bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature and humidity dependence of secondary organic aerosol yield from the ozonolysis of β-pinene
Authors: Stenby C. , Pöschl U. , von Hessberg P. , Bilde M. , Nielsen O. J. , Moortgat G. K.
Published: April 2010

Abstract. The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pinene was studied in a flow reactor at 263 K–303 K and 1007 hPa under dry and humid conditions (0% and 26%–68% relative humidity, respectively). The observed SOA yields were of similar magnitude as predicted by a two-product model based on detailed gas phase chemistry (Jenkin, 2004), reaching maximum values of 0.18–0.39 at high particle mass concentrations (Mo). Under dry conditions, however, the measurement data exhibited significant oscillatory deviations from the predicted linear increase with inverse temperature (up to 50% at high Mo). Under humid conditions the SOA yield exhibited a linear decrease with inverse temperature, which is opposite to modelled temperature dependence and implies that the model substantially overestimates the yield at low temperatures and underestimates it at high temperatures (deviations up to 80% at high Mo). For the atmospherically relevant concentration level of Mo=10 μg m−3 and temperature range 263 K–293 K, the results from humid experiments in this study indicate that the SOA yield of β-pinene ozonolysis may be well represented by an average value of 0.15 with an uncertainty estimate of ±0.05. When fitting the measurement data with a two-product model, both the partitioning coefficients (Kom,i) and the stoichiometric yields (αi) of the low-volatile and semi-volatile model species were found to vary with temperature. The results indicate that not only the reaction product vapour pressures but also the relative contributions of different gas-phase or multiphase reaction channels are strongly dependent on temperature and the presence of water vapour. In fact, the oscillatory positive temperature dependence observed under dry conditions and the negative temperature dependence observed under humid conditions indicate that the SOA yield is governed much more by the temperature and humidity dependence of the involved chemical reactions than by vapour pressure temperature dependencies. We suggest that the elucidation and modelling of SOA formation need to take into account the effects of temperature and humidity on the pathways and kinetics of the involved chemical reactions as well as on the gas-particle partitioning of the reaction products.
An overview of the HIBISCUS campaign
Authors: Pommereau J.-P. , Garnier A. , Held G. , Gomes A.-M. , Goutail F. , Durry G. , Borchi F. , Hauchecorne A. , Montoux N. , Cocquerez P. , Letrenne G. , Vial F. , Hertzog A. , Legras B. , Pisso I. , Pyle J. A. , Harris N. R. P. , Jones R. L. , Robinson A. , Hansford G. , Eden L. , Gardiner T. , Swann N. , Knudsen B. , Larsen N. , Nielsen J. , Christensen T. , Cairo F. , Pirre M. , Marécal V. , Huret N. , Riviére E. , Coe H. , Grosvenor D. , Edvarsen K. , Di Donfrancesco G. , Ricaud P. , Berthelier J.-J. , Godefroy M. , Seran E. , Longo K. , Freitas S.
Published: April 2010

Abstract. HIBISCUS was a field campaign for investigating the impact of deep convection on the Tropical Tropopause Layer (TTL) and the Lower Stratosphere, which took place during the Southern Hemisphere summer in February–March 2004 in the State of São Paulo, Brazil. Its objective was to provide a set of new observational data on meteorology, tracers of horizontal and vertical transport, water vapour, clouds, and chemistry in the tropical UT/LS from balloon observations at local scale over a land convective area, as well as at global scale using circumnavigating long-duration balloons. Overall, the composition of the TTL, the region between 14 and 19 km of intermediate lapse rate between the almost adiabatic upper troposphere and the stable stratosphere, appears highly variable. Tracers and ozone measurements performed at both the local and the global scale indicate a strong quasi-horizontal isentropic exchange with the lowermost mid-latitude stratosphere suggesting that the barrier associated to the tropical jet is highly permeable at these levels in summer. But the project also provides clear indications of strong episodic updraught of cold air, short-lived tracers, low ozone, humidity and ice particles across the lapse rate tropopause at about 15 km, up to 18 or 19 km at 420–440 K potential levels in the lower stratosphere, suggesting that, in contrast to oceanic convection penetrating little the stratosphere, fast daytime developing land convective systems could be a major mechanism in the troposphere-stratosphere exchange at the global scale. The present overview is meant to provide the background of the project, as well as overall information on the instrumental tools available, on the way they have been used within the highly convective context of the South Atlantic Convergence Zone, and a brief summary of the results, which will be detailed in several other papers of this special issue.
Observations of OH and HO2 radicals in coastal Antarctica
Authors: Bloss W. J. , Lee J. D. , Heard D. E. , Salmon R. A. , Bauguitte S. J.-B. , Roscoe H. K. , Jones A. E.
Published: April 2010

