bluuebunny/crossref_metadata_2025 huggingface dataset:
Airborne measurements of the spatial distribution of aerosol chemical composition across Europe and evolution of the organic fraction
Authors: Morgan W. T. , Allan J. D. , Bower K. N. , Highwood E. J. , Liu D. , McMeeking G. R. , Northway M. J. , Williams P. I. , Krejci R. , Coe H.
Published: April 2010

Abstract. The spatial distribution of aerosol chemical composition and the evolution of the Organic Aerosol (OA) fraction is investigated based upon airborne measurements of aerosol chemical composition in the planetary boundary layer across Europe. Sub-micron aerosol chemical composition was measured using a compact Time-of-Flight Aerosol Mass Spectrometer (cToF-AMS). A range of sampling conditions were evaluated, including relatively clean background conditions, polluted conditions in North-Western Europe and the near-field to far-field outflow from such conditions. Ammonium nitrate and OA were found to be the dominant chemical components of the sub-micron aerosol burden, with mass fractions ranging from 20–50% each. Ammonium nitrate was found to dominate in North-Western Europe during episodes of high pollution, reflecting the enhanced NOx and ammonia sources in this region. OA was ubiquitous across Europe and concentrations generally exceeded sulphate by 50–100%. A factor analysis of the OA burden was performed in order to probe the evolution across this large range of spatial and temporal scales. Two separate Oxygenated Organic Aerosol (OOA) components were identified; one representing an aged-OOA, termed Low Volatility-OOA and another representing fresher-OOA, termed Semi Volatile-OOA on the basis of their mass spectral similarity to previous studies. The factors derived from different flights were not chemically the same but rather reflect the range of OA composition sampled during a particular flight. Significant chemical processing of the OA was observed downwind of major sources in North-Western Europe, with the LV-OOA component becoming increasingly dominant as the distance from source and photochemical processing increased. The measurements suggest that the aging of OA can be viewed as a continuum, with a progression from a less oxidised, semi-volatile component to a highly oxidised, less-volatile component. Substantial amounts of pollution were observed far downwind of continental Europe, with OA and ammonium nitrate being the major constituents of the sub-micron aerosol burden. Such anthropogenically perturbed air masses can significantly perturb regional climate far downwind of major source regions.
Application of positive matrix factorization to on-road measurements for source apportionment of diesel- and gasoline-powered vehicle emissions in Mexico City
Authors: Thornhill D. A. , Williams A. E. , Onasch T. B. , Wood E. , Herndon S. C. , Kolb C. E. , Knighton W. B. , Zavala M. , Molina L. T. , Marr L. C.
Published: April 2010

Abstract. The goal of this research is to quantify diesel- and gasoline-powered motor vehicle emissions within the Mexico City Metropolitan Area (MCMA) using on-road measurements captured by a mobile laboratory combined with positive matrix factorization (PMF) receptor modeling. During the MCMA-2006 ground-based component of the MILAGRO field campaign, the Aerodyne Mobile Laboratory (AML) measured many gaseous and particulate pollutants, including carbon dioxide, carbon monoxide (CO), nitrogen oxides (NOx), benzene, toluene, alkylated aromatics, formaldehyde, acetaldehyde, acetone, ammonia, particle number, fine particulate mass (PM2.5), and black carbon (BC). These serve as inputs to the receptor model, which is able to resolve three factors corresponding to gasoline engine exhaust, diesel engine exhaust, and the urban background. Using the source profiles, we calculate fuel-based emission factors for each type of exhaust. The MCMA's gasoline-powered vehicles are considerably dirtier, on average, than those in the US with respect to CO and aldehydes. Its diesel-powered vehicles have similar emission factors of NOx and higher emission factors of aldehydes, particle number, and BC. In the fleet sampled during AML driving, gasoline-powered vehicles are responsible for 97% of mobile source emissions of CO, 22% of NOx, 95–97% of aromatics, 72–85% of carbonyls, 74% of ammonia, negligible amounts of particle number, 26% of PM2.5, and 2% of BC; diesel-powered vehicles account for the balance. Because the mobile lab spent 17% of its time waiting at stoplights, the results may overemphasize idling conditions, possibly resulting in an underestimate of NOx and overestimate of CO emissions. On the other hand, estimates of the inventory that do not correctly account for emissions during idling are likely to produce bias in the opposite direction. Nevertheless, the fuel-based inventory suggests that mobile source emissions of CO and NOx are overstated in the official inventory while emissions of VOCs may be understated. For NOx, the fuel-based inventory is lower for gasoline-powered vehicles but higher for diesel-powered ones compared to the official inventory.
Atmospheric wet deposition of mercury and other trace elements in Pensacola, Florida
Authors: Landing W. M. , Caffrey J. M. , Nolek S. D. , Gosnell K.
Published: April 2010

