bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of fossil fuel emission uncertainties over Europe for CO2 modeling: model intercomparison
Authors: Peylin P. , Houweling S. , Krol M. C. , Karstens U. , Rödenbeck C. , Geels C. , Vermeulen A. , Badawy B. , Aulagnier C. , Pregger T. , Delage F. , Pieterse G. , Ciais P. , Heimann M.
Published: April 2010

Abstract. Inverse modeling techniques used to quantify surface carbon fluxes commonly assume that the uncertainty of fossil fuel CO2 (FFCO2) emissions is negligible and that intra-annual variations can be neglected. To investigate these assumptions, we analyzed the differences between four fossil fuel emission maps with spatial and temporal differences over Europe and their impact on the model simulated CO2 concentration. Large temporal flux variations characterize the hourly fields (~40% and ~80% for the seasonal and diurnal cycles, peak-to-peak) and annual country totals differ by 10% on average and up to 40% for some countries (i.e., The Netherlands). These emissions have been prescribed to seven different transport models, resulting in 28 different FFCO2 concentrations fields. The modeled FFCO2 concentration time series at surface sites using time-varying emissions show larger seasonal cycles (+2 ppm at the Hungarian tall tower (HUN)) and smaller diurnal cycles in summer (−1 ppm at HUN) than when using constant emissions. The concentration range spanned by all simulations varies between stations, and is generally larger in winter (up to ~10 ppm peak-to-peak at HUN) than in summer (~5 ppm). The contribution of transport model differences to the simulated concentration std-dev is 2–3 times larger than the contribution of emission differences only, at typical European sites used in global inversions. These contributions to the hourly (monthly) std-dev's amount to ~1.2 (0.8) ppm and ~0.4 (0.3) ppm for transport and emissions, respectively. First comparisons of the modeled concentrations with 14C-based fossil fuel CO2 observations show that the large transport differences still hamper a quantitative evaluation/validation of the emission inventories. Changes in the estimated monthly biosphere flux (Fbio) over Europe, using two inverse modeling approaches, are relatively small (less that 5%) while changes in annual Fbio (up to ~0.15 Gt C/yr) are only slightly smaller than the differences in annual emission totals and around 30% of the mean European ecosystem carbon sink. These results point to an urgent need to improve not only the transport models but also the assumed spatial and temporal distribution of fossil fuel emission maps.
Emissions from biomass burning in the Yucatan
Authors: Yokelson R. , Crounse J. D. , DeCarlo P. F. , Karl T. , Urbanski S. , Atlas E. , Campos T. , Shinozuka Y. , Kapustin V. , Clarke A. D. , Weinheimer A. , Knapp D. J. , Montzka D. D. , Holloway J. , Weibring P. , Flocke F. , Zheng W. , Toohey D. , Wennberg P. O. , Wiedinmyer C. , Mauldin L. , Fried A. , Richter D. , Walega J. , Jimenez J. L. , Adachi K. , Buseck P. R. , Hall S. R. , Shetter R.
Published: April 2010

Abstract. In March 2006 two instrumented aircraft made the first detailed field measurements of biomass burning (BB) emissions in the Northern Hemisphere tropics as part of the MILAGRO project. The aircraft were the National Center for Atmospheric Research C-130 and a University of Montana/US Forest Service Twin Otter. The initial emissions of up to 49 trace gas or particle species were measured from 20 deforestation and crop residue fires on the Yucatan peninsula. This included two trace gases useful as indicators of BB (HCN and acetonitrile) and several rarely, or never before, measured species: OH, peroxyacetic acid, propanoic acid, hydrogen peroxide, methane sulfonic acid, and sulfuric acid. Crop residue fires emitted more organic acids and ammonia than deforestation fires, but the emissions from the main fire types were otherwise fairly similar. The Yucatan fires emitted unusually high amounts of SO2 and particle chloride, likely due to a strong marine influence on this peninsula. As smoke from one fire aged, the ratio ΔO3/ΔCO increased to ~15% in 1×107 molecules/cm3. Thus, more research is needed to understand critical post emission processes for the second-largest trace gas source on Earth. It is estimated that ~44 Tg of biomass burned in the Yucatan in the spring of 2006. Mexican BB (including Yucatan BB) and urban emissions from the Mexico City area can both influence the March–May air quality in much of Mexico and the US.
Physical properties of High Arctic tropospheric particles during winter
Authors: Bourdages L. , Duck T. J. , Lesins G. , Drummond J. R. , Eloranta E. W.
Published: April 2010

