bluuebunny/crossref_metadata_2025 huggingface dataset:
Retrieval of stratospheric and tropospheric BrO profiles and columns using ground-based zenith-sky DOAS observations at Harestua, 60° N
Authors: Hendrick F. , Van Roozendael M. , Chipperfield M. P. , Dorf M. , Goutail F. , Yang X. , Fayt C. , Hermans C. , Pfeilsticker K. , Pommereau J.-P. , Pyle J. A. , Theys N. , De Mazière M.
Published: April 2010

Abstract. A profiling algorithm based on the optimal estimation method is applied to ground-based zenith-sky UV-visible measurements from Harestua, Southern Norway (60° N, 11° E) in order to retrieve BrO vertical profiles. The sensitivity of the zenith-sky observations to the tropospheric BrO detection is increased by using for the spectral analysis a constant reference spectrum corresponding to clear-sky noon summer conditions. The information content and retrieval errors are characterized and it is shown that the retrieved stratospheric profiles and total columns are consistent with correlative balloon and satellite observations, respectively. Tropospheric BrO columns are derived from profiles retrieved at 80° solar zenith angle during sunrise and sunset for the 2000–2006 period. They show a marked seasonality with mean column value ranging from 1.52±0.51×1013 molec/cm2 in late winter/early spring to 0.92±0.31×1013 molec/cm2 in summer, which corresponds to 1.0±0.3 and 0.6±0.2 pptv, respectively, if we assume that BrO is uniformly mixed in the troposphere. These column values are also consistent with previous estimates made from balloon, satellite, and other ground-based observations. Daytime (10h30 local time) tropospheric BrO columns are compared to the p-TOMCAT 3-D tropospheric chemical transport model (CTM) for the 2002–2003 period. p-TOMCAT shows a good agreement with the retrieved columns except in late winter/early spring where an underestimation by the model is obtained. This feature could be explained by the non-inclusion of sea-ice bromine sources in the current version of p-TOMCAT, which can therefore not reproduce the possible transport from the polar region to Harestua of air-masses with enhanced BrO concentration due to bromine explosion events in late winter/early spring. The corresponding daytime stratospheric BrO columns are compared to the SLIMCAT 3-D stratospheric CTM. The model run used, which assumes 21.2 pptv for the Bry loading (15 pptv for long-lived bromine species + 6 extra pptv for very short-lived species (VSLS) added by a scaling of CH3Br), significantly underestimates the retrieved BrO columns. A sensitivity study shows that a good quantitative agreement can only be obtained if 8 pptv accounting for VSLS are added directly (and not by a scaling of CH3Br) to the SLIMCAT long-lived bromine species profile. This contribution of the VSLS to the total bromine loading is also consistent with recently published studies.
A new atmospheric aerosol phase equilibrium model (UHAERO): organic systems
Authors: Amundson N. R. , Caboussat A. , He J. W. , Martynenko A. V. , Landry C. , Tong C. , Seinfeld J. H.
Published: April 2010

Abstract. In atmospheric aerosols, water and volatile inorganic and organic species are distributed between the gas and aerosol phases in accordance with thermodynamic equilibrium. Within an atmospheric particle, liquid and solid phases can exist at equilibrium. Models exist for computation of phase equilibria for inorganic/water mixtures typical of atmospheric aerosols; when organic species are present, the phase equilibrium problem is complicated by organic/water interactions as well as the potentially large number of organic species. We present here an extension of the UHAERO inorganic thermodynamic model (Amundson et al., 2006c) to organic/water systems. Phase diagrams for a number of model organic/water systems characteristic of both primary and secondary organic aerosols are computed. Also calculated are inorganic/organic/water phase diagrams that show the effect of organics on inorganic deliquescence behavior. The effect of the choice of activity coefficient model for organics on the computed phase equilibria is explored.
Influence of trans-Pacific pollution transport on acyl peroxy nitrate abundances and speciation at Mount Bachelor Observatory during INTEX-B
Authors: Wolfe G. M. , Thornton J. A. , Faye McNeill V. , Jaffe D. A. , Reidmiller D. , Chand D. , Smith J. , Swartzendruber P. , Flocke F. , Zheng W.
Published: April 2010

Abstract. We present month-long observations of speciated acyl peroxy nitrates (APNs), including PAN, PPN, MPAN, APAN, and the sum of PiBN and PnBN, measured at the Mount Bachelor Observatory (MBO) as part of the INTEX-B collaborative field campaign during spring 2006. APN abundances, measured by thermal dissociation-chemical ionization mass spectrometry (TD-CIMS), are discussed in terms of differing contributions from the boundary layer and the free troposphere and in the context of previous APN measurements in the NE Pacific region. PAN mixing ratios range from 11 to 3955 pptv, with a mean value of 334 pptv for the full measurement period. PPN is linearly correlated with PAN (r2=0.96), with an average abundance of 6.5% relative to PAN; other APNs are generally <1% of PAN. Diurnal cycles and relationships of APNs with ozone reveal a gradient in hydrocarbon chemistry between the boundary layer and the free troposphere. On average, the highest levels of APNs, ozone and PPN/PAN are found in free tropospheric air masses, suggesting that this site is strongly influenced by distant pollution sources. To estimate the impact of long-range transport of Asian pollution on atmospheric composition at MBO, we perform a detailed analysis utilizing HYSPLIT back trajectories. This analysis suggests that trans-Pacific transport of Asian pollution leads to substantial increases in APN and ozone mixing ratios at MBO, especially when transport occurs via the free troposphere. The ensemble of trajectories indicate that Asian-influenced free tropospheric air was sampled in ~16% of our data and contained a median PAN mixing ratio double that of the full dataset.
Mesospheric N2O enhancements as observed by MIPAS on Envisat during the polar winters in 2002–2004
Authors: Funke B. , López-Puertas M. , García-Comas M. , Stiller G. P. , von Clarmann T. , Glatthor N.
Published: April 2010

