bluuebunny/crossref_metadata_2025 huggingface dataset:
Hit from both sides: tracking industrial and volcanic plumes in Mexico City with surface measurements and OMI SO2 retrievals during the MILAGRO field campaign
Authors: de Foy B. , Bei N. , Herndon S. C. , Huey L. G. , Martínez A.-P. , Ruiz-Suárez L. G. , Wood E. C. , Zavala M. , Molina L. T.
Published: April 2010

Abstract. Large sulfur dioxide plumes were measured in the Mexico City Metropolitan Area (MCMA) during the MILAGRO field campaign. This paper seeks to identify the sources of these plumes and the meteorological processes that affect their dispersion in a complex mountain basin. Surface measurements of SO2 and winds are analysed in combination with radar wind profiler data to identify transport directions. Satellite retrievals of vertical SO2 columns from the Ozone Monitoring Instrument (OMI) reveal the dispersion from both the Tula industrial complex and the Popocatepetl volcano. Numerical simulations are used to identify possible transport scenarios. The analysis suggests that both Tula and Popocatepetl contribute to SO2 levels in the MCMA, sometimes on the same day due to strong vertical wind shear. The evaluation of simulations with known sources and pollutants suggests that the combination of observations and meteorological models will be useful in identifying sources and transport processes of other plumes observed during MILAGRO.
Cirrus clouds in a global climate model with a statistical cirrus cloud scheme
Authors: Wang M. , Penner J. E.
Published: April 2010

Abstract. A statistical cirrus cloud scheme that accounts for mesoscale temperature perturbations is implemented into a coupled aerosol and atmospheric circulation model to better represent both cloud fraction and subgrid-scale supersaturation in global climate models. This new scheme is able to better simulate the observed probability distribution of relative humidity than the scheme that was implemented in an older version of the model. Heterogeneous ice nuclei (IN) are shown to affect not only high level cirrus clouds through their effect on ice crystal number concentration but also low level liquid clouds through the moistening effect of settling and evaporating ice crystals. As a result, the change in the net cloud forcing is not very sensitive to the change in ice crystal concentrations associated with heterogeneous IN because changes in high cirrus clouds and low level liquid clouds tend to cancel. Nevertheless, the change in the net radiative flux at the top of the atmosphere due to changes in IN is still large because of changes in the greenhouse effect of water vapor caused by the changes in ice crystal number concentrations. Changes in the magnitude of the assumed mesoscale temperature perturbations by 25% alter the ice crystal number concentrations and radiative fluxes by an amount that is similar to that from a factor of 10 change in the heterogeneous IN number concentrations.
Bromoform and dibromomethane in the tropics: a 3-D model study of chemistry and transport
Authors: Hossaini R. , Chipperfield M. P. , Monge-Sanz B. M. , Richards N. A. D. , Atlas E. , Blake D. R.
Published: April 2010

Abstract. We have developed a detailed chemical scheme for the degradation of the short-lived source gases bromoform (CHBr3) and dibromomethane (CH2Br2) and implemented it in the TOMCAT/SLIMCAT three-dimensional (3-D) chemical transport model (CTM). The CTM has been used to predict the distribution of the two source gases (SGs) and 11 of their organic product gases (PGs). These first global calculations of the organic PGs show that their abundance is small. The longest lived organic PGs are CBr2O and CHBrO, but their peak tropospheric abundance relative to the surface vmr of the SGs is less than 5%. We calculate their mean local tropospheric lifetimes in the tropics to be ~7 and ~2 days (due to photolysis), respectively. Therefore, the assumption in previous modelling studies that SG degradation leads immediately to inorganic bromine seems reasonable. We have compared observed tropical SG profiles from a number of aircraft campaigns with various model experiments. In the tropical tropopause layer (TTL) we find that the CTM run using p levels and vertical winds from analysed divergence overestimates the abundance of CH2Br2, and to a lesser extent CHBr3, although the data is sparse and comparisons are not conclusive. Better agreement in the TTL is obtained in the run using θ levels and vertical motion from diabatic heating rates. Trajectory estimates of residence times in the two model versions confirm the more realistic transport in the θ-level version. In the p-level model even when we switch off convection we still find significant amounts of the SGs considered may reach the cold point; the stratospheric source gas injection is only reduced by ~16% for CHBr3 and ~2% for CH2Br2 without convection. Overall, the relative importance of the SG pathway and the PG pathway for transport of bromine to the stratosphere has been assessed. Assuming a 10-day washout lifetime of Bry we find the delivery of total Br from CHBr3 to be 0.72 pptv with ~53% of this coming from SGI. Similary, for CH2Br2 we find a total Br value of 1.69 pptv with ~94% coming from SGI. We infer that these species contribute ~2.4 pptv of inorganic bromine to the lower stratosphere with SGI being the dominant pathway.
Summertime contributions of isoprene, monoterpenes, and sesquiterpene oxidation to the formation of secondary organic aerosol in the troposphere over Mt. Tai, Central East China during MTX2006
Authors: Fu P. Q. , Kawamura K. , Pochanart P. , Tanimoto H. , Kanaya Y. , Wang Z. F.
Published: April 2010

