bluuebunny/crossref_metadata_2025 huggingface dataset:
Tracer measurements in the tropical tropopause layer during the AMMA/SCOUT-O3 aircraft campaign
Authors: Homan C. D. , Volk C. M. , Kuhn A. C. , Werner A. , Baehr J. , Viciani S. , Ulanovski A. , Ravegnani F.
Published: April 2010

Abstract. We present airborne in situ measurements made during the AMMA (African Monsoon Multidisciplinary Analysis)/SCOUT-O3 campaign between 31 July and 17 August 2006 on board the M55 Geophysica aircraft, based in Ouagadougou, Burkina Faso. CO2 and N2O were measured with the High Altitude Gas Analyzer (HAGAR), CO was measured with the Cryogenically Operated Laser Diode (COLD) instrument, and O3 with the Fast Ozone ANalyzer (FOZAN). We analyze the data obtained during five local flights to study the dominant transport processes controlling the tropical tropopause layer (TTL) above West-Africa: deep convection up to the level of main convective outflow, overshooting of deep convection, horizontal inmixing across the subtropical tropopause, and horizontal transport across the subtropical barrier. Except for the flight of 13 August, distinct minima in CO2 indicate convective outflow of boundary layer air in the TTL. The CO2 profiles show that the level of main convective outflow was mostly located between 350 and 360 K, and for 11 August reached up to 370 K. While the CO2 minima indicate quite significant convective influence, the O3 profiles suggest that the observed convective signatures were mostly not fresh, but of older origin. When compared with the mean O3 profile measured during a previous campaign over Darwin in November 2005, the O3 minimum at the main convective outflow level was less pronounced over Ouagadougou. Furthermore O3 mixing ratios were much higher throughout the whole TTL and, unlike over Darwin, rarely showed low values observed in the regional boundary layer. Signatures of irreversible mixing following overshooting of convective air were scarce in the tracer data. Some small signatures indicative of this process were found in CO2 profiles between 390 and 410 K during the flights of 4 and 8 August, and in CO data at 410 K on 7 August. However, the absence of expected corresponding signatures in other tracer data makes this evidence inconclusive, and overall there is little indication from the observations that overshooting convection has a profound impact on TTL composition during AMMA. We find the amount of photochemically aged air isentropically mixed into the TTL across the subtropical tropopause to be not significant. Using the N2O observations we estimate the fraction of aged extratropical stratospheric air in the TTL to be 0.0±0.1 up to 370 K during the local flights, increasing above this level to 0.2±0.15 at 390 K. The subtropical barrier, as indicated by the slope of the correlation between N2O and O3 between 415 and 490 K, does not appear as a sharp border between the tropics and extratropics, but rather as a gradual transition region between 10 and 25° N latitude where isentropic mixing between these two regions may occur.
Optical, physical and chemical characteristics of Australian Desert dust aerosols: results from a field experiment
Authors: Radhi M. , Box M. A. , Box G. P. , Mitchell R. M. , Cohen D. D. , Stelcer E. , Keywood M. D.
Published: April 2010

Abstract. Mineral dust is one of the major components of the world's aerosol mix, having a number of impacts within the Earth system. However, the climate forcing impact of mineral dust is currently poorly constrained, with even its sign uncertain. As Australian deserts are more reddish than those in the northern hemisphere, it is important to better understand the physical, chemical and optical properties of this important aerosol. We have investigated the properties of Australian desert dust at a site in SW Queensland, which is strongly influenced by both dust and biomass burning aerosol. Three years of ground-based monitoring of spectral optical thickness has provided a statistical picture of gross aerosol properties. In November 2006 we undertook a field campaign which collected 4 sets of size-resolved aerosol samples for laboratory analysis – both ion beam analysis and ion chromatography. The aerosol optical depth data showed a weak seasonal cycle with an annual mean of 0.06±0.03. The Angstrom coefficient showed a stronger cycle, indicating the influence of the winter-spring burning season in Australia's north. Size distribution inversions showed a bimodal character, with the coarse mode assumed to be mineral dust, and the fine mode a mixture of biomass burning and marine biogenic material. Ion Beam Analysis was used to determine the elemental composition of all filter samples, although elemental ratios were considered the most reliable output. Scatter plots showed that Fe, Al and Ti were well correlated with Si, and Co reasonably well correlated, with the Fe/Si ratio higher than the crustal average, as expected. Scatter plots for Ca, Mn and K against Si showed clear evidence of a second population, which in some cases could be identified with a particular sample day or size fraction. Ion Chromatography was used to quantify water soluble ions for 2 of our sample sets, showing the importance of marine influences on both fine (biogenic) and coarse (sea salt) modes.
A laboratory based experimental study of mercury emission from contaminated soils in the River Idrijca catchment
Authors: Kocman D. , Horvat M.
Published: April 2010