Abstract. N2O abundances ranging from 0.5 to 6 ppbv were observed in the polar upper stratosphere/lower mesosphere by the MIPAS instrument on the Envisat satellite during the Arctic and Antarctic winters in the period July 2002 to March 2004. A detailed study of the observed N2O–CH4 correlations shows that such enhancements are of chemical rather than dynamical origin. The N2O enhancements observed at 58 km occurred in presence of NOx intrusions from the upper atmosphere which were related to energetic particle precipitation. Further, the inter-annual variability of mesospheric N2O correlates well with observed precipitating electron fluxes. The analysis of possible chemical production mechanisms shows that the major part of the observed N2O enhancements is most likely generated under dark conditions by the reaction of NO2 with atomic nitrogen at altitudes around 70–75 km in the presence of energetic particle precipitation. A possible additional source of N2O in the middle and upper polar atmosphere is the reaction of N2(A3Σu+), generated by precipitating electrons, with O2, which would lead to N2O production peaking at altitudes around 90–100 km. N2O produced by the latter mechanism could then descend to the mesosphere and upper stratosphere during polar winter.
Proposal of a new erythemal UV radiation amplification factor
Authors: Serrano A. , Antón M. , Cancillo M. L. , García J. A.
Published: April 2010

Abstract. This work is aimed to propose a natural expansion of radiation amplification factor (RAF) for erythemal irradiance to consider all solar zenith angles cases together. In this direction, the article analyzes the relationship between measurements of UV erythemal radiation (UVER) recorded at Badajoz (Spain) and the total ozone column estimated by the instrument TOMS/NASA for that location during the period February 2001–December 2005. The new RAF parameter is formulated by power equation using slant ozone and UVER atmospheric transmissivity values. Thus, reliable values of this parameter have been reported. These values could serve as a new relevant index for comparison with other studies and model's result. The new RAF is calculated with measurements recorded during completely clear cases using clearness index values higher than 0.75. The RAF value was 1.35±0.01, it is to say, when the slant ozone amount decreases 1% at Badajoz, UVER atmospheric transmissivity values and, therefore, UVER surface values approximately increase 1.35%. This result emphasizes the interest of measuring and monitoring simultaneous measurements of UV radiation and stratospheric ozone even for mid-latitudes. The influence of total ozone amount and cloudiness changes on new RAF values is analyzed. Cloud-free conditions allow to study the ozone influences while cloud effects are analyzed with all data by means of monthly average of slant ozone and UVER atmospheric transmissivities values.
Validation of water vapour transport in the tropical tropopause region in coupled Chemistry Climate Models
Authors: Kremser S. , Rex M. , Langematz U. , Dameris M. , Wohltmann I.
Published: April 2010

Abstract. In this study backward trajectories from the tropical lower stratosphere were calculated for the Northern Hemisphere (NH) winters 1995–1996, 1997–1998 (El Niño) and 1998–1999 (La Niña) and summers 1996, 1997 and 1999 using both ERA-40 reanalysis data of the European Centre for Medium-Range Weather Forecast (ECMWF) and coupled chemistry climate model (CCM) data. The calculated trajectories were analyzed to determine the distribution of points where individual air masses encounter the minimum temperature and thus minimum water vapour mixing ratio during their ascent through the tropical tropopause layer (TTL) into the stratosphere. The geographical distribution of these dehydration points and the local conditions there determine the overall water vapour entry into the stratosphere. Results of two CCMs are presented: the ECHAM4.L39(DLR)/CHEM (hereafter: E39/C) from the German Aerospace Center (DLR) and the Freie Universität Berlin Climate Middle Atmosphere Model with interactive chemistry (hereafter: FUB-CMAM-CHEM). In the FUB-CMAM-CHEM model the minimum temperatures are overestimated by about 7 K in Northern Hemisphere (NH) winter as well as in NH summer, resulting in too high water vapour entry values compared to ERA-40. However, the geographical distribution of dehydration points is fairly reproduced for NH winter 1995–1996 and 1998–1999 and in all boreal summers. The distribution of dehydration points suggests an influence of the Indian monsoon upon the water vapour transport. The E39/C model displays a temperature bias of about +3 K. Hence, the minimum water vapour mixing ratios are higher relative to ERA-40. The geographical distribution of dehydration points is satisfactory in NH winter 1995–1996 and 1997–1998 with respect to ERA-40. The distribution is not reproduced for the NH winter 1998–1999 (La Niña event) compared to ERA-40. There is excessive mass flux through warm regions e.g. Africa, leading to excessive water vapour flux in the NH winter and summer. The possible influence of the Indian monsoon on the transport is not seen in the boreal summer. Further, the residence times of air parcels in the TTL were derived from the trajectory calculations. The analysis of the residence times reveals that in both CCMs residence times in the TTL are underestimated compared to ERA-40 and the seasonal variation is hardly present.
Radiation transfer in stratus clouds at the BSRN Payerne site
Authors: Nowak D. , Vuilleumier L. , Ohmura A.
Published: April 2010