Abstract. OH and HO2 radical concentrations have been measured in the boundary layer of coastal Antarctica for a six-week period during the austral summer of 2005. The measurements were performed at the British Antarctic Survey's Halley Research Station (75° 35'S, 26° 19'W), using the technique of on-resonance laser-induced fluorescence to detect OH, with HO2 measured following chemical conversion through addition of NO. The mean radical levels were 3.9×105 molecule cm−3 for OH, and 0.76 ppt for HO2 (ppt denotes parts per trillion, by volume or pmol mol−1). Typical maximum (local noontime) levels were 7.9×105 molecule cm−3 and 1.50 ppt for OH and HO2 respectively. The main sources of HOx were photolysis of O3 and HCHO, with potentially important but uncertain contributions from HONO and higher aldehydes. Of the measured OH sinks, reaction with CO and CH4 dominated, however comparison of the observed OH concentrations with those calculated via the steady state approximation indicated that additional co-reactants were likely to have been present. Elevated levels of NOx resulting from snowpack photochemistry contributed to HOx cycling and enhanced levels of OH, however the halogen oxides IO and BrO dominated the CH3O2-HO2-OH conversion in this environment, with associated ozone destruction.
Predicting arene rate coefficients with respect to hydroxyl and other free radicals in the gas-phase: a simple and effective method using a single topological descriptor
Authors: McGillen M. R. , Percival C. J. , Pieterse G. , Watson L. A. , Shallcross D. E.
Published: April 2010

Abstract. The reactivity of aromatic compounds is of great relevance to pure and applied chemical disciplines, yet existing methods for estimating gas-phase rate coefficients for their reactions with free radicals lack accuracy and universality. Here a novel approach is taken, whereby strong relationships between rate coefficients of aromatic hydrocarbons and a Randić-type topological index are investigated, optimized and developed into a method which requires no specialist software or computing power. Measured gas-phase rate coefficients for the reaction of aromatic hydrocarbons with OH radicals were correlated with a calculated Randić-type index, and optimized by including a term for side chain length. Although this method is exclusively for use with hydrocarbons, it is more diverse than any single existing methodology since it incorporates alkenylbenzenes into correlations, and can be extended towards other radical species such as O(3P) (and tentatively NO3, H and Cl). A comparison (with species common to both techniques) is made between the topological approach advocated here and a popular approach based on electrophilic subsituent constants, where it compares favourably. A modelling study was carried out to assess the impact of using estimated rate coefficients as opposed to measured data in an atmospheric model. The difference in model output was negligible for a range of NOx concentrations, which implies that this method has utility in complex chemical models. Strong relationships (e.g.~for OH, R2 = 0.96) between seemingly diverse compounds including benzene, multisubstituted benzenes with saturated, unsaturated, aliphatic and cyclic substitutions and the nonbenzenoid aromatic, azulene suggests that the Randić-type index presented here represents a new and effective way of describing aromatic reactivity, based on a quantitative structure-activity relationship (QSAR).
Air quality in North America's most populous city – overview of MCMA-2003 Campaign
Authors: Molina L. T. , Kolb C. E. , de Foy B. , Lamb B. K. , Brune W. H. , Jimenez J. L. , Molina M. J.
Published: April 2010

Abstract. Exploratory field measurements in the Mexico City Metropolitan Area (MCMA) in February 2002 set the stage for a major air quality field measurement campaign in the spring of 2003 (MCMA-2003). Involving over 100 scientists from more than 30 institutions in Mexico, the United States and Europe, MCMA-2003 revealed important new insights into the meteorology, primary pollutant emissions, ambient secondary pollutant precursor concentrations, photochemical oxidant production and secondary aerosol particle formation in North America's most populated and polluted megacity. A description of meteorological and atmospheric chemistry and aerosol microphysics measurements performed during MCMA-2003 is presented. More than three dozen published or submitted MCMA-2003 research papers are reviewed and key discoveries pertinent to understanding and improving air quality in Mexico City and similar megacities in the developing world are summarized.
Impact of land convection on troposphere-stratosphere exchange in the tropics
Authors: Ricaud P. , Barret B. , Attié J.-L. , Le Flochmoën E. , Motte E. , Teyssèdre H. , Peuch V.-H. , Livesey N. , Lambert A. , Pommereau J.-P.
Published: April 2010

Abstract. The mechanism of troposphere-stratosphere exchange in the tropics was investigated from space-borne observations of the horizontal distributions of nitrous oxide (N2O), methane (CH4) and carbon monoxide (CO) at 17 km in March-April-May by the ODIN/Sub-Millimeter Radiometer (SMR), the Upper Atmosphere Research Satellite (UARS)/Halogen Occultation Experiment (HALOE) and the TERRA/Measurements Of Pollution In The Troposphere (MOPITT) instruments in 2002–2004, completed by recent observations of the AURA/Microwave Limb Sounder (MLS) instrument during the same season in 2005. At the top of the Tropical Tropopause Layer (TTL), all gases show significant longitudinal gradients with maximum amounts primarily over Africa and, depending on the species, secondary more or less pronounced maxima above northern South America and South-East Asia. The Maritime continent in the Western Pacific never appears as a source region for the stratosphere. The large longitudinal gradient at latitudes where the circulation is essentially zonal, and the co-location of the maximum tropospheric trace gases concentrations with the overshooting features reported by the Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar, strongly supports that rapid uplift over land convective regions is the dominating process of troposphere-stratosphere exchange. Calculations carried out with the MOCAGE-Climat chemical transport model well capture the location of the maximum gas concentration in the TTL but of lesser amplitude. Although there are obvious misrepresentations of some of the sources in the model, i.e. CH4 emissions by evergreen forests, the main reason for discrepancy appears to be the underestimation of the maximum altitude reached by land convective transport in MOCAGE.
Investigation of molar volume and surfactant characteristics of water-soluble organic compounds in biomass burning aerosol
Authors: Asa-Awuku A. , Nenes A. , Sullivan A. P. , Hennigan C. J. , Weber R. J.
Published: April 2010

