bluuebunny/crossref_metadata_2025 huggingface dataset:
Intercomparison of ILAS-II version 1.4 and version 2 target parameters with MIPAS-Envisat measurements
Authors: Griesfeller A. , von Clarmann T. , Griesfeller J. , Höpfner M. , Milz M. , Nakajima H. , Steck T. , Sugita T. , Tanaka T. , Yokota T.
Published: April 2010

Abstract. This paper assesses the mean differences between the two ILAS-II data versions (1.4 and 2) by comparing them with MIPAS measurements made between May and October 2003. For comparison with ILAS-II results, MIPAS data processed at the Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany (IMK) in cooperation with the Instituto de Astrofísica de Andalucía (IAA) in Granada, Spain, were used. The coincidence criteria of ±300 km in space and ±12 h in time for H2O, N2O, and CH4 and the coincidence criteria of ±300 km in space and ±6 h in time for ClONO2, O3, and HNO3 were used. The ILAS-II data were separated into sunrise (= Northern Hemisphere) and sunset (= Southern Hemisphere). For the sunrise data, a clear improvement from version 1.4 to version 2 was observed for H2O, CH4, ClONO2, and O3. In particular, the ILAS-II version 1.4 mixing ratios of H2O and CH4 were unrealistically small, and those of ClONO2 above altitudes of 30 km unrealistically large. For N2O and HNO3, there were no large differences between the two versions. Contrary to the Northern Hemisphere, where some exceptional profiles deviated significantly from known climatology, no such outlying profiles were found in the Southern Hemisphere for both versions. Generally, the ILAS-II version 2 data were in better agreement with the MIPAS data than the version 1.4, and are recommended for quantitative analysis in the stratosphere. For H2O data in the Southern Hemisphere, further data quality evaluation is necessary.
The interaction of N2O5 with mineral dust: aerosol flow tube and Knudsen reactor studies
Authors: Wagner C. , Hanisch F. , Holmes N. , de Coninck H. , Schuster G. , Crowley J. N.
Published: April 2010

Abstract. The interaction of mineral dust with N2O5 was investigated using both airborne mineral aerosol (using an aerosol flow reactor with variable relative humidity) and bulk samples (using a Knudsen reactor at zero humidity). Both authentic (Saharan, SDCV) and synthetic dust samples (Arizona test dust, ATD and calcite, CaCO3) were used to derive reactive uptake coefficients (γ). The aerosol experiments (Saharan dust only) indicated efficient uptake, with e.g. a value of γ(SDCV)=(1.3±0.2)×10−2 obtained at zero relative humidity. The values of γ obtained for bulk substrates in the Knudsen reactor studies are upper limits due to assumptions of available surface area, but were in reasonable agreement with the AFT measurements, with: γ(SDCV)=(3.7±1.2)×10−2, γ(ATD)=(2.2±0.8)×10−2 and γ(CaCO3=(5±2)×10−2. The errors quoted are statistical only. The results are compared to literature values and assessed in terms of their impact on atmospheric N2O5.
Comparison of emissions from on-road sources using a mobile laboratory under various driving and operational sampling modes
Authors: Zavala M. , Herndon S. C. , Wood E. C. , Jayne J. T. , Nelson D. D. , Trimborn A. M. , Dunlea E. , Knighton W. B. , Mendoza A. , Allen D. T. , Kolb C. E. , Molina M. J. , Molina L. T.
Published: April 2010

Abstract. Mobile sources produce a significant fraction of the total anthropogenic emissions burden in large cities and have harmful effects on air quality at multiple spatial scales. Mobile emissions are intrinsically difficult to estimate due to the large number of parameters affecting the emissions variability within and across vehicles types. The MCMA-2003 Campaign in Mexico City has showed the utility of using a mobile laboratory to sample and characterize specific classes of motor vehicles to better quantify their emissions characteristics as a function of their driving cycles. The technique clearly identifies "high emitter" vehicles via individual exhaust plumes, and also provides fleet average emission rates. We have applied this technique to Mexicali during the Border Ozone Reduction and Air Quality Improvement Program (BORAQIP) for the Mexicali-Imperial Valley in 2005. We analyze the variability of measured emission ratios for emitted NOx, CO, specific VOCs, NH3, and some primary fine particle components and properties by deploying a mobile laboratory in roadside stationary sampling, chase and fleet average operational sampling modes. The measurements reflect various driving modes characteristic of the urban fleets. The observed variability for all measured gases and particle emission ratios is greater for the chase and roadside stationary sampling than for fleet average measurements. The fleet average sampling mode captured the effects of traffic conditions on the measured on-road emission ratios, allowing the use of fuel-based emission ratios to assess the validity of traditional "bottom-up" emissions inventories. Using the measured on-road emission ratios, we estimate CO and NOx mobile emissions of 175±62 and 10.4±1.3 metric tons/day, respectively, for the gasoline vehicle fleet in Mexicali. Comparisons with similar on-road emissions data from Mexico City indicated that fleet average NO emission ratios were around 20% higher in Mexicali than in Mexico City whereas HCHO and NH3 emission ratios were higher by a factor of 2 in Mexico City than in Mexicali. Acetaldehyde emission ratios did not differ significantly whereas selected aromatics VOCs emissions were similar or smaller in Mexicali. Nitrogen oxides emissions for on-road heavy-duty diesel truck (HDDT) were measured near Austin, Texas, as well as in both Mexican cities, with NOy emission ratios in Austin < Mexico City < Mexicali.
Investigation of NOx emissions and NOx-related chemistry in East Asia using CMAQ-predicted and GOME-derived NO2 columns
Authors: Han K. M. , Song C. H. , Ahn H. J. , Park R. S. , Woo J. H. , Lee C. K. , Richter A. , Burrows J. P. , Kim J. Y. , Hong J. H.
Published: April 2010