Abstract. Clouds represent a major source of uncertainty in understanding climate change, because potential changes in the way they affect the atmospheric and surface energy budget are difficult to predict. It is therefore important to determine how clouds affect radiation. Stratiform clouds in particular have an important effect on climate as they cover large areas. This article presents results of radiation transfer calculations with MODTRANTM for well-defined stratus cloud cases detected at the meteorological station of Payerne, Switzerland. These stratus situations are selected in a data set covering the years from 2000 to 2005 with a method using data widely available at national meteorological observing stations. For 18 single layer stratus situations the shortwave radiation fluxes calculated with MODTRANTM are compared to surface observations from the Baseline Surface Radiation Network (BSRN) site at Payerne and top of atmosphere (TOA) observations from the Clouds and the Earth's Radiant Energy System (CERES) experiment. A median bias on the order of 20 Wm−2 (<9%) was found for the differences between modeled and observed reflected solar radiation at TOA. At the surface, good agreement is obtained by adjusting the vertical extinction in the modeled cloud layer within reasonable limits for a stratus cloud: The median bias of modeled minus observed shortwave downward radiation is well within instrument precision (<1%). The simultaneous agreement of modeled and observed radiation fluxes at the surface and TOA confirmed that radiation transfer in the atmosphere including a single cloud layer can be well simulated with MODTRANTM. Based on the present results, the absorbance was calculated within the stratus cloud layer (cloud base to cloud top). For the 18 single stratus layer situations the median absorbance is 0.07 [minimum 0.04, maximum 0.1], the median transmittance is 0.29 [0.15 0.39], and the median cloud reflectance is 0.70 [0.63, 0.80].
Technical Note: Formation of airborne ice crystals in a wall independent reactor (WIR) under atmospheric conditions
Authors: Fries E. , Haunold W. , Starokozhev E. , Palitzsch K. , Sitals R. , Jaeschke W. , Püttmann W.
Published: April 2010

Abstract. Both, gas and particle scavenging contribute to the transport of organic compounds by ice crystals in the troposphere. To simulate these processes an experimental setup was developed to form airborne ice crystals under atmospheric conditions. Experiments were performed in a wall independent reactor (WIR) installed in a walk-in cold chamber maintained constantly at −20°C. Aerosol particles were added to the carrier gas of ambient air by an aerosol generator to allow heterogeneous ice formation. Temperature variations and hydrodynamic conditions of the WIR were investigated to determine the conditions for ice crystal formation and crystal growth by vapour deposition. In detail, the dependence of temperature variations from flow rate and temperature of the physical wall as well as temperature variations with an increasing reactor depth were studied. The conditions to provide a stable aerosol concentration in the carrier gas flow were also studied. The temperature distribution inside the reactor was strongly dependent on flow rate and physical wall temperature. At an inlet temperature of −20°C, a flow rate of 30 L•min−1 and a physical wall temperature of +5°C turned out to provide ideal conditions for ice formation. At these conditions a sharp and stable laminar down draft "jet stream" of cold air in the centre of the reactor was produced. Temperatures measured at the chamber outlet were kept well below the freezing point in the whole reactor depth of 1.0 m. Thus, melting did not affect ice formation and crystal growth. The maximum residence time for airborne ice crystals was calculated to at 40 s. Ice crystal growth rates increased also with increasing reactor depth. The maximum ice crystal growth rate was calculated at 2.82 mg• s−1. Further, the removal efficiency of the cleaning device for aerosol particles was 99.8% after 10 min. A reliable particle supply was attained after a preliminary lead time of 15 min. Thus, the minimum lead time was determined at 25 min. Several test runs revealed that the WIR is suitable to perform experiments with airborne ice crystals.
A chemical model of meteoric ablation
Authors: Vondrak T. , Plane J. M. C. , Broadley S. , Janches D.
Published: April 2010

Abstract. Most of the extraterrestrial dust entering the Earth's atmosphere ablates to produce metal vapours, which have significant effects on the aeronomy of the upper mesosphere and lower thermosphere. A new Chemical Ablation Model (CAMOD) is described which treats the physics and chemistry of ablation, by including the following processes: sputtering by inelastic collisions with air molecules before the meteoroid melts; evaporation of atoms and oxides from the molten particle; diffusion-controlled migration of the volatile constituents (Na and K) through the molten particle; and impact ionization of the ablated fragments by hyperthermal collisions with air molecules. Evaporation is based on thermodynamic equilibrium in the molten meteoroid (treated as a melt of metal oxides), and between the particle and surrounding vapour phase. The loss rate of each element is then determined assuming Langmuir evaporation. CAMOD successfully predicts the meteor head echo appearance heights, observed from incoherent scatter radars, over a wide range of meteoroid velocities. The model also confirms that differential ablation explains common-volume lidar observations of K, Ca and Ca+ in fresh meteor trails. CAMOD is then used to calculate the injection rates into the atmosphere of a variety of elements as a function of altitude, integrated over the meteoroid mass and velocity distributions. The most abundant elements (Fe, Mg and Si) have peak injection rates around 85 km, with Na and K about 8 km higher. The more refractory element Ca ablates around 82 km with a Na:Ca ratio of 4:1, which does therefore not explain the depletion of atomic Ca to Na, by more than 2 orders of magnitude, in the upper mesosphere. Diffusion of the most volatile elements (Na and K) does not appear to be rate-limiting except in the fastest meteoroids. Non-thermal sputtering causes ~35% mass loss from the fastest (~60–70 km s−1) and smallest (10−17–10−13g) meteoroids, but makes a minor contribution to the overall ablation rate.
Global error maps of aerosol optical properties: an error propagation analysis
Authors: Tsigaridis K. , Balkanski Y. , Schulz M. , Benedetti A.
Published: April 2010