Abstract. Results obtained by a laboratory flux measurement system (LFMS) focused on investigating the kinetics of the mercury emission flux (MEF) from contaminated soils of the Idrija Hg-mine region, Slovenia are presented. Representative soil samples with respect to total Hg concentrations (4–417 μg g−1) and land cover (forest, meadow and alluvial soil) alongside the River Idrijca were analysed to determine the variation in MEF versus distance from the source, regulating three major environmental parameters comprising soil temperature, soil moisture and solar radiation. MEFs ranged from less than 2 to 530 ng m−2 h−1, with the highest emissions from contaminated alluvial soils and soils near the mining district in the town of Idrija. A significant decrease of MEF was then observed with increasing distance from these sites. The results revealed a strong positive effect of all three parameters investigated on momentum MEF. The light-induced flux was shown to be independent of the soil temperature, while the soil aqueous phase seems to be responsible for recharging the pool of mercury in the soil available for both the light- and thermally-induced flux. The overall flux response to simulated environmental conditions depends greatly on the form of Hg in the soil. Higher activation energies are required for the overall process to occur in soils where insoluble cinnabar prevails compared to soils where more mobile Hg forms and forms available for transformation processes are dominant.
The 16-day wave in the Arctic and Antarctic mesosphere and lower thermosphere
Authors: Day K. A. , Mitchell N. J.
Published: April 2010

Abstract. The 16-day planetary wave in the polar mesosphere and lower thermosphere has been investigated using meteor radars at Esrange (68° N, 21° E) in the Arctic and Rothera (68° S, 68° W) in the Antarctic. The measurements span the 10-year interval from October 1999 to July 2009 and the 5-year interval February 2005 to July 2009, respectively. The height range covered is about 80–100 km. The wave is seen to occur in intermittent bursts, where wave amplitudes typically reach a maximum of about 10 m s−1, and never more than about 20 m s−1. Horizontal wind variance within a wave-period range of 12 to 20 days is used as a proxy for the activity of the 16-day wave. Wave activity is strong for 3 to 4 months in winter, where it is present across the entire height range observed and monthly wave variance reaches about 65 m2 s−2. Some weak and intermittent activity is observed throughout the other seasons including summer. However, there is a high degree of inter-annual variability and in some individual years wave activity is almost absent. The data are used to construct a representative climatology for the Arctic and Antarctic. The seasonal cycle of the 16-day wave is found to be very similar in both polar regions. The 16-day wave has slightly greater amplitudes in the zonal component of the winds than in the meridional. Mesospheric temperatures measured by the radars were used to further investigate the 16-day wave. The temperatures reveal a clear signature of the 16-day wave. Temperature amplitudes are generally only a few Kelvin but occasional bursts of up to 10 K have been observed. Observations of the wave in summer are sometimes consistent with the suggestion of ducting from the winter hemisphere.
Iodine monoxide in the Antarctic snowpack
Authors: Frieß U. , Deutschmann T. , Gilfedder B. , Weller R. , Platt U.
Published: April 2010

Abstract. Recent ground-based and space borne observations suggest the presence of significant amounts of iodine monoxide in the boundary layer of Antarctica, which are expected to have an impact on the ozone budget and might contribute to the formation of new airborne particles. So far, the source of these iodine radicals has been unknown. This paper presents long-term measurements of iodine monoxide at the German Antarctic research station Neumayer, which indicate that the snowpack is the main source for iodine radicals. The measurements have been performed using multi-axis differential optical absorption spectroscopy (MAX-DOAS). Using a coupled atmosphere-snowpack radiative transfer model, the comparison of the signals observed from scattered skylight and from light reflected by the snowpack yields several ppb of iodine monoxide in the upper layers of the sunlit snowpack throughout the year. Snow pit samples from Neumayer Station contain up to 700 ng/l of total iodine, representing a sufficient reservoir for these extraordinarily high IO concentrations.
Modelling the optical and radiative properties of freshly emitted light absorbing carbon within an atmospheric chemical transport model
Authors: Kahnert M.
Published: April 2010

Abstract. Light absorbing carbon (LAC) aerosols have a complex, fractal-like aggregate structure. Their optical and radiative properties are notoriously difficult to model, and approximate methods may introduce large errors both in the interpretation of aerosol remote sensing observations, and in quantifying the direct radiative forcing effect of LAC. In this paper a method based on rigorous electromagnetic theory is employed for computing the optical properties of freshly emitted, externally mixed LAC aggregates. The computations are performed at wavelengths of 440 nm and 870 nm, and they cover the entire size range relevant for modelling these kinds of aerosols. The method for solving the electromagnetic scattering and absorption problem for aggregates proves to be sufficiently stable and fast to make accurate multiple-band computations of LAC optical properties feasible. The results from the electromagnetic computations are processed such that they can readily be integrated into a chemical transport model (CTM), which is a prerequisite for constructing robust observation operators for chemical data assimilation of aerosol optical observations. A case study is performed, in which results obtained with the coupled optics/CTM model are employed as input to detailed radiative transfer computations at a polluted European location. It is found that the still popular homogeneous sphere approximation significantly underestimates the radiative forcing at top of atmosphere as compared to the results obtained with the aggregate model. Notably, the LAC forcing effect predicted with the aggregate model is less than that one obtains by assuming a prescribed mass absorption coefficient for LAC.
Physical and optical properties of atmospheric aerosol by in-situ and radiometric measurements
Authors: Calvello M. , Esposito F. , Pavese G. , Serio C.
Published: April 2010