Abstract. To understand and quantify the impact of local, regional, and distant atmospheric mercury sources to rainfall mercury deposition in the Pensacola, Florida watershed, a program of event-based rainfall sampling was started in late 2004. Modified Aerochem-Metrics wet/dry rainfall samplers were deployed at three sites in the region around the Crist coal-fired power plant and event-based samples were collected continuously for three years. Samples were analyzed for total mercury, volatile elements As, Se, and Sn, and a suite of trace elements including Al, Bi, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ho, Ga, Gd, La, Li, Lu, Mg, Mn, Na, Nb, Nd, Ni, P, Pb, Pr, Rb, Sb, Sc, Si, Sm, Sr, Tb, Th, Ti, Tm, U, V, Y, Yb, and Zn. Nutrients and major ions were also measured on each sample. Multivariate statistical methods are used to sort these tracers into factors that represent potential source components that contribute to the rainfall chemistry. Hg, As, Se, Sn, Sb, and non sea-salt sulfate were all significantly correlated with one anthropogenic factor. Using various Hg/element ratios, we can estimate that 22–33% of the rainfall mercury in the region results from coal combustion.
Formation of secondary organic aerosol from isoprene oxidation over Europe
Authors: Karl M. , Tsigaridis K. , Vignati E. , Dentener F.
Published: April 2010

Abstract. The role of isoprene as a precursor to secondary organic aerosol (SOA) over Europe is studied with the two-way nested global chemistry transport model TM5. The inclusion of the formation of SOA from isoprene oxidation in our model almost doubles the atmospheric burden of SOA over Europe compared to SOA formation from terpenes and aromatics. The reference simulation, which considers SOA formation from isoprene, terpenes and aromatics, predicts a yearly European production rate of 1.0 Tg SOA yr−1 and an annual averaged atmospheric burden of about 50 Gg SOA over Europe. A fraction of 35% of the SOA produced in the boundary layer over Europe is transported to higher altitudes or to other world regions. Summertime measurements of particulate organic matter (POM) during the extensive EMEP OC/EC campaign 2002/2003 are better reproduced when SOA formation from isoprene is taken into account, reflecting also the strong seasonality of isoprene and other biogenic volatile organic compounds (BVOC) emissions from vegetation. However, during winter, our model strongly underestimates POM, likely caused by missing wood burning in the emission inventories. Uncertainties in the parameterisation of isoprene SOA formation have been investigated. Maximum SOA production is found for irreversible sticking (non-equilibrium partitioning) of condensable vapours on particles, with tropospheric SOA production over Europe increased by a factor of 4 in summer compared to the reference case. Completely neglecting SOA formation from isoprene results in the lowest estimate (0.51 Tg SOA yr−1). The amount and the nature of the absorbing matter are shown to be another key uncertainty when predicting SOA levels. Tropospheric isoprene SOA production over Europe in summer more than doubles when, in addition to pre-existing carbonaceous aerosols, condensation of semi volatile vapours on ammonium and sulphate aerosols is considered. Consequently, smog chamber experiments on SOA formation should be performed with different types of seed aerosols and without seed aerosols in order to derive an improved treatment of the absorption of SOA in the models. Consideration of a number of recent insights in isoprene SOA formation mechanisms reduces the tropospheric production of isoprene derived SOA over Europe from 0.4 Tg yr−1 in our reference simulation to 0.1 Tg yr−1.
Weather response to management of a large wind turbine array
Authors: Barrie D. B. , Kirk-Davidoff D. B.
Published: April 2010

Abstract. Electrical generation by wind turbines is increasing rapidly, and has been projected to satisfy 15% of world electric demand by 2030. The extensive installation of wind farms would alter surface roughness and significantly impact the atmospheric circulation, due to the additional surface roughness forcing. This forcing could be changed deliberately by adjusting the attitude of the turbine blades with respect to the wind. Using a General Circulation Model (GCM), we represent a continent-scale wind farm as a distributed array of surface roughness elements. Here we show that initial disturbances caused by a step change in roughness grow within four and a half days such that the flow is altered at synoptic scales. The growth rate of the induced perturbations is largest in regions of high atmospheric instability. For a roughness change imposed over North America, the induced perturbations involve substantial changes in the track and development of cyclones over the North Atlantic, and the magnitude of the perturbations rises above the level of forecast uncertainty.
An approach to retrieve information on the carbonyl fluoride (COF2) vertical distributions above Jungfraujoch by FTIR multi-spectrum multi-window fitting
Authors: Duchatelet P. , Mahieu E. , Ruhnke R. , Feng W. , Chipperfield M. , Demoulin P. , Bernath P. , Boone C. D. , Walker K. A.
Published: April 2010

