bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical distribution of aerosols in Mexico City during MILAGRO-2006 campaign
Authors: Lewandowski P. A. , Eichinger W. E. , Holder H. , Prueger J.
Published: April 2010

Abstract. On 7 March 2006, a mobile, ground-based, vertical pointing, elastic lidar system made a North-South transect through the Mexico City basin. Aerosol size distribution measurements, made concurrently, allowed calculation of the mass extinction efficiency (MEE) for the lidar system (1064 nm). MEE combined with an inverted lidar extinction coefficient resulted in total aerosol vertical mass estimates with 1.5 m vertical spatial and 1 s temporal resolution. The results showed that the aerosol loading within the basin is about twice what is observed outside of the basin. The total aerosol base concentrations observed in the basin are of the order of 200 μg/m3 and the base levels outside are of the order of 100 μg/m3. The local heavy traffic events can introduce aerosol levels near the ground as high as 900 μg/m3. The lidar-based total aerosol loading compares with the hourly-averaged PM10 ground observations conducted by the RAMA monitoring network throughout Mexico City.
Influence of particle size on the ice nucleating ability of mineral dusts
Authors: Welti A. , Lüönd F. , Stetzer O. , Lohmann U.
Published: April 2010

Abstract. The recently developed Zurich Ice Nucleation Chamber (ZINC) was used to explore ice nucleation of size-selected mineral dust particles at temperatures between −20°C and −55°C. Four different mineral dust species have been tested: montmorillonite, kaolinite, illite and Arizona test dust (ATD). The selected particle diameters are 100 nm, 200 nm, 400 nm and 800 nm. Relative humidities with respect to ice (RHi) required to activate 1% of the dust particles as ice nuclei (IN) are reported as a function of temperature. An explicit size dependence of the ice formation efficiency has been observed for all dust types. Deposition nucleation was found only below −30°C or −35°C dependent on particle size. 800 nm particles required the lowest RHi to activate. Minimum RHi for 1% activation were 105% for illite, kaolinite and montmorillonite at −40°C, respectively 110% for ATD at −45°C. In addition, a possible parameterisation for the measured activation spectra is proposed, which could be used in modeling studies.
Composition of the TTL over Darwin: local mixing or long-range transport?
Authors: Heyes W. J. , Vaughan G. , Allen G. , Volz-Thomas A. , Pätz H.-W. , Busen R.
Published: April 2010

Abstract. We present ozone and carbon monoxide measurements taken in Darwin, Australia, during the wet season of 2005/2006, to examine whether the composition of the Tropical Tropopause Layer (TTL) reflects that of the local boundary layer or is influenced more by advection from distant sources. We find that the latter predominates in the upper TTL, and is also the major influence in the lower TTL, except during an active monsoon phase. The day-to-day variability of ozone in the TTL is far greater than that in the lower troposphere, and correlates closely with air mass origin deduced from trajectory calculations based on standard ECMWF wind analyses. Although clear evidence of recent local uplift was found in CO measurements recorded inside convective anvils, no such signal was found in the background TTL, where the measured variability correlated well with air mass origin deduced from back-trajectories. This study suggests that the composition of the TTL is ultimately determined by vertical mixing in certain "hot spot" regions of the tropics, with advection from these regions dominating the composition elsewhere.
On the capability of IASI measurements to inform about CO surface emissions
Authors: Fortems-Cheiney A. , Chevallier F. , Pison I. , Bousquet P. , Carouge C. , Clerbaux C. , Coheur P.-F. , George M. , Hurtmans D. , Szopa S.
Published: April 2010

Abstract. Between July and November 2008, simultaneous observations were conducted by several orbiting instruments that monitor carbon monoxide in the atmosphere, among them the Infrared Atmospheric Sounding Instrument (IASI) and Measurements Of Pollution In The Troposphere (MOPITT). In this paper, the concentration retrievals at about 700 hPa from these two instruments are successively used in a variational Bayesian system to infer the global distribution of CO emissions. Our posterior estimate of CO emissions using IASI retrievals gives a total of 793 Tg for the considered period, which is 40% higher than the global budget calculated with the MOPITT data (566 Tg). Over six continental regions (Eurasian Boreal, South Asia, South East Asia, North American Boreal, Northern Africa and South American Temperate) and thanks to a better observation density, the theoretical uncertainty reduction obtained with the IASI retrievals is better or similar than with MOPITT. For the other continental regions, IASI constrains the emissions less than MOPITT because of lesser sensitivity in the lower troposphere. These first results indicate that IASI may play a major role in the quantification of the emissions of CO.
Aerosol size-dependent below-cloud scavenging by rain and snow in the ECHAM5-HAM
Authors: Croft B. , Lohmann U. , Martin R. V. , Stier P. , Wurzler S. , Feichter J. , Posselt R. , Ferrachat S.
Published: April 2010