Abstract. Physical and optical properties of atmospheric aerosols collected by using a high resolution (1.5 nm) spectroradiometer (spectral range 400–800 nm), a 13 stages Dekati Low Pressure Impactor (size range 30 nm–10 μm), and an AE31 Aethalometer (7 wavelenghts from 370 nm to 950 nm), have been examined in a semi-rural site in Southwest Italy (Tito Scalo, 40°35´ N, 15°41´ E, 750 m a.s.l.). In particular, daily averaged values of AOD and Ångström turbidity parameters from radiometric data together with mass-size distributions from impactor data and Black Carbon (BC) concentrations have been analyzed from May to October 2008. Furthermore, by inverting direct solar radiances, aerosol columnar number and volume size distributions have been obtained for the same period. Comparison of different observation methods, allowed to verify if, and in what conditions, changes in aerosol properties measured at ground are representative of columnar properties variations. Agreement between columnar and in-situ measurements has been obtained in case of anthropogenic aerosol loading, while in case of Saharan dust intrusions some discrepancies have been found when dust particles were located at high layers in the atmosphere (4–8 km) thus affecting columnar properties more than surface ones. For anthropogenic aerosols, a good correlation has been confirmed through the comparison of fine aerosol fraction contribution as measured by radiometer, impactor and aethalometer, suggesting that in this case particles are more homogeneously distributed over the lower layers of atmosphere and columnar aerosol optical properties are dominated by surface measured component.
Radiosondes stratospheric temperatures from 1957 to 2008 at Dumont d'Urville (Antarctica): trends and link with Polar Stratospheric Clouds
Authors: David C. , Keckhut P. , Armetta A. , Jumelet J. , Marchand M. , Bekki S.
Published: April 2010

Abstract. Temperature profiles measurements are performed daily (00:00 UT) in Dumont d'Urville by Météo-France, using standard radiosondes, since the International Geophysical Year in 1957. A significant cooling of about 2.3 K/decade at 20 km appears between 1957 and 2008, consistent with other Antarctic studies. Due to a 16 years data gap between 1963 and 1978, only the most recent series, between 1979 and 2008, is used to investigate the inter-annual stratospheric temperatures variability. Over Dumont d'Urville, at the edge of the vortex, the annual mean temperature cooling of about 1 K/decade is the result of the cooling trends between 0.5 and 1.4 K/decade, in summer and autumn and a warming of about 1.1 K/decade in spring. These values are consistent with values obtained using data from inner vortex stations, but with smaller amplitude. No statistically significant trend is detected in winter. Despite the absence of mean temperature trend during winter, the occurrence of temperatures below the NAT threshold, between 1989 and 2008, reveals a significant trend of about +6%/decade. The PSCs occurrences frequency exhibits a concomitant trend of about +3%/decade, although not statistically significant. Yet, this is consistent with results obtained in the Northern Hemisphere. Such a possible positive trend in PSC occurrence has to be further explored to be confirmed or invalidated.
A new modeling tool for the diffusion of gases in ice or amorphous binary mixture in the polar stratosphere and the upper troposphere
Authors: Varotsos C. A. , Zellner R.
Published: April 2010

Abstract. To elaborate stratospheric ozone depletion processes, measurements of diffusion coefficients of selected gas phase molecules (i.e. HCl, CH3OH, HCOOH and CH3COOH) in ice in the temperature range 170–195 K have been analyzed with respect to the mechanisms and rates of diffusion. It is argued that the diffusion in ice of these compounds is governed by a vacancy – mediated mechanism, i.e. H2O vacancies are required to diffuse to lattice sites adjacent to these compounds prior to the diffusion of the corresponding molecule into the vacancy sites. In addition, we show that the diffusion coefficients of these compounds exhibit a specific interconnection, i.e. a linear relationship holds between the logarithm of the pre-exponential factor, Do, and the activation energy E. The physical meaning of this interconnection is discussed.
Measurements of iodine monoxide at a semi polluted coastal location
Authors: Furneaux K. L. , Whalley L. K. , Heard D. E. , Atkinson H. M. , Bloss W. J. , Flynn M. J. , Gallagher M. W. , Ingham T. , Kramer L. , Lee J. D. , Leigh R. , McFiggans G. B. , Mahajan A. S. , Monks P. S. , Oetjen H. , Plane J. M. C. , Whitehead J. D.
Published: April 2010

Abstract. Point source measurements of IO by laser induced fluorescence spectroscopy were made at a semi-polluted coastal location during the Reactive Halogens in the Marine Boundary Layer campaign in September 2006. The site, on the NW French coast, was characterised by extensive intertidal macroalgae beds which were exposed at low tide. The closest known iodine active macroalgae beds were at least 300 m from the measurement point. From 20 days of measurements, IO was observed above the instrument limit of detection on 14 days, of which a clear diurnal profile was observed on 11 days. The maximum IO mixing ratio was 30.0 pptv (10 s integration period) during the day, amongst the highest concentrations ever observed in the atmosphere, and 1–2 pptv during the night. IO concentrations were strongly dependent on tidal height, the intensity of solar irradiation and meteorological conditions. An intercomparison of IO measurements made using point source and spatially averaged DOAS instruments confirms the presence of hot-spots of IO caused by an inhomogeneous distribution of macroalgae. The co-incident, point source measurement of IO and ultra fine particles (2.5 nm≥d≥10 nm) displayed a strong correlation, providing evidence that IO is involved in the production pathway of ultra fine particles at coastal locations. Finally, a modelling study shows that high IO concentrations which are likely to be produced in a macrolagae rich environment can significantly perturb the concentrations of OH and HO2 radicals. The effect of IO on HOx is reduced as NOx concentrations increase.
Sediment records of highly variable mercury inputs to mountain lakes in Patagonia during the past millennium
Authors: Ribeiro Guevara S. , Meili M. , Rizzo A. , Daga R. , Arribére M.
Published: April 2010