Abstract. A climatology of particle properties in the wintertime High Arctic troposphere is constructed using measurements from a lidar and cloud radar located at Eureka, Nunavut Territory (80° N, 86° W). Four different particle groupings are considered: aerosols, mixed-phase clouds, ice clouds and boundary-layer ice crystals. Two-dimensional histograms of occurrence probabilities against depolarization and radar/lidar colour ratio, as well as their vertical distributions, are presented. The largest ice crystals originate from mixed-phase clouds, whereas the smallest are topographic blowing snow residuals in the boundary layer. Ice cloud crystals have depolarization and size decreasing with height. The depolarization trend is associated with the large ice crystal sub-population. Small crystals depolarize more than large ones in ice clouds at a given altitude, and show constant modal depolarization with height. Ice clouds in the mid-troposphere are sometimes observed to precipitate to the ground. Water clouds are constrained to the lower troposphere and are associated with the surface inversion layer depth. Aerosols are most abundant near the ground and are frequently mixed with the other particle types. The data are used to construct a classification chart for particle scattering in wintertime Arctic conditions.
Eddy covariance flux measurements of pollutant gases in urban Mexico City
Authors: Velasco E. , Pressley S. , Grivicke R. , Allwine E. , Coons T. , Foster W. , Jobson T. , Westberg H. , Ramos R. , Hernández F. , Molina L. T. , Lamb B.
Published: April 2010

Abstract. Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The data show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not present in the mobile emissions inventory.
Intercomparison of integrated IASI and AATSR calibrated radiances
Authors: Illingworth S. M. , Remedios J. J. , Parker R. J.
Published: April 2010

Abstract. The mission objectives of the Infrared Atmospheric Sounding Interferometer (IASI) are driven by the needs of the Numerical Weather Prediction (NWP) and climate monitoring communities. These objectives rely upon the IASI instrument being able to measure top of atmosphere radiances accurately. This paper presents a technique and results for the validation of the radiometric calibration of radiances for IASI, using a cross-calibration with the Advanced Along Track Scanning Radiometer (AATSR). The AATSR is able to measure Brightness Temperature (BT) to an accuracy of 30 mK, and by applying the AATSR spectral filter function to the IASI measured radiances we are able to compare AATSR and IASI Brightness Temperatures. By choosing coincidental data points that are over the sea and in clear sky conditions, a threshold of homogeneity is derived. It is found that in these homogenous conditions, the IASI BTs agree with those measured by the AATSR to within 0.5 K, with a precision of order 0.04 K. These results indicate that IASI is likely to be meeting its target objective of 0.5 K accuracy. It is believed that a refinement of the AATSR spectral filter function will hopefully permit a tighter error constraint on the quality of the IASI data and hence further assessment of the climate quality of the radiances.
Surface ozone trend details and interpretations in Beijing, 2001–2006
Authors: Tang G. , Li X. , Wang Y. , Xin J. , Ren X.
Published: April 2010

Abstract. Beijing is a megacity situated in the rapidly developing Beijing-Tianjin-Hebei region of northern China. In this study, we analyze data on ozone and nitrogen oxide levels obtained at six urban sites in Beijing between the months of July and September. Our goal is to investigate average trends and interpretations over the 2001–2006 period. Average concentrations of NOx (NOx=NO+NO2), O3, and Ox (Ox=O3+NO2) were 49.2±5.9 ppbv, 26.6±2.8 ppbv, and 60.3±1.9 ppbv, respectively. NOx concentrations decreased linearly at a rate of 3.9±0.5 ppbv/yr after 2002, while ozone concentrations increased at a rate of 1.1±0.5 ppbv/yr in a two-year cycle during 2001–2006, and Ox concentrations remained nearly constant. The reduction of NOx emissions and elevated non-methane hydrocarbon (NMHCs) emissions may have contributed to the increased O3 concentrations in Beijing. When the contributions from Beijings urban and surrounding areas were disaggregated via trajectory cluster analysis, daily maximum and average Ox concentrations attributable to Beijing local emissions increased linearly at rates of 1.3±0.6 ppbv/yr and 0.8±0.6 ppbv/yr, while the Ox concentrations attributable to regional areas decreased linearly at rates of 0.6±0.3 ppbv/yr and 0.5±0.3 ppbv/yr, respectively. The decrease in Ox concentrations of surrounding areas was found to counteract increasing Beijing urban Ox production, leading to nearly constant Ox concentrations in the Beijing region over the study period. Our results may be helpful for redefining government strategies to control the photochemical formation of air pollutants in the Beijing region. Our conclusions have relevance for developing megacities worldwide.
New particle formation from the oxidation of direct emissions of pine seedlings
Authors: Hao L. Q. , Yli-Pirilä P. , Tiitta P. , Romakkaniemi S. , Vaattovaara P. , Kajos M. K. , Rinne J. , Heijari J. , Kortelainen A. , Miettinen P. , Kroll J. H. , Holopainen J.-K. , Joutsensaari J. , Kumala M. , Worsnop D. R. , Laaksonen A.
Published: April 2010

