bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the ice growth rate on the incorporation of gaseous HCl
Authors: Domine F. , Rauzy C.
Published: April 2010

Abstract. Ice crystals were grown in the laboratory at −15°C, at different growth rates and in the presence of a partial pressure of HCl of 1.63×10-3 Pa, to test whether the ice growth rate influences the amount of HCl taken up, XHCl, as predicted by the ice growth mechanism of Domine and Thibert (1996). The plot of HCl concentration in ice as a function of growth rate has the aspect predicted by that mechanism: XHCl decreases with increasing growth rate, from a value that depends on thermodynamic equilibrium to a value that depends only on kinetic factors. The height of the growth steps of the ice crystals is determined to be about 150 nm from these experiments. We discuss that the application of these laboratory experiments to cloud ice crystals and to snow metamorphism is not quantitatively possible at this stage, because the physical variables that determine crystal growth in nature, and in particular the step height, are not known. Qualitative applications are attempted for HCl and HNO3 incorporation in cloud ice and snowpack crystals.
Retrieval methods of effective cloud cover from the GOME instrument: an intercomparison
Authors: Tuinder O. N. E. , de Winter-Sorkina R. , Builtjes P. J. H.
Published: April 2010

Abstract. The radiative scattering by clouds leads to errors in the retrieval of column densities and concentration profiles of atmospheric trace gas species from satellites. Moreover, the presence of clouds changes the UV actinic flux and the photo-dissociation rates of various species significantly. The Global Ozone Monitoring Experiment (GOME) instrument on the ERS-2 satellite, principally designed to retrieve trace gases in the atmosphere, is also capable of detecting clouds. Four cloud fraction retrieval methods for GOME data that have been developed are discussed in this paper (the Initial Cloud Fitting Algorithm, the PMD Cloud Recognition Algorithm, the Optical Cloud Recognition Algorithm (an in-house version and the official implementation) and the Fast Retrieval Scheme for Clouds from the Oxygen A-band). Their results of cloud fraction retrieval are compared to each-other and also to synoptic surface observations. It is shown that all studied retrieval methods calculate an effective cloud fraction that is related to a cloud with a high optical thickness. Generally, we found ICFA to produce the lowest cloud fractions, followed by our in-house OCRA implementation, FRESCO, PC2K and finally the official OCRA implementation along four processed tracks (+2%, +10%, +15% and +25% compared to ICFA respectively). Synoptical surface observations gave the highest absolute cloud fraction when compared with individual PMD sub-pixels of roughly the same size.
Internal mixing of the organic aerosol by gas phase diffusion of semivolatile organic compounds
Authors: Marcolli C. , Luo B. P. , Peter Th. , Wienhold F. G.
Published: April 2010

Abstract. This paper shows that most of the so far identified constituents of the tropospheric organic particulate matter belong to a semivolatile fraction for which gas phase diffusion in the lower troposphere is sufficiently fast to establish thermodynamic equilibrium between aerosol particles. For the first time analytical expressions for this process are derived. Inspection of vapor pressure data of a series of organic substances allows a rough estimate for which substances this mixing process must be considered. As general benchmarks we conclude that for typical aerosol radii between 0.1 and 1 µm this mixing process is efficient at 25°C for polar species with molecular weights up to 200 and for non-polar species up to 320. At −10°C, these values are shifted to 150 for polar and to 270 for non-polar substances. The extent of mixing of this semivolatile fraction is governed by equilibrium thermodynamics, leading to a selectively, though not completely, internally mixed aerosol. The internal mixing leads to a systematic depression of melting and deliquescence points of organic and mixed organic/inorganic aerosols, thus leading to an aerosol population in the lower troposphere which is predominantly liquid.
Particle size distribution and particle mass measurements at urban,near-city and rural level in the Copenhagen area and Southern Sweden
Authors: Ketzel M. , Wåhlin P. , Kristensson A. , Swietlicki E. , Berkowicz R. , Nielsen O. J. , Palmgren F.
Published: April 2010

Abstract. Particle size distribution (size-range 3-900nm) and PM10 was measured simultaneously at an urban background station in Copenhagen, a near-city background and a rural location during a period in September-November 2002. The study investigates the contribution from urban versus regional sources of particle number and mass concentration. The total particle number (ToN) and NOx are well correlated at the urban and near-city level and show a distinct diurnal variation, indicating the common traffic source. The average ToN at the three stations differs by a factor of 3. The observed concentrations are 2500#cm, 4500#cm and 7700#cm at rural, near-city and urban level, respectively. PM10 and total particle volume (ToV) are well correlated between the three different stations and show similar concentration levels, in average within 30% relative difference, indicating a common source from long-range transport that dominates the concentrations at all locations. Measures to reduce the local urban emissions of NOx and ToN are likely to affect both the street level and urban background concentrations, while for PM10 and ToV only measurable effects at the street level are probable. Taking into account the supposed stronger health effects of ultrafine particles reduction measures should address particle number emissions. The traffic source contributes strongest in the 10-200nm particle size range. The maximum of the size distribution shifts from about 20-30nm at kerbside to 50-60nm at rural level. Particle formation events were observed in the 3-20nm size range at rural location in the afternoon hours, mainly under conditions with low concentrations of pre-existing aerosol particles. The maximum in the size distribution of the "traffic contribution" seems to be shifted to about 28nm in the urban location compared to 22nm at kerbside. Assuming NOx as an inert tracer on urban scale allows to estimate that ToN at urban level is reduced by 15-30% compared to kerbside. Particle removal processes, e.g. deposition and coagulation, which are most efficient for smallest particle sizes (20nm) and condensational growth are likely mechanisms for the loss of particle number and the shift in particle size.
Aerosol-cirrus interactions: a number based phenomenon at all?
Authors: Seifert M. , Ström J. , Krejci R. , Minikin A. , Petzold A. , Gayet J.-F. , Schlager H. , Ziereis H. , Schumann U. , Ovarlez J.
Published: April 2010