Abstract. In this study, NO2 columns from the US EPA Models-3/CMAQ model simulations carried out using the 2001 ACE-ASIA (Asia Pacific Regional Aerosol Characterization Experiment) emission inventory over East Asia were compared with the GOME-derived NO2 columns. There were large discrepancies between the CMAQ-predicted and GOME-derived NO2 columns in the fall and winter seasons. In particular, while the CMAQ-predicted NO2 columns produced larger values than the GOME-derived NO2 columns over South Korea for all four seasons, the CMAQ-predicted NO2 columns produced smaller values than the GOME-derived NO2 columns over North China for all seasons with the exception of summer (summer anomaly). It is believed that there might be some error in the NOx emission estimates as well as uncertainty in the NOx chemical loss rates over North China and South Korea. Regarding the latter, this study further focused on the biogenic VOC (BVOC) emissions that were strongly coupled with NOx chemistry during summer in East Asia. This study also investigated whether the CMAQ-modeled NO2/NOx ratios with the possibly overestimated isoprene emissions were higher than those with reduced isoprene emissions. Although changes in both the NOx chemical loss rates and NO2/NOx ratios from CMAQ-modeling with the different isoprene emissions affected the CMAQ-modeled NO2 levels, the effects were found to be limited, mainly due to the low absolute levels of NO2 in summer. Seasonal variations of the NOx emission fluxes over East Asia were further investigated by a set of sensitivity runs of the CMAQ model. Although the results still exhibited the summer anomaly possibly due to the uncertainties in both NOx-related chemistry in the CMAQ model and the GOME measurements, it is believed that consideration of both the seasonal variations in NOx emissions and the correct BVOC emissions in East Asia are critical. Overall, it is estimated that the NOx emissions are underestimated by ~57.3% in North China and overestimated by ~46.1% in South Korea over an entire year. In order to confirm the uncertainty in NOx emissions, the NOx emissions over South Korea and China were further investigated using the ACE-ASIA, REAS (Regional Emission inventory in ASia), and CAPSS (Clean Air Policy Support System) emission inventories. The comparison between the CMAQ-calculated and GOME-derived NO2 columns indicated that both the ACE-ASIA and REAS inventories have some uncertainty in NOx emissions over North China and South Korea, which can also lead to some errors in modeling the formation of ozone and secondary aerosols in South Korea and North China.
Evaluating the performance of pyrogenic and biogenic emission inventories against one decade of space-based formaldehyde columns
Authors: Stavrakou T. , Müller J.-F. , De Smedt I. , Van Roozendael M. , van der Werf G. R. , Giglio L. , Guenther A.
Published: April 2010

Abstract. A new one-decade (1997–2006) dataset of formaldehyde (HCHO) columns retrieved from GOME and SCIAMACHY is compared with HCHO columns simulated by an updated version of the IMAGES global chemical transport model. This model version includes an optimized chemical scheme with respect to HCHO production, where the short-term and final HCHO yields from pyrogenically emitted non-methane volatile organic compounds (NMVOCs) are estimated from the Master Chemical Mechanism (MCM) and an explicit speciation profile of pyrogenic emissions. The model is driven by the Global Fire Emissions Database (GFED) version 1 or 2 for biomass burning, whereas biogenic emissions are provided either by the Global Emissions Inventory Activity (GEIA), or by a newly developed inventory based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN) algorithms driven by meteorological fields from the European Centre for Medium-Range Weather Forecasts (ECMWF). The comparisons focus on tropical ecosystems, North America and China, which experience strong biogenic and biomass burning NMVOC emissions reflected in the enhanced measured HCHO columns. These comparisons aim at testing the ability of the model to reproduce the observed features of the HCHO distribution on the global scale and at providing a first assessment of the performance of the current emission inventories. The high correlation coefficients (r>0.7) between the observed and simulated columns over most regions indicate a good consistency between the model, the implemented inventories and the HCHO dataset. The use of the MEGAN-ECMWF inventory improves the model/data agreement in almost all regions, but biases persist over parts of Africa and Australia. Although neither GFED version is consistent with the data over all regions, a better agreement is achieved over Indonesia and Southern Africa when GFEDv2 is used, but GFEDv1 succeeds better in getting the correct seasonal patterns and intensities of the fire episodes over the Amazon basin, as reflected in the significantly higher correlations calculated in this region. Although the uncertainties in the HCHO retrievals, especially over fire scenes, can be quite large, this study provides a first assessment about whether the improved methodologies and input data implemented in GFEDv2 and MEGAN-ECMWF lead to better results in the comparisons of modelled with observed HCHO column measurements.
Simulation of dust aerosol and its regional feedbacks over East Asia using a regional climate model
Authors: Zhang D. F. , Zakey A. S. , Gao X. J. , Giorgi F. , Solmon F.
Published: April 2010