Abstract. Measurements of particle formation following the gas phase oxidation of volatile organic compounds (VOCs) emitted by Scots pine (Pinus sylvestris L.) seedlings are reported. Particle nucleation and condensational growth both from ozone (O3) and hydroxyl radical (OH) initiated oxidation of pine emissions (about 20–120 ppb) were investigated in a~smog chamber. During experiments, tetramethylethylene (TME) and 2-butanol were added to control the concentrations of O3 and OH. Particle nucleation and condensational growth rates were interpreted with a chemical kinetics model. Scots pine emissions mainly included α-pinene, β-pinene, Δ3-carene, limonene, myrcene, β-phellandrene and isoprene, composing more than 95% of total emissions. Modeled OH concentration in the O3+OH induced experiments was at a level of ~106 molecular cm−3. Our results demonstrate that OH-initiated oxidation of VOCs plays an important role in the nucleation process during the initial new particle formation stage. The highest average nucleation rate of 360 cm−3 s−1 was observed for the OH-dominated nucleation events and the lowest aerosol mean formation rate less than 0.5 cm−3 s−1 for the case with only O3 present as an oxidant. On the other hand, ozonolysis of monoterpenes appears to be much more efficient to the aerosol growth process following nucleation. Higher contributions of more oxygenated products to the SOA mass loadings from OH-dominating oxidation systems were found as compared to the ozonolysis systems. Comparison of mass and volume distributions from the aerosol mass spectrometer and differential mobility analyzer yields estimated effective density of these SOA to be 1.34±0.06 g cm−3 with the OH plus O3 initiated oxidation systems and 1.38±0.03 g cm−3 with the ozonolysis dominated chemistry.
Study of columnar aerosol size distribution in Hong Kong
Authors: Yang X. , Wenig M.
Published: April 2010

Abstract. This paper presents studies on columnar aerosol optical properties in Hong Kong with focus on aerosol volume size distribution. Long-term ground measurements in the wet season in the years of 2002, 2003, 2004 and 2008 have been performed using a sun-sky radiometer. A bimodal size distribution is found with the fine mode centering at ~0.2 μm and coarse mode centering at ~6 μm, respectively. The fine and coarse mode have close volume concentrations of nearly 50% fraction in composing local aerosols. Intercomparison of different years shows similar aerosol properties while a small increase of fine mode aerosol could be observed. A systematic shift of size distribution parameters is observed with different atmospheric conditions, where higher aerosol loadings and Angstrom exponent correspond to more fine aerosols. The fine mode is found to be more closely correlated with this shift than the coarse mode. A higher fine mode volume fraction and smaller median fine radius correspond to a larger Angstrom exponent. The fine aerosol hygroscopic growth is one of the main mechanisms for such systematic shifting. A third mode centering at ~1–2 μm could be discovered under high aerosol loading and high fine aerosol conditions. It becomes more pronounced with high aerosol optical depth and larger Angstrom exponent. Investigation of its variation with corresponding optical parameters and correlation with atmospheric conditions indicates that it is mainly due to the fine aerosol hygroscopic growth and coagulation rather than the contribution from the coarse mode. While the very humid environment facilitates the aerosol hygroscopic growth, aerosol coagulation might further produce more large aerosols under high fine aerosol conditions. The continental outflow with transported ageing aerosols and biomass burning might have also contributed to this additional mode.
The impact of resolution on ship plume simulations with NOx chemistry
Authors: Charlton-Perez C. L. , Evans M. J. , Marsham J. H. , Esler J. G.
Published: April 2010

Abstract. A high resolution chemical transport model of the marine boundary layer is designed in order to investigate the detailed chemical evolution of a ship plume. To estimate systematic errors due to finite model resolution, otherwise identical simulations are run at a range of model resolutions. Notably, to obtain comparable plumes in the different simulations, it is found necessary to use an advection scheme consistent with the Large Eddy Model representation of sub-grid winds for those simulations with degraded resolution. Our simulations show that OH concentration, NOx lifetime and ozone production efficiency of the model change by 8%, 32% and 31% respectively between the highest (200 mx200 mx40 m) and lowest resolution (9600 mx9600 mx1920 m) simulations. Interpolating to the resolution of a typical global composition transport model (CTM, 5°x5°), suggests that a CTM overestimates OH, NOx lifetime and ozone production efficiency by approximately 15%, 55% and 59% respectively. For the first time, it is shown explicitly that the reduction in model skill is due to the coarse resolution of these CTMs and the non-linear nature of atmospheric chemistry. These results are significant for the assessment and forecasting of the climate impact of ship NOx and indicate that for realistic representation of ship plume emissions in CTMs, some suitable parametrisation is necessary at current global model resolutions.
Sensitivity of ensemble Lagrangian reconstructions to assimilated wind time step resolution
Authors: Pisso I. , Marécal V. , Legras B. , Berthet G.
Published: April 2010

Abstract. The aim of this study is to define the optimal temporal and spatial resolution required for accurate offline diffusive Lagrangian reconstructions of high resolution in-situ tracers measurements based on meteorological wind fields and on coarse resolution 3-D tracer distributions. Increasing the time resolution of the advecting winds from three to one hour intervals has a modest impact on diffusive reconstructions in the case studied. This result is discussed in terms of the effect on the geometry of transported clouds of points in order to set out a method to assess the effect of meteorological flow on the transport of atmospheric tracers.
Mobile mini-DOAS measurement of the emission of NO2 and HCHO from Mexico City
Authors: Johansson M. , Rivera C. , de Foy B. , Lei W. , Song J. , Zhang Y. , Galle B. , Molina L.
Published: April 2010

