bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameterizing the competition between homogeneous and heterogeneous freezing in ice cloud formation – polydisperse ice nuclei
Authors: Barahona D. , Nenes A.
Published: April 2010

Abstract. This study presents a comprehensive ice cloud formation parameterization that computes the ice crystal number, size distribution, and maximum supersaturation from precursor aerosol and ice nuclei with any size distribution and chemical composition. The parameterization provides an analytical solution of the cloud parcel model equations and accounts for the competition effects between homogeneous and heterogeneous freezing, and, between heterogeneous freezing in different modes. The diversity of heterogeneous nuclei is described through a nucleation spectrum function which is allowed to follow any form (i.e., derived from classical nucleation theory or from empirical observations). The parameterization reproduced the predictions of a detailed numerical parcel model over a wide range of conditions, and several expressions for the nucleation spectrum. The average error in ice crystal number concentration was −2.0±8.5% for conditions of pure heterogeneous freezing, and, 4.7±21% when both homogeneous and heterogeneous freezing were active. Apart from its rigor, excellent performance and versatility, the formulation is extremely fast and free from requirements of numerical integration.
Technical Note: Ensuring consistent, global measurements of short-lived halocarbon gases in the ocean and atmosphere
Authors: Butler J. H. , Bell T. G. , Hall B. D. , Quack B. , Carpenter L. J. , Williams J.
Published: April 2010

Abstract. Short-lived halocarbons are significant sources of reactive halogen in the troposphere and likely the lower stratosphere. Quantifying ambient concentrations in the surface ocean and atmosphere is essential for understanding the impact of fluxes of these gases on marine boundary layer oxidation and lower stratospheric ozone-depletion processes. Despite the body of literature increasing substantially over recent years, calibration issues complicate comparison of results and limit the utility of building larger-scale databases that would enable further development of the science (e.g. sea-air flux quantification, model validation, etc.). With this in mind, thirty-two scientists representing eight nations and from both atmospheric and oceanic halocarbon communities gathered in London in February 2008 to discuss the scientific issues and plan an international effort toward a common calibration scale. Here, we discuss the outputs from this meeting, suggest the compounds that should be targeted initially, identify opportunities for beginning calibration and comparison efforts, and make recommendations for ways to improve the comparability of previous and future measurements.
An intensive study of aerosol optical properties in Beijing urban area
Authors: He X. , Li C. , Lau A. K. H. , Deng Z. , Mao J. , Wang M. , Liu X.
Published: April 2010

Abstract. In order to quantify the aerosol impact on climate, a range of aerosol parameters is required. In this paper, two-year ground-based observations of aerosol optical properties are conducted at an urban site in Beijing of China. Aerosol absorption coefficient (σa) and scattering coefficient (σs), as well as single scattering albedo (ω) are analyzed for characterizing Beijing urban aerosol. Two-year averages (and standard deviations) for σa, σs and ω are 56±49 Mm−1, 288±281 Mm−1 and 0.80±0.09, respectively. Meanwhile, there is a distinct diurnal variation for σa, with its minimum occurs about 14:00 to 15:00 and maximum in the evening. While, σs peaks in late morning and the minimum occurs in the evening. σs in summer is higher than that in winter. ω in summer is higher than that in winter except before 07:00 a.m. and it peaks in the early afternoon. Both σa and σs show strong dependence on local wind in four seasons. When the wind blows from north with low speed (0–4 m/s), both σa and σs are high, while very low with wind speed higher than 4 m/s. When the wind blows from south with low speed (0–4 m/s), σa and σs are intermediate. ω also shows wind dependence to some extent though not as strong as σa and σs.
Tropospheric ozone from IASI: comparison of different inversion algorithms and validation with ozone sondes in the northern middle latitudes
Authors: Keim C. , Eremenko M. , Orphal J. , Dufour G. , Flaud J.-M. , Höpfner M. , Boynard A. , Clerbaux C. , Payan S. , Coheur P.-F. , Hurtmans D. , Claude H. , Dier H. , Johnson B. , Kelder H. , Kivi R. , Koide T. , López Bartolomé M. , Lambkin K. , Moore D. , Schmidlin F. J. , Stübi R.
Published: April 2010

Abstract. This paper presents a first statistical validation of tropospheric ozone products derived from measurements of the satellite instrument IASI. Since end of 2006, IASI (Infrared Atmospheric Sounding Interferometer) aboard the polar orbiter Metop-A measures infrared spectra of the Earth's atmosphere in nadir geometry. This validation covers the northern mid-latitudes and the period from July 2007 to August 2008. The comparison of the ozone products with the vertical ozone concentration profiles from balloon sondes leads to estimates of the systematic and random errors in the IASI ozone products. The intercomparison of the retrieval results from four different sources (including the EUMETSAT ozone products) shows systematic differences due to the used methods and algorithms. On average the tropospheric columns have a small bias of less than 2 Dobson Units (DU) when compared to the sonde measured columns. The comparison of the still pre-operational EUMETSAT columns shows higher mean differences of about 5 DU.
Dust events in Beijing, China (2004–2006): comparison of ground-based measurements with columnar integrated observations
Authors: Wu Z. J. , Cheng Y. F. , Hu M. , Wehner B. , Sugimoto N. , Wiedensohler A.
Published: April 2010