Abstract. In situ measurements of the partitioning of aerosol particles within cirrus clouds were used to investigate aerosol-cloud interactions in ice clouds. The number density of interstitial aerosol particles (non-activated particles in between the cirrus crystals) was compared to the number density of cirrus crystal residuals. The data was obtained during the two INCA (Interhemispheric Differences in Cirrus Properties from Anthropogenic Emissions) campaigns, performed in the Southern Hemisphere (SH) and Northern Hemisphere (NH) midlatitudes. Different aerosol-cirrus interactions can be linked to the different stages of the cirrus lifecycle. Cloud formation is linked to positive correlations between the number density of interstitial aerosol (Nint) and crystal residuals (Ncvi), whereas the correlations are smaller or even negative in a dissolving cloud. Unlike warm clouds, where the number density of cloud droplets is positively related to the aerosol number density, we observed a rather complex relationship when expressing Ncvi as a function of Nint for forming clouds. The data sets are similar in that they both show local maxima in the Nint range 100 to 200cm, where the SH- maximum is shifted towards the higher value. For lower number densities Nint and Ncvi are positively related. The slopes emerging from the data suggest that a tenfold increase in the aerosol number density corresponds to a 3 to 4 times increase in the crystal number density. As Nint increases beyond the ca. 100 to 200cm, the mean crystal number density decreases at about the same rate for both data sets. For much higher aerosol number densities, only present in the NH data set, the mean Ncvi remains low. The situation for dissolving clouds allows us to offer two possible, but at this point only speculative, alternative interactions between aerosols and cirrus: evaporating clouds might be associated with a source of aerosol particles, or air pollution (high aerosol number density) might retard ice particle evaporation rates.
Study of the effect of different type of aerosols on UV-B radiation from measurements during EARLINET
Authors: Balis D. S. , Amiridis V. , Zerefos C. , Kazantzidis A. , Kazadzis S. , Bais A. F. , Meleti C. , Gerasopoulos E. , Papayannis A. , Matthias V. , Dier H. , Andreae M. O.
Published: April 2010

Abstract. Routine lidar measurements of the vertical distribution of the aerosol extinction coefficient and the extinction-to-backscatter ratio have been performed at Thessaloniki, Greece using a Raman lidar system in the frame of the EARLINET project since 2000. Co-located spectral and broadband solar UV-B irradiance measurements, as well as total ozone observations, were available whenever lidar measurements were obtained. From the available measurements several cases could be identified that allowed the study of the effect of different types of aerosol on the levels of the UV-B solar irradiance at the Earth's surface. The TUV radiative transfer model has been used to simulate the irradiance measurements, using total ozone and the lidar aerosol data as input. From the comparison of the model results with the measured spectra the effective single scattering albedo was determined using an iterative procedure, which has been verified against results from the 1998 Lindenberg Aerosol Characterization Experiment. It is shown that for the same aerosol optical depth and for the same total ozone values the UV-B irradiances at the Earth's surface can show differences up to 10%, which can be attributed to differences in the aerosol type. It is shown that the combined use of the estimated single scattering albedo and of the measured extinction-to-backscatter ratio leads to a better characterization of the aerosol type probed.
Hygroscopic properties of water-soluble matter and humic-like organics in atmospheric fine aerosol
Authors: Gysel M. , Weingartner E. , Nyeki S. , Paulsen D. , Baltensperger U. , Galambos I. , Kiss G.
Published: April 2010