Abstract. To better understand the contribution of biogenic volatile organic compounds to the formation of secondary organic aerosol (SOA) in high mountain regions, ambient aerosols were collected at the summit of Mt. Tai (1534 m, a.s.l.), Central East China (CEC) during the Mount Tai eXperiment 2006 campaign (MTX2006) in early summer. Biogenic SOA tracers of isoprene, monoterpenes, and β-caryophyllene oxidation products were measured using gas chromatography/mass spectrometry. All the biogenic SOA tracers showed no clear diurnal variations, suggesting that they are formed during long-range atmospheric transport. Although isoprene- and monoterpene-derived SOA tracers did not correlate with levoglucosan (a biomass burning tracer), β-caryophyllinic acid showed a good correlation with levoglucosan, indicating that biomass burning may be a source for this compound. Total concentrations of isoprene oxidation products are much higher than those of monoterpene and β-caryophyllene oxidation products. The ratio of isoprene to monoterpene oxidation products (Riso/mono) was found to co-vary with ozone and NOx during the summer campaign. The average Riso/mono value was 6.94 at daytime and 10.0 at nighttime. These values are among the highest in the aerosols studied in different regions, which may be due to the large isoprene fluxes, high O3 and NOx levels and relatively high OH concentrations in CEC. Using a tracer-based method, we estimated the average concentrations of secondary organic carbon (SOC) derived from isoprene, monoterpenes, and β-caryophyllene to be 1.76 μgC m−3 at daytime and 1.85 μgC m−3 at nighttime. These values correspond to 11.2% and 11.0% of the total OC concentrations, in which isoprene-derived SOC are 7.4% and 8.0% at day- and night-time, respectively. This study suggests that isoprene is a more significant precursor for biogenic SOA than monoterpenes and β-caryophyllene in high altitude in CEC.
Trend in ice moistening the stratosphere – constraints from isotope data of water and methane
Authors: Notholt J. , Toon G. C. , Fueglistaler S. , Wennberg P. O. , Irion F. W. , McCarthy M. , Scharringhausen M. , Rhee T. S. , Kleinböhl A. , Velazco V.
Published: April 2010

Abstract. Water plays a major role in the chemistry and radiative budget of the stratosphere. Air enters the stratosphere predominantly in the tropics, where the very low temperatures around the tropopause constrain water vapour mixing ratios to a few parts per million. Observations of stratospheric water vapour show a large positive long-term trend, which can not be explained by change in tropopause temperatures. Trends in the partitioning between vapour and ice of water entering the stratosphere have been suggested to resolve this conundrum. We present measurements of stratospheric H2O, HDO, CH4 and CH3D in the period 1991–2007 to evaluate this hypothesis. Because of fractionation processes during phase changes, the hydrogen isotopic composition of H2O is a sensitive indicator of changes in the partitioning of vapour and ice. We find that the seasonal variations of H2O are mirrored in the variation of the ratio of HDO to H2O with a slope of the correlation consistent with water entering the stratosphere mainly as vapour. The variability in the fractionation over the entire observation period is well explained by variations in H2O. The isotopic data allow to conclude that the trend in ice arising from particulate water is no more than 0.01±0.13 ppmv/decade in the observation period. Our observations suggest that between 1991 and 2007 the contribution from changes in particulate water transported through the tropopause plays only a minor role in altering in the amount of water entering the stratosphere.
Biomass burning aerosol emissions from vegetation fires: particle number and mass emission factors and size distributions
Authors: Janhäll S. , Andreae M. O. , Pöschl U.
Published: April 2010

Abstract. Aerosol emissions from vegetation fires have a large impact on air quality and climate. In this study, we use published experimental data and different fitting procedures to derive dynamic particle number and mass emission factors (EFPN, EFPM) related to the fuel type, burning conditions and the mass of dry fuel burned, as well as characteristic CO-referenced emission ratios (PN/CO, PM/CO). Moreover, we explore and characterize the variability of the particle size distribution of fresh smoke, which is typically dominated by a lognormal accumulation mode with count median diameter around 120 nm (depending on age, fuel and combustion efficiency), and its effect on the relationship between particle number and mass emission factors. For the particle number emission factor of vegetation fires, we found no dependence on fuel type and obtained the following parameterization as a function of modified combustion efficiency (MCE): EFPN=34·1015×(1-MCE) kg−1±1015 kg−1 with regard to dry fuel mass (d.m.). For the fine particle mass emission factors (EFPM) we obtained (86–85×MCE) g kg−1±3 g kg−1 as an average for all investigated fires; (93–90×MCE) g kg
Carbonyl sulfide exchange in a temperate loblolly pine forest grown under ambient and elevated CO2
Authors: White M. L. , Zhou Y. , Russo R. S. , Mao H. , Talbot R. , Varner R. K. , Sive B. C.
Published: April 2010