Abstract. Three-year particle number size distributions were analyzed to characterize the size distributions and optical properties of the particles in the urban atmosphere of Beijing, China during dust events in the springs of 2004–2006 in combination with AERONET sun/sky radiometer data. The dust events were categorized as two different types (type 1 and 2). This categorization of the dust events was confirmed by the aerosol index images, columnar aerosol optical properties, and vertical potential temperature profiles. Dust particles dominated the total particle volume concentration (3–10000 nm) (over 70%) for the dust events in type 1, which happened under strong wind speeds. In this type, relatively purer dust particles were observed in the urban atmosphere. The events in type 2 with a longer stagnation time in the urban area and lower ratio of coarse mode particle to the total particle volume concentration occurred under stable local weather conditions. During the events in type 2, a superposition of the dust particles and anthropogenic aerosols was observed. The comparison of columnar optical properties among type 1, 2, and heavy pollution periods shows that the superposition of dust particles and anthropogenic aerosols can result in much higher AOD than pure dust particles in the urban atmosphere of Beijing. By comparing the particle volume size distributions retrieved from AERONET with those obtained from the Twin Differential Mobility Particle Sizer measurements, a discrepancy between the ground-based and column integrated particle volume size distributions was found, especially obvious for the coarse mode particles.
Direct measurements of the effect of biomass burning over the Amazon on the atmospheric temperature profile
Authors: Davidi A. , Koren I. , Remer L.
Published: April 2010

Abstract. Aerosols suspended in the atmosphere interact with the solar radiation and thus change the radiation energy fluxes in the atmospheric column. In particular, absorbing aerosols can stabilize the lower atmosphere by warming the aerosol layer; while cooling both: the layers beneath and the surface. Changes in atmospheric stability can affect cloud formation and cloud properties. In this paper we measure changes in the atmospheric temperature profile as a function of the smoke loading and the cloudiness over the Amazon basin, during the dry seasons (August and September) of 2005–2007. We show that as the aerosol optical depth (AOD) increases from 0.02 to a value of ~0.6, there is a decrease of ~4.3°C at 1000 hPa, and an increase of ~1.6°C at 850 hPa. The warming of the aerosol layer at 850 hPa is likely due to aerosol absorption when the particles are exposed to direct illumination by the sun. The large values of cooling in the lower layers are explained by a combination of aerosol extinction of the solar flux in the layers aloft and by an aerosol-induced increase of cloud cover and further shading of the lower atmosphere. We estimate that the increase in cloud fraction due to aerosol contributes about half of the observed cooling in the lower layers.
Retrieval of cloud liquid water distributions from a single scanning microwave radiometer aboard a mobile platform – Part 2: Observation system simulation experiments
Authors: Huang D. , Gasiewski A. , Wiscombe W.
Published: April 2010

Abstract. Part 1 of this research reveals that many conditions of the 2003 cloud tomography experiment at the Wakasa Bay were not ideal for the tomographic retrieval purpose. For example, the aircraft flew too fast and its altitude was too high. Part 2 (this paper) then focuses on the examination of several possible improvements on the mobile cloud tomography method by means of observation system simulation experiment. We find that the incorporation of the L1 norm total variation regularization in the tomographic retrieval algorithm better reproduces small scale discontinuous structure than the widely used L2 norm Tikhonov regularization and successfully resolves sharp cloud edges. The simulation experiments reveal that a typical ground-based mobile cloud tomography setup substantially outperforms an airborne one because of its slower moving speed and greater contrast in microwave brightness between clouds and the cosmic background. The simulations show that, as expected, the retrieval error increases monotonically with radiometer noise level and the uncertainty in background brightness temperature. It is also revealed that a slower platform or a faster scanning radiometer results in more scan cycles and better overlapping between the swaths of successive scan cycles, both of which are highly favorable for cloud tomography retrieval. The last factor examined is aircraft height. It is shown that the best retrieval is obtained when the aircraft data are collected at the altitudes between 500 m to 1000 m above the cloud top. To summarize, this research demonstrates the feasibility of tomographically retrieving cloud structure using current scanning microwave radiometer technology and provides several general guidelines by which to improve future field-based studies of cloud tomography.
Source regions of some Persistent Organic Pollutants measured in the atmosphere at Birkenes, Norway
Authors: Eckhardt S. , Breivik K. , Li Y. F. , Manø S. , Stohl A.
Published: April 2010