Abstract. In this study, we characterize the CCN activity of the water-soluble organics in biomass burning aerosol. The aerosol after collection upon filters is dissolved in water using sonication. Hydrophobic and hydrophilic components are fractionated from a portion of the original sample using solid phase extraction, and subsequently desalted. The surface tension and CCN activity of these different samples are measured with a KSV CAM 200 goniometer and a DMT Streamwise Thermal Gradient CCN Counter, respectively. The measurements show that the strongest surfactants are isolated in the hydrophobic fraction, while the hydrophilics exhibit negligible surface tension depression. The presence of salts (primarily (NH4)2SO4) in the hydrophobic fraction substantially enhances surface tension depression; their synergistic effects considerably enhance CCN activity, exceeding that of pure (NH4)2SO4. For our analysis, average thermodynamic properties (i.e., molar volume) are determined for samples using our newly developed Köhler Theory Analysis (KTA) method. We have found that, the molar mass of the hydrophilic and hydrophobic aerosol components is estimated to be 87±26 g mol−1 and 780±231 g mol−1, respectively. KTA also suggests that the relative proportion (in moles) of hydrophobic to hydrophilic compounds in the original sample to be 1:3. For the first time, KTA is applied to an aerosol with this level of complexity and displays its potential for providing physically-based constraints for GCM parameterizations of the aerosol indirect effect.
Evaluation and modeling of the size fractionated aerosol number concentration measurements near a major road in Helsinki
Authors: Hussein T. , Kukkonen J. , Korhonen H. , Pohjola M. , Pirjola L. , Wraith D. , Härkönen J. , Teinilä K. , Koponen I. K. , Karppinen A. , Hillamo R. , Kulmala M.
Published: April 2010

Abstract. This study presents an evaluation and modeling of the size fractionated aerosol number concentrations that were measured near a major road of Itäväylä in Helsinki, during 23 August – 19 September 2003 and 14 January – 11 February 2004. The measurement system contained also electronic traffic counts, on-site meteorological measurements, and urban background concentration measurements. We have evaluated the temporal variations and the dependencies on local meteorological conditions of the measured aerosol number concentrations and size distributions. The ultrafine particle (UFP) number concentrations at the roadside site were approximately an order of magnitude higher than those at the urban background site during daytime, due to vehicular emissions from the road. We also determined the statistical correlations of the sequential time series of the particle number size distributions at the roadside site, and the traffic densities. The computed Pearson correlation coefficients for the downwind cases were substantially high for UFP's (>0.6), and low for accumulation mode particles; the latter is due to the substantial contribution of long-range transported particles in that size range. We also utilized this dataset for evaluating the performance of a modeling system that consists of a roadside dispersion model CAR-FMI (Contaminants in the Air from a Road – Finnish Meteorological Institute), a meteorological pre-processing model MPP-FMI and an aerosol process model UHMA (University of Helsinki Model for Aerosol processes). Model simulations underpredicted the particle number concentrations at the measurement site, which was caused by uncertainties in the emission modeling, especially in the UFP size range.
The multi-seasonal NOy budget in coastal Antarctica and its link with surface snow and ice core nitrate: results from the CHABLIS campaign
Authors: Jones A. E. , Wolff E. W. , Ames D. , Bauguitte S. J.-B. , Clemitshaw K. C. , Fleming Z. , Mills G. P. , Saiz-Lopez A. , Salmon R. A. , Sturges W. T. , Worton D. R.
Published: April 2010

Abstract. Measurements of individual NOy components were carried out at Halley station in coastal Antarctica. The measurements were made as part of the CHABLIS campaign (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) and cover over half a year, from austral winter 2004 through to austral summer 2005. They are the longest duration and most extensive NOy budget study carried out to date in polar regions. Results show clear dominance of organic NOy compounds (PAN and MeONO2) during the winter months, with low concentrations of inorganic NOy, but a reversal of this situation towards summer when the balance shifts in favour of inorganic NOy. Multi-seasonal measurements of surface snow nitrate correlate strongly with inorganic NOy species. One case study in August suggested that particulate nitrate was the dominant source of nitrate to the snowpack, but this was not the consistent picture throughout the measurement period. An analysis of NOx production rates showed that emissions of NOx from the snowpack dominate over gas-phase sources of "new NOx", suggesting that, for certain periods in the past, the flux of NOx into the boundary layer can be calculated from ice core nitrate data.
SCIAMACHY tropospheric NO2 over the Alpine region and importance of pixel surface pressure for the column retrieval
Authors: Schaub D. , Boersma K. F. , Keller J. , Folini D. , Brunner D. , Buchmann B. , Berresheim H. , Staehelin J.
Published: April 2010