Abstract. Vegetation, soil and ecosystem level carbonyl sulfide (COS) exchange was observed at Duke Forest, a temperate loblolly pine forest, grown under ambient (Ring 1, R1) and elevated (Ring 2, R2) carbon dioxide (CO2). During calm meteorological conditions, ambient COS mixing ratios at the top of the forest canopy followed a distinct diurnal pattern in both CO2 growth regimes, with maximum COS mixing ratios during the day (R1=380±4 pptv and R2=373±3 pptv, daytime mean ±standard error) and minimums at night (R1=340±6 pptv and R2=346±5 pptv, nighttime mean ±standard error) reflecting a significant nighttime sink. Nocturnal vegetative uptake (−11 to −21 pmol m−2 s−1, negative values indicate uptake from the atmosphere) dominated nighttime net ecosystem COS flux estimates (−10 to −30 pmol m−2 s−1) in both CO2 regimes. In comparison, soil uptake (−0.8 to −1.7 pmol m−2 s−1) was a minor component of net ecosystem COS flux. In both CO2 regimes, loblolly pine trees exhibited substantial COS consumption overnight (50% of daytime rates) that was independent of CO2 assimilation. This suggests current estimates of the global vegetative COS sink, which assume that COS and CO2 are consumed simultaneously, may need to be reevaluated. Ambient COS mixing ratios, species specific diurnal patterns of stomatal conductance, temperature and canopy position were the major factors influencing the vegetative COS flux at the branch level. While variability in branch level vegetative COS consumption measurements in ambient and enhanced CO2 environments could not be attributed to CO2 enrichment effects, estimates of net ecosystem COS flux based on ambient canopy mixing ratio measurements suggest less nighttime uptake of COS in R2, the CO2 enriched environment.
Aerosol number fluxes over the Amazon rain forest during the wet season
Authors: Ahlm L. , Nilsson E. D. , Krejci R. , Mårtensson E. M. , Vogt M. , Artaxo P.
Published: April 2010

Abstract. Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt=2.4×10−3·u∗ where u∗ is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, primary aerosol emission had a limited impact on the total aerosol number population in this study, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. It seems that a significant contribution of secondary aerosol particles to the aerosol population is the most reasonable explanation for the net downward flux. This is an indication that secondary aerosol particles may dominate the aerosol number population in the Amazon boundary layer and that the contribution of primary aerosol particles may be low in terms of numbers. However, aerosol flux measurements should be repeated in a more remote area of the Amazon with less influence from anthropogenic sources before any final conclusions may be drawn.
Comparison of in situ and columnar aerosol spectral measurements during TexAQS-GoMACCS 2006: testing parameterizations for estimating aerosol fine mode properties
Authors: Atkinson D. B. , Massoli P. , O'Neill N. T. , Quinn P. K. , Brooks S. , Lefer B.
Published: April 2010

Abstract. During the 2006 Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS-GoMACCS 2006), the optical, chemical and microphysical properties of atmospheric aerosols were measured on multiple mobile platforms and at ground based stations. In situ measurements of the aerosol light extinction coefficient (σep) were performed by two multi-wavelength cavity ring-down (CRD) instruments, one located on board the NOAA R/V Ronald H. Brown (RHB) and the other located at the University of Houston, Moody Tower (UHMT). An AERONET sunphotometer was also located at the UHMT to measure the columnar aerosol optical depth (AOD). The σep data were used to extract the extinction Ångström exponent (åep), a measure of the wavelength dependence of σep. There was general agreement between the åep (and to a lesser degree σep measurements by the two spatially separated CRD instruments during multi-day periods, suggesting a regional scale consistency of the sampled aerosols. Two spectral models are applied to the σep and AOD data to extract the fine mode fraction of extinction (η) and the fine mode effective radius (Reff f). These two parameters are robust measures of the fine mode contribution to total extinction and the fine mode size distribution respectively. The results of the analysis are compared to Reff f values extracted using AERONET V2 retrievals and calculated from in situ particle size measurements on the RHB and at UHMT. During a time period when fine mode aerosols dominated the extinction over a large area extending from Houston/Galveston Bay and out into the Gulf of Mexico, the various methods for obtaining Reff f agree qualitatively (showing the same temporal trend) and quantitatively (pooled standard deviation=28 nm).
Initial fate of fine ash and sulfur from large volcanic eruptions
Authors: Niemeier U. , Timmreck C. , Graf H.-F. , Kinne S. , Rast S. , Self S.
Published: April 2010

Abstract. Large volcanic eruptions emit huge amounts of sulfur and fine ash into the stratosphere. These products cause an impact on radiative processes, temperature and wind patterns. In simulations with a General Circulation Model including detailed aerosol microphysics, the relation between the impact of sulfur and fine ash is determined for different eruption strengths and locations, one in the tropics and one in high Northern latitudes. Fine ash with effective radii between 1 μm and 15 μm has a lifetime of several days only. Nevertheless, the strong absorption of shortwave and longwave radiation causes additional heating and cooling of ±20 K/day and impacts the evolution of the volcanic cloud. Depending on the location of the volcanic eruption, transport direction changes due to the presence of fine ash, vortices develop and temperature anomalies at ground increase. The results show substantial impact on the local scale but only minor impact on the evolution of sulfate in the stratosphere in the month after the simulated eruptions.
Influence of ice particle model on retrieving cloud optical thickness from satellite measurements: model comparison and implication for climate study
Authors: Zhang Z. , Yang P. , Kattawar G. , Riedi J. , Labonnote L. C. , Baum B. , Platnick S. , Huang H.-L.
Published: April 2010