Abstract. A key feature of POPs (Persistent Organic Pollutants) is their potential for long-range atmospheric transport. In order to better understand and predict atmospheric source-receptor relationships of POPs, we have modified an existing Lagrangian transport model (FLEXPART) to include some of the key processes that control the atmospheric fate of POPs. We also present four years (2004–2007) of new atmospheric measurement data for polychlorinated biphenyls (PCBs) and hexachlorocyclohexanes (HCHs) obtained at Birkenes, an EMEP (European Monitoring and Evaluation Programme) site in Southern Norway. The model overestimates measured PCB-28 and γ-HCH concentrations by factors of 2 and 8, respectively, which is most likely because the emissions used as input to the model are overestimated. FLEXPART captures the temporal variability in the measurements very well and, depending on season, explains 31–67% (14–62%) of the variance of measured PCB-28 (γ-HCH) concentrations. FLEXPART, run in a time-reversed (adjoint) mode, was used to identify the source regions responsible for the POP loading at the Birkenes station. Emissions in Central Europe and Eastern Europe contributed 32% and 24%, respectively, to PCB-28 at Birkenes, while Western Europe was found to be the dominant source (50%) for γ-HCH. Intercontinental transport from North America contributed 13% γ-HCH. While FLEXPART has no treatment of the partitioning of POPs between different surface media, it was found a very useful tool for studying atmospheric source-receptor relationships for POPs and POP-like chemicals that do not sorb strongly to atmospheric particles and whose atmospheric levels are believed to be mainly controlled by primary sources.
Technical Note: a combined SBUV and SAGE zonal-mean ozone data set
Authors: McLinden C. A. , Tegtmeier S. , Fioletov V.
Published: April 2010

Abstract. A stratospheric monthly, zonal-mean combined ozone data set based on Satellite Aerosol and Gas Experiment (SAGE) and Solar Backscatter UltraViolet (SBUV) data spanning 1978–2005 is presented. Drifts in individual SBUV instruments and inter-SBUV biases are corrected using SAGE I and II by calculating differences between coincident SAGE-SBUV measurements. In this way the daily, near-global coverage of SBUV(/2) is combined with the stability of SAGE to provide a homogeneous ozone record. The resultant data set shows, for example, a more realistic Quasi-Biennial Oscillation signal compared to the one derived from SBUV data alone. Furthermore, this methodology can be used to extend the present data set beyond the lifetime of SAGE II.
Reactive nitrogen in atmospheric emission inventories – a review
Authors: Reis S. , Pinder R. W. , Zhang M. , Lijie G. , Sutton M. A.
Published: April 2010

Abstract. Excess reactive Nitrogen (Nr) has become one of the most pressing environmental problems leading to air pollution, acidification and eutrophication of ecosystems, biodiversity impacts, leaching of nitrates into groundwater and global warming. This paper investigates how current inventories cover emissions of Nr to the atmosphere in Europe, the United States of America, and The People's Republic of China. The focus is on anthropogenic sources, assessing the state-of-the-art of quantifying emissions of Ammonia (NH3), Nitrogen Oxides (NOx) and Nitrous Oxide (N2O), the different purposes for which inventories are compiled, and to which extent current inventories meet the needs of atmospheric dispersion modelling. The paper concludes with a discussion of uncertainties involved and a brief outlook on emerging trends in the three regions investigated is conducted. Key issues are substantial differences in the overall magnitude, but as well in the relative sectoral contribution of emissions in the inventories that have been assessed. While these can be explained by the use of different methodologies and underlying data (e.g. emission factors or activity rates), they may lead to quite different results when using the emission datasets to model ambient air quality or the deposition with atmospheric dispersion models. Hence, differences and uncertainties in emission inventories are not merely of academic interest, but can have direct policy implications when the development of policy actions is based on these model results. The robustness of emission estimates varies greatly between substances, regions and emission source sectors. This has implications for the direction of future research needs and indicates how existing gaps between modelled and measured concentration or deposition rates could be most efficiently addressed. The observed current trends in emissions display decreasing NOx emissions and only slight reductions for NH3 in both Europe and the US. However, in China projections indicate a steep increase of both.
Aerosol optical properties relevant to regional remote sensing of CCN activity and links to their organic mass fraction: airborne observations over Central Mexico and the US West Coast during MILAGRO/INTEX-B
Authors: Shinozuka Y. , Clarke A. D. , DeCarlo P. F. , Jimenez J. L. , Dunlea E. J. , Roberts G. C. , Tomlinson J. M. , Collins D. R. , Howell S. G. , Kapustin V. N. , McNaughton C. S. , Zhou J.
Published: April 2010