Abstract. We here present the result of one mobile measurement using two ground based zenith viewing Differential Optical Absorption Spectroscopy (DOAS) instrument performed in a cross-section of the plume from the MCMA on the 10 March 2006 as part of the MILAGRO field campaign. The two instruments operated in the UV and the visible wavelength region respectively and have been used to derive the differential vertical columns of HCHO and NO2 above the measurement route. Using a mass-averaged wind speed and wind direction from the WRF model the instantaneous flux of HCHO and NO2 has been calculated from the two measurements and the results compared to the CAMx chemical model. The calculated flux through the measured cross-section was 1.9 (1.5–2.2) kg/s of HCHO and 4.4 (4.0–5.0) kg/s of NO2 using the UV instrument and 3.66 (3.63–3.73) kg/s of NO2 using the visible light instrument. The comparison with modeled values from CAMx shows a good agreement for the outflow of both NO2 and HCHO at this occasion.
BrO, blizzards, and drivers of polar tropospheric ozone depletion events
Authors: Jones A. E. , Anderson P. S. , Begoin M. , Brough N. , Hutterli M. A. , Marshall G. J. , Richter A. , Roscoe H. K. , Wolff E. W.
Published: April 2010

Abstract. The source of bromine that drives polar boundary layer ozone depletion events (ODEs) is still open to some debate. While ODEs are generally noted to form under conditions of a shallow stable boundary layer, observations of depleted air under high wind conditions are taken as being transport-related. Here we report observations from Antarctica in which an unusually large cloud of BrO formed over the Weddell Sea. The enhanced BrO was observed over Halley station in coastal Antarctica, providing an opportunity to probe the conditions within an active "bromine explosion" event. On this occasion, enhanced BrO and depleted boundary layer ozone coincided with high wind speeds and saline blowing snow. We derive a simple model to consider the environmental conditions that favour ODEs and find two maxima, one at low wind/stable boundary layer and one at high wind speeds with blowing snow. Modelling calculations aiming to reproduce the wider regional or global impacts of ODEs, either via radiative effects or as a halogen source, will also need to account for high wind speed mechanisms.
Simulation of Mexico City plumes during the MIRAGE-Mex field campaign using the WRF-Chem model
Authors: Tie X. , Madronich S. , Li G. , Ying Z. , Weinheimer A. , Apel E. , Campos T.
Published: April 2010

Abstract. The quantification of tropospheric O3 production in the Mexico City outflow is a major objective of the MIRAGE-Mex field campaign. We used a regional chemistry-transport model (WRF-Chem) to predict the distribution of O3 and its precursors in Mexico City and the surrounding region during March 2006, and compared with in-situ aircraft measurement of O3, CO, VOCs, NOx, and NOy concentrations. The comparison shows that the model is capable of capturing the timing/location of the measured city plumes, and the calculated variability along the flights is generally consistent with the measured results, showing a rapid enhancement of O3 and its precursors when city plumes are detected. However, there are some notable differences between the calculated and measured values, suggesting that, during transport from the surface of the city to the outflow plume, pollution levels are underestimated by about 0–25% during different flights. The calculated O3-NOx, O3-CO, and O3-NOz correlations generally agree with the measured values, and the analysis of these correlations suggest that photochemical O3 production continues in the plume downwind of the city (aged plume), adding to the O3 already produced in the city and exported with the plume. The model is also used to quantify the contributions to OH reactivity from various compounds in the aged plume. This analysis suggests that oxygenated organics (OVOCs) have the highest OH reactivity and play important roles for the O3 production in the aging plume. Furthermore, O3 production per NOx molecule consumed (O3 production efficiency) is more efficient in the aged plume than in the young plume near the city. The major contributor to the high O3 production efficiency in the aged plume is the reaction RO2+NO. By contrast, the reaction of HO2+NO is rather uniformly distributed in the plume.
BrO measurements over the Eastern North-Atlantic
Authors: Martin M. , Pöhler D. , Seitz K. , Sinreich R. , Platt U.
Published: April 2010

Abstract. The aim of the work presented here was to detect BrO in the marine boundary layer over the Eastern North-Atlantic by Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) of scattered sunlight. With this technique, information about the concentration and the vertical profile of trace gases in the atmosphere can be gained. BrO can be formed in the marine atmosphere by degradation of biogenic organohalogens or by oxidation of bromide in sea salt aerosol. BrO influences the chemistry in marine air in many was, e.g. since it catalytically destroys ozone, changes the NO2/NO-ratio as well as the OH/HO2-ratio and oxidises DMS. However, the abundance and the significance of BrO in the marine atmosphere are not yet fully understood. We report on data collected during a ship cruise, which took place along the West African Coast in February 2007, within the framework of the Surface Ocean PRocesses in the ANthropocene project (SOPRAN). Tropospheric BrO could be detected during this cruise at peak mixing ratios of (10.2±3.7) ppt at an assumed layer height of 1 km on 18 February 2007. Furthermore, it was found that the mean BrO concentrations increased when cruising close to the African Coast suggesting that at least part of the BrO might have originated from the African coast.
Performance of the line-by-line radiative transfer model (LBLRTM) for temperature and species retrievals: IASI case studies from JAIVEx
Authors: Shephard M. W. , Clough S. A. , Payne V. H. , Smith W. L. , Kireev S. , Cady-Pereira K. E.
Published: April 2010