Abstract. The influence is investigated of the assumed ice particle microphysical and optical model on inferring ice cloud optical thickness (τ) from satellite measurements of the Earth's reflected shortwave radiance. Ice cloud τ are inferred, and subsequently compared, using products from MODIS (MODerate resolution Imaging Spectroradiometer) and POLDER (POLarization and Directionality of the Earth's Reflectances). POLDER τ values are found to be substantially smaller than those from collocated MODIS data. It is shown that this difference is caused primarily by the use of different ice particle bulk scattering models in the two retrievals, and more specifically, the scattering phase function. Furthermore, the influence of the ice particle model on the derivation of ice cloud radiative forcing (CRF) from satellite retrievals is studied. Three sets of shortwave CRF are calculated using different combinations of the retrieval and associated ice particle models. It is shown that the uncertainty associated with an ice particle model may lead to two types of errors in estimating CRF from satellite retrievals. One stems from the retrieval itself and the other is due to the optical properties, such as the asymmetry factor, used for CRF calculations. Although a comparison of the CRFs reveals that these two types of errors tend to cancel each other, significant differences are still found between the three CRFs, which indicates that the ice particle model affects not only optical thickness retrievals but also CRF calculations. In addition to CRF, the effect of the ice particle model on the derivation of seasonal variation of τ from satellite measurements is discussed. It is shown that optical thickness retrievals based on the same MODIS observations, but derived using different assumptions of the ice particle model, can be substantially different. These differences can be divided into two parts. The first-order difference is mainly caused by the differences in the asymmetry factor. The second-order difference is related to seasonal changes in the sampled scattering angles and therefore dependent on the sun-satellite viewing geometry. Because of this second-order difference, the use of different ice particle models may lead to a different understanding of the seasonal variation of τ.
Measurements of OH and HO2 yields from the gas phase ozonolysis of isoprene
Authors: Malkin T. L. , Goddard A. , Heard D. E. , Seakins P. W.
Published: April 2010

Abstract. The reactions of ozone with alkenes are an important source of hydroxyl (OH) radicals; however, quantification of their importance is hindered by uncertainties in the absolute OH yield. Hydroxyl radical yields for the gas-phase ozonolysis of isoprene are determined in this paper by four different methods: (1) The use of cyclohexane as an OH scavenger, and the production of cyclohexanone, (2) The use of 1,3,5-trimethylbenzene as an OH tracer, and the diminution in its concentration, (3) A kinetic method in which the OH yield was obtained by performing a series of pseudo-first-order experiments in the presence or absence of an OH scavenger (cyclohexane), (4) The OH and HO2 yields were determined by fitting the temporal OH and HO2 profiles following direct detection of absolute OH and HO2 concentrations by laser induced fluorescence at low pressure (Fluorescence Assay by Gas Expansion-FAGE). The following OH yields for the ozonolysis of isoprene were obtained, relative to alkene consumed, for each method: (1) Scavenger (0.25 ± 0.04), (2) Tracer (0.25 ± 0.03), (3) Kinetic study (0.27 ± 0.02), and (4) Direct observation (0.26 ± 0.02), the error being one standard deviation. An averaged OH yield of 0.26 ± 0.02 is recommended at room temperature and atmospheric pressure and this result is compared with recent literature determinations. The HO2 yield was directly determined for the first time using FAGE to be 0.26 ± 0.03.
Seasonal climate and air quality simulations for the northeastern US – Part 1: Model evaluation
Authors: Mao H. , Chen M. , Hegarty J. D. , Talbot R. W. , Koermer J. P. , Thompson A. M. , Avery M. A.
Published: April 2010

Abstract. Regional climate and air quality simulations were conducted for summers 2001–2005 in the eastern US and subjected to extensive evaluation using various ground and airborne measurements. Climate evaluation focused on transport by comparing modeled dominant map types with ones from reanalysis. Reasonable agreement was found for their frequency of occurrence and distinctness of circulation patterns. The two most frequent map types from reanalysis were the Bermuda High (22%) and passage of a Canadian cold frontal over the northeastern US (20%). The model captured their frequency of occurrence at 25% and 18% respectively. The simulated five average distributions of daily 1-h ozone (O3) daily maxima using the Community Multiscale Air Quality (CMAQ) modeling system reproduced salient features in observations. This suggests that the ability of the regional climate model to depict transport processes accurately is critical for reasonable simulations of surface O3. Comparison of mean bias, root mean square error, and index of agreement for CMAQ summer surface 8-h O3 daily maxima and observations showed −0.6±14 nmol/mol, 14 nmol/mol, and 71% respectively. CMAQ performed best in moderately polluted conditions and less satisfactorily in highly polluted ones. This highlights the common problem of overestimating/underestimating lower/higher modeled O3 levels. Diagnostic analysis suggested that significant overestimation of inland nighttime low O3 mixing ratios may be attributed to underestimates of nitric oxide (NO) emissions at night. The absence of the second daily peak in simulations for the Appledore Island marine site possibly resulted from coarse grid resolution misrepresentation of land surface type. Comparison with shipboard measurements suggested that CMAQ has an inherent problem of underpredicting O3 levels in continental outflow. Modeled O3 vertical profiles exhibited a lack of structure indicating that key processes missing from CMAQ, such as lightning produced NO and stratospheric intrusions, are important for accurate upper tropospheric representations.
Annual cycle of ozone at and above the tropical tropopause: observations versus simulations with the Chemical Model of the Stratosphere (CLaMS)
Authors: Konopka P. , Grooß J.-U. , Günther G. , Plöger F. , Pommrich R. , Müller R. , Livesey N.
Published: April 2010