Abstract. Among the numerous atmospheric constituents, aerosols play a unique role on climate, due to their scattering and absorbing capabilities, visibility degradation and their effect on incoming and outgoing radiation. The most important optical properties are the aerosol optical depth (AOD), the asymmetry parameter (g) and the single scattering albedo (SSA). Uncertainties in aerosol microphysics in global models, which in turn affect their optical properties, propagate to uncertainties on the effect of aerosols on climate. This study aims to estimate the uncertainty of AOD, g and SSA attributable to the aerosol representation in models, namely mixing state, aerosol size and aerosol associated water. As a reference, the monthly mean output of the general circulation model LMDz-INCA from the international comparison exercise AEROCOM B was used. For the optical properties calculations, aerosols were considered either externally mixed, homogeneously internally mixed or coated spheres. The radius was allowed to vary by ±20% (with 2% intervals) and the aerosol water content by ±50% (with 5% intervals) with respect to the reference model output. All of these possible combinations were assumed to be equally likely and the optical properties were calculated for each one of them. A probability density function (PDF) was constructed at each model grid point for AOD, g and SSA. From this PDF, the 1σ and 2σ uncertainties of the AOD, g and SSA were calculated and are available as global maps for each month. For the range of the cases studied, we derive a maximum 2σ uncertainty range in AOD of 70%, while for g and SSA the maxima reach 18% and 28% respectively. The mixing state was calculated to be important, with the aerosol absorption and SSA being the most affected properties when absorbing aerosols are present.
A quasi-Lagrangian coordinate system based on high resolution tracer observations: implementation for the Antarctic polar vortex
Authors: Ivanova E. V. , Volk C. M. , Riediger O. , Klein H. , Sitnikov N. M. , Ulanovskii A. E. , Yushkov V. A. , Ravegnani F. , Möbius T. , Schmidt U.
Published: April 2010

Abstract. In order to quantitatively analyse the chemical and dynamical evolution of the polar vortex it has proven extremely useful to work with coordinate systems that follow the vortex flow. We propose here a two-dimensional quasi-Lagrangian coordinate system {χi, Δχi}, based on the mixing ratio of a long-lived stratospheric trace gas i, and its systematic use with i = N2O, in order to describe the structure of a well-developed Antarctic polar vortex. In the coordinate system {χi, Δχi} the mixing ratio χi is the vertical coordinate and Δχi = χi(Θ)−χivort(Θ) is the meridional coordinate (χivort(Θ) being a vertical reference profile in the vortex core). The quasi-Lagrangian coordinates {χi, Δχi} persist for much longer time than standard isentropic coordinates, potential temperature Θ and equivalent latitude φe, do not require explicit reference to geographic space, and can be derived directly from high-resolution in situ measurements. They are therefore well-suited for studying the evolution of the Antarctic polar vortex throughout the polar winter with respect to the relevant chemical and microphysical processes. By using the introduced coordinate system {χN2O, ΔχN2O} we analyze the well-developed Antarctic vortex investigated during the APE-GAIA (Airborne Polar Experiment – Geophysica Aircraft in Antarctica – 1999) campaign (Carli et al., 2000). A criterion, which uses the local in-situ measurements of χi=χi(Θ) and attributes the inner vortex edge to a rapid change (δ-step) in the meridional profile of the mixing ratio χi, is developed to determine the (Antarctic) inner vortex edge. In turn, we suggest that the outer vortex edge of a well-developed Antarctic vortex can be attributed to the position of a local minimum of the χH2O gradient in the polar vortex area. For a well-developed Antarctic vortex, the ΔχN2O-parametrization of tracer-tracer relationships allows to distinguish the tracer inter-relationships in the vortex core, vortex boundary region and surf zone and to examine their meridional variation throughout these regions. This is illustrated by analyzing the tracer-tracer relationships χi : χN2O obtained from the in-situ data of the APE-GAIA campaign for i = CFC-11, CFC-12, H-1211 and SF6. A number of solitary anomalous points in the CFC-11 : N2O correlation, observed in the Antarctic vortex core, are interpreted in terms of small-scale cross-isentropic dispersion.
Secondary organic aerosol formation from reaction of tertiary amines with nitrate radical
Authors: Erupe M. E. , Price D. J. , Silva P. J. , Malloy Q. G. J. , Qi L. , Warren B. , Cocker III D. R.
Published: April 2010

Abstract. Secondary organic aerosol formation from the reaction of tertiary amines with nitrate radical was investigated in an indoor environmental chamber. Particle chemistry was monitored using a high resolution aerosol mass spectrometer while gas-phase species were detected using a proton transfer reaction mass spectrometer. Trimethylamine, triethylamine and tributylamine were studied. Results indicate that tributylamine forms the most aerosol mass followed by trimethylamine and triethylamine respectively. Spectra from the aerosol mass spectrometer indicate the formation of complex non-salt aerosol products. We propose a reaction mechanism that proceeds via abstraction of a proton by nitrate radical followed by RO2 chemistry. Rearrangement of the aminyl alkoxy radical through hydrogen shift leads to the formation of hydroxylated amides, which explain most of the higher mass ions in the mass spectra. These experiments show that oxidation of tertiary amines by nitrate radical may be an important night-time source of secondary organic aerosol.
Observing three dimensional water vapour using a surface network of GPS receivers
Authors: de Haan S. , van der Marel H.
Published: April 2010