Abstract. Presented here are comparisons between the Infrared Atmospheric Sounding instrument (IASI) and the "Line-By- Line Radiative Transfer Model" (LBLRTM). Spectral residuals from radiance closure studies during the IASI JAIVEx validation campaign provide insight into a number of spectroscopy issues relevant to remote sounding of temperature, water vapor and trace gases from IASI. In order to perform quality IASI trace gas retrievals the temperature and water vapor fields must be retrieved as accurately as possible. In general, the residuals in the CO2 ν2 region are of the order of the IASI instrument noise. However, outstanding issues in the CO2 spectral regions remain. There is a large residual ~−1.5 K in the 667 cm−1 Q-branch, and residuals in the CO2 ν2 and N2O/CO2 ν3 spectral regions that sample the troposphere are inconsistent, with the N2O/CO2 ν3 region being too negative (warmer) by ~0.6 K. Residuals on this lower wavenumber side of the CO2 ν3 band will be improved by line parameter updates, while future efforts to reduce the residuals reaching ~−0.5 K on the higher wavenumber side of the CO2 ν3 band will focus on addressing limitations in the modeling of the CO2 line shape (line coupling and duration of collision) effects. Brightness temperature residuals from the radiance closure studies in the ν2 water vapor band have standard deviations of ~0.2–0.3 K with some large peak residuals reaching ±0.5–1.0 K. These are larger than the instrument noise indicating that systematic errors still remain. New H2O line intensities and positions from Coudert have a significant impact on the retrieved water vapor, particularly in the upper troposphere where the water vapor retrievals are 10% drier when using line intensities from Coudert compared with HITRAN2004. In addition to O3, CH4, and CO, the high radiometric calibration of the IASI instrument combined with an accurate forward model allows for the detection of minor species with weak atmospheric signatures in the nadir radiances, such as HNO3 and OCS.
Aerosol composition of the tropical upper troposphere
Authors: Froyd K. D. , Murphy D. M. , Sanford T. J. , Thomson D. S. , Wilson J. C. , Pfister L. , Lait L.
Published: April 2010

Abstract. Aerosol composition was measured by the NOAA single particle mass spectrometer (PALMS) aboard the NASA WB-57 high altitude aircraft platform during two Aura Validation Experiment (AVE) campaigns based in Costa Rica in 2004 and 2006. These studies yielded the most complete set of aerosol composition measurements to date throughout the tropical tropopause layer (TTL) and tropical lower stratosphere. We describe the aerosol properties of the tropical atmosphere and use composition tracers to examine particle sources, the role of recent convection, and cirrus-forming potential in the TTL. Tropical dynamics and regional air sources played principal roles in dictating tropospheric aerosol properties. There was a sharp change in aerosol chemical composition at about 12 km altitude coincident with a change in convective influence. Below this level, maritime convection lofted condensable material that generated acidic, sulfate-rich aerosol. These particles contained significant amounts of methanesulfonic acid (MSA) and showed evidence of cloud processes. In contrast, continental convection injected particles and precursors directly into the TTL, yielding a population of neutralized, organic-rich aerosol. The organics were often highly oxidized and particles with oxidized organics also contained nitrate. Above the tropopause, chemical composition gradually changed toward sulfuric acid particles but neutralized particles were still abundant 2 km above the tropopause. Deep continental convection, though sporadic and geographically localized, may strongly influence TTL aerosol properties on a global scale. The abundance of organic-rich aerosol may inhibit ice nucleation and formation of tropopause level cirrus.
Comment on Kokkola et al. (2008) – Comparisons with analytical solutions from Khvorostyanov and Curry (2007) on the critical droplet radii and supersaturations of CCN with insoluble fractions
Authors: Khvorostyanov V. I. , Curry J. A.
Published: April 2010

Abstract. Analytical solutions for the critical radii rcr and supersaturations scr of the cloud condensation nuclei with insoluble fractions were derived by Khvorostyanov and Curry (2007, hereafter KC07). Similar solutions were found later by Kokkola et al. (2008, hereafter Kok08); however, Kok08 used the approximation of an ideal dilute solution, while KC07 used more accurate assumptions that account for nonideality of solutions. Kok08 found a large discrepancy with KC07 in the critical supersaturations. Various possible reasons of this are analyzed. It is shown that the major discrepancy was caused by a simple mistake in Kok08 in the equation for the critical supersaturation: erroneous ''plus'' sign between the Kelvin and Raoult terms instead of correct ''minus'' sign. If this mistake is corrected, the equations from Kok08 mostly repeat the equations from KC07, except that Kok08 use the dilute solution approximation. If the mistake in Kok08 is corrected, then the differences in the critical radii and supersaturations do not exceed 16–18%, which characterizes the possible errors of an ideal diluted solution approximation. If the Kok08 scheme is corrected and applied to a nonideal solution, then the difference with KC07 does not exceed 0.4–1%.
Towards closing the gap between hygroscopic growth and activation for secondary organic aerosol: Part 1 – Evidence from measurements
Authors: Wex H. , Petters M. D. , Carrico C. M. , Hallbauer E. , Massling A. , McMeeking G. R. , Poulain L. , Wu Z. , Kreidenweis S. M. , Stratmann F.
Published: April 2010

