the new cumulus parameterization and of aerosol-cloud interaction improved the simulation of precipitation patterns and total amount.
Inversion analysis of carbon monoxide emissions using data from the TES and MOPITT satellite instruments
Authors: Jones D. B. A. , Bowman K. W. , Logan J. A. , Heald C. L. , Liu J. , Luo M. , Worden J. , Drummond J.
Published: April 2010

Abstract. We conduct an inverse modeling analysis of measurements of atmospheric CO from the TES and MOPITT satellite instruments using the GEOS-Chem global chemical transport model. This is the first quantitative analysis of the consistency of the information provided by these two instruments on surface emissions of CO in an inverse modeling context. We focus on observations of CO for November 2004, when the climatological emission inventory in the GEOS-Chem model significantly underestimated the atmospheric abundance of CO as observed by TES and MOPITT. We find that both datasets suggest significantly greater emissions of CO from sub-equatorial Africa and the Indonesian/Australian region. The a posteriori emissions from sub-equatorial Africa based on TES and MOPITT data were 173 Tg CO/yr and 184 Tg CO/yr, respectively, compared to the a priori of 95 Tg CO/yr. In the Indonesian/Australian region, the a posteriori emissions inferred from TES and MOPITT data were 155 Tg CO/yr and 185 Tg CO/yr, respectively, whereas the a priori was 69 Tg CO/yr. The differences between the a posteriori emission estimates obtained from the two datasets are generally less than 20%, and are likely due to the different spatio-temporal sampling of the measurements. The a posteriori emissions significantly improve the simulated distribution of CO, however, large regional residuals remain, reflecting systematic errors in the analysis. For example, the a posteriori emissions obtained from both datasets do not completely reduce the underestimate in the model of CO column abundances over the southern tropical Atlantic, southern Africa, and over the Indian Ocean, where biases of 3–7% remain. Over eastern Asia the a posteriori emissions overestimate the CO column abundances by about 3–6%. These residuals reflect the sensitivity of the top-down source estimates to systematic errors in the analysis. Our results indicate that improving the accuracy of top-down emission estimates will require further characterization of model biases (chemical and transport) and the use of spatial-temporal inversion resolutions consistent with the information content of the observations.
The Total Solar Eclipse of March 2006: overview
Authors: Gerasopoulos E. , Zerefos C. S. , Tsagouri I. , Founda D. , Amiridis V. , Bais A. F. , Belehaki A. , Christou N. , Economou G. , Kanakidou M. , Karamanos A. , Petrakis M. , Zanis P.
Published: April 2010

Abstract. This paper provides an overview of integrated, multi-disciplinary effort to study the effects of a total solar eclipse on the environment, with special focus on the atmosphere. On the occasion of the 29 March 2006 total solar eclipse, visible over the Eastern Mediterranean, several research and academic institutes organised co-ordinated experimental campaigns, at different distances from the totality and in various environments in terms of air quality. The detailed results are presented in a number of scientific papers included in a Special Issue of Atmospheric Chemistry and Physics. The effects of the eclipse on the meteorology and the spectral solar radiation, the chemical response of the atmosphere to the abrupt "switch off" of the sun and the induced changes in the stratosphere and the ionosphere, have been among the issues covered. The rare event of a total solar eclipse provided the opportunity to evaluate 1-D and 3-D radiative transfer models (in the atmosphere and underwater), mesoscale meteorological, regional air quality and photochemical box models, against measurements. Within the challenging topics of this effort has been the investigation of eclipse impacts on ecosystems (field crops and marine plankton) and the identification of eclipse induced gravity waves, for the first time with simultaneous measurements at three altitudes namely the troposphere, the stratosphere and the ionosphere.
Simulation study of the aerosol information content in OMI spectral reflectance measurements
Authors: Veihelmann B. , Levelt P. F. , Stammes P. , Veefkind J. P.
Published: April 2010

Abstract. The Ozone Monitoring Instrument (OMI) is designed and used primarily to retrieve trace gases like O3 and NO2 from the measured Earth reflectance spectrum in the UV-visible (270–500 nm). However, also aerosols are an important science target of OMI. Therefore, a Principal Component Analysis (PCA) is performed to quantify the information content of OMI reflectance measurements on aerosols. This analysis is applied to synthetic reflectance measurements for desert dust, biomass burning aerosols, and weakly absorbing anthropogenic aerosol with a variety of aerosol optical thicknesses, aerosol layer altitudes, refractive indices and size distributions. The range of aerosol parameters considered covers the natural variability of tropospheric aerosols. This theoretical analysis is performed for a large number of scenarios with various geometries and surface albedo spectra for ocean, soil and vegetation. When the surface albedo spectrum is accurately known and clouds are absent, OMI reflectance measurements have 2 to 4 degrees of freedom that can be attributed to aerosol parameters. This information content depends on the observation geometry, the surface albedo spectrum, and on the aerosol parameters themselves. An additional wavelength band is evaluated, that comprises the O2-O2 absorption band at a wavelength of 477 nm. It is found that this wavelength band adds significantly more information than any other individual band. The PCA is applied to assess the capability of the aerosol retrieval to discern various aerosol types as well as clouds.