Abstract. This study evaluates NO2 vertical tropospheric column densities (VTCs) retrieved from measurements of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) above Switzerland and the Alpine region. A clear relationship between a spatially and temporally highly resolved Swiss NOx emission inventory and SCIAMACHY NO2 columns under anticyclonic meteorological conditions supports the general ability of SCIAMACHY to detect sources of NOx pollution in Switzerland. Summertime NOx lifetime estimates derived from this relation agree reasonably with values from literature. A further evaluation of the SCIAMACHY data is based on the comparison with NO2 VTCs retrieved from the Global Ozone Monitoring Experiment (GOME). The annual mean NO2 VTCs calculated from both data sets clearly show the advantage of the improved SCIAMACHY pixel resolution for qualitatively estimating the NOx pollution distribution in a small country such as Switzerland. However, a more quantitative comparison of seasonally averaged NO2 VTCs gives evidence for SCIAMACHY NO2 VTCs being systematically underestimated over the Swiss Plateau during winter. A possible explanation for this problem (not reported in earlier literature) is the use of inaccurate satellite pixel surface pressures derived from coarsely resolved global models in the retrieval. The marked topography in the Alpine region can lead to deviations of several hundred meters between the assumed and the real mean surface height over a pixel. A sensitivity study based on selected clear sky SCIAMACHY NO2 VTCs over the Swiss Plateau and two fixed a priori NO2 profile shapes indicates that inaccurate pixel surface pressures have a considerable effect of up to 40% on the retrieved NO2 columns. For retrievals in the UV-visible spectral range with a decreasing sensitivity towards the earth's surface, this effect is of major importance when the NO2 resides close to the ground, which occurs most pronounced during the winter season.
Size-segregated mass distributions of aerosols over Eastern Mediterranean: seasonal variability and comparison with AERONET columnar size-distributions
Authors: Gerasopoulos E. , Koulouri E. , Kalivitis N. , Kouvarakis G. , Saarikoski S. , Mäkelä T. , Hillamo R. , Mihalopoulos N.
Published: April 2010

Abstract. This work provides long-term (2004–2006) size segregated measurements of aerosol mass at a remote coastal station in the southern Europe, with the use of size-selective samplings (SDI impactor). PM2.5 and PM1 account for 60% and 40% of PM10 mass in average, respectively. Seven distinct modes were identified in the range 0–10 μm and the dominant were the "Accumulation 1" (0.25–0.55 μm) and the "Coarse 2" (3–7 μm) modes. Different sources for submicron and supermicron particles were identified, the first being related to local/regional and transported pollution with maximum in summer and the latter to dust from deserted areas in Northern Africa maximizing in spring. The representativity of the ground-based measurements for the total column was also investigated by comparing the measured aerosol mass distributions with the AERONET volume size distribution data and similar seasonal patterns were revealed.
Simulation of hurricane response to suppression of warm rain by sub-micron aerosols
Authors: Rosenfeld D. , Khain A. , Lynn B. , Woodley W. L.
Published: April 2010

Abstract. The feasibility of hurricane modification was investigated for hurricane Katrina using the Weather Research and Forecasting Model (WRF). The possible impact of seeding of clouds with submicron cloud condensation nuclei (CCN) on hurricane structure and intensity as measured by nearly halving of the area covered by hurricane force winds was simulated by "turning–off" warm rain formation in the clouds at Katrina's periphery (where wind speeds were less than 22 m s−1). This simplification of the simulation of aerosol effects is aimed at evaluating the largest possible response. This resulted in the weakening of the hurricane surface winds compared to the "non-seeded" simulated storm during the first 24 h within the entire tropical cyclone (TC) area compared to a control simulation without warm rain suppression. Later, the seeding-induced evaporative cooling at the TC periphery led to a shrinking of the eye and hence to some increase in the wind within the small central area of the TC. Yet, the overall strength of the hurricane decreased in response to the suppressed warm rain at the periphery, as measured by a 25% reduction in the radius of hurricane force winds. In a simulation with warm rain suppression throughout the hurricane, the relative weakening compared to the control continued throughout the simulations and the eye shrunk even further. This shows that the main mechanism by which suppressing warm rain weakens the TC is the low level evaporative cooling of the un-precipitated cloud drops and the added cooling due to melting of precipitation that falls from above.
Use of neural networks for tropospheric ozone time series approximation and forecasting – a review
Authors: Argiriou A. A.
Published: April 2010

Abstract. The use of artificial neural networks in atmospheric science expands constantly. During the last years, many papers were published dealing with air pollution modeling. A number of papers deals with the time series approximation and forecasting of tropospheric ozone concentration. Neural networks have been found to outperform other statistical techniques like multiple regression etc. This paper reviews and discusses some practical aspects of the proposed neural network models applied to ozone concentration approximation and forecasting.
Ambient aerosol concentrations of sugars and sugar-alcohols at four different sites in Norway
Authors: Yttri K. E. , Dye C. , Kiss G.
Published: April 2010