Abstract. Wet deposition processes are highly efficient in the removal of aerosols from the atmosphere, and thus strongly influence global aerosol concentrations, and clouds, and their respective radiative forcings. In this study, physically detailed size-dependent below-cloud scavenging parameterizations for rain and snow are implemented in the ECHAM5-HAM global aerosol-climate model. Previously, below-cloud scavenging by rain in the ECHAM5-HAM was simply a function of the aerosol mode, and then scaled by the rainfall rate. The below-cloud scavenging by snow was a function of the snowfall rate alone. The global mean aerosol optical depth, and sea salt burden are sensitive to the below-cloud scavenging coefficients, with reductions near to 15% when the more vigorous size-dependent below-cloud scavenging by rain and snow is implemented. The inclusion of a prognostic rain scheme significantly reduces the fractional importance of below-cloud scavenging since there is higher evaporation in the lower troposphere, increasing the global mean sea salt burden by almost 15%. Thermophoretic effects are shown to produce increases in the global and annual mean below-cloud number removal of Aitken size particles of near to 15%, but very small increases (near 1%) in the global mean below-cloud mass scavenging of carbonaceous and sulfate aerosols. Changes in the assumptions about the below-cloud scavenging of ultra-fine particles by rain do not cause any significant changes to the global mean aerosol mass or number burdens, despite a change in the below-cloud number removal rate for nucleation mode particles by near to 10%. For nucleation mode particles, changes to the assumptions about the below-cloud scavenging by snow produce a greater change in the number removal rate, in excess of one order of magnitude. Closer agreement with different observations is found when the more physically detailed below-cloud scavenging parameterization is employed in the ECHAM5-HAM model.
The influence of foreign vs. North American emissions on surface ozone in the US
Authors: Reidmiller D. R. , Fiore A. M. , Jaffe D. A. , Bergmann D. , Cuvelier C. , Dentener F. J. , Duncan B. N. , Folberth G. , Gauss M. , Gong S. , Hess P. , Jonson J. E. , Keating T. , Lupu A. , Marmer E. , Park R. , Schultz M. G. , Shindell D. T. , Szopa S. , Vivanco M. G. , Wild O. , Zuber A.
Published: April 2010

Abstract. As part of the Hemispheric Transport of Air Pollution (HTAP; http://www.htap.org/) project, we analyze results from 16 global and hemispheric chemical transport models and compare these to Clean Air Status and Trends Network (CASTNet) observations in the United States (US) for 2001. Using the policy-relevant maximum daily 8-h ozone (MDA8 O3) statistic, the multi-model ensemble represents the observations well (mean r2=0.57, ensemble bias=+4.1 ppbv for all regions and all seasons) despite a wide range in the individual model results. Correlations are strongest in the NorthEastern US during spring and fall (r2=0.68); and weakest in the Midwestern US in summer (r2=0.46). However, large positive mean biases exist during summer for all Eastern US regions, ranging from 10–20 ppbv, and a smaller negative bias is present in the Western US during spring (~3 ppbv). In most all other regions and seasons, the biases of the model ensemble simulations are ≤5 ppbv. Sensitivity simulations in which anthropogenic O3-precursor emissions (NOx+NMVOC+CO+aerosols) were decreased by 20% in each of four source regions: East Asia (EA), South Asia (SA), Europe (EU) and North America (NA) show that the greatest response of MDA8 O3 to the summed foreign emissions reductions occurs during spring in the West (0.9 ppbv reduction due to 20% reductions from EA+SA+EU). East Asia is the largest contributor to MDA8 O3 at all ranges of the O3 distribution for most regions (typically ~0.45 ppbv). The exception is in the NorthEastern US where European emissions reductions had the greatest impact on MDA8 O3, particularly in the middle of the MDA8 O3 distribution (response of ~0.35 ppbv between 35–55 ppbv). In all regions and seasons, however, O3-precursor emissions reductions of 20% in the NA source region decrease MDA8 O3 the most – by a factor of 2 to nearly 10 relative to foreign emissions reductions. The O3 response to anthropogenic NA emissions is greatest in the Eastern US during summer at the high end of the O3 distribution (5–6 ppbv for 20% reductions). While the impact of foreign emissions on surface O3 in the US is not negligible – and is of increasing concern given the growth in emissions upwind of the US – domestic emissions reductions remain a far more effective means of decreasing MDA8 O3 values, particularly those above 75 ppb (the current US standard).
IASI temperature and water vapor retrievals – error assessment and validation
Authors: Pougatchev N. , August T. , Calbet X. , Hultberg T. , Oduleye O. , Schlüssel P. , Stiller B. , Germain K. S. , Bingham G.
Published: April 2010

Abstract. The METOP-A satellite Infrared Atmospheric Sounding Interferometer (IASI) Level 2 products comprise retrievals of vertical profiles of temperature and water vapor. The error covariance matrices and biases of the most recent version (4.3.1) of the L2 data were assessed, and the assessment was validated using radiosonde data for reference. The radiosonde data set includes dedicated and synoptic time launches at the Lindenberg station in Germany. For optimal validation, the linear statistical Validation Assessment Model (VAM) was used. The VAM uses radiosonde profiles as input and provides optimal estimate of the nominal IASI retrieval by utilizing IASI averaging kernels and statistical characteristics of the ensembles of the reference radiosondes. For temperature temperatures above 900 mb and water retrievals above 700 mb, level expected and assessed errors are in good agreement. Below those levels, noticeable excess in assessed error is observed, possibly due to inaccurate surface parameters and undetected clouds/haze.
Monitoring of atmospheric composition using the thermal infrared IASI/MetOp sounder
Authors: Clerbaux C. , Boynard A. , Clarisse L. , George M. , Hadji-Lazaro J. , Herbin H. , Hurtmans D. , Pommier M. , Razavi A. , Turquety S. , Wespes C. , Coheur P.-F.
Published: April 2010