Abstract. We present an original multi-spectrum fitting procedure to retrieve volume mixing ratio (VMR) profiles of carbonyl fluoride (COF2) from ground-based high resolution Fourier transform infrared (FTIR) solar spectra. The multi-spectrum approach consists of simultaneously combining, during the retrievals, all spectra recorded consecutively during the same day and with the same resolution. Solar observations analyzed in this study with the SFIT-2 v3.91 fitting algorithm correspond to more than 2900 spectra recorded between January 2000 and December 2007 at high zenith angles, with a Fourier Transform Spectrometer operated at the high-altitude International Scientific Station of the Jungfraujoch (ISSJ, 46.5° N latitude, 8.0° E longitude, 3580 m altitude), Switzerland. The goal of the retrieval strategy described here is to provide information about the vertical distribution of carbonyl fluoride. The microwindows used are located in the ν1 or in the ν4 COF2 infrared (IR) absorption bands. Averaging kernel and eigenvector analysis indicates that our FTIR retrieval is sensitive to COF2 inversion between 17 and 30 km, with the major contribution to the retrieved information always coming from the measurement. Moreover, there was no significant bias between COF2 partial columns, total columns or VMR profiles retrieved from the two bands. For each wavenumber region, a complete error budget including all identified sources has been carefully established. In addition, comparisons of FTIR COF2 17–30 km partial columns with KASIMA and SLIMCAT 3-D CTMs are also presented. If we do not notice any significant bias between FTIR and SLIMCAT time series, KASIMA COF2 17–30 km partial columns are lower of around 25%, probably due to incorrect lower boundary conditions. For each times series, linear trend estimation for the 2000–2007 time period as well as a seasonal variation study are also performed and critically discussed. We further demonstrate that all time series are able to reproduce the COF2 seasonal cycle, which main seasonal characteristics deduced from each data set agree quite well.
Observations of NOx, ΣPNs, ΣANs, and HNO3 at a rural site in the California Sierra Nevada Mountains: summertime diurnal cycles
Authors: Day D. A. , Farmer D. K. , Goldstein A. H. , Wooldridge P. J. , Minejima C. , Cohen R. C.
Published: April 2010

Abstract. Observations of NO, NO2, total peroxy nitrates (ΣPNs), total alkyl nitrates (ΣANs), HNO3, CO, O3, and meteorological parameters were obtained from October 2000 through February 2002 at 1315 m a.s.l., 38.97° N, 120.6° W on Sierra Pacific Industries land, adjacent to the University of California Blodgett Forest Research Station (UC-BFRS). We describe the data set with emphasis on the diurnal cycles during summertime 2001. We show that transport of the Sacramento urban plume is a primary factor responsible for diurnal variation in total reactive nitrogen mixing ratios as well as in NOx, ΣPNs and ΣANs, all of which exhibit a late afternoon/early evening peak. In contrast, HNO3 has a peak just after local noon indicating that HNO3 is in near steady state during the day with production due to photochemistry and removal by deposition and mixing with the background free troposphere. Boundary layer dynamics influence mixing ratios of all species in the early morning. Analysis of the morning feature suggests that higher mixing ratios of NOx and HNO3 persist in the residual layer than in the nocturnal boundary layer indicating the presence of nocturnal sinks of both species. Nighttime observations also indicate large HNO3 and ΣANs production through oxidation of alkenes by NO3.
The formation, properties and impact of secondary organic aerosol: current and emerging issues
Authors: Hallquist M. , Wenger J. C. , Baltensperger U. , Rudich Y. , Simpson D. , Claeys M. , Dommen J. , Donahue N. M. , George C. , Goldstein A. H. , Hamilton J. F. , Herrmann H. , Hoffmann T. , Iinuma Y. , Jang M. , Jenkin M. , Jimenez J. L. , Kiendler-Scharr A. , Maenhaut W. , McFiggans G. , Mentel Th. F. , Monod A. , Prévôt A. S. H. , Seinfeld J. H. , Surratt J. D. , Szmigielski R. , Wildt J.
Published: April 2010

Abstract. Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with a description of the current state of knowledge on the global SOA budget and the atmospheric degradation mechanisms for SOA precursors. The topic of gas-particle partitioning theory is followed by an account of the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail; molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.
A statistical analysis of the influence of deep convection on water vapor variability in the tropical upper troposphere
Authors: Wright J. S. , Fu R. , Heymsfield A. J.
Published: April 2010

Abstract. The factors that control the influence of deep convective detrainment on water vapor in the tropical upper troposphere are examined using observations from multiple satellites in conjunction with a trajectory model. Deep convection is confirmed to act primarily as a moisture source to the upper troposphere, modulated by the ambient relative humidity (RH). Convective detrainment provides strong moistening at low RH and offsets drying due to subsidence across a wide range of RH. Strong day-to-day moistening and drying takes place most frequently in relatively dry transition zones where the frequency of deep convective events is neither very high nor very low. Many of these strong moistening events can be directly attributed to detrainment from recent tropical convection. The temporal and spatial limits of the convective source are estimated to be about 36–48 h and 600–1500 km, respectively, consistent with the lifetimes of detrainment cirrus clouds. Larger amounts of detrained ice and smaller ice particle sizes are both associated with enhanced upper tropospheric moistening.
Technical Note: Feasibility of CO2 profile retrieval from limb viewing solar occultation made by the ACE-FTS instrument
Authors: Foucher P. Y. , Chédin A. , Dufour G. , Capelle V. , Boone C. D. , Bernath P.
Published: April 2010