Abstract. The ICTP regional climate model (RegCM3) coupled with a desert dust aerosol model is used to simulate the net radiative forcing (short-wave and long-wave) and related climate effects of dust aerosols over East Asia. Two sets of experiments are completed and intercompared, one without (Exp. 1) and one with (Exp. 2) the radiative effects of dust aerosols. The experiments encompass the main dust producing months, February through May, for 10 years (1997–2006), and the simulation results are evaluated against ground station and satellite data. The model captures the basic observed climatology over the area of interest. The spatial and temporal variations of near surface concentration, mass load, optical depth and emission of dust aerosols from the main source regions are reproduced by model. The main model deficiency is an overestimate of dust amounts over the source regions and an underestimate downwind of these source areas, which indicates an underestimate of dust dispersal. Over the desert source regions, the net TOA radiative forcing is positive, while it is small over the other regions as a result of high surface albedo values which reduce the short-wave radiative forcing. The net surface radiative fluxes are decreased by dust and this causes a surface cooling locally up to −1°C. The inclusion of net (short-wave and long-wave) dust radiative forcing leads to a reduction of dust emission in the East Asia source regions, which is mainly caused by an increase in local stability and a corresponding decrease in dust lifting. Our results indicate that dust effects should be included in the assessment of climate change over East Asia.
Clear sky UV simulations for the 21st century based on ozone and temperature projections from Chemistry-Climate Models
Authors: Tourpali K. , Bais A. F. , Kazantzidis A. , Zerefos C. S. , Akiyoshi H. , Austin J. , Brühl C. , Butchart N. , Chipperfield M. P. , Dameris M. , Deushi M. , Eyring V. , Giorgetta M. A. , Kinnison D. E. , Mancini E. , Marsh D. R. , Nagashima T. , Pitari G. , Plummer D. A. , Rozanov E. , Shibata K. , Tian W.
Published: April 2010

Abstract. We have estimated changes in surface solar ultraviolet (UV) radiation under cloud free conditions in the 21st century based on simulations of 11 coupled Chemistry-Climate Models (CCMs). The total ozone columns and vertical profiles of ozone and temperature projected from CCMs were used as input to a radiative transfer model in order to calculate the corresponding erythemal irradiance levels. Time series of monthly erythemal irradiance received at the surface during local noon are presented for the period 1960 to 2100. Starting from the first decade of the 21st century, the surface erythemal irradiance decreases globally as a result of the projected stratospheric ozone recovery at rates that are larger in the first half of the 21st century and smaller towards its end. This decreasing tendency varies with latitude, being more pronounced over areas where stratospheric ozone has been depleted the most after 1980. Between 2000 and 2100 surface erythemal irradiance is projected to decrease over midlatitudes by 5 to 15%, while at the southern high latitudes the decrease is twice as much. In this study we have not included effects from changes in cloudiness, surface reflectivity and tropospheric aerosol loading, which will likely be affected in the future due to climate change. Consequently, over some areas the actual changes in future UV radiation may be different depending on the evolution of these parameters.
Technical Note: Measurement of the tropical UTLS composition in presence of clouds using millimetre-wave heterodyne spectroscopy
Authors: Dinelli B. M. , Castelli E. , Carli B. , Del Bianco S. , Gai M. , Santurri L. , Moyna B. P. , Oldfield M. , Siddans R. , Gerber D. , Reburn W. J. , Kerridge B. J. , Keim C.
Published: April 2010

Abstract. The MARSCHALS (Millimetre-wave Airborne Receiver for Spectroscopic CHaracterisation of Atmospheric Limb-Sounding) project has the general objectives of demonstrating the measurement capabilities of a limb viewing instrument working in the millimetre and sub-millimetre spectral regions (from 294 to 349 GHz) for the study of the Upper Troposphere – Lower Stratosphere (UTLS). MARSCHALS has flown on board the M-55 stratospheric aircraft (Geophysica) in two measurements campaigns. Here we report the results of the analysis of MARSCHALS measurements during the SCOUT-O3 campaign held in Darwin (Australia) in December 2005 obtained with MARC (Millimetre-wave Atmospheric-Retrieval Code). MARSCHALS measured vertical distributions of temperature, water vapour, ozone and nitric acid in the altitude range from 10 to 20 km in presence of clouds that obscure measurements in the middle infrared spectroscopic region. The minimum altitude at which the retrieval has been possible is determined by the high water concentration typical of the tropical region rather than the extensive cloud coverage experienced during the flight. Water has been measured from 10 km to flight altitude (~18 km) with a 10% accuracy, ozone from 14 km to flight altitude with accuracy ranging from 10% to 60%, while the retrieval of nitric acid has been possible with an accuracy not better than 40% only from 16 km to flight altitude due to the low signal to noise ratio of its emission in the analysed spectral region. The results have been validated using measurement made in a less cloudy region by MIPAS-STR, an infrared limb-viewing instrument on board the M-55, during the same flight.
Evaluation of the global oceanic isoprene source and its impacts on marine organic carbon aerosol
Authors: Arnold S. R. , Spracklen D. V. , Williams J. , Yassaa N. , Sciare J. , Bonsang B. , Gros V. , Peeken I. , Lewis A. C. , Alvain S. , Moulin C.
Published: April 2010