Abstract. Atmospheric remote sensing from satellite is an essential component of the observational strategy deployed to monitor atmospheric pollution and changing composition. The IASI nadir looking thermal infrared sounder onboard MetOp will provide 15 years of global scale observations for a series of key atmospheric species, with unprecedented spatial sampling and coverage. This paper gives an overview of the instrument's capability for measuring atmospheric composition in the perspective of chemistry and air quality studies. The assessment is made in terms of species, accuracy and vertical information. Global distributions are presented for CO, CH4, O3 (total and tropospheric), HNO3, NH3 and volcanic SO2. Local distributions of organic species measured during fire events, such as C2H4, CH3OH, HCOOH, and PAN are also shown. For each species or process, the link is made to specialized papers in this issue.
Variability and trends in stratospheric NO2 in Antarctic summer, and implications for the Brewer-Dobson circulation
Authors: Cook P. A. , Roscoe H. K.
Published: April 2010

Abstract. NO2 measurements during 1990–2007, obtained from a zenith-sky spectrometer in the Antarctic, are analysed to determine the long-term changes. The changes in midsummer should be indicative of any changes in the Brewer-Dobson circulation. An atmospheric photochemical box model and a radiative transfer model are used to improve the accuracy of determination of the vertical columns from the slant column measurements, and to deduce the amount of NOy from NO2. We find that the NO2 and NOy columns in midsummer have large inter-annual variability superimposed on a broad maximum in 2000, with little overall trend over the full time period. These changes are robust to a variety of alternative settings when determining vertical columns from slant columns or determining NOy from NO2. They suggest similar changes in speed of the Brewer-Dobson circulation but with opposite sign, i.e. a broad minimum around 2000.
One year of CNR-IMAA multi-wavelength Raman lidar measurements in correspondence of CALIPSO overpass: Level 1 products comparison
Authors: Mona L. , Pappalardo G. , Amodeo A. , D'Amico G. , Madonna F. , Boselli A. , Giunta A. , Russo F. , Cuomo V.
Published: April 2010

Abstract. At CNR-IMAA, an aerosol lidar system is operative since May 2000 in the framework of EARLINET (European Aerosol Research Lidar Network), the first lidar network for tropospheric aerosol study on continental scale. High quality multi-wavelength measurements make this system a reference point for the validation of data products provided by CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations), the first satellite-borne lidar specifically designed for aerosol and cloud study. Since 14 June 2006, devoted measurements are performed at CNR-IMAA in coincidence of CALIPSO overpasses. For the first time, results on 1-year comparisons between ground-based multi-wavelength Raman lidar measurements and corresponding CALIPSO lidar Level 1 profiles are presented. A methodology for the comparison is presented and discussed into details. Cases with the detection of cirrus clouds in CALIPSO data are separately analysed for taking into account eventual multiple scattering effects. For cirrus cloud cases, few cases are available to draw any conclusions. For clear sky conditions, the comparison shows good performances of the CALIPSO on-board lidar: the mean relative difference between the ground-based and CALIPSO Level 1 measurements is always within its standard deviation at all altitudes, with a mean difference in the 3–8 km altitude range of (−2±12)%. At altitude ranges corresponding to the typical PBL height observed at CNR-IMAA, a mean underestimation of (−24±20)% is observed in CALIPSO data, probably due to the difference in the aerosol content at the location of PEARL and CALIPSO ground-track location. Finally, the mean differences are on average lower for the closest overpasses (at about 40 km), with an increment of the differences at all altitude ranges when the 80 km overpasses are considered.
Observations of heterogeneous reactions between Asian pollution and mineral dust over the Eastern North Pacific during INTEX-B
Authors: McNaughton C. S. , Clarke A. D. , Kapustin V. , Shinozuka Y. , Howell S. G. , Anderson B. E. , Winstead E. , Dibb J. , Scheuer E. , Cohen R. C. , Wooldridge P. , Perring A. , Huey L. G. , Kim S. , Jimenez J. L. , Dunlea E. J. , DeCarlo P. F. , Wennberg P. O. , Crounse J. D. , Weinheimer A. J. , Flocke F.
Published: April 2010