Abstract. Atmospheric water vapour is highly variable both in space and time. In an operational sense, only radiosonde provide vertical information on water vapour. Radiosondes are generally launched two to four times per day at synoptic times and sample primarily synoptic scales. For nowcasting purposes these observations are very valuable but obviously lose their importance with elapsing time. Water vapour observations from a surface network of Global Positioning System (GPS) receivers can fill this information gap. In this paper, a GPS network is used to observe integral water vapour quantities along the line of sight, so-called Slant Water Vapour (SWV). Using a variational technique (3DVAR) a three-dimensional water vapour field is reconstructed and its performance is investigated by assimilating SWV observations deduced from a simulated atmosphere (so-called nature run). The forecasts from a high resolution limited area model (HIRLAM) embedded in the synthetic atmosphere of the nature run is compared to the separate GPS-3DVAR estimates. This experiment showed that assimilation of SWV resulted in a smaller bias and standard deviation than the HIRLAM forecast with the nature run. Besides simulated data, real SWV observations are used to assess impact. Two experiments were conducted; one with a HIRLAM six hour forecast as a background field (updated every six hours) and one with persistence as background (updated every hour). The first experiment showed a reduction of the bias between radiosonde observations compared to HIRLAM forecast. The second experiment, which has no information inherited from HIRLAM, showed to have smaller biases with independent radiosonde observations than the HIRLAM analysis. The used network, however was too sparse to detect water vapour inversions correctly.
A case study on biomass burning aerosols: effects on solar UV irradiance, retrieval of aerosol single scattering albedo
Authors: Bagheri A. , Kjeldstad B. , Johnsen B.
Published: April 2010

Abstract. The aerosol optical depth (AOD) from biomass burning aerosols from eastern Europe was measured in Trondheim, Norway (63.43° N , 10.43° E) in May 2006. The event was observed as far as the Arctic. In the first part of this paper, the surface measurements of direct and global UV radiation (and retrieved AOD) are used to simulate the data using a radiative transfer model. Measured and simulated data were used to study the effect of biomass aerosol on the levels of surface UV radiation. We found reductions of up to 31%, 15% and 2% in direct, global and diffuse surface UV irradiance (at 350 nm, SZA=50°±0.5°) as compared to typical aerosol conditions. In the second part of our study, surface measurements of global and direct irradiance at five wavelength in UVB and UVA (305, 313, 320, 340 and 380 nm) were coupled with a radiative transfer model to produce values of aerosol single scattering albedo, ω. The aerosol single scattering albedo for biomass aerosols is compared to ω for background aerosols. The values of ω for biomass aerosols were 0.76 at 305 nm, 0.75 at 313 nm, 0.79 at 320 nm, 0.72 at 340 nm and 0.80 at 380 nm.
The CO2 inhibition of terrestrial isoprene emission significantly affects future ozone projections
Authors: Young P. J. , Arneth A. , Schurgers G. , Zeng G. , Pyle J. A.
Published: April 2010

Abstract. Simulations of future tropospheric composition often include substantial increases in biogenic isoprene emissions arising from the Arrhenius-like leaf emission response and warmer surface temperatures, and from enhanced vegetation productivity in response to temperature and atmospheric CO2 concentration. However, a number of recent laboratory and field data have suggested a direct inhibition of leaf isoprene production by increasing atmospheric CO2 concentration, notwithstanding isoprene being produced from precursor molecules that include some of the primary products of carbon assimilation. The cellular mechanism that underlies the decoupling of leaf photosynthesis and isoprene production still awaits a full explanation but accounting for this observation in a dynamic vegetation model that contains a semi-mechanistic treatment of isoprene emissions has been shown to change future global isoprene emission estimates notably. Here we use these estimates in conjunction with a chemistry-climate model to compare the effects of isoprene simulations without and with a direct CO2-inhibition on late 21st century O3 and OH levels. The impact on surface O3 was significant. Including the CO2-inhibition of isoprene resulted in opposing responses in polluted (O3 decreases of up to 10 ppbv) vs. less polluted (O3 increases of up to 10 ppbv) source regions, due to isoprene nitrate and peroxy acetyl nitrate (PAN) chemistry. OH concentration increased with relatively lower future isoprene emissions, decreasing methane lifetime by ~7 months. Our simulations underline the large uncertainties in future chemistry and climate studies due to biogenic emission patterns and emphasize the problems of using globally averaged climate metrics to quantify the atmospheric impact of reactive, heterogeneously distributed substances.
A mechanism for biologically-induced iodine emissions from sea-ice
Authors: Saiz-Lopez A. , Boxe C. S.
Published: April 2010