Abstract. We have combined the first satellite maps of the global distribution of phytoplankton functional type and new measurements of phytoplankton-specific isoprene productivities, with available remote marine isoprene observations and a global model, to evaluate our understanding of the marine isoprene source and its impacts on organic aerosol abundances. Using satellite products to scale up data on phytoplankton-specific isoprene productivity to the global oceans, we infer a mean "bottom-up" oceanic isoprene emission of 0.31±0.08 (1σ) Tg/yr. By minimising the mean bias between the model and isoprene observations in the marine atmosphere remote from the continents, we produce a "top-down" oceanic isoprene source estimate of 1.9 Tg/yr. We suggest our reliance on limited atmospheric isoprene data, difficulties in simulating in-situ isoprene production rates in laboratory phytoplankton cultures, and limited knowledge of isoprene production mechanisms across the broad range of phytoplankton communities in the oceans under different environmental conditions as contributors to this difference between the two estimates. Inclusion of secondary organic aerosol (SOA) production from oceanic isoprene in the model with a 2% yield produces small contributions (0.01–1.4%) to observed organic carbon (OC) aerosol mass at three remote marine sites in the Northern and Southern Hemispheres. Based on these findings we suggest an insignificant role for isoprene in modulating remote marine aerosol abundances, giving further support to a recently postulated primary OC source in the remote marine atmosphere.
Seasonal variation of aerosol size distributions in the free troposphere and residual layer at the puy de Dôme station, France
Authors: Venzac H. , Sellegri K. , Villani P. , Picard D. , Laj P.
Published: April 2010

Abstract. Particle number concentration and size distribution are important variables needed to constrain the role of atmospheric particles in the Earth radiation budget, both directly and indirectly through CCN activation. They are also linked to regulated variables such as particle mass (PM) and therefore of interest to air quality studies. However, data on their long-term variability are scarce, in particular at high altitudes. In this paper, we investigate the diurnal and seasonal variability of the aerosol total number concentration and size distribution at the puy de Dôme research station (France, 1465 m a.s.l.). We report a variability of aerosol particle total number concentration measured over a five-year (2003–2007) period for particles larger than 10 nm and aerosol size distributions between 10 and 500 nm over a two-year period (January 2006 to December 2007). Concentrations show a strong seasonality with maxima during summer and minima during winter. A diurnal variation is also observed with maxima between 12:00 and 18:00 UTC. At night (00:00–06:00 UTC), the median hourly total concentration varies from 600 to 800 cm−3 during winter and from 1700 to 2200 cm−3 during summer. During the day (08:00–18:00 UTC), the concentration is in the range of 700 to 1400 cm−3 during winter and of 2500 to 3500 cm−3 during summer. An averaged size distribution of particles (10–500 nm) was calculated for each season. The total aerosol number concentrations are dominated by the Aitken mode integral concentrations, which drive most of the winter to summer total concentrations increase. The night to day increase in dominated by the nucleation mode integral number concentration. Because the site is located in the free troposphere only a fraction of the time, in particular at night and during the winter season, we have subsequently analyzed the variability for nighttime and free tropospheric (FT)/residual layer (RL) conditions only. We show that a seasonal variability is still observed for these FT/RL conditions. The FT/RL seasonal variation is due to both seasonal changes in the air mass origin from winter to summer and enhanced concentrations of particles in the residual layer/free troposphere in summer. The later observation can be explained by higher emissions intensity in the boundary layer, stronger exchanges between the boundary layer and the free troposphere as well as enhanced photochemical processes. Finally, aerosols mean size distributions are calculated for a given air mass type (marine/continental/regional) according to the season for the specific conditions of the residual layer/free troposphere. The seasonal variability in aerosol sources seems to be predominant over the continent compared to the seasonal variation of marine aerosol sources. These results are of regional relevance and can be used to constrain chemical-transport models over Western Europe.
Isoprene photooxidation: new insights into the production of acids and organic nitrates
Authors: Paulot F. , Crounse J. D. , Kjaergaard H. G. , Kroll J. H. , Seinfeld J. H. , Wennberg P. O.
Published: April 2010

Abstract. We describe a nearly explicit chemical mechanism for isoprene photooxidation guided by chamber studies that include time-resolved observation of an extensive suite of volatile compounds. We provide new constraints on the chemistry of the poorly-understood isoprene δ-hydroxy channels, which account for more than one third of the total isoprene carbon flux and a larger fraction of the nitrate yields. We show that the cis branch dominates the chemistry of the δ-hydroxy channel with less than 5% of the carbon following the trans branch. The modelled yield of isoprene nitrates is 12±3% with a large difference between the δ and β branches. The oxidation of these nitrates releases about 50% of the NOx. Methacrolein nitrates (modelled yield ~15±3% from methacrolein) and methylvinylketone nitrates (modelled yield ~11±3% yield from methylvinylketone) are also observed. Propanone nitrate, produced with a yield of 1% from isoprene, appears to be the longest-lived nitrate formed in the total oxidation of isoprene. We find a large molar yield of formic acid and suggest a novel mechanism leading to its formation from the organic nitrates. Finally, the most important features of this mechanism are summarized in a condensed scheme appropriate for use in global chemical transport models.
The impact of biogenic carbon sources on aerosol absorption in Mexico City
Authors: Marley N. A. , Gaffney J. S. , Tackett M. , Sturchio N. C. , Heraty L. , Martinez N. , Hardy K. D. , Marchany-Rivera A. , Guilderson T. , MacMillan A. , Steelman K.
Published: April 2010