Abstract. In-situ airborne measurements of trace gases, aerosol size distributions, chemistry and optical properties were conducted over Mexico and the Eastern North Pacific during MILAGRO and INTEX-B. Heterogeneous reactions between secondary aerosol precursor gases and mineral dust during long-range transport lead to irreversible sequestration of sulfur and nitrogen compounds in the supermicrometer particulate size range. Simultaneous measurements of aerosol size distributions and weak-acid soluble calcium result in an estimate of 11 wt% of CaCO3 for Asian dust. During transport across the North Pacific, 10–30% of the CaCO3 is converted to CaSO4 or Ca(NO3)2 through reactions with trace gases. The 11-year record from the Mauna Loa Observatory confirm these findings, indicating that, on average, 16% of the CaCO3 has reacted to form CaSO4 and 14% has reacted to form Ca(NO3)2. Heterogeneous reactions resulting in ~3% increase in dust solubility is shown to have an insignificant effect on their optical properties compared to their variability in-situ. However, competition between supermicrometer dust and submicrometer primary aerosol for condensing secondary aerosol species led to a 25% smaller number median diameter for the accumulation mode aerosol. A 10–25% reduction of accumulation mode number median diameter results in a 30–70% reduction in submicrometer light scattering at relative humidities in the 80–95% range. At 80% RH submicrometer light scattering is only reduced ~3% due to a higher mass fraction of hydrophobic refractory components in the dust-affected accumulation mode aerosol. Thus reducing the geometric mean diameter of the submicrometer aerosol has a much larger effect on aerosol optics than changes to the hygroscopic:hydrophobic mass fractions of the aerosol. In the presence of dust, nitric acid concentrations are reduced to <50% of total nitrate (nitric acid plus particulate nitrate). NOy as a fraction of total nitrogen (NOy plus particulate nitrate), is reduced from >85% to 60–80% in the presence of dust. These observations support previous model studies which predict irreversible sequestration of reactive nitrogen species through heterogeneous reactions with mineral dust during long-range transport.
Ozone in the Boundary Layer air over the Arctic Ocean – measurements during the TARA expedition
Authors: Bottenheim J. W. , Netcheva S. , Morin S. , Nghiem S. V.
Published: April 2010

Abstract. A full year of measurements of surface ozone over the Arctic Ocean far removed from land is presented (81° N – 88° N latitude). The data were obtained during the drift of the French schooner TARA between September 2006 and January 2008, while frozen in the Arctic Ocean. The data confirm that long periods of virtually total absence of ozone occur in the spring (mid March to mid June) after Polar sunrise. At other times of the year ozone concentrations are comparable to other oceanic observations with winter mole fractions of ca. 30–40 nmol mol−1 and summer minima of ca. 20 nmol mol−1. Contrary to earlier observations from ozone sonde data obtained at Arctic coastal observatories, the ambient temperature was well above −20°C during most ODEs (ozone depletion episodes). Backwards trajectory calculations suggest that during these ODEs the air had previously been in contact with the frozen ocean surface for several days and originated largely from the Siberian coast where several large open flaw leads developed in the spring of 2007.
Aerosol- and updraft-limited regimes of cloud droplet formation: influence of particle number, size and hygroscopicity on the activation of cloud condensation nuclei (CCN)
Authors: Reutter P. , Trentmann J. , Su H. , Simmel M. , Rose D. , Wernli H. , Andreae M. O. , Pöschl U.
Published: April 2010

Abstract. We have investigated the formation of cloud droplets under (pyro-)convective conditions using a cloud parcel model with detailed spectral microphysics and with the κ-Köhler model approach for efficient and realistic description of the cloud condensation nucleus (CCN) activity of aerosol particles. Assuming a typical biomass burning aerosol size distribution (accumulation mode centred at 120 nm), we have calculated initial cloud droplet number concentrations (NCD) for a wide range of updraft velocities (w=0.5–20 m s−1) and aerosol particle number concentrations (NCN=103–105 cm−3) at the cloud base. Depending on the ratio between updraft velocity and particle number concentration (w/NCN), we found three distinctly different regimes of CCN activation and cloud droplet formation: 1. An aerosol-limited regime that is characterized by high w/NCN ratios (>≈10−3 m s−1 cm3), high maximum values of water vapour supersaturation (Smax>≈0.5%), and high activated fractions of aerosol particles (NCD/NCN>≈90%). In this regime NCD is directly proportional to NCN and practically independent of w. 2. An updraft-limited regime that is characterized by low w/NCN ratios (
Direct estimates of emissions from the megacity of Lagos
Authors: Hopkins J. R. , Evans M. J. , Lee J. D. , Lewis A. C. , Marsham J. H. , McQuaid J. B. , Parker D. J. , Stewart D. J. , Reeves C. E. , Purvis R. M.
Published: April 2010

Abstract. We report here top-down emissions estimate for an African megacity. A boundary-layer circumnavigation of Lagos, Nigeria was completed using the FAAM BAe146 aircraft as part of the AMMA project. These observations together with an inferred boundary-layer height allow the flux of pollutants to be calculated. Extrapolation gives annual emissions for CO, NOx and VOCs of 0.72 Tg C yr−1, 0.02 Tg N yr−1 and 0.28 Tg C yr−1 respectively, consistent with bottom-up estimates for other developing megacities. These emissions are attributed to the evaporation of fuels, mobile combustion and natural gas emissions.
Retrieval of atmospheric profiles and cloud properties from IASI spectra using super-channels
Authors: Liu X. , Zhou D. K. , Larar A. M. , Smith W. L. , Schluessel P. , Newman S. M. , Taylor J. P. , Wu W.
Published: April 2010