Abstract. Ambient continental-rural fine aerosol (K-puszta, Hungary, PM1.5) was sampled on quartz fibre filters in winter and summer 2001. Water-soluble matter (WSM) was extracted in MilliQ-water, and, in a second step, solid phase extraction was used to isolate the less hydrophilic fraction (ISOM) of the water-soluble organic matter (WSOM) from remaining inorganic salts and "most" hydrophilic organic matter (MHOM). This approach allowed ISOM, which constitutes the major fraction of WSOM, to be isolated from ambient aerosols and investigated in pure form. Hygroscopic properties of both WSM and ISOM extracts as well as of aquatic reference fulvic and humic acids were investigated using a Hygroscopicity Tandem Differential Mobility Analyser (H-TDMA). ISOM deliquesced between 30% and 60% relative humidity (RH), and hygroscopic growth factors at 90% RH ranged from 1.08 to 1.17. The hygroscopicity of ISOM is comparable to secondary organic aerosols obtained in smog chamber experiments, but lower than the hygroscopicity of highly soluble organic acids. The hygroscopic behaviour of investigated fulvic and humic acids had similarities to ISOM, but hygroscopic growth factors were slightly smaller and deliquescence was observed at higher RH (75-85% and 85-95% RH for fulvic acid and humic acid, respectively). These differences probably originate from larger average molecular mass and lower solubility of fulvic and humic acids. Inorganic composition data, measured ISOM hygroscopicity, and a presumed value for the hygroscopicity of the small remaining MHOM fraction were used to predict hygroscopic growth of WSM extracts. Good agreement between model prediction and measured water uptake was observed with differences (by volume) ranging from +1% to -18%. While deliquescence properties of WSM extracts were mainly determined by the inorganic salts (42-53 wt % of WSM), the WSOM accounted for a significant fraction of particulate water. At 90% RH, according to model predictions and measurements, about 80-62% of particulate water in the samples are associated with inorganic salts and about 20-38% with WSOM. The relative contributions of both distinguished WSOM fractions, ISOM and MHOM, remains uncertain since MHOM was not available in isolated form, but the results suggest that the less abundant MHOM is also important due to its presumably larger hygroscopicity.
Space-borne observations link the tropical atlantic ozone maximum and paradox to lightning
Authors: Jenkins G. S. , Ryu J.-H.
Published: April 2010

Abstract. The potential enhancement of tropospheric column ozone values over the Tropical Atlantic Ocean on a seasonal basis by lightning is investigated using satellite derived ozone data, TRMM lightning data, ozonesonde data and NCEP reanalysis during 1998-2001. Our results show that the number of lightning flashes in Africa and South America reach a maximum during September, October and November (SON). The spatial patterns of winds in combination with lightning from West Africa, Central Africa and South America is likely responsible for enriching middle/upper troposphere ozone over the Tropical South Atlantic during SON. Moreover, lightning flashes are high in the hemisphere opposite to biomass burning during December, January, and February (DJF) and June, July and August (JJA). This pattern leads to an enrichment of ozone in the middle/upper troposphere in the Southern Hemisphere Tropics during DJF and the Northern Hemisphere Tropics during JJA. During JJA the largest numbers of lightning flashes are observed in West Africa, enriching tropospheric column ozone to the north of 5S in the absence of biomass burning. During DJF, lightning is concentrated in South America and Central Africa enriching tropospheric column ozone south of the Equator in the absence of biomass burning.
Urban aerosol number size distributions
Authors: Hussein T. , Puustinen A. , Aalto P. P. , Mäkelä J. M. , Hämeri K. , Kulmala M.
Published: April 2010

Abstract. Aerosol number size distributions have been measured since 5 May 1997 in Helsinki, Finland. The presented aerosol data represents size distributions within the particle diameter size range 8-400nm during the period from May 1997 to March 2003. The daily, monthly and annual patterns of the aerosol particle number concentrations were investigated. The temporal variation of the particle number concentration showed close correlations with traffic activities. The highest total number concentrations were observed during workdays; especially on Fridays, and the lowest concentrations occurred during weekends; especially Sundays. Seasonally, the highest total number concentrations were observed during winter and spring and lower concentrations were observed during June and July. More than 80% of the number size distributions had three modes: nucleation mode (Dp<30nm), Aitken mode (20-100nm) and accumulation mode (Dp>90nm). Less than 20% of the number size distributions had either two modes or consisted of more than three modes. Two different measurement sites were used; in the first (Siltavuori, 5.5.1997-5.3.2001), the arithmetic means of the particle number concentrations were 7000cm-3, 6500cm-3, and 1000cm-3 respectively for nucleation, Aitken, and accumulation modes. In the second site (Kumpula, 6.3.2001-28.2.2003) they were 5500cm-3, 4000cm-3, and 1000cm-3. The total number concentration in nucleation and Aitken modes were usually significantly higher during workdays than during weekends. The temporal variations in the accumulation mode were less pronounced. The lower concentrations at Kumpula were mainly due to building construction and also the slight overall decreasing trend during these years. During the site changing a period of simultaneous measurements over two weeks were performed showing nice correlation at both sites.
Effects of various meteorological conditions and spatial emissionresolutions on the ozone concentration and ROG/NOx limitationin the Milan area (I)
Authors: Baertsch-Ritter N. , Keller J. , Dommen J. , Prevot A. S. H.
Published: April 2010