Abstract. Only recently, ground- and satellite-based measurements have reported high concentrations of IO in coastal Antarctica. The sources of such a large iodine burden in the Antarctic atmosphere remain unknown. We propose a novel mechanism for iodine release from sea-ice surfaces. The release is triggered by the biological production of iodide (I-) and hypoiodous acid (HOI) from marine algae, contained within and underneath sea-ice, and their diffusion through sea-ice brine channels to accumulate in the quasi-liquid layer on the surface of sea-ice. A multiphase chemical model of polar atmospheric chemistry has been developed to investigate the biology-ice-atmosphere coupling in the polar environment. Model simulations were conducted to interpret recent observations of elevated IO in the coastal Antarctic springtime. The results show that the levels of inorganic iodine (i.e. I2, IBr, ICl) released from sea-ice through this mechanism account for the observed IO concentrations in the Antarctic springtime environment. The model results also indicate that iodine may trigger the catalytic release of bromine from sea-ice through phase equilibration of IBr. Considering the extent of sea-ice around the Antarctic continent, we suggest that the resulting high levels of iodine may have widespread impact on catalytic ozone destruction and aerosol formation in the Antarctic lower troposphere.
Validation of NO2and NO from the Atmospheric Chemistry Experiment (ACE)
Authors: Kerzenmacher T. , Wolff M. A. , Strong K. , Dupuy E. , Walker K. A. , Amekudzi L. K. , Batchelor R. L. , Bernath P. F. , Berthet G. , Blumenstock T. , Boone C. D. , Bramstedt K. , Brogniez C. , Brohede S. , Burrows J. P. , Catoire V. , Dodion J. , Drummond J. R. , Dufour D. G. , Funke B. , Fussen D. , Goutail F. , Griffith D. W. T. , Haley C. S. , Hendrick F. , Höpfner M. , Huret N. , Jones N. , Kar J. , Kramer I. , Llewellyn E. J. , López-Puertas M. , Manney G. , McElroy C. T. , McLinden C. A. , Melo S. , Mikuteit S. , Murtagh D. , Nichitiu F. , Notholt J. , Nowlan C. , Piccolo C. , Pommereau J.-P. , Randall C. , Raspollini P. , Ridolfi M. , Richter A. , Schneider M. , Schrems O. , Silicani M. , Stiller G. P. , Taylor J. , Tétard C. , Toohey M. , Vanhellemont F. , Warneke T , Zawodny J. M. , Zou J.
Published: April 2010

Abstract. Vertical profiles of NO2 and NO have been obtained from solar occultation measurements by the Atmospheric Chemistry Experiment (ACE), using an infrared Fourier Transform Spectrometer, ACE-FTS, and an ultraviolet-visible-near-infrared spectrometer, MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation). In this paper, the quality of the ACE-FTS version 2.2 NO2 and NO and the MAESTRO version 1.2 NO2 data are assessed using other solar occultation measurements (HALOE, SAGE II, SAGE III, POAM III, SCIAMACHY), stellar occultation measurements (GOMOS), limb measurements (MIPAS, OSIRIS), nadir measurements (SCIAMACHY), balloon measurements (SPIRALE, SAOZ) and ground-based measurements (UV-VIS, FTIR). Time differences between the comparison measurements were reduced using either a tight coincidence criterion, or where possible, chemical box models. ACE-FTS NO2 and NO and the MAESTRO NO2 are generally consistent with the correlative data. The ACE-FTS NO2 VMRs agree with the satellite data sets to within about 20% between 25 and 40 km, and suggest a negative bias between 23 and 40 km of about \\textminus10%. In comparisons with HALOE, ACE-FTS NO VMRs typically agree to ±8% from 22 to 64 km and to +10% from 93 to 105 km. Partial column comparisons for NO2 show that there is fair agreement between the ACE instruments and the FTIRs, with a mean difference of +7.3% for ACE-FTS and +12.8% for MAESTRO.
Total column ozone variations over oceanic region around Indian sub-continent during pre-monsoon of 2006
Authors: Kalapureddy M. C. R. , Ernest Raj P. , Devara P. C. S.
Published: April 2010

Abstract. Special campaign mode ship-based sun photometric observations of total column ozone over the oceanic regions around the Indian sub-continent (56° E–6° E, 4° N–° N) during the pre-monsoon period (18 March–11 May) of 2006 have been used to investigate the spatial and temporal distributions. The overall mean ozone content over the sea region during this period is 298 DU with a variability of ±10 DU. There is a well defined diurnal (daytime) variation in total column ozone with maximum content around the noon-time hours. The amplitude of diurnal variation is higher over the Arabian Sea compared to that over Bay of Bengal. Spatial distribution of total ozone shows higher values over the Head Bay (North Bay of Bengal) and all along the west coast of India strongly pointing to continental origin of possible anthropogenic source. This is further corroborated from the spatial distribution of simultaneously measured aerosol optical thickness (AOT, at 1020 nm) and precipitable water. The overall mean AOT over the oceanic region is 0.09 and mean precipitable water (water vapor) over Indian Ocean region was 3.25 cm which is almost 1 cm higher than that observed over Bay of Bengal and Arabian Sea during the above pre-monsoon period.
The chemistry influencing ODEs in the Polar Boundary Layer in spring: a model study
Authors: Piot M. , von Glasow R.
Published: April 2010