Abstract. The Infrared Atmospheric Sounding Interferometer (IASI) is an ultra-spectral satellite sensor with 8461 spectral channels. IASI spectra contain high information content on atmospheric, cloud, and surface properties. The instrument presents a challenge for using thousands of spectral channels in a physical retrieval system or in a Numerical Weather Prediction (NWP) data assimilation system. In this paper we describe a method of simultaneously retrieving atmospheric temperature, moisture, and cloud properties using all available IASI channels without sacrificing computational speed. The essence of the method is to convert the IASI channel radiance spectra into super-channels by an Empirical Orthogonal Function (EOF) transformation. Because the EOFs are orthogonal to each other, about 100 super-channels are adequate to capture the information content of the radiance spectra. A Principal Component-based Radiative Transfer Model (PCRTM) is used to calculate both the super-channel magnitudes and derivatives with respect to atmospheric profiles and other properties. A physical retrieval algorithm then performs an inversion of atmospheric, cloud, and surface properties in super channel domain directly therefore both reducing the computational need and preserving the information content of the IASI measurements.
Oceanic influence on atmospheric mercury at coastal and inland sites: a springtime noreaster in New England
Authors: Sigler J. M. , Mao H. , Sive B. C. , Talbot R.
Published: April 2010

Abstract. Continuous measurements of elemental (Hg0) and reactive mercury were conducted at two sites in New Hampshire during a powerful April 2007 noreaster. During the most intense period of the storm, enhancements of ~30–50 ppqv in Hg0 were observed at a coastal and a high elevation inland site. This enhancement occurred simultaneously with elevated mixing ratios of three marine tracers, CH3I, CH2Br2 and CHBr3. These observations suggest a marine source of Hg0, possibly outgassing from the ocean surface during strong turbulence. The Hg0 enhancement observed 100 km inland suggests that the impact of coastal storms on terrestrial Hg cycling may not be limited to near-shore environments. Combining Hg0 and marine tracer measurements during the storm with estimates of oceanic tracer fluxes during previous strong storms yields an order-of-magnitude estimate of the oceanic source of Hg0 during the storm (~7 ppqv hr
NASA LaRC airborne high spectral resolution lidar aerosol measurements during MILAGRO: observations and validation
Authors: Rogers R. R. , Hair J. W. , Hostetler C. A. , Ferrare R. A. , Obland M. D. , Cook A. L. , Harper D. B. , Burton S. P. , Shinozuka Y. , McNaughton C. S. , Clarke A. D. , Redemann J. , Russell P. B. , Livingston J. M. , Kleinman L. I.
Published: April 2010

Abstract. The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) measures vertical profiles of aerosol extinction, backscatter, and depolarization at both 532 nm and 1064 nm. In March of 2006 the HSRL participated in the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign along with several other suites of instruments deployed on both aircraft and ground based platforms. This paper presents high spatial and vertical resolution HSRL measurements of aerosol extinction and optical depth from MILAGRO and comparisons of those measurements with similar measurements from other sensors and model predictions. HSRL measurements coincident with airborne in situ aerosol scattering and absorption measurements from two different instrument suites on the C-130 and G-1 aircraft, airborne aerosol optical depth (AOD) and extinction measurements from an airborne tracking sunphotometer on the J-31 aircraft, and AOD from a network of ground based Aerosol Robotic Network (AERONET) sun photometers are presented as a validation of the HSRL aerosol extinction and optical depth products. Regarding the extinction validation, we find bias differences between HSRL and these instruments to be less than 3% (0.01 km−1) at 532 nm, the wavelength at which the HSRL technique is employed. The rms differences at 532 nm were less than 50% (0.015 km−1). To our knowledge this is the most comprehensive validation of the HSRL measurement of aerosol extinction and optical depth to date. The observed bias differences in ambient aerosol extinction between HSRL and other measurements is within 15–20% at visible wavelengths, found by previous studies to be the differences observed with current state-of-the-art instrumentation (Schmid et al., 2006).
Isoprene oxidation by nitrate radical: alkyl nitrate and secondary organic aerosol yields
Authors: Rollins A. W. , Kiendler-Scharr A. , Fry J. , Brauers T. , Brown S. S. , Dorn H.-P. , Dubé W. P. , Fuchs H. , Mensah A. , Mentel T. F. , Rohrer F. , Tillmann R. , Wegener R. , Wooldridge P. J. , Cohen R. C.
Published: April 2010

Abstract. Alkyl nitrates and secondary organic aerosol (SOA) produced during the oxidation of isoprene by nitrate radicals has been observed in the SAPHIR chamber. We find the yield of nitrates is 70±8% from the isoprene+NO3 reaction, and the yield for secondary dinitrates produced in the reaction of primary isoprene nitrates with NO3 is 40±20%. We find an effective rate constant for reaction of NO3 with the group of first generation oxidation products to be 7×10−14 cm3 s−1. At the low total organic aerosol concentration in the chamber (max ≈0.6 μg m−3) we observed a mass yield (ΔSOA mass/Δisoprene mass) of 2% for the entire 16 h experiment. However a comparison of the timing of the observed SOA production to a box model simulation of first and second generation oxidation products shows that the yield from the first generation products was <0.2% while the further oxidation of the initial products leads to a yield of 10% (defined as ΔSOA/Δisoprene2x where Δisoprene2x is the mass of isoprene which reacted twice with NO3). The SOA yield of 10% is consistent with equilibrium partitioning of highly functionalized C5 products of isoprene oxidation.
Orographic cirrus in the future climate
Authors: Joos H. , Spichtinger P. , Lohmann U.
Published: April 2010