Abstract. Major limitations of our present knowledge of the global distribution of CO2 in the atmosphere are the uncertainty in atmospheric transport mixing and the sparseness of in situ concentration measurements. Limb viewing space-borne sounders, observing the atmosphere along tangential optical paths, offer a vertical resolution of a few kilometres for profiles, which is much better than currently flying or planned nadir sounding instruments can achieve. In this paper, we analyse the feasibility of obtaining CO2 vertical profiles in the 5–25 km altitude range from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS, launched in August 2003), high spectral resolution solar occultation measurements. Two main difficulties must be overcome: (i) the accurate determination of the instrument pointing parameters (tangent heights) and pressure/temperature profiles independently from an a priori CO2 profile, and (ii) the potential impact of uncertainties in the temperature knowledge on the retrieved CO2 profile. The first difficulty has been solved using the N2 collision-induced continuum absorption near 4 μm to determine tangent heights, pressure and temperature from the ACE-FTS spectra. The second difficulty has been solved by a careful selection of CO2 spectral micro-windows. Retrievals using synthetic spectra made under realistic simulation conditions show a vertical resolution close to 2.5 km and accuracy of the order of 2 ppm after averaging over 25 profiles. These results open the way to promising studies of transport mechanisms and carbon fluxes from the ACE-FTS measurements.
Validation of conventional Lagrangian stochastic footprint models against LES driven footprint estimates
Authors: Markkanen T. , Steinfeld G. , Kljun N. , Raasch S. , Foken T.
Published: April 2010

Abstract. In this study we compare the performance of conventional Lagrangian stochastic (LS) footprint models that use parameterised flow field characteristics with results of a Lagrangian trajectory model embedded in a large eddy simulation (LES) framework. The two conventional models follow the particles backward and forward in time while the trajectories in LES only evolve forward in time. We assess their performance in unstably and neutrally stratified boundary layers at observation levels covering the whole depth of the atmospheric boundary layer. We present a concept for footprint model comparison that can be applied for 2-D footprints and demonstrate that comparison of only cross wind integrated footprints is not sufficient for purposes facilitating two dimensional footprint information. Because the flow field description among the three models is most realistic in LES we use those results as the reference in the comparison. We found that the agreement of the two conventional models against the LES is generally better for intermediate measurement heights and for the convective case, whereas the two conventional flux footprint models agree best under near neutral conditions.
Long-term study of VOCs measured with PTR-MS at a rural site in New Hampshire with urban influences
Authors: Jordan C. , Fitz E. , Hagan T. , Sive B. , Frinak E. , Haase K. , Cottrell L. , Buckley S. , Talbot R.
Published: April 2010

Abstract. A long-term, high time-resolution volatile organic compound (VOC) data set from a ground site that experiences urban, rural, and marine influences in the northeastern United States is presented. A proton-transfer-reaction mass spectrometer (PTR-MS) was used to quantify 15 VOCs: a marine tracer dimethyl sulfide (DMS), a biomass burning tracer acetonitrile, biogenic compounds (monoterpenes, isoprene), oxygenated VOCs (OVOCs: methyl vinyl ketone (MVK) plus methacrolein (MACR), methanol, acetone, methyl ethyl ketone (MEK), acetaldehyde, and acetic acid), and aromatic compounds (benzene, toluene, C8 and C9 aromatics). Time series, overall and seasonal medians, with 10th and 90th percentiles, seasonal mean diurnal profiles, and inter-annual comparisons of mean summer and winter diurnal profiles are shown. Methanol and acetone exhibit the highest overall median mixing ratios 1.44 and 1.02 ppbv, respectively. Comparing the mean diurnal profiles of less well understood compounds (e.g., MEK) with better known compounds (e.g., isoprene, monoterpenes, and MVK+MACR) that undergo various controls on their atmospheric mixing ratios provides insight into possible sources of the lesser known compounds. The constant diurnal value of ≈0.7 for the toluene:benzene ratio in winter, may possibly indicate the influence of wood-based heating systems in this region. Methanol exhibits an initial early morning release in summer unlike any other OVOC (or isoprene) and a dramatic late afternoon mixing ratio increase in spring. Although several of the OVOCs appear to have biogenic sources, differences in features observed between isoprene, methanol, acetone, acetaldehyde, and MEK suggest they are produced or emitted in unique ways.
Measurements of particle masses of inorganic salt particles for calibration of cloud condensation nuclei counters
Authors: Kuwata M. , Kondo Y.
Published: April 2010

Abstract. We measured the mobility equivalent critical dry diameter for CCN activation (dcme) and the particle mass of size-selected (NH4)2SO4 and NaCl particles to calibrate a CCN counter (CCNC) precisely. The CCNC was operated downstream of a differential mobility analyzer (DMA) for the measurement of dcme. The particle mass was measured using an aerosol particle mass analyzer (APM) operated downstream of the DMA. The measurement of particle mass was conducted for 50–150-nm particles. Effective densities (ρeff) of (NH4)2SO4 particles were 1.67–1.75 g cm−3, which correspond to the dynamic shape factors (χ) of 1.01–1.04. This shows that (NH4)2SO4 particles are not completely spherical. In the case of NaCl particles, ρeff was 1.75–1.99 g cm−3 and χ was 1.05–1.14, demonstrating that their particle shape was non-spherical. Using these experimental data, the volume equivalent critical dry diameter (dcve) was calculated, and it was used as an input parameter for calculations of critical supersaturation (S). Several thermodynamics models were used for the calculation of water activity. When the Pitzer model was employed for the calculations, the critical S calculated for (NH4)2SO4 and NaCl agreed to well within the uncertainty of 2% (relative). This result demonstrates that the use of the Pitzer model for the calibration of CCNCs gives the most probable value of S.
Photodegradation of secondary organic aerosol generated from limonene oxidation by ozone studied with chemical ionization mass spectrometry
Authors: Pan X. , Underwood J. S. , Xing J.-H. , Mang S. A. , Nizkorodov S. A.
Published: April 2010