Abstract. High Hg levels in the pristine lacustrine ecosystems of the Nahuel Huapi National Park, a protected zone situated in the Andes of Northern Patagonia, Argentina, have initiated further investigations on Hg cycling and source identification. Here we report Hg records in sedimentary sequences aiming at identifying atmospheric sources during the past millennium. In addition to global transport and deposition, a potential atmospheric Hg source to be considered is the local emissions associated with volcanic activity, considering that the Park is situated in the Southern Volcanic Zone. Two sediment cores were extracted from Lake Tonček, a small, high-altitude system reflecting mainly direct inputs associated with atmospheric contributions, and Lake Moreno Oeste, a much larger and deeper lake having an extended watershed covered mostly by native forest. The sedimentary sequences were dated based on both 210Pb and 137Cs profiles. In addition, tephra layers were identified and geochemically characterized for chronological application and to investigate any association of volcanic eruptions with Hg records. Hg concentrations in sediments were measured along with 32 other elements, as well as organic matter, fossil chironomids, and biogenic silica. Observed background Hg concentrations, determined from the sequence domains with lower values, ranged from 50 to 100 ng g−1 DW (dry weight), whereas the surficial layers reached 200 to 500 ng g−1 DW. In addition to this traditional pattern, however, two deep domains in both sequences showed dramatically increased Hg levels reaching 400 to 650 ng g−1 DW; the upper dated to the 18th to 19th centuries, and the lower around the 13th century. These concentrations are not only elevated in the present profiles but also many-fold above the background values determined in other fresh water sediments, as were also the Hg fluxes, reaching 120 to 150 μg m−2 y−1 in Lake Tonček. No correlation was observed between Hg concentrations and the contents of organic matter, fossil chironomids, biogenic silica, or the other elements determined. However, a distinct increase of Hg concentrations was observed immediately above some tephra layers, suggesting a link to volcanic events. Extended fires is another potential atmospheric source to be considered because the earlier Hg peaks coincide with reported charcoal peaks, whereas the upper Hg peaks coincide with evidences of extended forest fires from tree-ring data and historical records.
A multi-model analysis of vertical ozone profiles
Authors: Jonson J. E. , Stohl A. , Fiore A. M. , Hess P. , Szopa S. , Wild O. , Zeng G. , Dentener F. J. , Lupu A. , Schultz M. G. , Duncan B. N. , Sudo K. , Wind P. , Schulz M. , Marmer E. , Cuvelier C. , Keating T. , Zuber A. , Valdebenito A. , Dorokhov V. , De Backer H. , Davies J. , Chen G. H. , Johnson B. , Tarasick D. W.
Published: April 2010

Abstract. A multi-model study of the long-range transport of ozone and its precursors from major anthropogenic source regions was coordinated by the Task Force on Hemispheric Transport of Air Pollution (TF HTAP) under the Convention on Long-range Transboundary Air Pollution (LRTAP). Vertical profiles of ozone at 12-h intervals in year 2001 are available from twelve of the models contributing to this study and are compared here with observed profiles from ozonesondes. The contributions from each major source region are analysed for selected sondes, and this analysis is supplemented by retroplume calculations using the FLEXPART Lagrangian particle dispersion model to provide insight into the origin of ozone transport events and the cause of differences between the models and observations. In the boundary layer ozone levels are in general strongly affected by regional sources and sinks. With a considerably longer lifetime in the free troposphere, ozone here is to a much larger extent affected by processes on a larger scale such as intercontinental transport and exchange with the stratosphere. Such individual events are difficult to trace over several days or weeks of transport. As a result statistical relationships between models and ozone sonde measurements are far less satisfactory than for surface measurements at all seasons. The lowest bias between model calculated ozone profiles and the ozone sonde measurements is seen in the winter and autumn months. Following the increase in photochemical activity in the spring and summer months the spread in model results increases and the agreement between ozone sonde measurements and the individual models deteriorates further. At selected sites calculated contributions to ozone levels in the free troposphere from intercontinental transport are presented. Intercontinental transport is identified based on differences in model calculations with unperturbed emissions and emissions reduced by 20% by region. With emissions perturbed by 20% per region calculated intercontinental contributions to ozone in the free troposphere range from less than 1 ppb to 3 ppb, with small contributions in winter. The results are corroborated by the retroplume calculations. At several locations the seasonal contributions to ozone in the free troposphere from intercontinental transport differ from what has been shown earlier at the surface using the same dataset. The large spread in model results points to a need of further evaluation of the chemical and physical processes in order to improve the credibility of global model results.
Iodine-mediated coastal particle formation: an overview of the Reactive Halogens in the Marine Boundary Layer (RHaMBLe) Roscoff coastal study
Authors: McFiggans G. , Bale C. S. E. , Ball S. M. , Beames J. M. , Bloss W. J. , Carpenter L. J. , Dorsey J. , Dunk R. , Flynn M. J. , Furneaux K. L. , Gallagher M. W. , Heard D. E. , Hollingsworth A. M. , Hornsby K. , Ingham T. , Jones C. E. , Jones R. L. , Kramer L. J. , Langridge J. M. , Leblanc C. , LeCrane J.-P. , Lee J. D. , Leigh R. J. , Longley I. , Mahajan A. S. , Monks P. S. , Oetjen H. , Orr-Ewing A. J. , Plane J. M. C. , Potin P. , Shillings A. J. L. , Thomas F. , von Glasow R. , Wada R. , Whalley L. K. , Whitehead J. D.
Published: April 2010