Abstract. A cloud resolving model (CRM) is used to investigate the formation of orographic cirrus clouds in the current and future climate. The formation of cirrus clouds depends on a variety of dynamical and thermodynamical processes, which act on different scales. First, the capability of the CRM in realistically simulating orographic cirrus clouds has been tested by comparing the simulated results to aircraft measurements of an orographic cirrus cloud. The influence of a warmer climate on the microphysical and optical properties of cirrus clouds has been investigated by initializing the CRM with vertical profiles of horizontal wind, temperature and moisture from IPCC A1B simulations for the current climate and for the period 2090–2099 for two regions representative for North and South America. In a future climate, the increase in moisture dampens the vertical propagation of gravity waves and the occurring vertical velocities. Together with higher temperatures fewer ice crystals nucleate homogeneously. Assuming that the relative humidity does not change in a warmer climate the specific humidity in the model is increased. This increase in specific humidity in a warmer climate results in a higher ice water content. The net effect of a reduced ice crystal number concentration and a higher ice water content is an increased optical depth.
Source apportionment of fine organic aerosols in Beijing
Authors: Wang Q. , Shao M. , Zhang Y. , Wei Y. , Hu M. , Guo S.
Published: April 2010

Abstract. Fine particles (PM2.5, i.e., particles with an aerodynamic diameter of ≤2.5 μm) were collected from the air in August 2006, August–September 2006, and January–February 2007, in Beijing, China. Particulate organic matter in the ambient samples was quantified by gas chromatography/mass spectrometry. The dominant compounds identified in summertime were n-alkanoic acids, followed by dicarboxylic acids and sugars, while sugars became the most abundant species in winter, followed by polycyclic aromatic hydrocarbons, n-alkanes, and n-alkanoic acids. The contributions of seven emission sources (i.e., gasoline/diesel vehicles, coal burning, wood/straw burning, cooking, and vegetative detritus) to particulate organic matter in PM2.5 were estimated using a chemical mass balance receptor model. The model runs the present seasonal trends regarding the contributions of various sources to organic aerosols. Biomass burning (straw and wood) had the highest contribution in winter, followed by coal burning, vehicle exhaust, and cooking. The contribution of cooking was the highest in summer, followed by vehicle exhaust and biomass burning, while coal smoke showed only a minor contribution to ambient organic carbon.
Surface ozone at the Caucasian site Kislovodsk High Mountain Station and the Swiss Alpine site Jungfraujoch: data analysis and trends (1990–2006)
Authors: Tarasova O. A. , Senik I. A. , Sosonkin M. G. , Cui J. , Staehelin J. , Prévôt A. S. H.
Published: April 2010

Abstract. Long-term ozone measurements of two background mountain sites, namely the Kislovodsk High Mountain Station in Caucasus, Russia (KHMS, 43.70° N, 42.70° E, 2070 m a.s.l.) and the Jungfraujoch in Switzerland (JFJ, 46.55° N, 7.98° E, 3580 m a.s.l.) are compared. Despite of more than 1.5 km altitude difference ozone concentrations are comparable at JFJ an KHMS in the beginning of measurements (1990–1993) while the annually averaged levels at JFJ are around 15 ppb higher than the ones at KHMS for the most recent years (1997–2006). Averaged for different periods ozone concentrations at KHMS are comparable with the respective values observed at the elevated sites in the midlatitudes, situated in the altitude range 1600–2400 m a.s.l. Distribution function of the hourly concentrations has two peaks at JFJ and it is close to Gaussian distribution in the case of KHMS. Seasonality at both sites is characterized by double spring-summer maximum. Spring maximum at both stations is more pronounced for the air masses with the longest contact with upper free troposphere and stratosphere. Average concentrations increased at JFJ but decreased at KHMS for the period 1990–2006. Trends are more pronounced for the 1990s (+0.73±0.20 ppb/year at JFJ and −0.91±0.17 ppb/year at KHMS for the period 1991–2001) in comparison with later years (+0.04±0.21 ppb/year at JFJ and −0.37±0.14 ppb/year at KHMS for the period 1997–2006). Trends show a distinct seasonality, which is different for the different periods. To investigate possible reasons for this remarkable trends difference 3-D trajectories using LAGRANTO trajectory model are used. Effects of the horizontal and vertical transport on ozone trends are considered. In general we could not find any systematic changes in the transport patterns which could explain the significant changes of the trends between 1991–2001 and 1997–2006. It is likely that the position of the main emission source areas relative to the stations is among the main reason for the opposite surface ozone trends. During the 1990s the JFJ trend reflects increase of the ozone in the upper free troposphere/lower stratosphere. In contrary KHSM is much more influenced by dramatic emission decrease in the earlier 1990s in former USSR and emissions regulations in Western Europe. For later years ozone trends at KHMS are controlled by slight emission increase in the region, while trends at JFJ correspond to the scenario of European emissions control.
A comparison study of regional atmospheric simulations with an elastic backscattering Lidar and Sunphotometry in an urban area
Authors: Landulfo E. , Freitas S. R. , Longo K. M. , Uehara S. T. , Sawamura P.
Published: April 2010