Abstract. The three-dimensional photochemical model UAM-V is used to investigate the effects of various meteorological conditions and of the coarseness of emission inventories on the ozone concentration and ROG/NOx limitation of the ozone production in the Po Basin in the northern part of Italy. As a base case, the high ozone episode with up to 200ppb on 13 May 1998 was modelled and previously thoroughly evaluated with measurements gained during a large field experiment. Systematic variations in meteorology are applied to mixing height, air temperature, specific humidity and wind speed. Three coarser emission inventories are obtained by resampling from 3x3km2 up to 54x54km2 emission grids. The model results show that changes in meteorological input files strongly influence ozone in this area. For instance, temperature changes peak ozone by 10.1ppb/°C and the ozone concentrations in Milan by 2.8ppb/°C. The net ozone formation in northern Italy is more strongly temperature than humidity dependent, while the humidity is very important for the ROG/NOx limitation of the ozone production. For all meteorological changes (e.g. doubling the mixing height), the modelled peak ozone remains ROG limited. A strong change towards NOx sensitivity in the ROG limited areas is only found if much coarser emission inventories were applied. Increasing ROG limited areas with increasing wind speed are found, because the ROG limited ozone chemistry induced by point sources is spread over a larger area. Simulations without point sources tend to increase the NOx limited areas.
Volatile particles formation during PartEmis: a modelling study
Authors: Vancassel X. , Sorokin A. , Mirabel P. , Petzold A. , Wilson C.
Published: April 2010

Abstract. A modelling study of the formation of volatile particles in a combustor exhaust has been carried out in the frame of the PartEmis European project. A kinetic model has been used in order to investigate nucleation efficiency of the H2O-H2SO4 binary mixture in the sampling system. A value for the fraction of the fuel sulphur S(IV) converted into S(VI) has been indirectly deduced from comparisons between model results and measurements. In the present study, ranges between roughly 2.5% and 6%, depending on the combustor settings and on the value assumed for the parameter describing sulphuric acid wall losses. Soot particles hygroscopicity has also been investigated as their activation is a key parameter for contrail formation. Growth factors of monodisperse particles exposed to high relative humidity (95%) have been calculated and compared with experimental results. The modelling study confirms that the growth factor increases as the soot particle size decreases.
Observations of meteor-head echoes using the Jicamarca 50MHz radar in interferometer mode
Authors: Chau J. L. , Woodman R. F.
Published: April 2010

Abstract. We present results of recent observations of meteor-head echoes obtained with the high-power large-aperture Jicamarca 50MHz radar (11.95°S, 76.87°W) in an interferometric mode. The large power-aperture of the system allows us to record more than 3000 meteors per hour in the small volume subtended by the 1° antenna beam, albeit when the cluttering equatorial electrojet (EEJ) echoes are not present or are very weak. The interferometry arrangement allows the determination of the radiant (trajectory) and speed of each meteor. It is found that the radiant distribution of all detected meteors is concentrated in relative small angles centered around the Earth's Apex as it transits over the Jicamarca sky, i.e. around the corresponding Earth heading for the particular observational day and time, for all seasons observed so far. The dispersion around the Apex is ~18° in a direction transverse to the Ecliptic plane and only 8.5° in heliocentric longitude in the Ecliptic plane both in the Earth inertial frame of reference. No appreciable interannual variability has been observed. Moreover, no population related to the optical (larger meteors) Leonid showers of 1998-2002 is found, in agreement with other large power-aperture radar observations. A novel cross-correlation detection technique (adaptive match-filtering) is used in combination with a 13 baud Barker phase-code. The technique allows us to get good range resolution (0.75km) without any sensitivity deterioration for the same average power, compared to the non-coded long pulse scheme used at other radars. The matching Doppler shift provides an estimation of the velocity within a pulse with the same accuracy as if a non-coded pulse of the same length had been used. The velocity distribution of the meteors is relatively narrow and centered around 60kms-1. Therefore most of the meteors have an almost circular retrograde orbit around the Sun. Less than 8% of the velocities correspond to interstellar orbits, i.e. with velocities larger than the solar escape velocity (72kms-1). Other statistical distributions of interest are also presented.
Ice supersaturation as seen from TOVS
Authors: Gierens K. , Kohlhepp R. , Spichtinger P. , Schroedter-Homscheidt M.
Published: April 2010

Abstract. We have analysed the upper tropospheric humidity with respect to ice (UTHi) data product obtained from the Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) instrument onboard the National Oceanic and Atmospheric Administration NOAA-14 polar orbiting satellite. While in the production of the official UTHi product values in excess of 100% are ignored, we do not so - in view of many recent results obtained from a variety of other in-situ and remote sensing instruments showing that ice supersaturation frequently occurs in the upper troposphere. We show that TOVS is able to detect ice supersaturation at the correct locations (however, only in less than one percent of its soundings, presumably because of TOVS's low vertical resolution), and that the supersaturation follows the well known exponential behaviour. We conclude that values of UTHi in excess of saturation should not be considered a measurement error anymore. The similar re-analysis of TOVS data back to 1979 could give important insights into trends of upper tropospheric humidity.
Growth of upper tropospheric aerosols due to uptake of HNO3
Authors: Romakkaniemi S. , Kokkola H. , Petzold A. , Laaksonen A.
Published: April 2010