Abstract. Sugars and sugar-alcohols are demonstrated to be important constituents of the ambient aerosol water-soluble organic carbon fraction (WSOC), and to be tracers for primary biological aerosol particles (PBAP). In the present study, levels of four sugars (fructose, glucose, sucrose, trehalose) and three sugar-alcohols (arabitol, inositol, mannitol) in ambient aerosols have been quantified using a novel HPLC/HRMS-TOF (High Performance Liquid Chromatography in combination with High Resolution Mass Spectrometry – Time of Flight) method to assess the contribution of PBAP to PM10 and PM2.5. Samples were collected at four sites in Norway at different times of the year in order to reflect the various contributing sources and the spatial and seasonal variation of the selected compounds. Sugars and sugar-alcohols were present at all sites investigated, underlining the ubiquity of these highly polar organic compounds. The highest concentrations were reported for sucrose, reaching a maximum concentration of 320 ng m−3 in PM10 and 55 ng m−3 in PM2.5. The mean concentration of sucrose was up to 10 times higher than fructose, glucose and trehalose. The mean concentrations of the sugar-alcohols were typically lower, or equal, to that of the monomeric sugars and trehalose. Peak concentrations of arabitol and mannitol did not exceed 30 ng m−3 in PM10, and for PM2.5 all concentrations were below 6 ng m−3. Sugars and sugar-alcohols were associated primarily with coarse aerosols except during wintertime at the suburban site in Elverum, where a shift towards sub micron aerosols was observed. It is proposed that this shift was due to the intensive use of wood burning for residential heating at this site during winter, confirmed by high concurrent concentrations of levoglucosan. Elevated concentrations of sugars in PM2.5 were observed during spring and early summer at the rural background site Birkenes. It is hypothesized that this was due to ruptured pollen.
A long-term comparison of wind and tide measurements in the upper mesosphere recorded with an imaging Doppler interferometer and SuperDARN radar at Halley, Antarctica
Authors: Hibbins R. E. , Jarvis M. J.
Published: April 2010

Abstract. Data from a co-located imaging Doppler interferometer and SuperDARN radar recorded since 1996 have been analysed in a consistent manner to determine daily mean winds and tides in the upper mesosphere. By comparing only days when both techniques were recording good quality data it is shown that the SuperDARN radar winds and tides correlate best with the IDI height bin 90–95 km. On timescales of one hour the winds derived from each technique correlate poorly, whereas the daily mean winds are in much better agreement suggesting that the two radars are sensitive to different parts of the gravity wave spectrum. Regression analysis reveals that the observed SuperDARN daily mean meridional wind strength is approximately 65% that recorded by the IDI while the zonal winds are of similar magnitude, in good quantitative agreement with previous studies which have shown contamination to SuperDARN-derived winds due to the significant back lobe of the radar radiation pattern. Climatologically the two techniques observe similar monthly mean winds with the SuperDARN meridional winds suppressed compared to the IDI which tends to record winds more poleward and eastward than those derived by the SuperDARN radar during the summer months, and to be slightly more equatorward during the winter. The 12-h tidal amplitude and phase in both the zonal and meridional components derived from both techniques are in excellent agreement, whereas the 24-h tides are seen much more strongly in the SuperDARN radar, especially in wintertime, with poor phase agreement. Long term comparison of the two techniques reveals a tendency for the IDI meridional winds to be more poleward during solar maximum especially during summer time; an effect which is not reproduced in the meridional winds derived from the SuperDARN radar. These results are discussed in the context of previous studies to independently determine the veracity of each technique.
Emissions from forest fires near Mexico City
Authors: Yokelson R. , Urbanski S. , Atlas E. , Toohey D. , Alvarado E. , Crounse J. , Wennberg P. , Fisher M. , Wold C. , Campos T. , Adachi K. , Buseck P. R. , Hao W. M.
Published: April 2010

Abstract. The emissions of NOx and HCN (per unit amount of fuel burned) from fires in the pine-savannas that dominate the mountains surrounding Mexico City (MC) are about 2 times higher than normally observed for forest burning. The NH3 emissions are about average for forest burning. The NOx/VOC mass ratio for the MC-area mountain fires was ~0.38, which is similar to the NOx/VOC ratio in the MC urban area emissions inventory of 0.43, but much larger than the NOx/VOC ratio for tropical forest fires in Brazil (~0.068). The nitrogen enrichment in the fire emissions may be due to deposition of nitrogen-containing pollutants in the outflow from the MC urban area. This effect may occur worldwide wherever biomass burning coexists with large urban areas (e.g. the tropics, southeastern US, Los Angeles Basin). The molar emission ratio HCN/CO for the mountain fires was ~0.0128±0.0096: 2–9 times higher than widely used literature values for biomass burning. The MC-area/downwind molar ratio of HCN/CO is about 0.003±0.0003. Thus, if other types of biomass burning are relatively insignificant, the mountain fires may be contributing about 23% of the CO production in the MC-area (~98–100 W and 19–20 N). Comparing the PM10/CO mass ratio in the MC Metropolitan Area emission inventory (0.011) to the PM1/CO mass ratio for the mountain fires (0.133) then suggests that these fires could produce as much as ~78% of the fine particle mass generated in the MC-area.
Aerosol climatology: dependence of the Angstrom exponent on wavelength over four AERONET sites
Authors: Kaskaoutis D. G. , Kambezidis H. D. , Hatzianastassiou N. , Kosmopoulos P. G. , Badarinath K. V. S.
Published: April 2010