Abstract. We describe a comparison study of aerosol optical thickness (AOT) from numerical simulations using a regional atmospheric model with an elastic backscattering lidar operating at 532 nm and a sunphotometer belonging to the AERONET network at São Paulo (23° S 46° W) city, Brazil, a very populated urban area. The atmospheric model includes an aerosol emission, transport and deposition module coupled to a radiative transfer parameterization, which takes the interaction between aerosol particles and short and long wave radiation into account. A period of one week was taken as case study during the dry season (late August) when intense biomass burning activities occur in remote areas in South America, and meteorological conditions disfavor the pollution dispersion in the city of São Paulo. The situation showed points out how smoke from biomass burning in remote areas is transported to the Southeast part of Brazil and affects the optical atmospheric conditions in São Paulo. The numerical simulations are corroborated by in-situ measurements of Aerosol Optical Thickness.
Particle number size distributions in urban air before and after volatilisation
Authors: Birmili W. , Heinke K. , Pitz M. , Matschullat J. , Wiedensohler A. , Cyrys J. , Wichmann H.-E. , Peters A.
Published: April 2010

Abstract. Aerosol particle number size distributions (size range 0.003–10 μm) with and without using a thermodenuder are measured continuously in the city of Augsburg, Germany. Here, the data between 2004 and 2006 are examined with respect to the governing anthropogenic sources and meteorological factors. The two-year average particle number concentration in Augsburg was found to be 12 200 cm−3, similar to previous observations in other European cities. A seasonal analysis yielded twice the total particle number concentrations in winter as compared to summer, a consequence of more frequent inversion situations and particulate emissions in winter. The diurnal variation of the size distribution is shaped by a remarkable increase in the morning along with the peak traffic hours. After a mid-day decrease along with the onset of vertical mixing, an evening increase in concentration could frequently be observed, suggesting a re-stratification of the urban atmosphere. The mixed layer height turned out to be the most influential meteorological parameter on particle size distribution. Its influence was greater than that of the geographical origin of the synoptic-scale air masses. By heating every second aerosol sample to 300°C in a thermodenuder, the volume fraction of non-volatile compounds in the urban aerosol was retrieved. The obtained results compared well with an independent measurement of the aerosol absorption coefficient (R2=0.9). The balance of particle number upstream and downstream of the thermodenuder suggests that all particles >12 nm contain a non-volatile core at 300°C. As an artefact of the volatility analysis, nucleation of particles smaller than 6 nm was observed in the cooling section of the thermodenuder. An average diameter ratio of particles before and after volatilisation was determined as a function of particle size. It indicated that particles >60 nm contain significantly higher fractions of non-volatile compounds, most likely soot, than particles <60 nm.
H216O and HDO measurements with IASI/MetOp
Authors: Herbin H. , Hurtmans D. , Clerbaux C. , Clarisse L. , Coheur P.-F.
Published: April 2010

Abstract. In this paper we analyze distributions of water vapour isotopologues in the troposphere using infrared spectra recorded by the Infrared Atmospheric Sounding Interferometer (IASI), which operates onboard the Metop satellite in nadir geometry. The simultaneous uncorrelated retrieval of H216O and HDO was performed on radiance measurements using a line-by-line radiative transfer model and an inversion procedure based on the Optimal Estimation Method (OEM). The characterizations of the retrieved products in terms of vertical sensitivity and error budgets show that IASI measurements contain up to 6 independent pieces of information on the vertical distribution of H216O and up to 3.5 for HDO from the surface up to the upper troposphere (0–20 km). The H216O retrieved profiles are in good agreement with local sonde measurements at different latitudes during different times of the year. Our results demonstrate the ability of the IASI instrument to monitor atmospheric isotopologic water vapour distributions with unprecedented sensitivity. As a case study, we analyse concentration distributions and spatio-temporal variations of H216O and HDO during the October 2007 Krosa super-typhoon over South-East Asia and show with this example the IASI potential to capture variations in the HDO/H216O isotopologic ratio values over space and time.
Analysing spatio-temporal patterns of the global NO2-distribution retrieved from GOME satellite observations using a generalized additive model
Authors: Hayn M. , Beirle S. , Hamprecht F. A. , Platt U. , Menze B. H. , Wagner T.
Published: April 2010