Abstract. Remote sensing of cloud condensation nuclei (CCN) would help evaluate the indirect effects of tropospheric aerosols on clouds and climate. To assess its feasibility, we examined relationships of submicron aerosol composition to CCN activity and optical properties observed during the MILAGRO/INTEX-B aircraft campaigns. An indicator of CCN activity, κ, was calculated from hygroscopicity measured under saturation. κ for dry 100-nm particles decreased with the organic fraction of non-refractory mass of submicron particles (OMF) as 10(−0.43−0.44*OMF) over Central Mexico and 10(−0.29−0.70*OMF) over the US West Coast. These fits represent the critical dry diameter, centered near 100 nm for 0.2% supersaturation but varied as κ(−1/3), within measurement uncertainty (~20%). The decreasing trends of CCN activity with the organic content, evident also in our direct CCN counts, were consistent with previous ground and laboratory observations of highly organic particles. The wider range of OMF, 0–0.8, for our research areas means that aerosol composition will be more critical for estimation of CCN concentration than at the fixed sites previously studied. Furthermore, the wavelength dependence of extinction was anti-correlated with OMF as −0.70*OMF+2.0 for Central Mexico's urban and industrial pollution air masses, for unclear reasons. The Angstrom exponent of absorption increased with OMF, more rapidly under higher single scattering albedo, as expected for the interplay between soot and colored weak absorbers (some organic species and dust). Because remote sensing products currently use the wavelength dependence of extinction albeit in the column integral form and may potentially include that of absorption, these regional spectral dependencies are expected to facilitate retrievals of aerosol bulk chemistry and CCN activity over Central Mexico.
Variability of residence time in the Tropical Tropopause Layer during Northern Hemisphere winter
Authors: Krüger K. , Tegtmeier S. , Rex M.
Published: April 2010

Abstract. For the first time the long-term interannual and spatial variability of residence time (τ) is presented for the TTL between 360 K and 400 K theta (~14 to 18 km altitude). The analysis is based on a Lagrangian approach using offline calculated diabatic heating rates as vertical velocities, covering Northern Hemisphere (NH) winters from 1962–2004. The residence time varies spatially. τ, analysed for the Lagrangian Cold Point (LCP), displays a longer duration time of air parcels between LCP and 400 K over the maritime continent (>50 days), as the LCP tropopause has a minimum over the maritime continent (<370 K theta). Comparing three theta layers within the TTL reveals the vertical dependence of τ. We derive a mean duration time of 34 days for 360–380 K (lower TTL), 38 days for 380–400 K (upper TTL) and 70 days for 360–400 K theta layers for the 1962–2001 period. A case analysis reveals, that τ is positively skewed for 360–380 K and 380–400 K during La Niña and El Niño Southern Oscillation (ENSO) neutral years. For these cases, ~60% of air parcels travel from 360 K to 380 K within 25 days. There is large interannual variability for τ varying up to ±20% from the long-term mean, with strongest variability seen in the lower part of the TTL. The interannual variability is influenced by extratropical and subtropical wave driving. Statistical analysis reveals a significant anti-correlation between the residence time and the extratropical and subtropical wave driving in the lowermost stratosphere.
Influence of scintillation on GOMOS ozone retrievals
Authors: Sofieva V. F. , Kan V. , Dalaudier F. , Kyrölä E. , Tamminen J. , Bertaux J.-L. , Hauchecorne A. , Fussen D. , Vanhellemont F.
Published: April 2010

Abstract. The stellar light passed through the Earth atmosphere is affected by refractive effects, which should be taken into account in retrievals from stellar occultation measurements. Scintillation caused by air density irregularities is a nuisance for retrievals of atmospheric composition. In this paper, we consider the influence of scintillation on stellar occultation measurements and on quality of ozone retrievals from these measurements, based on experience of the GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite. In the GOMOS retrievals, the scintillation effect is corrected using scintillation measurements by the fast photometer. We present quantitative estimates of the current scintillation correction quality and of the impact of scintillation on ozone retrievals by GOMOS. The analysis has shown that the present scintillation correction efficiently removes the distortion of transmission spectra caused by anisotropic scintillations. The impact of errors of dilution and anisotropic scintillation correction on quality of ozone retrievals is negligible. However, the current scintillation correction is not able to remove the wavelength-dependent distortion of transmission spectra caused by isotropic scintillations, which can be present in off-orbital-plane occultations. This distortion may result in error of ozone retrievals of 0.5–1.5% at altitudes 20–40 km. This contribution to the error budget is significant for bright stars. The advanced inversion methods that can minimize the influence of scintillation correction error are also discussed.
Simultaneous measurements of OClO, NO2 and O3 in the Arctic polar vortex by the GOMOS instrument
Authors: Tétard C. , Fussen D. , Bingen C. , Capouillez N. , Dekemper E. , Loodts N. , Mateshvili N. , Vanhellemont F. , Kyrölä E. , Tamminen J. , Sofieva V. , Hauchecorne A. , Dalaudier F. , Bertaux J.-L. , Fanton d'Andon O. , Barrot G. , Guirlet M. , Fehr T. , Saavedra L.
Published: April 2010

Abstract. We present the first nighttime measurements of OClO from a limb-viewing satellite instrument in the Arctic polar vortex. The relationship between OClO, NO2 and O3 slant column densities in the Arctic polar vortex are analyzed from the GOMOS measurements. The retrieval process is based on a differential optical absorption spectroscopy (DOAS) method applied on the weighted median GOMOS transmittances. A study about the longitudinal distributions of OClO, NO2 and O3 above 65° north in January 2008 is presented. It shows a strong halogen activation in the lower stratosphere and a strong denoxification in the entire stratosphere inside the Arctic polar vortex. Time series of temperatures and OClO, NO2 and O3 slant column densities for the winters 2002/2003 to 2007/2008 are also presented. They highlight the correlation between temperature, OClO and NO2. The GOMOS instrument appears to be a very suitable instrument for the monitoring of OClO, NO2 and O3 in the stratosphere during nighttime.
Theoretical implication of reversals of the ozone weekend effect systematically observed in Japan
Authors: Kannari A. , Ohara T.
Published: April 2010