Abstract. The Ångström exponent, α, is often used as a qualitative indicator of aerosol particle size. In this study, aerosol optical depth (AOD) and Ångström exponent (α) data were analyzed to obtain information about the adequacy of the simple use of the Ångström exponent for characterizing aerosols, and for exploring possibilities for a more efficient characterization of aerosols. This was made possible by taking advantage of the spectral variation of α, the so-called curvature. The data were taken from four selected AERONET stations, which are representative of four aerosol types, i.e. biomass burning, pollution, desert dust and maritime. Using the least-squares method, the Ångström-α was calculated in the spectral interval 340–870 nm, along with the coefficients α1 and α2 of the second order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength, and the second derivative of α. The results show that the spectral curvature can provide important additional information about the different aerosol types, and can be effectively used to discriminate between them, since the fine-mode particles exhibit negative curvature, while the coarse-mode aerosols positive. In addition, the curvature has always to be taken into account in the computations of Ångström exponent values in the spectral intervals 380–440 nm and 675–870 nm, since fine-mode aerosols exhibit larger α675–870 than α380–440 values, and vice-versa for coarse-mode particles. A second-order polynomial fit simulates the spectral dependence of the AODs very well, while the associated constant term varies proportionally to the aerosol type. The correlation between the coefficients α1 and α2 of the second-order polynomial fit and the Ångström exponent α, and the atmospheric turbidity, is further investigated. The obtained results reveal important features, which can be used for better discriminating between different aerosol types.
Boundary layer physics over snow and ice
Authors: Anderson P. S. , Neff W. D.
Published: April 2010

Abstract. A general understanding of the physics of advection and turbulent mixing within the near surface atmosphere assists the interpretation and predictive power of air chemistry theory. The theory of the physical processes involved in diffusion of trace gas reactants in the near surface atmosphere is still incomplete. Such boundary layer theory is least understood over snow and ice covered surfaces, due in part to the thermo-optical properties of the surface. Polar boundary layers have additional aspects to consider, due to the possibility of long periods without diurnal forcing and enhanced Coriolis effects. This paper provides a review of present concepts in polar boundary layer meteorology, which will generally apply to atmospheric flow over snow and ice surfaces. It forms a companion paper to the chemistry review papers in this special issue of ACP.
The role of iron and black carbon in aerosol light absorption
Authors: Derimian Y. , Karnieli A. , Kaufman Y. J. , Andreae M. O. , Andreae T. W. , Dubovik O. , Maenhaut W. , Koren I.
Published: April 2010

Abstract. Iron is a major component of atmospheric aerosols, influencing the light absorption ability of mineral dust, and an important micronutrient that affects oceanic biogeochemistry. The regional distribution of the iron concentration in dust is important for climate studies; however, this is difficult to obtain since it requires in-situ aerosol sampling or simulation of complex natural processes. Simultaneous studies of aerosol chemical composition and radiometric measurements of aerosol optical properties, which were performed in the Negev desert of Israel continuously for about eight years, suggest a potential for deriving a relationship between chemical composition and light absorption properties, in particular the spectral single-scattering albedo. The two main data sets of the present study were obtained by a sun/sky radiometer and a stacked filter unit sampler that collects particles in coarse and fine size fractions. Analysis of chemical and optical data showed the presence of mixed dust and pollution aerosol in the study area, although their sources appear to be different. Spectral SSA showed an evident response to increased concentrations of iron, black carbon equivalent matter, and their mixing state. An empirical relationship that relates the spectral SSA, the percentage of iron in total particulate mass, and the pollution components was derived. Results calculated using this relationship were compared with measurements from dust episodes in several locations around the globe. The comparison reveals that dust over the eastern Mediterranean and Saudi Arabia contains less iron than that over Asia and the Sahara desert.
Operational retrieval of Asian sand and dust storm from FY-2C geostationary meteorological satellite and its application to real time forecast in Asia
Authors: Hu X. Q. , Lu N. M. , Niu T. , Zhang P.
Published: April 2010

Abstract. This paper describes an operational retrieval algorithm for the sand/dust storm (SDS) from FY-2C/S-VISSR (Stretched – Visible and Infrared Spin-Scan Radiometer) developed at the National Satellite Meteorological Center (NSMC) of China. This algorithm, called Dust Retrieval Algorithm based on Geostationary Imager (DRAGI), is based on the optical and radiative physical properties of SDS in mid-infrared and thermal infrared spectral regions as well as the observation of all bands in the geostationary imager, which include the Brightness Temperature Difference (BTD) in split window channels, Infrared Difference Dust Index (IDDI) and the ratio of middle infrared reflectance to visible reflectance. It also combines the visible and water vapor bands observation of the geostationary imager to identify the dust clouds from the surface targets and meteorological clouds. The output product is validated by and related to other dust aerosol observations such as the synoptic weather reports, surface visibility, aerosol optical depth (AOD) and ground-based PM10 observations. Using the SDS-IDDI data and a data assimilation scheme, the dust forecast model CUACE/Dust achieved a substantial improvement to the SDS predictions in spring 2006.
The Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CATT-BRAMS) – Part 1: Model description and evaluation
Authors: Freitas S. R. , Longo K. M. , Silva Dias M. A. F. , Chatfield R. , Silva Dias P. , Artaxo P. , Andreae M. O. , Grell G. , Rodrigues L. F. , Fazenda A. , Panetta J.
Published: April 2010