Abstract. Secondary Organic Aerosols (SOA) studied in laboratory experiments generally was found to show only slight hygroscopic growth, but a much better activity as a CCN (Cloud Condensation Nucleus) than indicated by the hygroscopic growth. This discrepancy was examined at LACIS (Leipzig Aerosol Cloud Interaction Simulator), using a portable generator that produced SOA particles from the ozonolysis of α-pinene, and adding butanol or butanol and water vapor during some of the experiments. The light scattering signal of dry SOA-particles was measured by the LACIS optical particle spectrometer and was used to derive a refractive index for SOA of 1.45. LACIS also measured the hygroscopic growth of SOA particles up to 99.6% relative humidity (RH), and a CCN counter was used to measure the particle activation. SOA-particles were CCN active with critical diameters of e.g. 100 and 55 nm at supersaturations of 0.4 and 1.1%, respectively. But only slight hygroscopic growth with hygroscopic growth factors ≤1.05 was observed at RH<98% RH. The hygroscopic growth increased slightly with the OH concentration present during the SOA-generation. At RH>98%, the hygroscopic growth increased stronger than would be expected if a constant hygroscopicity parameter for the particle/droplet solution was assumed. An increase of the hygroscopicity parameter by a factor of 4–6 was observed in the RH-range from below 90 to 99.6%, and this increase continued for increasingly diluted particle solutions for activating particles. This explains an observation already made in the past: that the relation between critical supersaturation and dry diameter for activation is steeper than what would be expected for a constant value of the hygroscopicity. The increase in the hygroscopicity parameter could be explained by either an increase in the number of ions/molecules in solution (e.g. due to the presence of slightly soluble particles with deliquescence RHs above 98%), or a change in the non-ideal behaviour (see companion paper Petters et al., 2008). Combining measurements of hygroscopic growth and activation, it was found that the surface tension that has to be assumed to interpret the measurements consistently is greater than 55 mN/m, possibly close to that of pure water, depending on the different SOA-types produced, and therefore only in part accounts for the discrepancy between hygroscopic growth and CCN activity observed for SOA particles in the past.
Parameterization of vertical diffusion and the atmospheric boundary layer height determination in the EMEP model
Authors: Jeričević A. , Kraljević L. , Grisogono B. , Fagerli H.
Published: April 2010

Abstract. A new vertical diffusion scheme, called Grisogono, has been implemented in the Unified EMEP (European Monitoring and Evaluation Programme) model. It is shown based on Large Eddy Simulation (LES) that the Grisogono method performs better than the operational O'Brien's polynomial, especially in the stable conditions. In this work, the operational and proposed new parameterization for eddy diffusivity K(z) have been validated against observed daily surface nitrogen dioxide (NO2), sulphur dioxide (SO2) and sulphate (SO4−2) concentrations at different EMEP stations during year 2001. Moderate improvement in the correlation coefficient and bias for NO2 and SO2 and slight improvement for sulphate is found for most of the analyzed stations with the Grisogono K(z) scheme, which is recommended for further application due to its scientific and technical advantages. Special emphasis is given to the representation of the atmospheric boundary layer (ABL) in order to capture vertical transport and dispersion of atmospheric air pollution. Two different ABL schemes are evaluated against radiosounding data in January and July 2001, and against data from the Cabauw tower, the Netherlands, in the same year. Based on validation of the ABL parameterizations, it is found that the EMEP model is able to reproduce spatial and temporal mixing height variability. Improvements are identified especially in stable conditions with the new ABL scheme based on the bulk Richardson number (RiB).
Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget
Authors: Dusanter S. , Vimal D. , Stevens P. S. , Volkamer R. , Molina L. T. , Baker A. , Meinardi S. , Blake D. R. , Sheehy P. , Merten A. , Zhang R. , Zheng J. , Fortner E. C. , Junkermann W. , Dubey M. K. , Rahn T. , Eichinger W. E. , Lewandowski P. , Prueger J. , Holder H.
Published: April 2010

Abstract. Measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals were made during the Mexico City Metropolitan Area (MCMA) field campaign as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) project during March 2006. These measurements provide a unique opportunity to test current models of atmospheric ROx (OH+HO2+RO2) photochemistry under polluted conditions. A zero-dimensional box model based on the Regional Atmospheric Chemical Mechanism (RACM) was constrained by 10-min averages of 24 J-values and the concentrations of 97 chemical species. Several issues related to the ROx chemistry under polluted conditions are highlighted in this study: (i) median concentrations of both OH and HO2 were underpredicted during morning hours, suggesting a significant source of radicals is missing from current atmospheric models under polluted conditions, consistent with previous urban field campaigns. (ii) The predicted HO2/OH ratios were underestimated for NO mixing ratios higher than 5 ppb, also consistent with previous urban field campaigns. This suggests that under high NOx conditions, the HO2 to OH propagation rate may be overestimated by the model or a process converting OH into HO2 may be missing from the chemical mechanism. On a daily basis (08:40 a.m.–06:40 p.m.), an analysis of the radical budget indicates that HONO photolysis, HCHO photolysis, O3-alkene reactions and dicarbonyls photolysis are the main radical sources. O3 photolysis contributes to less than 6% of the total radical production.
Closing the peroxy acetyl (PA) radical budget: observations of acyl peroxy nitrates (PAN, PPN, and MPAN) during BEARPEX 2007
Authors: LaFranchi B. W. , Wolfe G. M. , Thornton J. A. , Harrold S. A. , Browne E. C. , Min K. E. , Wooldridge P. J. , Gilman J. B. , Kuster W. C. , Goldan P. D. , deGouw J. A. , McKay M. , Goldstein A. H. , Ren X. , Mao J. , Cohen R. C.
Published: April 2010