Abstract. In order to determine the wavelength dependence of fine (<1 micron) atmospheric aerosol absorption in the Mexico City area, the absorption Ångstrom exponents (AAEs) were calculated from hourly averages of aerosol absorption measured at seven wavelengths (370, 450, 520, 590, 660, 880, and 950 nm) with an aethalometer during two field campaigns, the Mexico City Metropolitan Area study in April 2003 (MCMA 2003) and the Megacity Initiative: Local and Global Research Observations in March 2006 (MILAGRO). These results were compared to AAEs determined in the laboratory from 850–280 nm (350 points) on 12-h fine aerosol samples collected at the same sites. The aerosol AAEs varied from 0.76 to 1.5 in 2003 and from 0.63 to 1.4 in 2006. The AAE values determined in the afternoon were consistently higher than the corresponding morning values, suggesting the photochemical aging of the aerosols leading to the formation of more highly UV absorbing organic aerosol species in the afternoon. The AAE values were compared to stable and radiocarbon isotopic measurements of the 12-h aerosol samples to determine the sources of the aerosol carbon. The fraction of modern carbon (fM) in the aerosol samples, as determined from
An analytical inversion method for determining regional and global emissions of greenhouse gases: Sensitivity studies and application to halocarbons
Authors: Stohl A. , Seibert P. , Arduini J. , Eckhardt S. , Fraser P. , Greally B. R. , Lunder C. , Maione M. , Mühle J. , O'Doherty S. , Prinn R. G. , Reimann S. , Saito T. , Schmidbauer N. , Simmonds P. G. , Vollmer M. K. , Weiss R. F. , Yokouchi Y.
Published: April 2010

Abstract. A new analytical inversion method has been developed to determine the regional and global emissions of long-lived atmospheric trace gases. It exploits in situ measurement data from three global networks and builds on backward simulations with a Lagrangian particle dispersion model. The emission information is extracted from the observed concentration increases over a baseline that is itself objectively determined by the inversion algorithm. The method was applied to two hydrofluorocarbons (HFC-134a, HFC-152a) and a hydrochlorofluorocarbon (HCFC-22) for the period January 2005 until March 2007. Detailed sensitivity studies with synthetic as well as with real measurement data were done to quantify the influence on the results of the a priori emissions and their uncertainties as well as of the observation and model errors. It was found that the global a posteriori emissions of HFC-134a, HFC-152a and HCFC-22 all increased from 2005 to 2006. Large increases (21%, 16%, 18%, respectively) from 2005 to 2006 were found for China, whereas the emission changes in North America (−9%, 23%, 17%, respectively) and Europe (11%, 11%, −4%, respectively) were mostly smaller and less systematic. For Europe, the a posteriori emissions of HFC-134a and HFC-152a were slightly higher than the a priori emissions reported to the United Nations Framework Convention on Climate Change (UNFCCC). For HCFC-22, the a posteriori emissions for Europe were substantially (by almost a factor 2) higher than the a priori emissions used, which were based on HCFC consumption data reported to the United Nations Environment Programme (UNEP). Combined with the reported strongly decreasing HCFC consumption in Europe, this suggests a substantial time lag between the reported time of the HCFC-22 consumption and the actual time of the HCFC-22 emission. Conversely, in China where HCFC consumption is increasing rapidly according to the UNEP data, the a posteriori emissions are only about 40% of the a priori emissions. This reveals a substantial storage of HCFC-22 and potential for future emissions in China. Deficiencies in the geographical distribution of stations measuring halocarbons in relation to estimating regional emissions are also discussed in the paper. Applications of the inversion algorithm to other greenhouse gases such as methane, nitrous oxide or carbon dioxide are foreseen for the future.
Laboratory studies of ice formation pathways from ammonium sulfate particles
Authors: Wise M. E. , Baustian K. J. , Tolbert M. A.
Published: April 2010

Abstract. Cirrus clouds are composed of ice particles and their formation pathways have been studied extensively in the laboratory. The ability of ammonium sulfate particles to act as nuclei for cirrus clouds has been of particular importance because of their ubiquitous presence in the upper troposphere. The results of past laboratory experiments of homogeneous ice nucleation from ammonium sulfate particles show a wide range of freezing conditions. In the present study, a flow tube apparatus equipped with Fourier transform infrared spectroscopy was used to reexamine these discrepancies. It was found that when ammonium sulfate particles were preconditioned at 100% relative humidity (RH) prior to experimentation, the particles began to freeze at conditions predicted by the homogeneous ice nucleation model developed by Koop et al. (2000). If the particles were not preconditioned at 100% RH, some froze at warmer temperatures and lower ice saturation ratios than predicted by Koop et al. (2000). It is hypothesized that a population of effloresced particles affected freezing conditions for particles that were not preconditioned at 100% RH.
SCIAMACHY formaldehyde observations: constraint for isoprene emission estimates over Europe?
Authors: Dufour G. , Wittrock F. , Camredon M. , Beekmann M. , Richter A. , Aumont B. , Burrows J. P.
Published: April 2010