Abstract. We introduce the Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CATT-BRAMS). CATT-BRAMS is an on-line transport model fully consistent with the simulated atmospheric dynamics. Emission sources from biomass burning and urban-industrial-vehicular activities for trace gases and aerosol particles are obtained from several published datasets and remote sensing information. The tracer and aerosol mass concentration prognostic includes the effects of sub-grid scale turbulence in the planetary boundary layer, convective transport by shallow and deep moist convection, wet and dry deposition, and plume rise associated with vegetation fires in addition to the grid scale transport. The radiation parameterization takes into account the interaction between aerosol particles and short and long wave radiation. The atmospheric model BRAMS is based on the Regional Atmospheric Modeling System (RAMS), with several improvements associated with cumulus convection representation, soil moisture initialization and surface scheme tuned for the tropics, among others. In this paper the CATT-BRAMS model is used to simulate carbon monoxide and particulate material (PM2.5) surface fluxes and atmospheric transport during the 2002 LBA field campaigns, conducted during the transition from the dry to wet season in the southwest Amazon Basin. Model evaluation is addressed with comparisons between model results and near surface, radiosonde and airborne measurements performed during the field campaign, as well as remote sensing derived products. We show the matching of emissions strengths to observed carbon monoxide in the LBA campaign. A relatively good comparison to the MOPITT data, in spite of the fact that MOPITT a priori assumptions imply several difficulties, is also obtained.
The Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CATT-BRAMS) – Part 2: Model sensitivity to the biomass burning inventories
Authors: Longo K. M. , Freitas S. R. , Setzer A. , Prins E. , Artaxo P. , Andreae M. O.
Published: April 2010

Abstract. We describe an estimation technique for biomass burning emissions in South America based on a combination of remote sensing fire products and field observations. For each fire pixel detected by remote sensing, the mass of the emitted tracer is calculated based on field observations of fire properties related to the type of vegetation burning. The burnt area is estimated from the instantaneous fire size retrieved by remote sensing, when available, or from statistical properties of the burn scars. The sources are then spatially and temporally distributed and assimilated daily by the Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CATT-BRAMS) in order to perform the prognostic of related tracer concentrations. Two other biomass burning inventories are simultaneously used to compare the emission strength in terms of the resultant tracer distribution. Several evaluations of the model with the three emission estimations were performed, comparing results with direct measurements of carbon monoxide both near-surface and airborne, as well as remote sensing derived products. Model results with the methodology of estimation introduced in this paper show a relatively good agreement with the direct measurements and MOPITT data product; pointing out the reliability of the model from local to regional scales.
Secondary organic aerosol in the global aerosol – chemistry transport model Oslo CTM2
Authors: Hoyle C. R. , Berntsen T. , Myhre G. , Isaksen I. S. A.
Published: April 2010

Abstract. The global chemical transport model Oslo CTM2 has been extended to include the formation, transport and deposition of secondary organic aerosol (SOA). Precursor hydrocarbons which are oxidised to form condensible species include both biogenic species such as terpenes and isoprene, as well as species emitted predominantly by anthropogenic activities (toluene, m-xylene, methylbenzene and other aromatics). A model simulation for 2004 gives an annual global SOA production of approximately 55 Tg. Of this total, 2.5 Tg is found to consist of the oxidation products of anthropogenically emitted hydrocarbons, and about 15 Tg is formed by the oxidation products of isoprene. The global production of SOA is increased to about 76 Tg yr−1 by allowing semi-volatile species to condense on ammonium sulphate aerosol. This brings modelled organic aerosol values closer to those observed, however observations in Europe remain significantly underestimated, raising the possibility of an unaccounted for SOA source. Allowing SOA to form on ammonium sulphate aerosol increases the contribution of anthropogenic SOA from about 4.5% to almost 9% of the total production. The importance of NO3 as an oxidant of SOA precursors is found to vary regionally, causing up to 50%–60% of the total amount of SOA near the surface in polluted regions and less than 25% in more remote areas. This study underscores the need for SOA to be represented in a more realistic way in global aerosol models in order to better reproduce observations of organic aerosol burdens in industrialised and biomass burning regions.
Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006
Authors: Fountoukis C. , Nenes A. , Sullivan A. , Weber R. , VanReken T. , Fischer M. , Matías E. , Moya M. , Farmer D. , Cohen R. C.
Published: April 2010