Abstract. Systematic changes of the ozone weekend effect are found over broad areas of Japan. These changes are characterized by (1) spatial reversals from a weekend increase in the vicinity of huge precursor source areas to a weekend decrease in the surrounding rural areas, and (2) temporal reversals from a weekend increase under relatively unsuitable meteorological conditions for ozone formation to a weekend decrease under relatively suitable conditions. We developed a simple numerical advection-reaction model to explain the relationship between the duration of advection and the supplied solar energy, which causes the daily maximum ozone concentration to be lower near the precursor source. Ozone isopleth diagrams for individual advection durations (equivalent to the distance from the source) for a wide range of initial precursor conditions show that both VOC-limited and NOx-limited regimes exist for each advection duration, but the area of NOx-limited regime becomes dominant as the advection duration increases because of the increased exposure of the air mass to solar energy. For given initial VOC and NOx concentrations, the area remote from the source becomes a NOx-limited regime even if the precursor source area is in the VOC-limited regime. The rate of reduction of weekend emissions of NOx is larger than that of VOC, causing a weekend increase in a VOC-limited regime near the source, but a weekend decrease in remote areas with a NOx-limited regime. The boundary between these two ozone formation regimes depends on meteorological conditions: when sunlight intensity and temperature are relatively low, the change from a VOC-limited to a NOx-limited regime occurs at a point more remote from the source than when they are relatively high, which causes a prevailing ozone weekend increase over a wide geographical area on days with lower ozone potential. Therefore, observations of ozone weekend changes can be interpreted in light of the theoretical implications of our model; they can be used for determination of ozone formation regimes, which change in different locations and under different meteorological conditions.
Impact of nucleation on global CCN
Authors: Merikanto J. , Spracklen D. V. , Mann G. W. , Pickering S. J. , Carslaw K. S.
Published: April 2010

Abstract. Cloud condensation nuclei (CCN) are derived from particles emitted directly into the atmosphere (primary emissions) or from the growth of nanometer-sized particles nucleated in the atmosphere. It is important to separate these two sources because they respond in different ways to gas and particle emission control strategies and environmental changes. Here, we use a global aerosol microphysics model to quantify the contribution of primary and nucleated particles to global CCN. The model considers primary emissions of sea spray, sulfate and carbonaceous particles, and nucleation processes appropriate for the free troposphere and boundary layer. We estimate that 45% of global low-level cloud CCN at 0.2% supersaturation are secondary aerosol derived from nucleation (ranging between 31–49% taking into account uncertainties primary emissions and nucleation rates), the remainder being directly emitted as primary aerosol. The model suggests that 35% of CCN (0.2%) in low-level clouds were created in the free and upper troposphere. In the marine boundary layer 55% of CCN (0.2%) are from nucleation, 45% being entrained from the free troposphere. Both in global and marine boundary layer 10% of CCN (0.2%) is nucleated in the boundary layer. Combinations of model runs show that primary and nucleated CCN are non-linearly coupled. In particular, boundary layer nucleated CCN are strongly suppressed by both primary emissions and entrainment of particles nucleated in the free troposphere. Elimination of all primary emissions reduces global CCN (0.2%) by only 20% and elimination of upper tropospheric nucleation reduces CCN (0.2%) by only 12% because of increased impact of boundary layer nucleation on CCN.
Cold oceans enhance terrestrial new-particle formation in near-coastal forests
Authors: Suni T. , Sogacheva L. , Lauros J. , Hakola H. , Bäck J. , Kurtén T. , Cleugh H. , van Gorsel E. , Briggs P. , Sevanto S. , Kulmala M.
Published: April 2010

Abstract. The world's forests produce atmospheric aerosol by emitting volatile organic compounds (VOC) which, after being oxidized in the atmosphere, readily condense on the omnipresent nanometer-sized nuclei and grow them to climatically relevant sizes. The cooling effect of aerosols is the greatest uncertainty in current climate models and estimates of radiative forcing. Therefore, identifying the environmental factors influencing the biogenic formation of aerosols is crucial. We show that, in addition to local meteorological factors in the forest, the magnitude of evaporation from oceans hundreds of kilometers upwind can effectively suppress or enhance new-particle formation. Our findings indicate that, unlike warm waters, the cold polar oceans provide excellent clean and dry background air that enhances aerosol formation above near-coastal forests in Fennoscandia and South-East Australia.
Patterns of Saharan dust transport over the Atlantic: winter vs. summer, based on CALIPSO first year data
Authors: Ben-Ami Y. , Koren I. , Altaratz O.
Published: April 2010