Abstract. Photodegradation of secondary organic aerosol (SOA) prepared by ozone-initiated oxidation of D-limonene is studied with an action spectroscopy approach, which relies on detection of volatile photoproducts with chemical ionization mass-spectrometry as a function of the UV irradiation wavelength. Efficient photodegradation is observed for a broad range of ozone and D-limonene concentrations (0.1–300 ppm) used in the preparation of SOA. The observed photoproducts are dominated by oxygenated C1-C3 compounds such as methanol, formic acid, acetaldehyde, acetic acid, and acetone. The irradiation wavelength dependence of the combined yield of the photoproducts closely tracks the absorption spectrum of the SOA material suggesting that photodegradation is not limited to the UV wavelengths. Kinetic simulations suggest that RO2+HO2/RO2 reactions represent the dominant route to photochemically active carbonyl and peroxide species in the limonene SOA material. Similar photodegradation processes are likely to occur in realistic SOA produced by OH- or O3-initiated oxidation of biogenic volatile organic compounds in clean air.
Equatorial transport as diagnosed from nitrous oxide variability
Authors: Ricaud P. , Pommereau J.-P. , Attié J.-L. , Le Flochmoën E. , El Amraoui L. , Teyssèdre H. , Peuch V.-H. , Feng W. , Chipperfield M. P.
Published: April 2010

Abstract. The mechanisms of transport on annual, semi-annual and quasi-biennial time scales in the equatorial (10° S–10° N) stratosphere are investigated using the nitrous oxide (N2O) measurements of the space-borne ODIN Sub-Millimetre Radiometer instrument from November 2001 to June 2005, and the simulations of the three-dimensional Chemistry Transport Models MOCAGE and SLIMCAT. Both models are forced with analyses from the European Centre for Medium-range Weather Forecasts, but the vertical transport is derived either from the forcing analyses by solving the continuity equation (MOCAGE), or from diabatic heating rates using a radiation scheme (SLIMCAT). The N2O variations in the mid-to-upper stratosphere at levels above 32 hPa are shown to be generally captured by the models though significant differences appear with the observations as well as between the models, attributed to the difficulty of capturing correctly the slow vertical velocities of the Brewer-Dobson circulation. In the lower stratosphere (LS), below 32 hPa, the variations are shown to be principally seasonal with peak amplitude at 400 K (~19 km), and are totally missed by the models. The decrease in diabatic radiative heating in the LS during the Northern Hemisphere summer is found to be out of phase by one month and far too small to explain the observed N2O seasonal cycle. The proposed explanation for this annual variation is a combination of i) the annual cycle of tropopause height of 1 km amplitude, ii) the convective overshooting above 400 K peaking in May and absent in the models, and iii) an annual cycle of 15 ppbv amplitude of the N2O concentration at the tropopause, but for which no confirmation exists in the upper troposphere in the absence of global-scale measurements. The present study indicates i) a significant contribution of deep convective overshooting on the chemical composition of the LS at global scale up to 500 K, ii) a preferred region for that over the African continent, and iii) a maximum impact in May when the overshoot intensity is the largest and horizontal winds are the slowest.
Charged and total particle formation and growth rates during EUCAARI 2007 campaign in Hyytiälä
Authors: Manninen H. E. , Nieminen T. , Riipinen I. , Yli-Juuti T. , Gagné S. , Asmi E. , Aalto P. P. , Petäjä T. , Kerminen V.-M. , Kulmala M.
Published: April 2010

Abstract. Despite the fact that frequent aerosol formation has been observed in various locations in the atmosphere, the overall magnitude of the new particle formation as a particle source is still unclear. In order to understand the particle formation and growth processes, we investigate the magnitudes of the particle formation and growth rates at the size where the real atmospheric nucleation and activation occurs. The relative contribution of neutral and charged particles to the new particle formation rate is also studied. The data include particle and ion number size distributions and total particle concentration measurements at a boreal forest site in Hyytiälä, Finland, during the spring 2007 EUCAARI field campaign. The total and charged particle formation rates differed from each other by approximately an order of magnitude. The median formation rates of 2 nm total and charged particles were 0.65 cm−3 s−1 and 0.03 cm−3 s−1, respectively. The median growth rates of particles in size classes 1.3–3, 3–7 and 7–30 nm were 1.9, 3.6 and 4.2 nm h−1, respectively. The calculated ion-ion recombination rates were about the same order of magnitude as the ion-induced formation rates. The results indicate that the ion-induced nucleation involving the ion-ion recombination products, i.e. ion mediated nucleation, contributes approximately 10% to the boreal forest new particle formation events.
Tula industrial complex (Mexico) emissions of SO2 and NO2 during the MCMA 2006 field campaign using a Mini-DOAS system
Authors: Rivera C. , Sosa G. , Wöhrnschimmel H. , de Foy B. , Johansson M. , Galle B.
Published: April 2010