Abstract. This paper presents a summary of the measurements that were made during the heavily-instrumented Reactive Halogens in the Marine Boundary Layer (RHaMBLe) coastal study in Roscoff on the North West coast of France. It was clearly demonstrated that iodine-mediated coastal particle formation occurs, driven by daytime low tide emission of molecular iodine, I2, by macroalgal species fully or partially exposed by the receding waterline. Ultrafine particle concentrations strongly correlate with the rapidly recycled reactive iodine species, IO, produced at high concentrations following photolysis of I2. The heterogeneous macroalgal I2 sources lead to variable relative concentrations of iodine species observed by path-integrated and in situ measurement techniques. Apparent particle emission fluxes were associated with an enhanced apparent depositional flux of ozone, consistent with both a direct O3 deposition to macroalgae and involvement of O3 in iodine photochemistry and subsequent particle formation below the measurement height. The magnitude of the particle formation events was observed to be greatest at the lowest tides with higher concentrations of ultrafine particles growing to much larger sizes, probably by the condensation of anthropogenically-formed condensable material. At such sizes the particles should be able to act as cloud condensation nuclei at reasonable atmospheric supersaturations.
Evaluation of stratospheric chlorine chemistry for the Arctic spring 2005 using modelled and measured OClO column densities
Authors: Oetjen H. , Wittrock F. , Richter A. , Chipperfield M. P. , Medeke T. , Sheode N. , Sinnhuber B.-M. , Sinnhuber M. , Burrows J. P.
Published: April 2010

Abstract. Chlorine dioxide, OClO, column amounts retrieved from measurements of the SCIAMACHY satellite instrument are presented and validated by comparison with simultaneous ground-based DOAS observations. In addition, the measurements are compared to model calculations taking into account the photochemical change along the light path. Although OClO does not participate directly in the destruction of ozone, its accurate measurement as well as modelling is crucial to understand the highly perturbed chlorine chemistry in the polar vortices. SCIAMACHY OClO slant columns retrieved during spring 2005 have been quantitatively validated by comparison with slant columns retrieved from measurements made in Ny-Ålesund (79° N, 12° E), Summit (73° N, 38° W) and Bremen (53° N, 9° E). Overall, good agreement is found. OClO slant column densities modelled with a set of stacked box models and considering the light path through the atmosphere are also included in this comparison. The model predictions differ significantly from the measured quantities. OClO amounts are underestimated for conditions of strong chlorine activation and at large solar zenith angles. Sensitivity studies for several parameters in the stacked box model have been performed and it is inferred that using the chemistry known to date, the observed OClO cannot be adequately reproduced within the range of uncertainties given for the various model parameters.
Continental Scale Antarctic deposition of sulphur and black carbon from anthropogenic and volcanic sources
Authors: Graf H.-F. , Shirsat S. V. , Oppenheimer C. , Jarvis M. J. , Podzun R. , Jacob D.
Published: April 2010

Abstract. While Antarctica is often described as a pristine environment, the potential threats from local pollution sources including tourist ships and emissions associated with scientific activities have recently been raised. However, to date there has been no systematic attempt to model the impacts of such pollutants at the continental scale. Indeed, until very recently there was not even a sulphur emission budget available for Antarctica. Here we present the first comprehensive study of atmospheric pollution in Antarctica using a limited area chemistry climate model, and a monthly emissions inventory for sulphur from maintenance of research stations, ground and air traffic, shipping and the active volcano Mt. Erebus. We find that ship emissions, both sulphurous and black carbon, dominate anthropogenic pollution near the ground. These are likely to rise considerably if recent trends in tourism continue.
Atmospheric observation-based global SF6 emissions – comparison of top-down and bottom-up estimates
Authors: Levin I. , Naegler T. , Heinz R. , Osusko D. , Cuevas E. , Engel A. , Ilmberger J. , Langenfelds R. L. , Neininger B. , Rohden C. v. , Steele L. P. , Weller R. , Worthy D. E. , Zimov S. A.
Published: April 2010

Abstract. Emissions of sulphur hexafluoride (SF6), one of the strongest greenhouse gases on a per molecule basis, are targeted to be collectively reduced under the Kyoto Protocol. Because of its long atmospheric lifetime (≈3000 years), the accumulation of SF6 in the atmosphere is a direct measure of its global emissions. Examination of our extended data set of globally distributed high-precision SF6 observations shows an increase in SF6 abundance from near zero in the 1970s to a global mean of 6.7 ppt by the end of 2008. In-depth evaluation of our long-term data records shows that the global source of SF6 decreased after 1995, most likely due to SF6 emission reductions in industrialised countries, but increased again after 1998. By subtracting those emissions reported by Annex I countries to the United Nations Framework Convention of Climatic Change (UNFCCC) from our observation-inferred SF6 source leaves a surprisingly large gap of more than 70–80% of non-reported SF6 emissions in the last decade.
Overview of mercury measurements in the Antarctic troposphere
Authors: Dommergue A. , Sprovieri F. , Pirrone N. , Ebinghaus R. , Brooks S. , Courteaud J. , Ferrari C.
Published: April 2010