Abstract. Acyl peroxy nitrates (APNs, also known as PANs) are formed from the oxidation of aldehydes and other oxygenated VOC (oVOC) in the presence of NO2. Formation of APNs suppresses NOx (NOx≡NO+NO2) in urban areas and enhances NOx downwind in urban plumes, increasing the rate of ozone production throughout an urban plume. APNs also redistribute NOx on global scales, enhancing NOx and thus ozone production. There are both anthropogenic and biogenic oVOC precursors to APNs, but a detailed evaluation of their chemistry against observations has proven elusive. Here we describe measurements of PAN, PPN, and MPAN along with the majority of chemicals that participate in their production and loss, including OH, HO2, numerous oVOC, and NO2. Observations were made during the Biosphere Effects on AeRosols and Photochemistry Experiment (BEARPEX 2007) in the outflow of the Sacramento urban plume. These observations are used to evaluate a detailed chemical model of APN ratios and concentrations. We find the ratios of APNs are nearly independent of the loss mechanisms and thus an especially good test of our understanding of their sources. We show that oxidation of methylvinyl ketone, methacrolein, methyl glyoxal, biacetyl and acetaldehyde are all significant sources of the PAN+peroxy acetyl (PA) radical reservoir, with methylvinyl ketone (MVK) often being the primary non-acetaldehyde source. At high temperatures, oxidation of non-acetaldehyde PA radical sources contributes over 60% to the total PA production rate. An analysis of absolute APN concentrations reveals a missing APN sink that can be resolved by increasing the PA+∑RO2 rate constant by a factor of 3.
Long-lived halocarbon trends and budgets from atmospheric chemistry modelling constrained with measurements in polar firn
Authors: Martinerie P. , Nourtier-Mazauric E. , Barnola J.-M. , Sturges W. T. , Worton D. R. , Atlas E. , Gohar L. K. , P Shine K. , Brasseur G. P.
Published: April 2010

Abstract. The budgets of seven halogenated gases (CFC-11, CFC-12, CFC-113, CFC-114, CFC-115, CCl4 and SF6) are studied by comparing measurements in polar firn air from two Arctic and three Antarctic sites, and simulation results of two numerical models: a 2-D atmospheric chemistry model and a 1-D firn diffusion model. The first one is used to calculate atmospheric concentrations from emission trends based on industrial inventories; the calculated concentration trends are used by the second one to produce depth concentration profiles in the firn. The 2-D atmospheric model is validated in the boundary layer by comparison with atmospheric station measurements, and vertically for CFC-12 by comparison with balloon and FTIR measurements. Firn air measurements provide constraints on historical atmospheric concentrations over the last century. Age distributions in the firn are discussed using a Green function approach. Finally, our results are used as input to a radiative model in order to evaluate the radiative forcing of our target gases. Multi-species and multi-site firn air studies allow to better constrain atmospheric trends. The low concentrations of all studied gases at the bottom of the firn, and their consistency with our model results confirm that their natural sources are insignificant. Our results indicate that the emissions, sinks and trends of CFC-11, CFC-12, CFC-113, CFC-115 and SF6 are well constrained, whereas it is not the case for CFC-114 and CCl4. Significant emission-dependent changes in the lifetimes of halocarbons destroyed in the stratosphere were obtained. Those result from the time needed for their transport from the surface where they are emitted to the stratosphere where they are destroyed. Efforts should be made to update and reduce the large uncertainties on CFC lifetimes.
Assessment of two methods for gravity field recovery from GOCE GPS-SST orbit solutions
Authors: Arsov K. , Pail R.
Published: April 2010

Abstract. In the course of the GOCE satellite mission, the high-low Satellite to Satellite Tracking (SST) observations have to be processed for the determination of the long wavelength part of the Earth’s gravity field. This paper deals with the formulation of the high-low SST observation equations, as well as the methods for gravity field recovery from orbit information. For this purpose, two approaches, i.e. the numerical integration of orbit perturbations, and the evaluation of the energy equation based on the Jacobi integral, are presented and discussed. Special concern is given to the numerical properties of the corresponding normal equations. In a closed-loop simulation, which is based on a realistic orbit GOCE configuration, these methods are compared and assessed. However, here we process a simplified case assuming that non-conservative forces can be perfectly modelled. Assuming presently achievable accuracies of the Precise Orbit Determination (POD), it turns out that the numerical integration approach is still superior, but the energy integral approach may be an interesting alternative processing strategy in the near future.Key words. High-low SST – gravity field – GOCE – variational equations – least squares adjustment
Improved nowcasting of precipitation based on convective analysis fields
Authors: Steinheimer M. , Haiden T.
Published: April 2010