Abstract. Formaldehyde (HCHO) is an important intermediate compound in the degradation of volatile organic compounds (VOCs) in the troposphere. Sources of HCHO are largely dominated by its secondary production from VOC oxidation, methane and isoprene being the main precursors in unpolluted areas. As a result of the moderate lifetime of HCHO, its spatial distribution is determined by reactive hydrocarbon emissions. We focus here on Europe and investigate the influence of the different emissions on HCHO tropospheric columns with the CHIMERE chemical transport model in order to interpret the comparisons between SCIAMACHY and simulated HCHO columns. Europe was never specifically studied before for these purposes using satellite observations. The bias between measurements and model is less than 20% on average. The differences are discussed according to the errors on the model and the observations and remaining discrepancies are attributed to a misrepresentation of biogenic emissions. This study requires the characterisation of: (1) the model errors and performances concerning formaldehyde. The errors on the HCHO columns, mainly related to chemistry and mixed emission types, are evaluated to 2×1015 molecule/cm2 and the model performances evaluated using surface measurements are satisfactory (~13%); (2) the observation errors that define the needs in spatial and temporal averaging for meaningful comparisons. Using SCIAMACHY observations as constraint for biogenic isoprene emissions in an inverse modelling scheme reduces their uncertainties by about a factor of two in region of intense emissions. The retrieved correction factors for the isoprene emissions range from a factor of 0.15 (North Africa) to a factor of 2 (Poland, the United Kingdom) depending on the regions.
Operational climate monitoring from space: the EUMETSAT Satellite Application Facility on Climate Monitoring (CM-SAF)
Authors: Schulz J. , Albert P. , Behr H.-D. , Caprion D. , Deneke H. , Dewitte S. , Dürr B. , Fuchs P. , Gratzki A. , Hechler P. , Hollmann R. , Johnston S. , Karlsson K.-G. , Manninen T. , Müller R. , Reuter M. , Riihelä A. , Roebeling R. , Selbach N. , Tetzlaff A. , Thomas W. , Werscheck M. , Wolters E. , Zelenka A.
Published: April 2010

Abstract. The Satellite Application Facility on Climate Monitoring (CM-SAF) aims at the provision of satellite-derived geophysical parameter data sets suitable for climate monitoring. CM-SAF provides climatologies for Essential Climate Variables (ECV), as required by the Global Climate Observing System implementation plan in support of the UNFCCC. Several cloud parameters, surface albedo, radiation fluxes at the top of the atmosphere and at the surface as well as atmospheric temperature and humidity products form a sound basis for climate monitoring of the atmosphere. The products are categorized in monitoring data sets obtained in near real time and data sets based on carefully intercalibrated radiances. The CM-SAF products are derived from several instruments on-board operational satellites in geostationary and polar orbit as the Meteosat and NOAA satellites, respectively. The existing data sets will be continued using data from the instruments on-board the new joint NOAA/EUMETSAT Meteorological Operational Polar satellite. The products have mostly been validated against several ground-based data sets both in situ and remotely sensed. The accomplished accuracy for products derived in near real time is sufficient to monitor variability on diurnal and seasonal scales. The demands on accuracy increase the longer the considered time scale is. Thus, interannual variability or trends can only be assessed if the sensor data are corrected for jumps created by instrument changes on successive satellites and more subtle effects like instrument and orbit drift and also changes to the spectral response function of an instrument. Thus, a central goal of the recently started Continuous Development and Operations Phase of the CM-SAF (2007–2012) is to further improve all CM-SAF data products to a quality level that allows for studies of interannual variability.
Sensitivity of aerosol concentrations and cloud properties to nucleation and secondary organic distribution in ECHAM5-HAM global circulation model
Authors: Makkonen R. , Asmi A. , Korhonen H. , Kokkola H. , Järvenoja S. , Räisänen P. , Lehtinen K. E. J. , Laaksonen A. , Kerminen V.-M. , Järvinen H. , Lohmann U. , Bennartz R. , Feichter J. , Kulmala M.
Published: April 2010

Abstract. The global aerosol-climate model ECHAM5-HAM was modified to improve the representation of new particle formation in the boundary layer. Activation-type nucleation mechanism was introduced to produce observed nucleation rates in the lower troposphere. A simple and computationally efficient model for biogenic secondary organic aerosol (BSOA) formation was implemented. Here we study the sensitivity of the aerosol and cloud droplet number concentrations (CDNC) to these additions. Activation-type nucleation significantly increases aerosol number concentrations in the boundary layer. Increased particle number concentrations have a significant effect also on cloud droplet number concentrations and therefore on cloud properties. We performed calculations with activation nucleation coefficient values of 2×10−7s−1, 2×10−6s−1 and 2×10−5s−1 to evaluate the sensitivity to this parameter. For BSOA we have used yields of 0.025, 0.07 and 0.15 to estimate the amount of monoterpene oxidation products available for condensation. The hybrid BSOA formation scheme induces large regional changes to size distribution of organic carbon, and therefore affects particle optical properties and cloud droplet number concentrations locally. Although activation-type nucleation improves modeled aerosol number concentrations in the boundary layer, the use of a global activation coefficient generally leads to overestimation of aerosol number. Overestimation can also arise from underestimation of primary emissions.
Measurements of Pollution In The Troposphere (MOPITT) validation through 2006
Authors: Emmons L. K. , Edwards D. P. , Deeter M. N. , Gille J. C. , Campos T. , Nédélec P. , Novelli P. , Sachse G.
Published: April 2010