Abstract. Polar ecosystems are considered to be the last pristine environments of the Earth relatively uninfluenced by human activities. Antarctica in particular, compared to the Arctic is considered to be even less affected by any kind of anthropogenic influences. Once contaminants reach the polar regions, their lifetime in the troposphere depends on local removal processes. Atmospheric mercury, in particular, has unique characteristics that include long-range transport to polar regions and the transformation to more toxic and water-soluble compounds that may potentially become bioavailable. These chemical-physical properties have given mercury on the priority list of an increasing number of international, European and national conventions and agreements aimed at the protection of the ecosystems including human health (i.e., GEO, UNEP, AMAP, UN-ECE, HELCOM, OSPAR) thus stimulating a significant amount of research including measurements of Hg0 reaction rate constant with atmospheric oxidants, experimental and modelling studies in order to understand the cycling of Hg in polar regions and its impact to these ecosystems. Special attention in terms of contamination of polar regions, is paid to the consequences of the springtime phenomena, referred to as ''atmospheric mercury depletion event'' (AMDE), during which elemental gaseous mercury (GEM or Hg0) through a series of photochemically-initiated reactions involving halogens, may be converted to a reactive form that may accumulate in polar ecosystems. The discovery of the AMDE, first noted in the Arctic, has also been observed at both poles and was initially considered to result in an important net input of atmospheric Hg into the polar surfaces. However, recent studies point out that complex processes take place after deposition that may result in less significant net-inputs from the atmosphere since a fraction, sometimes significant of deposited Hg may be recycled. Therefore, the contribution of this unique reactivity occurring in polar atmospheres to the global budget of atmospheric Hg and the role played by snow and ice surfaces of these regions are important issues. This paper presents a review of atmospheric mercury studies conducted in the Antarctic troposphere, both at coastal locations and on the Antarctic Plateau since 1985. Our current understanding of atmospheric reactivity in this region is also presented.
PTR-MS measurements of non-methane volatile organic compounds during an intensive field campaign at the summit of Mount Tai, China, in June 2006
Authors: Inomata S. , Tanimoto H. , Kato S. , Suthawaree J. , Kanaya Y. , Pochanart P. , Liu Y. , Wang Z.
Published: April 2010

Abstract. Owing to recent industrialization, Central East China has become a significant source of air pollutants. To examine the processes controlling the chemistry and transport of tropospheric ozone, we continuously measured non-methane volatile organic compounds (NMVOCs) as part of an intensive field campaign at Mount Tai, China, in June 2006 (MTX2006), using proton transfer reaction mass spectrometry (PTR-MS). Temporal variations of NMVOCs were recorded in mass-scan mode from m/z 17 to m/z 300 during 12–30 June 2006. More than thirty kinds of NMVOCs were detected up to m/z 160, including alkenes, aromatics, alcohols, aldehydes, and ketones. Oxygenated VOCs were the predominant NMVOCs. During the night of 12 June, we observed an episode of high NMVOCs concentrations attributed to the burning of agricultural biomass. The ΔNMVOCs/ΔCO ratios derived by PTR-MS measurements for this episode are compared to emission ratios from various types of biomass burning as reviewed by Andreae and Merlet (2001) and to ratios recently measured by PTR-MS in tropical forests (Karl et al., 2007) and at urban sites (Warneke et al., 2007).
Modeling the regional impact of ship emissions on NOx and ozone levels over the Eastern Atlantic and Western Europe using ship plume parameterization
Authors: Huszar P. , Cariolle D. , Paoli R. , Halenka T. , Belda M. , Schlager H. , Miksovsky J. , Pisoft P.
Published: April 2010

Abstract. In general, regional and global chemistry transport models apply instantaneous mixing of emissions into the model's finest resolved scale. In case of a concentrated source, this could result in erroneous calculation of the evolution of both primary and secondary chemical species. Several studies discussed this issue in connection with emissions from ships and aircrafts. In this study, we present an approach to deal with the non-linear effects during dispersion of NOx emissions from ships. It represents an adaptation of the original approach developed for aircraft NOx emissions, which uses an exhaust tracer to trace the amount of the emitted species in the plume and applies an effective reaction rate for the ozone production/destruction during the plume's dilution into the background air. In accordance with previous studies examining the impact of international shipping on the composition of the troposphere, we found that the contribution of ship induced surface NOx to the total reaches 90% over remote ocean and makes 10–30% near coastal regions. Due to ship emissions, surface ozone increases by up to 4–6 ppbv making 10% contribution to the surface ozone budget. When applying the ship plume parameterization, we showed that the large scale NOx decreases and the ship NOx contribution is reduced by up to 20–25%. Similar decrease was found in case of O3. The plume parameterization suppressed the ship induced ozone production by 15–30% over large areas of the focused region. To evaluate the presented parameterization, nitrogen oxide measurements over the English Channel were compared with modeled values and it was found that after activating the parameterization the model accuracy increases.
Cirrus cloud radiative effect on surface-level shortwave and longwave irradiances at regional and global scale
Authors: Dupont J.-C. , Haeffelin M. , Long C. N.
Published: April 2010