Abstract. One of the most important factors that determines the transported dust effect is its vertical distribution in the atmosphere. Until the launch of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), the vertical distribution was studied mostly by in-situ measurements and models. CALIPSO, as a part of the A-Train constellation has opened an opportunity to study the transported dust vertical structure in a large number of events (sufficient statistics). In this study the vertical structure of Saharan dust and stratiform clouds is analyzed over the Atlantic Ocean for the 2006–2007 winter (December–February) and the summer of 2006 (June–August). By using CALIPSO backscatter measurements over the dust route, we describe the differences in dust transport between the seasons. We show a bi-modal distribution of the average dust plumes height in both seasons (it is less clear in the winter). It suggests that a significant part of the dust is transported near and within the marine boundary layer and interacts with shallow clouds on both seasons.
Comparisons of WRF/Chem simulations in Mexico City with ground-based RAMA measurements during the MILAGRO-2006 period
Authors: Zhang Y. , Dubey M. K. , Olsen S. C.
Published: April 2010

Abstract. Comparison of the WRF/Chem (Weather Research and Forecasting – Chemistry) model simulations at 3-km resolution with measurements from the ground-based RAMA monitoring network during the MCMA-2006/MILAGRO field campaign is presented. The model resolves reasonably well the observed surface temperature, relative humidity and wind speed; however, large discrepancies are identified between the simulated and the observed surface wind direction for wind speeds below 2 m s−1. The simulated chemical species concentrations (CO, O3, NO, NO2 and NOy) compare favorably with the observations with the notable exception of SO2. Simulated O3 concentrations agree especially well with the observations. The model performs much better during daytime than nighttime for both chemical species and meteorological variables, although the model tends to underestimate daytime temperature and overestimate nighttime relative humidity. It is noted that the simulated nocturnal planetary boundary layer (PBL) height using the Yonsei University PBL scheme is unrealistically low. However, no combination of the available PBL schemes and land surface models (LSMs) is distinctly better than the others in reproducing the observations. The simulated meteorological fields under the O3-South, O3-North and EI Norte weather episodes exhibit similar correlation coefficients and biases for the same variable. However, the model performs best for the O3-South episode and performs poorest for the El Norte events in resolving the observed chemical species.
Sensitivity of polar stratospheric ozone loss to uncertainties in chemical reaction kinetics
Authors: Kawa S. R. , Stolarski R. S. , Newman P. A. , Douglass A. R. , Rex M. , Hofmann D. J. , Santee M. L. , Frieler K.
Published: April 2010

Abstract. The impact and significance of uncertainties in model calculations of stratospheric ozone loss resulting from known uncertainty in chemical kinetics parameters is evaluated in trajectory chemistry simulations for the Antarctic and Arctic polar vortices. The uncertainty in modeled ozone loss is derived from Monte Carlo scenario simulations varying the kinetic (reaction and photolysis rate) parameters within their estimated uncertainty bounds. Simulations of a typical winter/spring Antarctic vortex scenario and Match scenarios in the Arctic produce large uncertainty in ozone loss rates and integrated seasonal loss. The simulations clearly indicate that the dominant source of model uncertainty in polar ozone loss is uncertainty in the Cl2O2 photolysis reaction, which arises from uncertainty in laboratory-measured molecular cross sections at atmospherically important wavelengths. This estimated uncertainty in JCl2O2 from laboratory measurements seriously hinders our ability to model polar ozone loss within useful quantitative error limits. Atmospheric observations, however, suggest that the Cl2O2 photolysis uncertainty may be less than that derived from the lab data. Comparisons to Match, South Pole ozonesonde, and Aura Microwave Limb Sounder (MLS) data all show that the nominal recommended rate simulations agree with data within uncertainties when the Cl2O2 photolysis error is reduced by a factor of two, in line with previous in situ ClOx measurements. Comparisons to simulations using recent cross sections from Pope et al. (2007) are outside the constrained error bounds in each case. Other reactions producing significant sensitivity in polar ozone loss include BrO+ClO and its branching ratios. These uncertainties challenge our confidence in modeling polar ozone depletion and projecting future changes in response to changing halogen emissions and climate. Further laboratory, theoretical, and possibly atmospheric studies are needed.
A photochemical model and sensitivity study of the triple-oxygen isotopic (Δ17O) composition of NOy, HOx, and H2O2 in a polluted boundary layer
Authors: Dominguez G. , Wilkins G. , Thiemens M. H.
Published: April 2010

Abstract. We present a photochemical model developed for the explicit calculation of triple oxygen isotopic compositions (Δ17O) of major atmospheric species. While we focus on the Δ17O of HNO3 and aerosol nitrate (NO−3) and its precursors such as NO, NO2 and N2O5, the general implementation given here also provides Δ17O predictions for other important atmospheric compounds such as OH, H2O2, and HO2. Through the use of a simple aerosol surface area model, we calculate the Δ17O composition of aerosol nitrate produced as a function of aerosol size and aerosol surface type. We explore the sensitivity of the Δ17O of atmospheric species through a series of sensitivity studies and show that the Δ17O of atmospheric compounds is affected to various degrees by environmental factors such as temperature, relative humidity, ozone concentration, NOx flux, and total ozone column density. In addition, we find that Δ17O of these species is sensitive to photochemical conditions such as cloud albedo, latitude, and time of year. We compare the Δ17O calculation outputs to previous methods and find significant differences in the Δ17O of NO2. We describe the origins of these and suggest studies that may help to resolve these differences.
Assessment of vertically-resolved PM10 from mobile lidar observations
Authors: Raut J.-C. , Chazette P.
Published: April 2010