Abstract. The effect of nitric acid on the equilibrium size distributions of upper tropospheric aerosols is calculated as a function of relative humidity. It is shown that HNO3 concentrations above a few tenths of a ppb can cause substantial increases in haze mode particle concentrations at relative humidities at about 60% and above. The effect can be strongly magnified when letovicite particles are present in addition to sulfuric acid aerosols. Letovicite particles are less acidic than the sulfuric acid particles and so more nitric acid can be absorbed. This effect can be seen even at RH below 50% due to the lowering of the deliquescence RH of letovicite in the presence of gaseous nitric acid at low temperatures. We have also compared equilibrium calculations of the HNO3 effect with observations of increased haze mode concentrations at relative humidities above 50% (Petzold et al., 2000). Nitric acid mixing ratios on the order of 0.5-2ppb may explain the observed increase of haze mode particles at least partially.
Radiant measurement accuracy of micrometeors detected by the Arecibo 430 MHz Dual-Beam Radar
Authors: Janches D. , Nolan M. C. , Sulzer M.
Published: April 2010

Abstract. Precise knowledge of the angle between the meteor vector velocity and the radar beam axis is one of the largest source of errors in the Arecibo Observatory (AO) micrometeor observations. In this paper we study ~250 high signal-to-noise ratio (SNR) meteor head-echoes obtained using the dual-beam 430 MHz AO Radar in Puerto Rico, in order to reveal the distribution of this angle. All of these meteors have been detected first by the radar first side lobe, then by the main beam and finally seen in the side lobe again. Using geometrical arguments to calculate the meteor velocity in the plane perpendicular to the beam axis, we find that most of the meteors are travelling within ~15° with respect to the beam axis, in excellent agreement with previous estimates. These results suggest that meteoroids entering the atmosphere at greater angles may deposit their meteoric material at higher altitudes explaining at some level the missing mass inconsistency raised by the comparisson of meteor fluxes derived from satellite and traditional meteor radar observations. They also may be the source of the observed high altitude ions and metalic layers observed by radars and lidars respectively.
A time-resolved model of the mesospheric Na layer: constraints on the meteor input function
Authors: Plane J. M. C.
Published: April 2010

Abstract. A time-resolved model of the Na layer in the mesosphere/lower thermosphere region is described, where the continuity equations for the major sodium species Na, Na+ and NaHCO3 are solved explicity, and the other short-lived species are treated in steady-state. It is shown that the diurnal variation of the Na layer can only be modelled satisfactorily if sodium species are permanently removed below about 85 km, both through the dimerization of NaHCO3 and the uptake of sodium species on meteoric smoke particles that are assumed to have formed from the recondensation of vaporized meteoroids. When the sensitivity of the Na layer to the meteoroid input function is considered, an inconsistent picture emerges. The ratio of the column abundance of Na+ to Na is shown to increase strongly with the average meteoroid velocity, because the Na is injected at higher altitudes. Comparison with a limited set of Na+ measurements indicates that the average meteoroid velocity is probably less than about 25 km s-1, in agreement with velocity estimates from conventional meteor radars, and considerably slower than recent observations made by wide aperture incoherent scatter radars. The Na column abundance is shown to be very sensitive to the meteoroid mass input rate, and to the rate of vertical transport by eddy diffusion. Although the magnitude of the eddy diffusion coefficient in the 80–90 km region is uncertain, there is a consensus between recent models using parameterisations of gravity wave momentum deposition that the average value is less than 3×105 cm2 s-1. This requires that the global meteoric mass input rate is less than about 20 td-1, which is closest to estimates from incoherent scatter radar observations. Finally, the diurnal variation in the meteoroid input rate only slight perturbs the Na layer, because the residence time of Na in the layer is several days, and diurnal effects are effectively averaged out.
Online mass spectrometric aerosol measurements during the MINOS campaign (Crete, August 2001)
Authors: Schneider J. , Borrmann S. , Wollny A. G. , Bläsner M. , Mihalopoulos N. , Oikonomou K. , Sciare J. , Teller A. , Levin Z. , Worsnop D. R.
Published: April 2010

Abstract. Mass spectrometric analysis of volatile and semi-volatile (=non-refractory) aerosol particles have been performed during a field study in the summer Eastern Mediterranean. A size-resolved, quantitative mass spectrometric technique (the Aerodyne Aerosol Mass Spectrometer, AMS) has been used, and the results are compared to filter sampling methods and particle sizing techniques. The different techniques agree with the finding that the fine particle mode (D<1.2 mm) consisted mostly of ammonium sulfate and of organic material. The aerosol sulfate ranged between 2 and 12 mg/m3. On most days, ammonium was closely correlated with sulfate, suggesting ammonium sulfate as the major aerosol component, but on days with high sulfate mass concentrations, the sulfate was not fully neutralized by ammonium. Trajectories indicate that the aerosol and/or its precursors originate from South-Eastern Europe. The source of the ammonium sulfate aerosol is most likely fossil fuel burning, whereas the organic aerosol may also originate from biomass burning. Ion series analysis of the organics fraction in the mass spectrometer indicated that the major component of the organics were oxygenated organics which are a marker for aged, photochemically processed aerosol or biomass burning aerosol. The non-refractory aerosol compounds, measured with the Aerosol Mass Spectrometer, contributed between 37 and 50% to the total aerosol mass in the fine mode. A second mass spectrometer for single particle analysis by laser ablation has been used for the first time in the field during this study and yielded results, which agree with filter samples of the coarse particle mode. This mode consisted of sea salt particles and dust aerosol.
Aspect sensitivity of VHF echoes from field aligned irregularities in meteor trails and thin ionization layers
Authors: Zhou Q. H. , Morton Y. T. , Mathews J. D. , Janches D.
Published: April 2010