Abstract. Near-total depletions of ozone have been observed in the Arctic spring since the mid 1980s. The autocatalytic cycles involving reactive halogens are now recognized to be of main importance for Ozone Depletion Events (ODEs) in the Polar Boundary Layer (PBL). We present sensitivity studies using the model MISTRA in the box-model mode on the influence of chemical species on these ozone depletion processes. In order to test the sensitivity of the chemistry under polar conditions, we compared base runs undergoing fluxes of either Br2, BrCl, or Cl2 to induce ozone depletions, with similar runs including a modification of the chemical conditions. The role of HCHO, H2O2, DMS, Cl2, C2H4, C2H6, HONO, NO2, and RONO2 was investigated. Cases with elevated mixing ratios of HCHO, H2O2, DMS, Cl2, and HONO induced a shift in bromine speciation from Br/BrO to HOBr/HBr, while high mixing ratios of C2H6 induced a shift from HOBr/HBr to Br/BrO. Cases with elevated mixing ratios of HONO, NO2, and RONO2 induced a shift to BrNO2/BrONO2. The shifts from Br/BrO to HOBr/HBr accelerated the aerosol debromination, but also increased the total amount of deposited bromine at the surface (mainly via increased deposition of HOBr). These shifts to HOBr/HBr also hindered the BrO self-reaction. In these cases, the ozone depletion was slowed down, where increases in H2O2 and HONO had the greatest effect. The tests with increased mixing ratios of C2H4 highlighted the decrease in HOx which reduced the production of HOBr from bromine radicals. In addition, the direct reaction of C2H4 with bromine atoms led to less available reactive bromine. The aerosol debromination was therefore strongly reduced. Ozone levels were highly affected by the chemistry of C2H4. Cl2-induced ozone depletions were found unrealistic compared to field measurements due to the rapid production of CH3O2, HOx, and ROOH which rapidly convert reactive chlorine to HCl in a "chlorine counter-cycle". This counter-cycle efficiently reduces the concentration of reactive halogens in the boundary layer. Depending on the relative bromine and chlorine mixing ratios, the production of CH3O2, HOx, and ROOH from the counter-cycle can significantly affect the bromine chemistry. Therefore, the presence of both bromine and chlorine in the air may unexpectedly lead to a slow down in ozone destruction. For all NOy species studied (HONO, NO2, RONO2) the chemistry is characterized by an increased bromine deposition on snow reducing the amount of reactive bromine in the air. Ozone is less depleted under conditions of high mixing ratios of NOx. The production of HNO3 led to the acid displacement of HCl, and the release of chlorine out of salt aerosols (Cl2 or BrCl) increased.
Evaluation of the tropospheric flows to a major Southern Hemisphere stratospheric warming event using NCEP/NCAR Reanalysis data with a PSU/NCAR nudging MM5V3 model
Authors: Wang K.
Published: April 2010

Abstract. Previous studies of the exceptional 2002 Southern Hemisphere (SH) stratospheric warming event lead to some uncertainty, namely the question of whether excessive heat fluxes in the upper troposphere and lower stratosphere are a symptom or cause of the 2002 SH warming event. In this work, we use a hemispheric version of the MM5 model with nudging capability and we devised a novel approach to separately test the significance of the stratosphere and troposphere for this year. We paired the flow conditions from 2002 in the stratosphere and troposphere, respectively, against the conditions in 1998 (a year with displaced polar vortex) and in 1948 (a year with strong polar vortex that coincided with the geographical South Pole). Our experiments show that the flow conditions from below determine the stratospheric flow features over the polar region. Regardless of the initial stratospheric conditions in 1998 or 1948, when we simulated these past stratospheres with the troposphere/lower stratosphere conditions constrained to 2002 levels, the simulated middle stratospheres resemble those observed in 2002 stratosphere over the polar region. On the other hand, when the 2002 stratosphere was integrated with the troposphere/lower stratosphere conductions constrained to 1948 and 1998, respectively, the simulated middle stratospheric conditions over the polar region shift toward those of 1948 and 1998. Thus, our experiments further support the wave-forcing theory as the cause of the 2002 SH warming event.
Comparison of several wood smoke markers and source apportionment methods for wood burning particulate mass
Authors: Sandradewi J. , Prévôt A. S. H. , Alfarra M. R. , Szidat S. , Wehrli M. N. , Ruff M. , Weimer S. , Lanz V. A. , Weingartner E. , Perron N. , Caseiro A. , Kasper-Giebl A. , Puxbaum H. , Wacker L. , Baltensperger U.
Published: April 2010

Abstract. Residential wood combustion has only recently been recognized as a major contributor to air pollution in Switzerland and in other European countries. A source apportionment method using the aethalometer light absorption parameters was applied to five winter campaigns at three sites in Switzerland: a village with high wood combustion activity in winter, an urban background site and a highway site. The particulate mass from traffic (PMtraffic) and wood burning (PMwb) emissions obtained with this model compared fairly well with results from the 14C source apportionment method. PMwb from the model was also compared to well known wood smoke markers such as anhydrosugars (levoglucosan and mannosan) and fine mode potassium, as well as to a marker recently suggested from the Aerodyne aerosol mass spectrometer (mass fragment m/z 60). Additionally the anhydrosugars were compared to the 14C results and were shown to be comparable to literature values from wood burning emission studies using different types of wood (hardwood, softwood). The levoglucosan to PMwb ratios varied much more strongly between the different campaigns (4–13%) compared to mannosan to PMwb with a range of 1–1.5%. Possible uncertainty aspects for the various methods and markers are discussed.
Seasonal variations in aerosol optical properties over China
Authors: Wang Y. , Xin J. , Li Z. , Wang S. , Wang P. , Hao W. M. , Nordgren B. L. , Chen H. , Wang L. , Sun Y.
Published: April 2010