Abstract. Multi-annual simulations with the Chemical Model of the Stratosphere (CLaMS) are used to study the seasonality of O3 and of the mean age within the stratospheric part of the tropical tropopause layer (TTL) In agreement with satellite (HALOE) and in-situ observations (SHADOZ), CLaMS simulations show above ≈360 K potential temperature, a pronounced annual cycle in O3 and in the mean age of air with highest values in the late boreal summer. Within the model, this seasonality is driven by the seasonality of both upwelling and in-mixing. The latter process describes enhanced meridional transport from the extratropics into the TTL. The strongest in-mixing occurs from the Northern Hemisphere during the boreal summer in the potential temperature range between 380 and 420 K. Contrary, an increase of upwelling with highest values in winter reduces O3 up to the lowest values in early spring. Both, CLaMS simulations and Aura MLS O3 observations show that this enhanced equatorward transport in summer is mainly driven by the Asian monsoon anticyclone.
Effect of surface reaction on the cloud nucleating properties of mineral dust: AMMA aircraft campaign in summer 2006
Authors: Matsuki A. , Schwarzenboeck A. , Venzac H. , Laj P. , Crumeyrolle S. , Gomes L.
Published: April 2010

Abstract. In order to gain insights into the characteristics of the mineral dust fraction which actually serves as cloud condensation nuclei (CCN) including the related cloud processing, this study proceeded to directly collect CCN and compare their mixing states with that of the clear-sky aerosol particles. To pursue this goal, the French ATR-42 research aircraft equipped both with a counterflow virtual impactor (CVI) and community aerosol inlet was deployed in Niamey, Niger (13°30´ N, 02°30´ E) in August 2006 during one of the special observation periods (SOP) of the African Monsoon Multidisciplinary Analysis (AMMA) project. Both cloud residual and clear-sky particles were collected separately and later analyzed individually using transmission electron microscope (TEM) and scanning electron microscope coupled with energy dispersive X-ray spectroscopy (SEM-EDX). The analysis revealed interesting characteristics on the coarse dust particles (Dp>1 μm), particularly those which likely had acted as CCN. Traces of heterogeneously formed secondary sulfate, chloride and nitrate were found on many dust particles. These secondary species were particularly enhanced in clouds (i.e. cloud processing). The study illustrates that carbonates (Calcite, Dolomite) contained the secondary species in significantly larger frequency and amount than the silicates (Quartz, Feldspar, Mica, Clay), confirming that carbonates represent the most reactive fraction of the mineral dust. Surprisingly large fraction of the carbonate particles were already found in deliquesced form even in clear-sky conditions, most probably reflecting their extreme hygroscopicity following the reaction with HNO3 gas. There were also some indications that the large carbonate particles may be acting primarily as CCN under very low supersaturations, unless there is sufficient hygroscopic coatings on the silicates particles.
Modeling the transport of very short-lived substances into the tropical upper troposphere and lower stratosphere
Authors: Aschmann J. , Sinnhuber B. M. , Atlas E. L. , Schauffler S. M.
Published: April 2010

Abstract. The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.
Increase of upper troposphere/lower stratosphere wave baroclinicity during the second half of the 20th century
Authors: Castanheira J. M. , Añel J. A. , Marques C. A. F. , Antuña J. C. , Liberato M. L. R. , de la Torre L. , Gimeno L.
Published: April 2010

Abstract. A strengthening of the equatorward temperature gradient in the upper troposphere/lower stratosphere (UTLS), at subtropics and midlatitudes, is consistently reproduced in several modelling studies of the atmospheric response to the increase of greenhouse gas radiative forcing. Some of those studies suggest an increase of the baroclinicity in the UTLS region because of the enhanced meridional temperature gradient. This study presents observational evidence of an increase of UTLS wave baroclinicity, during the second half of the 20th century. The evidence is given by significant positive trends in the energy of baroclinic normal modes of the NCEP/NCAR reanalysis, and significant positive trends in the eddy available potential energy of the ERA-40 reanalysis as well as in the eddy available potential energy of the JRA-25 reanalysis. Significant positive trends in the frequency of double tropopause events in radiosonde data are also interpreted as a manifestation of an increase of the UTLS wave baroclinicity.
The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 1: The role of the easterly wave critical layer
Authors: Montgomery M. T. , Lussier III L. L. , Moore R. W. , Wang Z.
Published: April 2010