Abstract. The aspect sensitivity of VHF echoes from field aligned irregularities (FAI) within meteor trails and thin ionization layers is studied using numerical models. Although the maximum power is obtained when a radar is pointed perpendicular to the field line (B), substantial power can be obtained off the B direction if the ionization trail/layer is thin. When the FAI length along B is 20 m, the power observed 6° off B is about 10 db below that perpendicular to the B direction. Meteoric FAI echoes can potentially be used to determine the diffusion rate in the mesopause region. Based on the aspect sensitivity analysis, we conclude that the range spread trail echoes far off B observed by powerful VHF radars are likely due to overdense meteors. Our simulation also shows that ionospheric FAI echoes can have an altitude smearing effect of about 4 km if the vertical extension of a FAI-layer is around 100 m, which has often been observed at Arecibo. The altitude smearing effect can account for the fact that the Es-layers observed by the Arecibo incoherent scatter radar are typically much narrower than FAI-layers and the occurrence of double spectral peaks around the Es-layer altitude in FAI echoes.
Direct evidence for coastal iodine particles from Laminaria macroalgae – linkage to emissions of molecular iodine
Authors: McFiggans G. , Coe H. , Burgess R. , Allan J. , Cubison M. , Alfarra M. R. , Saunders R. , Saiz-Lopez A. , Plane J. M. C. , Wevill D. , Carpenter L. , Rickard A. R. , Monks P. S.
Published: April 2010

Abstract. Renewal of ultrafine aerosols in the marine boundary layer may lead to repopulation of the marine distribution and ultimately determine the concentration of cloud condensation nuclei (CCN). Thus the formation of nanometre-scale particles can lead to enhanced scattering of incoming radiation and a net cooling of the atmosphere. The recent demonstration of the chamber formation of new particles from the photolytic production of condensable iodine-containing compounds from diiodomethane (CH2I2), (O'Dowd et al., 2002; Kolb, 2002; Jimenez et al., 2003a; Burkholder and Ravishankara, 2003), provides an additional mechanism to the gas-to-particle conversion of sulphuric acid formed in the photo-oxidation of dimethylsulphide for marine aerosol repopulation. CH2I2 is emitted from seaweeds (Carpenter et al., 1999, 2000) and has been suggested as an initiator of particle formation. We demonstrate here for the first time that ultrafine iodine-containing particles are produced by intertidal macroalgae exposed to ambient levels of ozone. The particle composition is very similar both to those formed in the chamber photo-oxidation of diiodomethane and in the oxidation of molecular iodine by ozone. The particles formed in all three systems are similarly aspherical. When small, those formed in the molecular iodine system swell only moderately when exposed to increased humidity environments, and swell progressively less with increasing size; this behaviour occurs whether they are formed in dry or humid environments, in contrast to those in the CH2I2 system. Direct coastal boundary layer observations of molecular iodine, ultrafine particle production and iodocarbons are reported. Using a newly measured molecular iodine photolysis rate, it is shown that, if atomic iodine is involved in the observed particle bursts, it is of the order of at least 1000 times more likely to result from molecular iodine photolysis than diiodomethane photolysis. A hypothesis for molecular iodine release from intertidal macroalgae is presented and the potential importance of macroalgal iodine particles in their contribution to CCN and global radiative forcing are discussed.
Cloud chemistry at the Puy de Dôme: variability and relationships with environmental factors
Authors: Marinoni A. , Laj P. , Sellegri K. , Mailhot G.
Published: April 2010

Abstract. The chemical composition of cloud water was investigated during the winter-spring months of 2001 and 2002 at the Puy de Dôme station (1465 m above sea level, 45°46′22′′ N, 2°57′43′′ E) in an effort to characterize clouds in the continental free troposphere. Cloud droplets were sampled with single-stage cloud collectors (cut-off diameter approximately 7 µm) and analyzed for inorganic and organic ions, as well as total dissolved organic carbon. Results show a very large variability in chemical composition and total solute concentration of cloud droplets, ranging from a few mg l-1 to more than 150 mg l-1. Samplings can be classified in three different categories with respect to their total ionic content and relative chemical composition: background continental (BG, total solute content lower than 18 mg l-1), anthropogenic continental (ANT, total solute content from 18 to 50 mg l-1), and special events (SpE, total solute content higher than 50 mg l-1). The relative chemical composition shows an increase in anthropogenic-derived species (NO3-, SO42- and NH4+) from BG to SpE, and a decrease in dissolved organic compounds (ionic and non-ionic) that are associated with the anthropogenic character of air masses. We observed a high contribution of solute in cloud water derived from the dissolution of gas phase species in all cloud events. This was evident from large solute fractions of nitrate, ammonium and mono-carboxylic acids in cloud water, relative to their abundance in the aerosol phase. The comparison between droplet and aerosol composition clearly shows the limited ability of organic aerosols to act as cloud condensation nuclei. The strong contribution of gas-phase species limits the establishment of direct relationships between cloud water solute concentration and LWC that are expected from nucleation scavenging.
Evaporation of high speed sporadic meteors
Authors: Murad E. , Roth C.
Published: April 2010