Abstract. The seasonal variations in background aerosol optical depth (AOD) and aerosol type are investigated over various ecosystems in China based upon three years' worth of meteorological data and data collected by the Chinese Sun Hazemeter Network. In most parts of China, AODs are at a maximum in spring or summer and at a minimum in autumn or winter. Minimum values (0.10~0.20) of annual mean AOD at 500 nm are found in the Qinghai-Tibetan Plateau, which is located in the remote northeast corner of China, the northern forest ecosystems and Hainan Island. Annual mean AOD ranges from 0.25 to 0.30 over desert and oasis areas as well as the desertification grasslands in northern China; the annual mean AOD over the Loess Plateau is moderately high at 0.36. Regions where the highest density of agricultural and industrial activities are located and where anthropogenic sulphate aerosol and soil aerosol emissions are consistently high throughout the whole year (e.g. the central-eastern, southern and eastern coastal regions of China) experience annual mean AODs ranging from 0.50~0.80. Remarkable seasonal changes in the main types of aerosol over northern China (characterized by the Angstrom exponent, α) are seen. Due to biomass and fossil fuel burning from extensive agricultural practices in northern rural areas, concentrations of smoke and soot aerosols rise dramatically during autumn and winter (high α), while the main types of aerosol during spring and summer are dust and soil aerosols (low α). Over southeast Asia, biomass burning during the spring leads to increases in smoke and soot emissions. Over the Tibetan Plateau and Hainan Island where the atmosphere is pristine, the main types of aerosol are dust and sea salt, respectively.
Absolute rate constant and O(3P) yield for the O(1D)+N2O reaction in the temperature range 227 K to 719 K
Authors: Vranckx S. , Peeters J. , Carl S. A.
Published: April 2010

Abstract. We have determined, in the temperature range 227 K to 719 K, the absolute rate constant for the reaction O(1D)+N2O → products and, in the temperature range 248 K to 600 K, the fraction of the reaction that yields O(3P). Both the rate constants and product yields were determined using a recently-developed chemiluminescence technique for monitoring O(1D) that allows for higher precision determinations for both rate constants, and, particularly, O(3P) yields, than do other methods. We found the rate constant, kR1, to be essentially independent of temperature between 400 K and 227 K, having a value of (1.37±0.09)×10−10 cm3 s−1. For temperatures greater than 450 K a marked decrease in value was observed, with a rate constant of only (0.94±0.11)×10−10 cm3 s−1 at 719 K. The rate constants determined over the 227 K–400 K range show very low scatter and are significantly greater, by 20% at room temperature and by 15% at 227 K, than the current recommended values. The fraction of O(3P) produced in this reaction was determined to be 0.002±0.002 at 250 K rising steadily to 0.010±0.004 at 600 K, thus the channel producing O(3P) can be entirely neglected in atmospheric kinetic modeling calculations. A further result of this study is an expression of the relative quantum yields as a function of temperature for the chemiluminescence reactions (kCL1) C2H+O(1D) → CH(A)+CO and (kCL2) C2H+O(3P) → CH(A)+CO, both followed by CH(A) → CH(X)+hν, as kCL1(T)/kCL2(T)=(32.8T−3050)/(6.29T+398).
An extreme CO pollution event over Indonesia measured by the MOPITT instrument
Authors: Nichitiu F. , Drummond J. R. , Kar J. , Zou J.
Published: April 2010

Abstract. In the fall of 2006, the Measurements Of Pollution In The Troposphere (MOPITT) instrument on the Terra satellite observed an extremely high Carbon monoxide (CO) concentration over Indonesia. This extreme event was caused by huge fire activity during the 2006 El Nino event. From our comparison with other high CO pollution events over Indonesia during similar and moderate El Nino events, we conclude that the 2006 fire activity, which caused large-scale pollution in this region, was probably amplified by an increase in frequency and/or intensity of lightning activity in a feedback mechanism. We also observed that after the fire episodes in El Nino years, the "lightning rate" was less than during the fire episode but displayed an increasing trend across the three events observed that might have been be caused by interactions with fire smoke plumes.
High temporal resolution VHF radar observations of stratospheric air intrusions in to the upper troposphere during the passage of a mesoscale convective system over Gadanki (13.5° N, 79.2° E)
Authors: Kumar K. K. , Uma K. N.
Published: April 2010

Abstract. A high temporal resolution VHF radar experiment, which was carried out to divulge the clear-air structure of a mesoscale convective system (MCS) at fine time scales over Gadanki, is discussed. The VHF radar was continuously operated for four hours with 11 seconds time resolution on 19 June 2006, which facilitated the study of finer details of stratospheric air intrusions into the upper troposphere during the passage of a MCS. Simultaneous GPS sonde and ground based optical rain gauge measurements are also used for the present study along with radar observations. The height-time section of range corrected signal to noise ratio (RSNR) revealed the convective cells reaching as high as 14 km altitude and the signature of the tropopause as a layered structure at around 16.5 km. The important observation from the radar RSNR is the time localized inclined echoes in the height region of 12–16 km region giving evidence for stratospheric air intrusion into the upper troposphere. Further, this observation is confirmed by the height–time section of vertical velocity, which showed the intense downdraughts in the height region of inclined radar echoes. A detailed examination of this down draft revealed an episode of high frequency gravity wave excitation, which is believed to be the consequence of intrusion of stable stratospheric air into the upper troposphere. Thus, the present study brings out for the first time, how the stratospheric intrusions will appear in the radar height-time sections and the consequences of such intrusions in the upper troposphere