Abstract. The Mexico City Metropolitan Area (MCMA) has presented severe pollution problems for many years. There are several point and mobile emission sources inside and outside the MCMA which are known to affect air quality in the area. In particular, speculation has risen as to whether the Tula industrial complex, located 60 km northwest of the MCMA has any influence on high SO2 levels occurring on the northern part of the city, in the winter season mainly. As part of the MILAGRO Field Campaign, from 24 March to 17 April 2006, the total columns of sulfur dioxide (SO2) and nitrogen dioxide (NO2) were measured during plume transects in the neighborhood of the Tula industrial complex using mini-DOAS instruments. Vertical profiles of wind speed and direction obtained from pilot balloons and radiosondes were used to calculate SO2 and NO2 fluxes in the plume. According to our measurements, calculated average flux emission for SO2 and NO2 were 155±120 and 9±8 ktons per year, respectively. The standard deviation of these estimations is due to actual variations in the observed emissions from the refinery and power plant, as well as to the uncertainty in the wind fields at the exact time of the measurements. These values are in good agreement with available datasets and with simulated plumes.
Eddy covariance methane measurements at a Ponderosa pine plantation in California
Authors: Smeets C. J. P. P. , Holzinger R. , Vigano I. , Goldstein A. H. , Röckmann T.
Published: April 2010

Abstract. Long term methane flux measurements have been mostly performed with plant or soil enclosure techniques on specific components of an ecosystem. New fast response methane analyzers make it possible to use the eddy covariance (EC) technique instead. The EC technique is advantageous because it allows continuous flux measurements integrating over a larger and more representative area including the complete ecosystem, and allows fluxes to be observed as environmental conditions change naturally without disturbance. We deployed the closed-path Fast Methane Analyser (FMA) from Los Gatos Research Ltd and demonstrate its performance for EC measurements at a Ponderosa pine plantation at the Blodgett Forest site in central California. CH4 concentrations measured at 10 Hz showed a relatively high noise level that was caused by a software related problem. Nevertheless, in the frequency range important for turbulent exchange, the cospectra of CH4 compare very well with all other scalar cospectra confirming the quality of the FMA measurements are good for the EC technique. The low-pass filtering characteristics of our closed-path system and the use of the Webb-Pearman-Leuning (WPL) corrections for a combination of open and closed-path sensors are discussed using a large ensemble of cospectra. The diurnal variation of the methane concentration was up to 60 ppbv with an average of 1843 ppbv. Concentrations increased from morning to late afternoon as upslope flow from the valley below carried polluted air to the site, and then decreased through the night as downslope flow carried cleaner air from aloft. The fluxes were consistently directed downward with a well defined diurnal pattern, averaging −35±40 ng m−2 s−1 during the daytime. The detection limit of the system was estimated at 22 ng m−2 s−1. The average CH4 deposition during the daytime was higher than the average value for warm temperate forests in a recent global inventory and the results from a process-based model study.
Accurate satellite-derived estimates of the tropospheric ozone impact on the global radiation budget
Authors: Joiner J. , Schoeberl M. R. , Vasilkov A. P. , Oreopoulos L. , Platnick S. , Livesey N. J. , Levelt P. F.
Published: April 2010

Abstract. Estimates of the radiative forcing due to anthropogenically-produced tropospheric O3 are derived primarily from models. Here, we use tropospheric ozone and cloud data from several instruments in the A-train constellation of satellites as well as information from the GEOS-5 Data Assimilation System to accurately estimate the radiative effect of tropospheric O3 for January and July 2005. Since we cannot distinguish between natural and anthropogenic sources with the satellite data, our derived radiative effect reflects the unadjusted (instantaneous) effect of the total tropospheric O3 rather than the anthropogenic component. We improve upon previous estimates of tropospheric ozone mixing ratios from a residual approach using the NASA Earth Observing System (EOS) Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) by incorporating cloud pressure information from OMI. We focus specifically on the magnitude and spatial structure of the cloud effect on both the short- and long-wave radiative budget. The estimates presented here can be used to evaluate the various aspects of model-generated radiative forcing. For example, our derived cloud impact is to reduce the radiative effect of tropospheric ozone by ~16%. This is centered within the published range of model-produced cloud effect on instantaneous radiative forcing.
Size resolved dust emission fluxes measured in Niger during 3 dust storms of the AMMA experiment
Authors: Sow M. , Alfaro S. C. , Rajot J. L. , Marticorena B.
Published: April 2010