Abstract. We investigate in this study the role of the Paris Peripherique (the ring around Paris agglomeration) in local particulate pollution and the horizontal gradient of pollution between Paris centre and its remote suburbs. For this purpose, we combine in situ surface measurements with active remote sensing observations obtained from a great number of research programs in Paris area since 1999. Two approaches, devoted to the conversion of vertical profiles of lidar-derived extinction coefficients into PM10, have been set up. A very good agreement is found between the theoretical and empirical methods with a discrepancy of 3%. Hence, specific extinction cross-sections at 355 nm are provided with a reasonable uncertainty for urban (4.5 m2/g), periurban (5.9 m2/g), rural (7.1 m2/g), biomass burning (2.6 m2/g) and dust (1.1 m2/g) aerosols. The high spatial and temporal resolutions of the mobile lidar (respectively 1.5 m and 1 min) enable to follow the spatiotemporal variability of various layers carrying aerosols in the troposphere. Appropriate specific extinction cross-sections are applied in each layer detected in the vertical heterogeneities from the lidar profiles. The standard deviation between lidar-derived PM10 at 200 m above ground and surface network stations measurements was ~14 μg m−3. This difference is particularly ascribed to a decorrelation of mass concentrations in the first meters of the boundary layer, as highlighted through multiangular lidar observations. Lidar signals can be used to follow mass concentrations at the surface and provide useful information on PM10 peak forecasting that affect air quality.
Time-span and spatial-scale of regional new particle formation events over Finland and Southern Sweden
Authors: Hussein T. , Junninen H. , Tunved P. , Kristensson A. , Dal Maso M. , Riipinen I. , Aalto P. P. , Hansson H.-C. , Swietlicki E. , Kulmala M.
Published: April 2010

Abstract. We investigated the time-span and spatial-scale of regional new particle formation (NPF) events in Finland and Southern Sweden using measured particle number size distributions at five background stations. We define the time-span of a NPF event as the time period from the first moment when the newly formed mode of aerosol particles is observable below 25 nm until the newly formed mode is not any more distinguishable from other modes of aerosol particles after growing to bigger sizes. We identified the spatial-scale of regional NPF events based on two independent approaches. The first approach is based on the observation within a network of stationary measurement stations, and the second approach is based on the time-span and the history of back-trajectories. According to the second approach, about 60% and 28% of the events can be traced to distances longer than 220 km upwind from where the events were observed in southern Finland (Hyytiälä) and northern Finland (Värriö). The analysis also showed that the observed regional NPF events started over the continents or over major ship routes but not over the Atlantic Ocean. The first approach showed that although large spatial-scale NPF events are frequently observed at several locations simultaneously, they are rarely identical (similar characteristics and temporal variations) due to differences in the initial meteorological and geographical conditions between the stations. On median, the growth of the newly formed particles during large spatial-scale NPF events can be followed for more than 30 h where the newly formed aerosol particles end up in the Aitken mode and accumulation mode size ranges (diameter >25 nm). This study showed clear evidences that regional NPF events can pose a significant source for accumulation mode particles over the European continent provided that these findings can be generalized to many of the air parcels traveling over the European continent.
Clouds, photolysis and regional tropospheric ozone budgets
Authors: Voulgarakis A. , Wild O. , Savage N. H. , Carver G. D. , Pyle J. A.
Published: April 2010

Abstract. We use a three-dimensional chemical transport model to examine the shortwave radiative effects of clouds on the tropospheric ozone budget. In addition to looking at changes in global concentrations as previous studies have done, we examine changes in ozone chemical production and loss caused by clouds and how these vary in different parts of the troposphere. On a global scale, we find that clouds have a modest effect on ozone chemistry, but on a regional scale their role is much more significant, with the size of the response dependent on the region. The largest averaged changes in chemical budgets (±10–14%) are found in the marine troposphere, where cloud optical depths are high. We demonstrate that cloud effects are small on average in the middle troposphere because this is a transition region between reduction and enhancement in photolysis rates. We show that increases in boundary layer ozone due to clouds are driven by large-scale changes in downward ozone transport from higher in the troposphere rather than by decreases in in-situ ozone chemical loss rates. Increases in upper tropospheric ozone are caused by higher production rates due to backscattering of radiation and consequent increases in photolysis rates, mainly J(NO2). The global radiative effect of clouds on isoprene is stronger than on ozone. Tropospheric isoprene lifetime increases by 7% when taking clouds into account. We compare the importance of clouds in contributing to uncertainties in the global ozone budget with the role of other radiatively-important factors. The budget is most sensitive to the overhead ozone column, while surface albedo and clouds have smaller effects. However, uncertainty in representing the spatial distribution of clouds may lead to a large sensitivity on regional scales.
In situ aerosol optics in Reno, NV, USA during and after the summer 2008 California wildfires and the influence of aerosol coatings
Authors: Gyawali M. , Arnott W. P. , Lewis K. , Moosmüller H.
Published: April 2010