Abstract. Data collected at four ground-level sites are analyzed (1) to determine the surface cloud radiative effect (CRE) induced by cirrus clouds at regional scale for shortwave (CRESW) and longwave (CRELW) fluxes and (2) to derive the sensitivity of surface CRESW to the cloud optical thickness (COT) modulated by the solar zenith angle and the atmospheric turbidity (noted CRESW*) and the sensitivity of surface CRELW to the infrared emissive power of cirrus cloud modulated by the water vapor content (noted CRELW*). The average CRESW* is −120 W m−2 COT−1 but it ranges from −80 to −140 m−2 COT−1 depending on the solar illumination with a residual variability ranges from +40 and −40 W m−2 COT−1 from pristine to turbid conditions, respectively. The CRELW*, that corresponds to the infrared transmissivity of the atmosphere, ranges from 3% to 40% from dry to wet atmospheric conditions, respectively. The subvisible cirrus class (COT<0.03) over mid-latitude sites, that represents 20% of the population, induces a significant increase in surface LW irradiance at the 2–7 W m−2 level. The semi-transparent cirrus class (0.03<COT<0.3), that represents 45% of the population, will affect the surface SW irradiance by −12 to −25 W m−2. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and the Atmospheric Infrared Sounder (AIRS) are used here to estimate the surface radiative effect at global scale. Global CRE estimations show very significant zonal and seasonal variability of each component of the CRENET. CRENET is 0.4 W m−2 during winter/autumn for 15–75° N and 1 W m−2 for 45–75° S whereas it is near −3 W m−2 for 15° S–15° N. The summer period shows a cirrus cloud global cooling at all the latitudes except for 75–45° S with a quasi null effect and a peak at −3.6 W m−2 for 15° S–45° N. The global average cumulative CRE is −2.8, 1.7 and −1.1 W m−2 for CRESW, CRELW, and CRENET, respectively.
Coupling aerosol surface and bulk chemistry with a kinetic double layer model (K2-SUB): oxidation of oleic acid by ozone
Authors: Pfrang C. , Shiraiwa M. , Pöschl U.
Published: April 2010

Abstract. We present a kinetic double layer model coupling aerosol surface and bulk chemistry (K2-SUB) based on the PRA framework of gas-particle interactions (Pöschl et al., 2007). K2-SUB is applied to a popular model system of atmospheric heterogeneous chemistry: the interaction of ozone with oleic acid. We show that our modelling approach allows de-convoluting surface and bulk processes, which has been a controversial topic and remains an important challenge for the understanding and description of atmospheric aerosol transformation. In particular, we demonstrate how a detailed treatment of adsorption and reaction at the surface can be coupled to a description of bulk reaction and transport that is consistent with traditional resistor model formulations. From literature data we have derived a consistent set of kinetic parameters that characterise mass transport and chemical reaction of ozone at the surface and in the bulk of oleic acid droplets. Due to the wide range of rate coefficients reported from different experimental studies, the exact proportions between surface and bulk reaction rates remain uncertain. Nevertheless, the model results suggest an important role of chemical reaction in the bulk and an upper limit of ~1×10−11 cm2 s−1 for the surface reaction rate coefficient. Sensitivity studies show that the surface accommodation coefficient of the gas-phase reactant has a strong non-linear influence on both surface and bulk chemical reactions. We suggest that K2-SUB may be used to design, interpret and analyse future experiments for better discrimination between surface and bulk processes in the oleic acid-ozone system as well as in other heterogeneous reaction systems of atmospheric relevance.
Biomass burning and urban air pollution over the Central Mexican Plateau
Authors: Crounse J. D. , DeCarlo P. F. , Blake D. R. , Emmons L. K. , Campos T. L. , Apel E. C. , Clarke A. D. , Weinheimer A. J. , McCabe D. C. , Yokelson R. J. , Jimenez J. L. , Wennberg P. O.
Published: April 2010

Abstract. Observations during the 2006 dry season of highly elevated concentrations of cyanides in the atmosphere above Mexico City (MC) and the surrounding plains, demonstrate that biomass burning (BB) significantly impacted air quality in the region. We find that during the period of our measurements, fires contribute more than half of the organic aerosol mass and submicron aerosol scattering, and one third of the enhancement in benzene, reactive nitrogen, and carbon monoxide in the outflow from the plateau. The combination of biomass burning and anthropogenic emissions will affect ozone chemistry in the MC outflow.
Evaluation of a regional air quality forecast model for tropospheric NO2 columns using the OMI/AURA satellite tropospheric NO2 product
Authors: Herron-Thorpe F. L. , Vaughan J. K. , Lamb B. K. , Mount G. H.
Published: April 2010