Abstract. Comparisons of aircraft measurements of carbon monoxide (CO) to the retrievals of CO using observations from the Measurements of Pollution in The Troposphere (MOPITT) instrument onboard the Terra satellite are presented. Observations made as part of the NASA INTEX-B and NSF MIRAGE field campaigns during March–May 2006 are used to validate the MOPITT CO retrievals, along with routine samples from 2001 through 2006 from NOAA and the MOZAIC measurements from commercial aircraft. A significant positive bias, around 20% for total column CO, in MOPITT CO was found in the comparison to in situ measurements during 2006. Comparisons to the long-term records of measurements from NOAA and MOZAIC revealed an increasing bias in the V3 MOPITT CO retrievals over time. The impact of an instrumental drift is illustrated through retrieval simulations.
Air-sea fluxes of biogenic bromine from the tropical and North Atlantic Ocean
Authors: Carpenter L. J. , Jones C. E. , Dunk R. M. , Hornsby K. E. , Woeltjen J.
Published: April 2010

Abstract. Air-sea fluxes and bulk seawater and atmospheric concentrations of bromoform (CHBr3) and dibromomethane (CH2Br2) were measured during two research cruises in the northeast Atlantic (53–59° N, June–July 2006) and tropical eastern Atlantic Ocean including over the African coastal upwelling system (16–35° N May–June 2007). Saturations and sea-air fluxes of these compounds generally decreased in the order coastal > upwelling > shelf > open ocean, and outside of coastal regions, a broad trend of elevated surface seawater concentrations with high chlorophyll-a was observed. We show that upwelling regions (coastal and equatorial) represent regional hot spots of bromocarbons, but are probably not of major significance globally, contributing at most a few percent of the total global emissions of CHBr3 and CH2Br2. From limited data from eastern Atlantic coastlines, we tentatively suggest that globally, coastal oceans (depth <180 m) together contribute ~2.5 (1.4–3.5) Gmol Br yr−1 of CHBr3, excluding influences from anthropogenic sources such as coastal power stations. This flux estimate is close to current estimates of the total open ocean source. We also show that the concentration ratio of CH2Br2/CHBr3 in seawater is a strong function of concentration (and location), with a lower CH2Br2/CHBr3 ratio found in coastal regions near to macroalgal sources.
Comparison of tropospheric gas-phase chemistry schemes for use within global models
Authors: Emmerson K. M. , Evans M. J.
Published: April 2010

Abstract. Methane and ozone are two important climate gases with significant tropospheric chemistry. Within chemistry-climate and transport models this chemistry is simplified for computational expediency. We compare the state of the art Master Chemical Mechanism (MCM) with six tropospheric chemistry schemes (CRI-reduced, GEOS-CHEM and a GEOS-CHEM adduct, MOZART-2, TOMCAT and CBM-IV) that could be used within composition transport models. We test the schemes within a box model framework under conditions derived from a composition transport model and from field observations from a regional scale pollution event. We find that CRI-reduced provides much skill in simulating the full chemistry, yet with greatly reduced complexity. We find significant variations between the other chemical schemes, and reach the following conclusions. 1) The inclusion of a gas phase N2O5+H2O reaction in one scheme and not others is a large source of uncertainty in the inorganic chemistry. 2) There are significant variations in the calculated concentration of PAN between the schemes, which will affect the long range transport of reactive nitrogen in global models. 3) The representation of isoprene chemistry differs hugely between the schemes, leading to significant uncertainties on the impact of isoprene on composition. 4) Differences are found in NO3 concentrations in the nighttime chemistry. Resolving these four issues through further investigative laboratory studies will reduce the uncertainties within the chemical schemes of global tropospheric models.
Large surface radiative forcing from topographic blowing snow residuals measured in the High Arctic at Eureka
Authors: Lesins G. , Bourdages L. , Duck T. J. , Drummond J. R. , Eloranta E. W. , Walden V. P.
Published: April 2010

Abstract. Ice crystals, also known as diamond dust, are suspended in the boundary layer air under clear sky conditions during most of the Arctic winter in Northern Canada. Occasionally ice crystal events can produce significantly thick layers with optical depths in excess of 2.0 even in the absence of liquid water clouds. Four case studies of high optical depth ice crystal events at Eureka in the Nunavut Territory of Canada during the winter of 2006/07 are presented. They show that the measured ice crystal surface infrared downward radiative forcing ranged from 8 to 36 W m−2 in the wavelength band from 5.6 to 20 μm for 532 nm optical depths ranging from 0.2 to 1.7. MODIS infrared and visible images and the operational radiosonde wind profile were used to show that these high optical depth events were caused by surface snow being blown off 600 to 800 m high mountain ridges about 20 to 30 km North-West of Eureka and advected by the winds towards Eureka as they settled towards the ground within the highly stable boundary layer. This work presents the first study that demonstrates the important role that surrounding topography plays in determining the occurrence of high optical depth ice crystal events from residual blowing snow that becomes a source of boundary layer ice crystals distinct from the classical diamond dust phenomenon.
Observation of nitrate coatings on atmospheric mineral dust particles
Authors: Li W. J. , Shao L. Y.
Published: April 2010