Abstract. Recent measurements conducted at the Arecibo Observatory report high-speed sporadic meteors having velocities near 50 km/s. The results seem to indicate a bimodal velocity distribution in the sporadic meteors (maxima at ~20 km/s and ~50 km/s). The particles have a maximum mass of ~1µg. This paper will present an analysis of the ablation of 1µg meteoroids having velocities of 20, 30, 50, and 70 km/s. The calculations show that there is fractionation even for the fast meteoroids, the effect being particularly noticeable for the 1µg sporadic particles, and less so for the heavier particles. The relevance of the calculations to the radar observations of the sporadic meteors will be discussed.
The mesospheric metal layer topside: a possible connection to meteoroids
Authors: Höffner J. , Friedman J. S.
Published: April 2010

Abstract. In the past, many studies have been carried out to demonstrate the influence of meteoroids on the atmospheric metal layer, observed roughly in the altitude range 80–105 km. Even with the capability of present day resonance lidars to measure metal densities within single meteor trails, it has been difficult to prove any influence of meteors on the average metal layer. In contrast to approaches taken earlier, we discuss here the seasonal characteristics of potassium, calcium, calcium ion, iron and sodium above 110 km altitude where the average nocturnal densities are so low that the existence of a baseline level of metal atoms and ions is often overlooked. By comparing simultaneous and common-volume observations of different metal layers at one location, we demonstrate that despite their different seasonal characteristics at lower altitudes remarkably similar seasonal characteristics are observed at higher altitudes. In addition, a qualitative agreement is also found for potassium at different latitudes. A comparison of metal densities at 113 km altitude with known meteor showers indicates a strong influence of shower meteoroids on the topside of the metal layers. Simultaneous observations of K along with Ca, Fe and/or Na permit the calculation of abundance ratios, which at 113 km altitude are quite similar to values measured in single meteor trails by ground based lidars. Furthermore, the increase in densities throughout summer is strong evidence for the influence of sporadic meteoroids on the high metal layers. This increase correlates well with the seasonal variation of sporadic micrometeor input independent of meteor showers. Given these evidences, we contend that there is a direct influence of ablating meteoroids on the topside of the mesospheric metal layer.
Trace gas transport in the 1999/2000 Arctic winter: comparison of nudged GCM runs with observations
Authors: van Aalst M. K. , van den Broek M. M. P. , Bregman A. , Brühl C. , Steil B. , Toon G. C. , Garcelon S. , Hansford G. M. , Jones R. L. , Gardiner T. D. , Roelofs G. J. , Lelieveld J. , Crutzen P.J.
Published: April 2010

Abstract. We have compared satellite and balloon observations of methane (CH4) and hydrogen fluoride (HF) during the Arctic winter 1999/2000 with results from the MA-ECHAM4 middle atmospheric general circulation model (GCM). For this purpose, the meteorology in the model was nudged towards ECMWF analyses. This nudging technique is shown to work well for this middle atmospheric model, and offers good opportunities for the simulation of chemistry and transport processes. However, caution must be used inside the polar vortex, particularly late in the winter. The current study focuses on transport of HF and CH4, initialized with satellite measurements from the HALOE instrument aboard the UARS satellite. We have compared the model results with HALOE data and balloon measurements throughout the winter, and analyzed the uncertainties associated with tracer initialization, boundary conditions and the passive tracer assumption. This comparison shows that the model represents some aspects of the Arctic vortex well, including relatively small-scale features. However, while profiles outside the vortex match observations well, the model underestimates HF and overestimates CH4 concentrations inside the vortex, particularly in the middle stratosphere. This problem is also evident in a comparison of vortex descent rates based upon vortex average tracer profiles from MA-ECHAM4, and various observations. This could be due to an underestimate of diabatic subsidence in the model, or due to too much mixing between vortex and non-vortex air.
Impact of different emission inventories on simulated tropospheric ozone over China: a regional chemical transport model evaluation
Authors: Ma J. , van Aardenne J. A.
Published: April 2010