Abstract. With the increasing availability of observations from different space-borne sensors, the joint analysis of observational data from multiple sources becomes more and more attractive. For such an analysis – oftentimes with little prior knowledge about local and global interactions between the different observational variables available – an explorative data-driven analysis of the remote sensing data may be of particular relevance. In the present work we used generalized additive models (GAM) in this task, in an exemplary study of spatio-temporal patterns in the tropospheric NO2-distribution derived from GOME satellite observations (1996 to 2001) at global scale. We modelled different temporal trends in the time series of the observed NO2, but focused on identifying correlations between NO2 and local wind fields. Here, our nonparametric modelling approach had several advantages over standard parametric models: While the model-based analysis allowed to test predefined hypotheses (assuming, for example, sinusoidal seasonal trends) only, the GAM allowed to learn functional relations between different observational variables directly from the data. This was of particular interest in the present task, as little was known about relations between the observed NO2 distribution and transport processes by local wind fields, and the formulation of general functional relationships to be tested remained difficult. We found the observed temporal trends – weekly, seasonal and linear changes – to be in overall good agreement with previous studies and alternative ways of data analysis. However, NO2 observations showed to be affected by wind-dominated processes over several areas, world wide. Here we were able to estimate the extent of areas affected by specific NO2 emission sources, and to highlight likely atmospheric transport pathways. Overall, using a nonparametric model provided favourable means for a rapid inspection of this large spatio-temporal data set,with less bias than parametric approaches, and allowing to visualize dynamical processes of the NO2 distribution at a global scale.
Modeling of secondary organic aerosol yields from laboratory chamber data
Authors: Chan M. N. , Chan A. W. H. , Chhabra P. S. , Surratt J. D. , Seinfeld J. H.
Published: April 2010

Abstract. A product-specific model for secondary organic aerosol (SOA) formation and composition based on equilibrium gas-particle partitioning is evaluated. The model is applied to represent laboratory data on the ozonolysis of α-pinene under dry, dark, and low-NOx conditions in the presence of ammonium sulfate seed aerosol. Using five major identified products, the model is fit to the chamber data. From the optimal fitting, SOA oxygen-to-carbon (O/C) and hydrogen-to-carbon (H/C) ratios are modeled. The discrepancy between measured H/C ratios and those based on the oxidation products used in the model fitting suggests the potential importance of particle-phase reactions. Data fitting is also carried out using the volatility basis set, wherein oxidation products are parsed into volatility bins. The product-specific model is best used for an SOA precursor for which a substantial fraction of the aerosol-phase oxidation products has been identified.
Application of φ-IASI to IASI: retrieval products evaluation and radiative transfer consistency
Authors: Masiello G. , Serio C. , Carissimo A. , Grieco G. , Matricardi M.
Published: April 2010

Abstract. Retrieval products for temperature, water vapour and ozone have been obtained from spectral radiances measured by the Infrared Atmospheric Sounding Interferometer flying onboard the first European Meteorological Operational satellite. These products have been used to check the consistency of the forward model and its accuracy and the expected retrieval performance. The study has been carried out using a research-oriented forward-inverse methodology, called φ-IASI, that the authors have specifically developed for the new sounding interferometer. The performance of the forward-inversion strategy has been assessed by comparing the retrieved profiles to profiles of temperature, water vapour and ozone obtained by co-locating in space and time profiles from radiosonde observations and from the European Centre for Medium-Range Weather Forecasts analysis. Spectral residuals have also been computed and analyzed to assess the quality of the forward model. Two versions of the high-resolution transmission molecular absorption database have been used. Their performance has been assessed by inter-comparing the results.
Why the 18.6 year tide cannot explain the change of sign observed in j2
Authors: Deleflie F. , Exertier P. , Metris G. , Berio P. , Laurain O. , Lemoine J.-M. , Biancale R.
Published: April 2010

Abstract. Recent studies show a change, starting in 1998, in the behavior of the variation of the dynamical flattening of the Earth (J2), supposed to be constant (secular), and mainly due to the post glacial rebound effect. In this paper, we study to what extent this behavior can be correlated or not with the 18.6 year tide: with more than twenty years of tracking data on LAGEOS-1, that is to say more than a period of 18.6 years, this effect can now be separated from the secular variation. We use our theory of mean orbital motion, dedicated to studies of the long period effects on the orbital motion. We build one single arc of LAGEOS-1 from 1980 to 2002, which provides a continuous description of the orbital parameters. This is the great originality of our approach. We focus our attention on the ascending node of LAGEOS-1, and we show that the change observed in j2 cannot be attributed to a statistical error due to a correlation, in short arcs results, between the secular variation of J2 and the 18.6 year tide. The proof is based on the adjustment of amplitudes and phases of the long period tides, and on the shape of the residuals.Key words. secular variation of J2, 18.6 year tide, mean orbital motione
Local gravity field continuation for the purpose of in-orbit calibration of GOCE SGG observations
Authors: Pail R.
Published: April 2010

Abstract. The use of ground gravity data in wellsurveyed areas, continued upward to satellite altitude, is one of the most promising external absolute in-orbit calibration/ validation methods for GOCE satellite gravity gradient (SGG) observations. Based on a synthetic gravity test environment – providing in addition to statistical error information also absolute error estimates – several upward continuation methods, e.g. least squares collocation, equivalent source techniques using point masses or area density distributions defined on a spherical surface section, are described, assessed and compared. It turns out that all these strictly local approaches fail to work sufficiently accurate. Consequently, a combined adjustment strategy is proposed, supporting the high-quality gravity field information within the well-surveyed test area with a low-accuracy, but globally defined Earth model. Under quite realistic assumptions the upward continuation is performed with rms errors in the order of 1 mE. The most crucial limiting factor of this method is spectral leakage in the course of an adequate representation of the initial gravity information, which can be overcome by an enlargement of the parameter model in combination with a priori filtering of the initial gravity data.Key words. Satellite gravity gradiometry – GOCE – calibration – least squares adjustment