Abstract. Results from a regional air quality forecast model, AIRPACT-3, are compared to OMI tropospheric NO2 integrated column densities for an 18 month period over the Pacific Northwest. AIRPACT column densities were well correlated with cloud-free monthly averages of tropospheric NO2 (R=0.75) to NASA retrievals for months without wildfires, but were poorly correlated with significant model overpredictions (R=0.21) for months with wildfires when OMI and AIRPACT were compared over the entire domain. AIRPACT forecasted higher NO2 in some US urban areas, and lower NO2 in many Canadian urban areas, when compared to OMI. There are significant changes in results after spatially averaging model results to the daily OMI swath. Also, it is shown that applying the averaging kernel to model results in cloudy conditions has a large effect, but applying the averaging kernel in cloud free conditions has little effect. The KNMI and NASA retrievals of tropospheric NO2 from OMI (collection 3) are compared. The NASA product is shown to be significantly different than the KNMI tropospheric NO2 product, i.e. July 2007 (R=0.60) and January 2008 (R=0.69).
Mercury emission from crematories in Japan
Authors: Takaoka M. , Oshita K. , Takeda N. , Morisawa S.
Published: April 2010

Abstract. Anthropogenic sources of mercury emissions have a significant impact on global pollution. Therefore, finding uncharacterised sources and assessing the emissions from these sources are important. However, limited data are available worldwide on mercury emissions from crematories. In Japan, 99.9% of dead bodies are cremated, which is the highest percentage in the world, and more than 1600 crematories are in operation. We thus focused on emissions from crematories in Japan. The number of targeted facilities was seven, and we used continuous emission monitoring to measure the mercury concentrations and investigate mercury behaviour. The total mercury concentrations in stack gases were a few μg/Nm3 (normal cubic meters). Considering the time profile of mercury and its species in cremations, the findings confirmed that the mercury in stack gas originated from dental amalgam. The amount of mercury emissions was calculated using the total concentration and gas flow rate. Furthermore, the annual amount of mercury emission from crematories in Japan was estimated by using the total number of corpses. The emission amount was considerably lower than that estimated in the UK. From statistical analyses on population demographics and measurements, future total emissions from crematories were also predicted. As a result, the amount of mercury emitted by crematories will likely increase by 2.6-fold from 2007 to 2037.
Effects of the 2006 El Niño on tropospheric ozone and carbon monoxide: implications for dynamics and biomass burning
Authors: Chandra S. , Ziemke J. R. , Duncan B. N. , Diehl T. L. , Livesey N. J. , Froidevaux L.
Published: April 2010

Abstract. We have studied the effects of the 2006 El Niño on tropospheric O3 and CO at tropical and sub-tropical latitudes measured from the OMI and MLS instruments on the Aura satellite. The 2006 El Niño-induced drought allowed forest fires set to clear land to burn out of control during October and November in the Indonesian region. The effects of these fires are clearly seen in the enhancement of CO concentration measured from the MLS instrument. We have used a global model of atmospheric chemistry and transport (GMI CTM) to quantify the relative importance of biomass burning and large scale transport in producing observed changes in tropospheric O3 and CO. The model results show that during October and November both biomass burning and meteorological changes contributed almost equally to the observed increase in tropospheric O3 in the Indonesian region. The biomass component was 4–6 DU but it was limited to the Indonesian region where the fires were most intense. The dynamical component was 4–8 DU but it covered a much larger area in the Indian Ocean extending from South East Asia in the north to western Australia in the south. By December 2006, the effect of biomass burning was reduced to zero and the observed changes in tropospheric O3 were mostly due to dynamical effects. The model results show an increase of 2–3% in the global burden of tropospheric ozone. In comparison, the global burden of CO increased by 8–12%.
Quantification of organic carbon sampling artifacts in US non-urban and urban networks
Authors: Chow J. C. , Watson J. G. , Chen L.-W. A. , Rice J. , Frank N. H.
Published: April 2010

Abstract. Different approaches to estimate organic sampling artifacts have been adopted by US long-term air quality monitoring networks. This study documents field blank (bQF) and backup filter (quartz-fiber behind quartz-fiber filter; QBQ) carbon levels for the: 1) Interagency Monitoring of Protected Visual Environments (IMPROVE); 2) Speciation Trends Network (STN; part of the Chemical Speciation Network [CSN]; and 3) Southeastern Aerosol Research and Characterization (SEARCH) networks. Filter pack sample handling procedures and blank correction methods are examined. Due to a relatively short (1–15 min) passive exposure period, STN/CSN and SEARCH network bQF organic carbon (OC; 0.8–1 μg/cm2) may underestimate positive and negative OC artifacts, respectively, resulting from passive adsorption or volatilization of volatile or semi-volatile organic compounds on quartz-fiber filters while they are in the sampler. This is evidenced by a lack of temporal or spatial variability and low bQF levels. With ~7 d of ambient passive exposure, average IMPROVE bQF and QBQ OC are comparable (2.4±0.5 and 3.1±0.8 μg/cm2) and more than twice those found in the STN/CSN and SEARCH networks. Lower STN/CSN flow rates and larger filter deposit areas result in 9–20% of the areal density (μg/cm2) compared to IMPROVE areal deposits. STN/CSN bQF values are 11–34% lower than linear regression intercepts derived from collocated IMPROVE-STN/CSN data pairs. Using a preceding organic denuder in the SEARCH network reduces the organic vapor adsorption on QBQ, though the longer QBQ period in the sampler may result from passive organic vapor adsorption as well as evaporated OC from the front filter deposits.