Abstract. The importance of emission inventory uncertainty on the simulation of summertime tropospheric ozone over China has been analyzed using a regional chemical transport model. Three independent emissions inventories, that are (i) emission estimates from the Emission Database for Global Atmospheric Research (EDGAR) for the year 1995, (ii) a regional emission inventory used in the Transport and Chemical Evolution over the Pacific (TRACE-P) program with emissions for the year 2000 and (iii) a national emission inventory used in the China Ozone Research Program (CORP) with emission estimates for the year 1995, are used for model simulation over a summer period. Methods used for the development of the inventories are discussed and differences in simulated ozone and its precursors with these emission inventories are analyzed. Comparison of the emission inventories revealed large differences in the emission estimates (up to 50% for NOx, ~100% for NMVOC and ~1000% for CO). Application of the different emission inventories in three model simulations showed minor differences in both surface O3 in rather unpolluted areas in China and at higher altitudes (500mbar). In polluted areas, differences in surface O3 are 30-50% between the different model simulations which seem rather small taking into account the large differences in the emission inventories. Additional sensitivity runs showed that the difference in NOx emissions as well NMVOC emissions is a dominant factor which controls the differences in simulated O3 concentrations while the impact of differences in CO emissions is relatively small. Although the CO emission estimate by CORP seems to be underestimated, there is no confidence to highlight one emission inventory better than the others.
Size-segregated aerosol mass closure and chemical composition in Monte Cimone (I) during MINATROC
Authors: Putaud J.-P. , Van Dingenen R. , Dell'Acqua A. , Raes F. , Matta E. , Decesari S. , Facchini M. C. , Fuzzi S.
Published: April 2010

Abstract. Physical and chemical characterizations of the atmospheric aerosol were carried out at Mt. Cimone (Italy) during the 4 June-4 July 2000 period. Particle size distributions in the size range 6nm-10µm were measured with a differential mobility analyzer (DMA) and an optical particle counter (OPC). Size-segregated aerosol was sampled using a 6-stage low pressure impactor. Aerosol samples were submitted to gravimetric and chemical analyses. Ionic, carbonaceous and refractory components of the aerosol were quantified. We compared the sub- and superµm aerosol mass concentrations determined by gravimetric measurements (mGM), chemical analyses (mmCA), and by converting particle size distribution to aerosol mass concentrations (mmSD). Mean random uncertainties associated with the determination of mmGM, mmCA, and mmSD were assessed. The three estimates of the sub-µm aerosol mass concentration agreed, which shows that within experimental uncertainty, the sub-µm aerosol was composed of the quantified components. The three estimates of the super-µm aerosol mass concentration did not agree, which indicates that random uncertainties and/or possible systematic errors in aerosol sampling, sizing or analyses were not adequately accounted for. Aerosol chemical composition in air masses from different origins showed differences, which were significant in regard to experimental uncertainties. During the Saharan dust advection period, coarse dust and fine anthropogenic particles were externally mixed. No anthropogenic sulfate could be found in the super-µm dust particles. In contrast, nitrate was shifted towards the aerosol super-µm fraction in presence of desert dust.
The annual cycle of hydrogen peroxide: an indicator of chemical instability?
Authors: Stewart R. W.
Published: April 2010

Abstract. A box model has been used to study the annual cycle in hydrogen peroxide concentrations with the objective of determining whether the observed difference in summer and winter values reflects instability in the underlying photochemistry. The model is run in both steady-state and time-dependent modes. The steady-state calculations show that, for some range of NOx background levels, two stable solutions to the continuity equations exist for a period of days in spring and fall. The corresponding time-dependent model indicates that, for sufficiently high background NOx concentrations, the spring and fall changes in H2O2 concentration may be interpreted as a forced transition between the two underlying stable regimes. The spring transition is more rapid than that in fall, an asymmetry that becomes more marked as background NOx increases. This asymmetry is related to the different time scales involved in chemical production and loss of H2O2. Observations of the spring increase in H2O2 concentration may therefore provide a better measure of the change in the underlying chemical regime than does the fall decrease. The model results developed in this paper will be compared with two sets of observations that cover annual variations of peroxide concentrations under different background pollution conditions.
Meteoroid velocity distribution derived from head echo data collected at Arecibo during regular world day observations
Authors: Sulzer M. P.
Published: April 2010

Abstract. We report the observation and analysis of ionization flashes associated with the decay of meteoroids (so-called head echos) detected by the Arecibo 430 MHz radar during regular ionospheric observations in the spring and autumn equinoxes. These two periods allow pointing well-above and nearly-into the ecliptic plane at dawn when the event rate maximizes. The observation of many thousands of events allows a statistical interpretation of the results, which show that there is a strong tendency for the observed meteoroids to come from the apex as has been previously reported (Chau and Woodman, 2004). The velocity distributions agree with Janches et al. (2003a) when they are directly comparable, but the azimuth scan used in these observations allows a new perspective. We have constructed a simple statistical model which takes meteor velocities as input and gives radar line of sight velocities as output. The intent is to explain the fastest part of the velocity distribution. Since the speeds interpreted from the measurements are distributed fairly narrowly about nearly 60 km s-1, double the speed of the earth in its orbit, is consistent with the interpretation that many of the meteoroids seen by the Arecibo radar are moving in orbits about the sun with similar parameters as the earth, but in the retrograde direction. However, it is the directional information obtained from the beam-swinging radar experiment and the speed that together provide the evidence for this interpretation. Some aspects of the measured velocity distributions suggest that this is not a complete description even for the fast part of the distribution, and it certainly says nothing about the slow part first described in Janches et al. (2003a). Furthermore, we cannot conclude anything about the entire dust population since there are probably selection effects that restrict the observations to a subset of the population.