Abstract. An observational and real-time model forecast study of the genesis of Typhoon Nuri during the Tropical Cyclone Structure 2008 (TCS-08) field campaign in the western North Pacific sector is presented. Analysis and observational data show that the surrounding base state flow was an easterly trade wind flow and the precursor disturbance to Typhoon Nuri was an easterly wave that originated in the ITCZ in the Central Pacific and can be tracked more than 10 days prior to tropical storm formation. An overview of the field data is presented here using a newly proposed dynamical framework for tropical cyclone formation within the critical layer of an easterly wave. Despite propagating through a hostile environment ripe with strong vertical wind shear and relatively dry air, the easterly wave critical layer protected the proto-vortex and allowed it to gestate until it reached a more favorable environment. Within this protective "Kelvin's cat's eye flow" located within the wave's critical layer existed a "sweet spot", defined as the intersection between the wave trough and critical latitude, which was the preferred location for tropical cyclogenesis. Global Forecast System Final Analyses and IR satellite imagery, which shows convective bands wrapping around the sweet spot as genesis nears, confirm that this sweet spot is the location where Typhoon Nuri's dominant low-level circulation emerges. United States Air Force C130 and Naval Research Laboratory P3 research flights on 16 and 17 August collected flight-level, dropwindsonde, and Doppler radar data that allowed an evaluation of the dynamic and thermodynamic processes within the cat's eye. The dropwindsonde analyses identified the precursor easterly wave disturbance on 16 August and identified an area of weak low-level cyclonic circulation on 17 August. During the TCS-08 experiment "real-time forecasts" were produced in real-time using operational global prediction model data to support scientific missions. These forecasts were found to be useful in flight planning discussions and predicted Nuri's genesis latitude within 1.5° 72 h in advance.
Constraint of anthropogenic NOx emissions in China from different sectors: a new methodology using multiple satellite retrievals
Authors: Lin J.-T. , McElroy M. B. , Boersma K. F.
Published: April 2010

Abstract. A new methodology is developed to constrain Chinese anthropogenic emissions of nitrogen oxides (NOx) from four major sectors (industry, power plants, mobile and residential) in July 2008. It combines tropospheric NO2 column retrievals from GOME-2 and OMI, taking advantage of their different passing time over China (9:30 a.m. local time versus 1:30 p.m.), and explicitly accounts for diurnal variations in anthropogenic emissions of NOx as well as their tropospheric lifetime and column concentrations. The approach is based on the daytime variation of NOx (when its lifetime is relatively short) alone; and potential errors in inverse modeling by neglecting horizontal transport are minimized. Separation of anthropogenic sectors relies on the estimated diurnal profiles and budget uncertainties. Our best top-down estimate suggests a national budget of 6.8 Tg N/yr (5.5 Tg N/yr for East China), close to the a priori bottom-up emission estimate from the INTEX-B mission. The top-down emissions are lower than the a priori near Beijing, in the northeastern provinces and along the east coast; yet they exceed the a priori over many inland regions. Systematic errors in satellite retrievals are estimated to lead to underestimation of top-down emissions by at most 17% (most likely 10%). Effects of other factors on the top-down estimate are typically less than 15%, including lightning, soil emissions, mixing in planetary boundary layer, anthropogenic emissions of carbon monoxide and volatile organic compounds, assumptions on emission diurnal variations, and uncertainties in the four sectors. The a posteriori emission budget is 5.7 Tg N/yr for East China.
Modelling surface ozone during the 2003 heat wave in the UK
Authors: Vieno M. , Dore A. J. , Stevenson D. S. , Doherty R. , Heal M. R. , Reis S. , Hallsworth S. , Tarrason L. , Wind P. , Fowler D. , Simpson D. , Sutton M. A.
Published: April 2010

Abstract. A high resolution (5×5 km2) UK-scale chemistry-transport model (EMEP4UK) is used to study ground-level ozone (O3) during the August 2003 heat-wave. Meteorology is generated by the Weather Research and Forecast (WRF) model, nudged every six hours with reanalysis data. We focus on SE England, where hourly average O3 reached up to 140 ppb during the heat-wave. EMEP4UK accurately reproduces observed annual and diurnal cycles of surface O3 at urban and rural sites. Elevated O3 and much of its day-to-day variability during the heat-wave are well captured. Key O3 precursors, nitrogen dioxide and isoprene (C5H8), are less well simulated, but show generally accurate diurnal cycles and concentrations to within a factor of ~2–3 of observations. The modelled surface O3 distribution has an intricate spatio-temporal structure, governed by a combination of meteorology, emissions and photochemistry. A series of sensitivity runs with the model are used to explore the factors that influenced O3 levels during the heat-wave. Various factors appear to be important on different days and at different sites. Ozone imported from outside the model domain, especially the south, is very important on several days during the heat-wave, contributing up to 85 ppb. Dry deposition of O3, when completely switched off, elevated simulated O3 by up to 50 ppb, and this may have been an important factor on several days. Modelled C5H8 concentrations are generally best simulated if C5H8 emissions are changed from the base emissions: typically doubled, but elevated by up to a factor of five on some days. Accurately modelling the exact positions of individual plumes of anthropogenically emitted nitrogen oxides and volatile organic compounds is crucial for the successful simulation of O3 at a particular time and location. Variations in surface temperature of ±5 K were found to have impacts on O3 of typically less than ±10 ppb.
A semi-analytical solution for the mean wind profile in the Atmospheric Boundary Layer: the convective case
Authors: Buligon L. , Degrazia G. A. , Acevedo O. C. , Szinvelski C. R. P. , Goulart A. G. O.
Published: April 2010