Abstract. The high-resolution analysis and nowcasting system INCA (Integrated Nowcasting through Comprehensive Analysis) developed at the Austrian national weather service provides three-dimensional fields of temperature, humidity, and wind on an hourly basis, and two-dimensional fields of precipitation rate in 15 min intervals. The system operates on a horizontal resolution of 1 km and a vertical resolution of 100–200 m. It combines surface station data, remote sensing data (radar, satellite), forecast fields of the numerical weather prediction model ALADIN, and high-resolution topographic data. An important application of the INCA system is nowcasting of convective precipitation. Based on fine-scale temperature, humidity, and wind analyses a number of convective analysis fields are routinely generated. These fields include convective boundary layer (CBL) flow convergence and specific humidity, lifted condensation level (LCL), convective available potential energy (CAPE), convective inhibition (CIN), and various convective stability indices. Based on the verification of areal precipitation nowcasts it is shown that the pure translational forecast of convective cells can be improved by using a decision algorithm which is based on a subset of the above fields, combined with satellite products.
On evaluation of ensemble precipitation forecasts with observation-based ensembles
Authors: Ahrens B. , Jaun S.
Published: April 2010

Abstract. Spatial interpolation of precipitation data is uncertain. How important is this uncertainty and how can it be considered in evaluation of high-resolution probabilistic precipitation forecasts? These questions are discussed by experimental evaluation of the COSMO consortium's limited-area ensemble prediction system COSMO-LEPS. The applied performance measure is the often used Brier skill score (BSS). The observational references in the evaluation are (a) analyzed rain gauge data by ordinary Kriging and (b) ensembles of interpolated rain gauge data by stochastic simulation. This permits the consideration of either a deterministic reference (the event is observed or not with 100% certainty) or a probabilistic reference that makes allowance for uncertainties in spatial averaging. The evaluation experiments show that the evaluation uncertainties are substantial even for the large area (41 300 km2) of Switzerland with a mean rain gauge distance as good as 7 km: the one- to three-day precipitation forecasts have skill decreasing with forecast lead time but the one- and two-day forecast performances differ not significantly.
Development and application of the modelling system J2000-S for the EU-water framework directive
Authors: Fink M. , Krause P. , Kralisch S. , Bende-Michl U. , Flügel W.-A.
Published: April 2010

Abstract. The scientific sound definition of measures to achieve the goals of the EU water framework directive (WFD) acquires spatially distributed analyses of the water and substance dynamics in meso- to macro-scale catchments. For this purpose, modelling tools or systems are needed which are robust and fast enough to be applied on such scales, but which are also able to simulate the impact of changes on single fields or small areas of a specific land use in the catchment. To face these challenges, we combined the fully-distributed hydrological model J2000 with the nitrogen transport routines of the Soil Water Assessment Tool SWAT model, which are normally applied in a semi-distributive approach. With this combination, we could extend the quantitative focus of J2000 with qualitative processes and could overcome the semi-distributed limitation of SWAT. For the implementation and combination of the components, we used the Jena Adaptable Modelling System JAMS (Kralisch and Krause, 2006) which helped tremendously in the relatively rapid and easy development of the new resultant model J2000-S (J2000-Substance). The modelling system was applied in the upper Gera watershed, located in Thuringia, Germany. The catchment has an area of 844 km2 and includes three of the typical landscape forms of Thuringia. The application showed, that the new modelling system was able to reproduce the daily hydrological as well as the nitrogen dynamics with a sufficient quality. The paper will describe the results of the new model and compare them with the results obtained with the original semi-distributed application of SWAT.
Application of two phosphorus models with different complexities in a mesoscale river catchment
Authors: Guse B. , Bronstert A. , Rode M. , Tetzlaff B. , Wendland F.
Published: April 2010

Abstract. The water balance and phosphorus inputs of surface waters of the Weiße Elster catchment, Germany, have been quantified using the models GROWA/MEPhos and SWAT. A comparison of the model results shows small differences in the mean long-term total runoff for the entire study area. All relevant pathways of phosphorus transport were considered in MEPhos with phosphorus inputs resulting to about 65% from point sources. SWAT focuses on agricultural areas and estimates a phosphorus input of about 60% through erosion. The mean annual phosphorus input from erosion calculated with SWAT is six times higher than the estimation with MEPhos due to the differing model concepts. This shows the uncertainty contributed by the modelling description of phosphorus pathways.
Model-based scenarios of Mediterranean droughts
Authors: Weiß M. , Flörke M. , Menzel L. , Alcamo J.
Published: April 2010

Abstract. This study examines the change in current 100-year hydrological drought frequencies in the Mediterranean in comparison to the 2070s as simulated by the global model WaterGAP. The analysis considers socio-economic and climate changes as indicated by the IPCC scenarios A2 and B2 and the global general circulation model ECHAM4. Under these conditions today's 100-year drought is estimated to occur 10 times more frequently in the future over a large part of the Northern Mediterranean while in North Africa, today's 100-year drought will occur less frequently. Water abstractions are shown to play a minor role in comparison to the impact of climate change, but can intensify the situation.