Abstract. During the 2006 and 2007 special observing periods of the African Monsoon Multidisciplinary Analysis campaign an original experimental system has been implemented in Banizoumbou (Niger) for measuring the size-resolved dust emission flux in natural conditions and documenting the possible influence of wind speed on its size distribution. The instrumental set-up, associated methodology, and the quality tests applied to the data set are described before the results acquired during 2 events of the Monsoon type and 1 of the convective type are analyzed in detail. In good agreement with the theory of sandblasting, it is found in all cases that saltation must take place for a vertical emission flux to be detected. During a particular erosion event, the magnitude of the vertical flux is controlled by the surface roughness, which conditions the saltation threshold, and by the wind friction velocity. The dust flux released by the high energy convective event is also found to be much richer in very fine (<2 μm) particles than those of the relatively moderate Monsoon event, which shows that aerodynamic conditions definitely influence the initial size distribution of the erosion flux as previously suggested by wind tunnel experiments. However, the size distribution of the dust released by a given event is fairly constant and insensitive to even relatively important variations of u*. This is interpreted as a possible result of the rather long duration (15') over which wind fluctuations must be averaged for computing u*, which could make it an inadequate parameter for representing the very short response-time physical processes that are at the origin of fine dust emission at the measurement sites.
Regional modelling of tracer transport by tropical convection – Part 1: Sensitivity to convection parameterization
Authors: Arteta J. , Marécal V. , Rivière E. D.
Published: April 2010

Abstract. The general objective of this series of papers is to evaluate long duration limited area simulations with idealised tracers as a tool to assess tracer transport in chemistry-transport models (CTMs). In this first paper, we analyse the results of six simulations using different convection parameterizations. The simulations are using the Grell and Dévényi (2002) mass-flux framework for the convection parameterization with different closures (Grell=GR, Arakawa-Shubert=AS, Kain-Fritch=KF, Low omega=LO, Moisture convergence=MC) and an ensemble parameterization (EN) based on the other five closures. The simulations are run for one month during the SCOUT-O3 field campaign lead from Darwin (Australia) and have a 60 km horizontal resolution and a fine vertical resolution in the upper troposphere/lower stratosphere. Meteorological results are compared with satellite products, radiosoundings and SCOUT-O3 aircraft campaign data. They show that the model is generally in good agreement with the measurements with less variability in the model. Except for the precipitation field the differences between the six simulations are small with respect to the differences with the meteorological observations. The comparison with TRMM rainrates shows that the six simulations have two different behaviours with the EN, AS and KF parameterizations (Group 1) providing better rain fields than LO, MC and GR (Group 2). The vertical distribution of tropospheric tracers is very different for the two groups showing significantly more transport into the TTL for Group 1 related to the larger average values of the upward velocities. Nevertheless the low values for the Group 1 fluxes at and above the cold point level indicate that the model does not simulate significant overshooting. For stratospheric tracers, the differences between the two groups of parameterizations are small indicating that the downward transport from the stratosphere is more related to the turbulent mixing parameterization than to the convection parameterization.
Airborne observations of a subvisible midlevel Arctic ice cloud: microphysical and radiative characterization
Authors: Lampert A. , Ehrlich A. , Dörnbrack A. , Jourdan O. , Gayet J.-F. , Mioche G. , Shcherbakov V. , Ritter C. , Wendisch M.
Published: April 2010

Abstract. During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign, which was conducted in March and April 2007, an optically thin ice cloud was observed at around 3 km altitude south of Svalbard. The microphysical and radiative properties of this particular subvisible midlevel cloud were investigated with complementary remote sensing and in-situ instruments. Collocated airborne lidar remote-sensing and spectral solar radiation measurements were performed at a flight altitude of 2300 m below the cloud base. Under almost stationary atmospheric conditions, the same subvisible midlevel cloud was probed with various in-situ sensors roughly 30 min later. From individual ice crystal samples detected with the Cloud Particle Imager and the ensemble of particles measured with the Polar Nephelometer, we retrieved the single-scattering albedo, the scattering phase function as well as the volume extinction coefficient and the effective diameter of the crystal population. Furthermore, a lidar ratio of 21 (±6) sr was deduced by two independent methods. These parameters in conjunction with the cloud optical thickness obtained from the lidar measurements were used to compute spectral and broadband radiances and irradiances with a radiative transfer code. The simulated results agreed with the observed spectral downwelling radiance within the range given by the measurement uncertainty. Furthermore, the broadband radiative simulations estimated a net (solar plus thermal infrared) radiative forcing of the subvisible midlevel ice cloud of −0.4 W m−2 (−3.2 W m−2 in the solar and +2.8 W m−2 in the thermal infrared wavelength range).
Taklimakan dust aerosol radiative heating derived from CALIPSO observations using the Fu-Liou radiation model with CERES constraints
Authors: Huang J. , Fu Q. , Su J. , Tang Q. , Minnis P. , Hu Y. , Yi Y. , Zhao Q.
Published: April 2010