Abstract. A novel methodology to derive the average wind profile from the Navier-Stokes equations is presented. The development employs the Generalized Integral Transform Technique (GITT), which joints series expansions with Integral Transforms. The new approach provides a solution described in terms of the quantities that control the wind vector with height. Parameters, such as divergence and vorticity, whose magnitudes represent sinoptic patterns are contained in the semi-analytical solution. The results of this new method applied to the convective boundary layer are shown to agree with wind data measured in Wangara experiment.
Assessment of parameters describing representativeness of air quality in-situ measurement sites
Authors: Henne S. , Brunner D. , Folini D. , Solberg S. , Klausen J. , Buchmann B.
Published: April 2010

Abstract. The atmospheric layer closest to the ground is strongly influenced by variable surface fluxes (emissions, surface deposition) and can therefore be very heterogeneous. In order to perform air quality measurements that are representative of a larger domain or a certain degree of pollution, observatories are placed away from population centres or within areas of specific population density. Sites are often categorised based on subjective criteria that are not uniformly applied within different administrative domains. A novel approach for the assessment of parameters reflecting site representativeness is presented here, taking emissions, deposition and transport towards 34 sites covering Western and Central Europe into account. These parameters are directly inter-comparable among the sites and can be used to select sites that are, on average, more or less suitable for data assimilation and comparison with satellite and model data. Advection towards these sites was simulated by backward Lagrangian Particle Dispersion Modelling (LPDM) to determine the sites' annual catchment areas for the year 2005 and advection times of 12, 24 and 48 h. Only variations caused by emissions and transport during these periods were considered assuming that these dominate the short-term variability of most but especially short lived trace gases. The parameters of representativeness derived were compared between sites and a novel, uniform and observation-independent categorisation of the sites based on a clustering approach was established. Six groups of European background sites were identified ranging from very remote coastal to polluted rural sites. These six categories explained 50 to 80% of the inter-site variability of median mixing ratios and their standard deviation for NO2 and O3, while differences between group means of the longer lived trace gas CO were insignificant. The derived annual catchment areas strongly depended on the applied LPDM and input wind fields, the catchment settings and the year of analysis. Nevertheless, the parameters of representativeness showed considerably less variability than the catchment geometry, supporting the robustness of the derived station categorisation.
First remote sensing measurements of ClOOCl along with ClO and ClONO2 in activated and deactivated Arctic vortex conditions using new ClOOCl IR absorption cross sections
Authors: Wetzel G. , Oelhaf H. , Kirner O. , Ruhnke R. , Friedl-Vallon F. , Kleinert A. , Maucher G. , Fischer H. , Birk M. , Wagner G. , Engel A.
Published: April 2010

Abstract. Active chlorine species play a dominant role in the catalytic destruction of stratospheric ozone in the polar vortices during the late winter and early spring seasons. Recently, the correct understanding of the ClO dimer cycle was challenged by the release of new laboratory absorption cross sections (Pope et al., 2007) yielding significant model underestimates of observed ClO and ozone loss (von Hobe et al., 2007). Under this aspect, Arctic stratospheric limb emission measurements carried out by the balloon version of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-B) from Kiruna (Sweden) on 11 January 2001 and 20/21 March 2003 have been reanalyzed with regard to the chlorine reservoir species ClONO2 and the active species, ClO and ClOOCl (Cl2O2). New laboratory measurements of IR absorption cross sections of ClOOCl for various temperatures and pressures allowed for the first time the retrieval of ClOOCl mixing ratios from remote sensing measurements. High values of active chlorine (ClOx) of roughly 2.3 ppbv at 20 km were observed by MIPAS-B in the cold mid-winter Arctic vortex on 11 January 2001. While nighttime ClOOCl shows enhanced values of nearly 1.1 ppbv at 20 km, ClONO2 mixing ratios are less than 0.1 ppbv at this altitude. In contrast, high ClONO2 mixing ratios of nearly 2.4 ppbv at 20 km have been observed in the late winter Arctic vortex on 20 March 2003. No significant ClOx amounts are detectable on this date since most of the active chlorine has already recovered to its main reservoir species ClONO2. The observed values of ClOx and ClONO2 are in line with the established chlorine chemistry. The thermal equilibrium constants between the dimer formation and its dissociation, as derived from the balloon measurements, are on the lower side of reported data and in good agreement with values recommended by von Hobe et al. (2007). Calculations with the ECHAM/MESSy Atmospheric Chemistry model (EMAC) using established kinetics show similar chlorine activation and deactivation, compared to the measurements in January 2001 and March 2003, respectively.
Evidence of the impact of deep convection on reactive volatile organic compounds in the upper tropical troposphere during the AMMA experiment in West Africa
Authors: Bechara J. , Borbon A. , Jambert C. , Colomb A. , Perros P. E.
Published: April 2010