Abstract. Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM2.5 is insensitive to changes in ammonia but is to acidic semivolatile species. Semi-volatile partitioning equilibrates on a timescale between 6 and 20 min. When the aerosol sulfate-to-nitrate molar ratio is less than 1, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as "equivalent sodium" (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramatically. This suggests that explicitly considering crustals in the thermodynamic calculations are required to accurately predict the partitioning and phase state of aerosols.
Effects of total solar eclipse of 29 March 2006 on surface radiation
Authors: Kazadzis S. , Bais A. , Blumthaler M. , Webb A. , Kouremeti N. , Kift R. , Schallhart B. , Kazantzidis A.
Published: April 2010

Abstract. Solar irradiance spectral measurements were performed during a total solar eclipse. The spectral effect of the limb darkening to the global, direct irradiance and actinic flux measurements was investigated. This effect leads to wavelength dependent changes in the measured solar spectra showing a much more pronounced decrease in the radiation at the lower wavelengths. Radiative transfer model results were used for the computation of a correction for the total ozone measurements due to the limb darkening. This correction was found too small to explain the large decrease in total ozone column derived from the standard Brewer measurements, which is an artifact in the measured irradiance due to the increasing contribution of diffuse radiation against the decreasing direct irradiance caused by the eclipse. Calculations of the Extraterrestrial spectrum and the effective sun's temperatures, as measured from ground based direct irradiance measurements, showed an artificial change in the calculations of both quantities due to the fact that radiation coming from the visible part of the sun during the eclipse phases differs from the back body radiation described by the Planck's law.
Optical and geometrical characteristics of cirrus clouds over a mid-latitude lidar station
Authors: Giannakaki E. , Balis D. S. , Amiridis V. , Kazadzis S.
Published: April 2010

Abstract. Optical and geometrical characteristics of cirrus clouds over Thessaloniki, Greece (40.6°, 22.9°) have been determined from the analysis of lidar and radiosonde measurements performed during the period from 2000 to 2006. Cirrus clouds are generally observed in a mid altitude region ranging from 7 to 12 km, with mid-cloud temperatures in the range from –65° to –25°C. A seasonality of cirrus geometrical and temperature properties is found. The cloud thickness ranges from 0.85 to 5 km and 37% of our cases have thickness between 2 and 3 km. The retrieval of cloud's optical depth and lidar ratio is performed using three different methods, taking into account multiple scattering effects. The mean optical depth is found to be 0.3±0.24 and the corresponding mean lidar ratio is 28±17 sr. Sub-visual, thin and opaque cirrus clouds are observed at 7.5%, 51% and 42.5% of the measured cases respectively. The multiple scattering errors of the measured effective extinction coefficients range from 20% to 60% depending on cloud optical depth. A comparison of the results between the three methods shows good agreement. In addition we present the advantages and limitations of each method applied. The temperature and thickness dependencies on optical properties have also been studied in detail. A maximum mid-cloud depth of ~3 km is found at temperatures around ~–45°C while there is an indication that optical depth increases with increasing thickness and mid-cloud temperature. No clear dependence of the lidar ratio values on the cloud temperature and thickness was found.
HDO measurements with MIPAS
Authors: Steinwagner J. , Milz M. , von Clarmann T. , Glatthor N. , Grabowski U. , Höpfner M. , Stiller G. P. , Röckmann T.
Published: April 2010

Abstract. We have used high spectral resolution spectroscopic measurements from the MIPAS instrument on the Envisat satellite to simultaneously retrieve vertical profiles of H2O and HDO in the stratosphere and uppermost troposphere. A thorough error analysis of the retrievals confirms that reliable δD data can be obtained up to an altitude of ~45 km. Averaging over multiple orbits and thus over longitudes further reduces the random part of the error. The absolute total error of averaged δD is between 36 ‰ and 111‰. With values lower than 42 ‰ the total random error is significantly smaller than the natural variability of δD. The data compare well with previous investigations. The MIPAS measurements now provide a unique global data set of high-quality δD data that will provide novel insight into the stratospheric water cycle.
Intercomparison of ILAS-II Version 1.4 and Version 2 target parameters with MIPAS-Envisat measurements
Authors: Griesfeller A. , von Clarmann T. , Griesfeller J. , Höpfner M. , Milz M. , Nakajima H. , Steck T. , Sugita T. , Tanaka T. , Yokota T.
Published: April 2010

Abstract. We compared measurements taken by two satellite-borne instruments, ILAS-II and MIPAS-Envisat, between May and October 2003. Using the coincidence criteria of ±300 km in space and ±12 h in time for H2O, N2O, and CH4 and the coincidence criteria of ±300 km in space and ±6 h in time for ClONO2, O3, and HNO3, a different number of coincidences have been found for the gases. The data were separated into sunrise and sunset measurements, which correspond to Northern and Southern Hemisphere data, respectively. For the sunrise data of ILAS-II, a clear improvement from Version 1.4 to Version 2.1 was observed for H2O, CH4, ClONO2, and O3. For ILAS-II N2O and HNO3 data there were no large differences between the two data sets. In particular, the ILAS-II Version 1.4 data were unrealistically small for H2O, CH4, and O3 and unrealistically large for ClONO2 above 20 km to 30 km. The differences between the two algorithm versions for the sunset data were not as large as for the sunrise data for all gases, and for H2O and CH4. ILAS-II Version 1.4 data fitted even better to the MIPAS-Envisat measurements than Version 2.0.