Abstract. Nitrate compounds have received much attention because of their ability to alter the hygroscopic properties and cloud condensation nuclei (CCN) activity of mineral dust particles in the atmosphere. However, very little is known about specific characteristics of ambient nitrate-coated mineral particles on an individual particle scale. In this study, sample collection was conducted during brown haze and dust episodes between 24 May and 21 June 2007 in Beijing, northern China. Sizes, morphologies, and compositions of 332 mineral dust particles together with their coatings were analyzed using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX) microanalyses. Structures of some mineral particles were verified using selected-area electron diffraction (SAED). TEM observation indicates that approximately 90% of the collected mineral particles are covered by visible coatings in haze samples whereas only 5% are coated in the dust sample. 92% of the analyzed mineral particles are covered with Ca-, Mg-, and Na-rich coatings, and 8% are associated with K- and S-rich coatings. The majority of coatings contain Ca, Mg, O, and N with minor amounts of S and Cl, suggesting that they are possibly nitrates mixed with small amounts of sulfates and chlorides. These nitrate coatings are strongly correlated with the presence of alkaline mineral components (e.g., calcite and dolomite). CaSO4 particles with diameters from 10 to 500 nm were also detected in the coatings including Ca(NO3)2 and Mg(NO3)2. Our results indicate that mineral particles in brown haze episodes were involved in atmospheric heterogeneous reactions with two or more acidic gases (e.g., SO2, NO2, HCl, and HNO3). Mineral particles that acquire hygroscopic nitrate coatings tend to be more spherical and larger, enhancing their light scattering and CCN activity, both of which have cooling effects on the climate.
A self-adapting and altitude-dependent regularization method for atmospheric profile retrievals
Authors: Ridolfi M. , Sgheri L.
Published: April 2010

Abstract. MIPAS is a Fourier transform spectrometer, operating onboard of the ENVISAT satellite since July 2002. The online retrieval algorithm produces geolocated profiles of temperature and of volume mixing ratios of six key atmospheric constituents: H2O, O3, HNO3, CH4, N2O and NO2. In the validation phase, oscillations beyond the error bars were observed in several profiles, particularly in CH4 and N2O. To tackle this problem, a Tikhonov regularization scheme has been implemented in the retrieval algorithm. The applied regularization is however rather weak in order to preserve the vertical resolution of the profiles. In this paper we present a self-adapting and altitude-dependent regularization approach that detects whether the analyzed observations contain information about small-scale profile features, and determines the strength of the regularization accordingly. The objective of the method is to smooth out artificial oscillations as much as possible, while preserving the fine detail features of the profile when related information is detected in the observations. The proposed method is checked for self consistency, its performance is tested on MIPAS observations and compared with that of some other regularization schemes available in the literature. In all the considered cases the proposed scheme achieves a good performance, thanks to its altitude dependence and to the constraints employed, which are specific of the inversion problem under consideration. The proposed method is generally applicable to iterative Gauss-Newton algorithms for the retrieval of vertical distribution profiles from atmospheric remote sounding measurements.
Peroxy radicals in the summer free troposphere: seasonality and potential for heterogeneous loss
Authors: Parker A. E. , Monks P. S. , Wyche K. P. , Balzani-Lööv J. M. , Staehelin J. , Reimann S. , Legreid G. , Vollmer M. K. , Steinbacher M.
Published: April 2010

Abstract. The sum of peroxy radicals (HO2+ΣiRiO2) and supporting trace gases were measured on the Jungfraujoch (3580 m a.s.l.) during the late summer of 2005. The period was marked by extended times of heavy snow which led to reduction in the observed peroxy radicals during the snowy periods that was greater than the concomitant reduction in j(O1D). In the limit a first order loss rate of 0.0063 s−1 can be derived for the peroxy radical loss in the snowy conditions that could be potentially ascribed to a heterogenous loss process. On snow free days photolysis of HCHO is shown to be a significant peroxy radical source. The seasonal trends of the peroxy radical concentrations have been mapped from the winter to summer transition in line with previous experiments. Net ozone production in late summer at the Jungfraujoch was net neutral to marginally ozone destructive. A value of 28±4 pptv is calculated for the ozone compensation point for the snow free days.
Reactions of isoprene and sulphoxy radical-anions – a possible source of atmospheric organosulphites and organosulphates
Authors: Rudziński K. J. , Gmachowski L. , Kuznietsova I.
Published: April 2010

Abstract. Transformation of isoprene coupled with auto-oxidation of SIV in aqueous solutions was studied experimentally and by chemical-kinetic modelling over a broad range of solution acidities (pH=3–9) to complement the research on aqueous-phase and heterogeneous transformation of isoprene reported recently by many laboratories. Isoprene significantly slowed down the auto-oxidation in acidic and basic solutions, and accelerated it slightly in neutral solutions. Simultaneously, production of sulphate ions and formation of solution acidity were significantly reduced. Formation of sulphite and sulphate derivatives of isoprene - sulphurous acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z=163), sulphurous acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z=165), sulphuric acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z=179), sulphuric acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z=181), and possible structural isomers of these species – was indicated by electrospray ionisation mass spectrometric analysis of post-reaction mixtures. The experimental results were explained by changes in a subtle quantitative balance of three superimposed processes whose rates depended in different manner on the acidity of reacting solutions – the scavenging of sulphoxy radical-anions by isoprene, the formation of sulphoxy radical-anions during further reactions of isoprene radicals, and the auto-oxidation of SIV itself. A chemical mechanism based on this idea was explored numerically to show good agreement with experimental data. In basic and neutral solutions, the model overestimated the consumption of isoprene, probably because reactions of primary sulphite and sulphate derivatives of isoprene with sulphoxy radical-anions were not included. Interaction of isoprene with sulphur(IV) species and oxygen can possibly result in formation of new organosulphate and organosulphite components of atmospheric aerosols and waters, and influence the distribution of reactive sulphur and oxygen species in isoprene-emitting organisms exposed to SIV pollutants.