Abstract. Hundreds of wildfires in Northern California were sparked by lightning during the summer of 2008, resulting in downwind smoke for the months of June and July. Comparisons are reported for aerosol optics measurements in Reno Nevada made during the very smoky summer month of July and the relatively clean month of August. Photoacoustic instruments equipped with integrating nephelometers were used to measure aerosol light scattering and absorption at wavelengths of 405 nm and 870 nm, revealing a strong variation of the aerosol light absorption with wavelength. Coated sphere calculations were used to show that Ångström exponents of absorption (AEA) as large as 1.6 are possible even with non-absorbing organic coatings on black carbon cores, suggesting care be exercised when diagnosing AEA. Insight on fuels burned is gleaned from comparison of AEA versus single scattering albedo (SSA) of the ambient measurements with laboratory biomass smoke measurements for many fuels. Measurements during the month of August, which were largely unaffected by fire smoke, exhibit surprisingly low AEA for aerosol light absorption when the SSA is highest, again likely as a consequence of the underappreciated wavelength dependence of aerosol light absorption by particles coated with non absorbing organic and inorganic matter.
Now you see it, now you don't: impact of temporary closures of a coal-fired power plant on air quality in the Columbia River Gorge National Scenic Area
Authors: Jaffe D. A. , Reidmiller D. R.
Published: April 2010

Abstract. We have analyzed 14 years of aerosol data spanning 1993–2006 from the IMPROVE site at Wishram, Washington (45.66° N, 121.00° W; 178 m above sea level) in the Columbia River Gorge (CRG) National Scenic Area (http://www.fs.fed.us/r6/columbia/) of the Pacific Northwest of the US. Two types of analyses were conducted. First, we examined the transport for days with the highest fine mass concentrations (particulate matter with diameter <2.5μm or, PM2.5) using HYSPLIT back-trajectories. We found that the highest PM2.5 concentrations occurred during autumn and were associated with easterly flow, down the CRG. Such flow transports emissions from a large coal power plant and a large agricultural facility into the CRG. This transport was found on 20 out of the 50 worst PM2.5 days and resulted in an average daily concentration of 20.1 μg/m3, compared with an average of 18.8 μg/m3 for the 50 highest days and 5.9 μg/m3 for all days. These airmasses contain not only high PM2.5 concentrations but also elevated aerosol NO3− concentrations. These results suggest that emissions from large industrial and agricultural sources on the east end of the CRG, including the coal-fired power plant at Boardman, Oregon, have a significant impact on air quality in the region. In the second analysis, we examined PM2.5 concentrations in the CRG during periods when the Boardman power plant was shut down due to repairs and compared these values with concentrations when the facility was operating at near full capacity. We also examined this relationship on the days when trajectories suggested the greatest influence from the power plant on air quality in the CRG. From this analysis, we found significantly higher PM concentrations when the power plant was operating at or near full capacity. We use these data to calculate that the contribution to PM2.5 mass in the CRG from the Boardman plant was 0.90 μg/m3 averaged over the entire year, 3.94 μg/m3 if only the month of November is considered and 7.40 ug/m3 if only November days when the airflow is "down-gorge" (from east to west). This represents 15–56% of PM2.5 mass in the CRG. In all 3 cases the difference in PM2.5 concentrations are statistically significant at a >95% confidence interval for the comparison of normal plant emissions vs shutdown conditions. We, therefore, find that the coal-fired power plant at Boardman, Oregon is a significant contributor to PM2.5 concentrations in the CRG.
Planetary wave activity in the Arctic and Antarctic lower stratospheres during 2007 and 2008
Authors: Alexander S. P. , Shepherd M. G.
Published: April 2010

Abstract. Temperature data from the COSMIC GPS-RO satellite constellation are used to study planetary wave activity in both polar stratospheres from September 2006 until November 2008. One major and several minor sudden stratospheric warmings (SSWs) were recorded during the boreal winters of 2006/2007 and 2007/2008. Planetary wave morphology is studied using space-time spectral analysis while individual waves are extracted using a linear least squares fitting technique. Results show the planetary wave frequency and zonal wavenumber distribution varying between hemisphere and altitude. Most of the large Northern Hemisphere wave activity is associated with the winter SSWs, while the largest amplitude waves in the Southern Hemisphere occur during spring. Planetary wave activity during the 2006/2007 and 2007/2008 Arctic SSWs is due largely to travelling waves with zonal wavenumbers |s|=1 and |s|=2 having periods of 12, 16 and 23 days and stationary waves with |s|=1 and |s|=2. The latitudinal variation of wave amplification during the two Northern Hemisphere winters is studied. Most planetary waves show different structure and behaviour during each winter. Abrupt changes in the latitude of maximum amplitude of some planetary waves is observed co-incident in time with some of the SSWs.