Abstract. A large dataset of reactive trace gases was collected for the first time over West Africa during the African Monsoon Multidisciplinary Analysis (AMMA) field experiment in August 2006. Volatile Organic Compounds (VOC from C5–C9) were measured onboard the two French aircrafts the ATR-42 and the Falcon-20 by a new instrument AMOVOC. The goal of this study is (i) to characterize VOC distribution in the tropical region of West Africa (ii) to determine the impact of deep convection on VOC distribution and chemistry in the tropical upper troposphere (UT) and (iii) to characterize its spatial and temporal extensions. Experimental strategy consisted in sampling at altitudes between 0 and 12 km downwind of Mesoscale Convective Systems (MCS) and at cloud base. Biogenic and anthropogenic VOC distribution in West Africa is clearly affected by North to South emission gradient. Isoprene, the most abundant VOC, is at maximum level over the forest (1.26 ppb) while benzene reaches its maximum over the urban areas (0.11 ppb). First, a multiple physical and chemical tracers approach using CO, O3 and relative humidity was implemented to distinguish between convective and non-convective air masses. Then, additional tools based on VOC observations (tracer ratios, proxy of emissions and photochemical clocks) were adapted to characterize deep convection on a chemical, spatial and temporal basis. VOC vertical profiles show a "C-shaped" trend indicating that VOC-rich air masses are transported from the surface to the UT by deep convective systems. VOC mixing ratios in convective outflow are up to two times higher than background levels even for reactive and short-lived VOC (e.g. isoprene up to 0.19 ppb at 12 km-altitude) and are dependent on surface emission type. As a consequence, UT air mass reactivity increases from 0.52 s−1 in non-convective conditions to 0.95 s−1 in convective conditions. Fractions of boundary layer air contained in convective outflow are estimated to be 40±15%. Vertical transport timescale is calculated to be 25±10 min. These results characterize deep convection occurring over West Africa and provide relevant information for tropical convection parameterization in regional/global models.
Light absorption by organic carbon from wood combustion
Authors: Chen Y. , Bond T. C.
Published: April 2010

Abstract. Carbonaceous aerosols affect the radiative balance of the Earth by absorbing and scattering light. While BC is highly absorbing, some organic compounds also have significant absorption, which is greater at near-ultraviolet and blue wavelengths. To the extent that OC absorbs visible light, it may be a non-negligible contributor to direct aerosol radiative forcing. In this work, we examine absorption by primary OC emitted from solid fuel pyrolysis. We provide absorption spectra of this material, which can be related to the imaginary refractive index. This material has polar character but is not fully water-soluble: more than 92% was extractable by methanol or acetone, compared with 73% for water and 52% for hexane. Water-soluble organic carbon contributed to light absorption at both ultraviolet and visible wavelengths. However, a larger portion came from organic carbon that is extractable only by methanol. The spectra of water-soluble organic carbon are similar to others in the literature. We compared spectra for material generated with different wood type, wood size and pyrolysis temperature. Higher wood temperature is the main factor creating organic aerosol with higher absorption, causing about a factor of four increase in mass-normalized absorption at visible wavelengths. A simple model suggests that, despite the absorption, both high-temperature and low-temperature carbon have negative climate forcing over a surface with average albedo.
Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus
Authors: Jensen E. J. , Pfister L. , Bui T.-P. , Lawson P. , Baumgardner D.
Published: April 2010

Abstract. In past modeling studies, it has generally been assumed that the predominant mechanism for nucleation of ice in the uppermost troposphere is homogeneous freezing of aqueous aerosols. However, recent in situ and remote-sensing measurements of the properties of cirrus clouds at very low temperatures in the tropical tropopause layer (TTL) are broadly inconsistent with theoretial predictions based on the homogeneous freezing assumption. The nearly ubiquitous occurence of gravity waves in the TTL makes the predictions from homogeneous nucleation theory particularly difficult to reconcile with measurements. These measured properties include ice number concentrations, which are much lower than theory predicts; ice crystal size distributions, which are much broader than theory predicts; and cloud extinctions, which are much lower than theory predicts. Although other explanations are possible, one way to limit ice concentrations is to have on the order of 50 L−1 effective ice nuclei (IN) that could nucleate ice at relatively low supersaturations. We suggest that ammonium sulfate particles, which would be dry much of the time in the cold TTL, are a potential IN candidate for TTL cirrus. Possible implications of the observed cloud microphysical properties for ice sedimentation, dehydration, and cloud persistence are also discussed.