Abstract. The dust aerosol radiative forcing and heating rate over the Taklimakan Desert in northwestern China in July 2006 are estimated using the Fu-Liou radiative transfer model along with satellite observations. The vertical distributions of the dust aerosol extinction coefficient are derived from the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) lidar measurements. The CERES (Cloud and the Earth's Energy Budget Scanner) measurements of reflected solar radiation are used to constrain the dust aerosol type in the radiative transfer model, which determines the dust aerosol single-scattering albedo and asymmetry factor as well as the aerosol optical properties spectral dependencies. We find that the dust aerosol radiative heating and effect have a significant impact on the energy budget over the Taklimakan desert. In the atmospheres containing light, moderate and heavy dust layers, the dust aerosols heat the atmosphere by up to 1, 2, and 3 K day−1, respectively. The maximum daily mean radiative heating rate reaches 5.5 K day−1 at 5 km on 29 July. The averaged daily mean net radiative effect of the dust are 44.4, −41.9, and 86.3 W m−2, respectively, at the top of the atmosphere (TOA), surface, and in the atmosphere. Among these effects about two thirds of the warming effect at the TOA is related to the longwave radiation, while about 90% of the atmospheric warming is contributed by the solar radiation. At the surface, about one third of the dust solar radiative cooling effect is compensated by its longwave warming effect. The large modifications of radiative energy budget by the dust aerosols over Taklimakan Desert should have important implications for the atmospheric circulation and regional climate, topics for future investigations.
Gas/particle partitioning of water-soluble organic aerosol in Atlanta
Authors: Hennigan C. J. , Bergin M. H. , Russell A. G. , Nenes A. , Weber R. J.
Published: April 2010

Abstract. Gas and particle-phase organic carbon compounds soluble in water (e.g., WSOC) were measured simultaneously in Atlanta throughout the summer of 2007 to investigate gas/particle partitioning of ambient secondary organic aerosol (SOA). Previous studies have established that, in the absence of biomass burning, particulate WSOC (WSOCp) is mainly from secondary organic aerosol (SOA) production. Comparisons between WSOCp, organic carbon (OC) and elemental carbon (EC) indicate that WSOCp was a nearly comprehensive measure of SOA in the Atlanta summertime. To study SOA formation mechanisms, WSOC gas-particle partitioning was investigated as a function of temperature, RH, NOx, O3, and organic aerosol mass concentration. Identifying a clear temperature effect on partitioning was confounded by other temperature-dependent processes, which likely included the emissions of biogenic SOA precursors and photochemical SOA formation. Relative humidity data indicated a linear dependence between partitioning and fine particle liquid water. Lower NOx concentrations were associated with greater partitioning to particles, but WSOC partitioning had no visible relation to O3 or fine particle OC mass concentration. There was, however, a relationship between WSOC partitioning and the WSOCp concentration, suggesting a compositional dependence between partitioning semi-volatile gases and the phase state of the aerosol. Combined, the overall results suggest that partitioning to liquid water, followed by heterogeneous reactions may represent the main process by which SOA is formed in urban Atlanta during summer.
First steps towards the assimilation of IASI ozone data into the MOCAGE-PALM system
Authors: Massart S. , Clerbaux C. , Cariolle D. , Piacentini A. , Turquety S. , Hadji-Lazaro J.
Published: April 2010

Abstract. The Infrared Atmospheric Sounding Interferometer (IASI) is one of the five European new generation instruments carried by the polar-orbiting MetOp-A satellite. Data assimilation is a powerful tool to combine these data with a numerical model. This paper presents the first steps made towards the assimilation of the total ozone columns from the IASI measurements into a chemistry transport model. The IASI ozone data used are provided by an inversion of radiances performed at the LATMOS (Laboratoire Atmosphères, Milieux, Observations Spatiales). As a contribution to the validation of this dataset, the LATMOS-IASI data are compared to a four dimensional ozone field, with low systematic and random errors compared to ozonesondes and OMI-DOAS data. This field results from the combined assimilation of ozone profiles from the MLS instrument and of total ozone columns from the SCIAMACHY instrument. It is found that on average, the LATMOS-IASI data tends to overestimate the total ozone columns by 2% to 8%. The random observation error of the LATMOS-IASI data is estimated to about 6%, except over polar regions and deserts where it is higher. Using this information, the LATMOS-IASI data are then assimilated, combined with the MLS data. This first LATMOS-IASI data assimilation experiment shows that the resulting analysis is quite similar to the one obtained from the combined MLS and SCIAMACHY data assimilation.
Simultaneous factor analysis of organic particle and gas mass spectra: AMS and PTR-MS measurements at an urban site
Authors: Slowik J. G. , Vlasenko A. , McGuire M. , Evans G. J. , Abbatt J. P. D.
Published: April 2010

Abstract. During the winter component of the SPORT (Seasonal Particle Observations in the Region of Toronto) field campaign, particulate non-refractory chemical composition and concentration of selected volatile organic compounds (VOCs) were measured by an Aerodyne time-of-flight aerosol mass spectrometer (AMS) and a proton transfer reaction-mass spectrometer (PTR-MS), respectively. Sampling was performed in downtown Toronto ~15 m from a major road. The mass spectra from the AMS and PTR-MS were combined into a unified dataset, which was analyzed using positive matrix factorization (PMF). The two instruments were given equal weight in the PMF analysis by application of a scaling factor to the uncertainties of each instrument. A residual based metric, Δesc, was used to evaluate the relative weight. The PMF analysis yielded a 5-factor solution that included factors characteristic of regional transport, local traffic emissions, charbroiling, and oxidative processing. The unified dataset provides information on particle and VOC sources and atmospheric processing that cannot be obtained from the datasets of the individual instruments, such as apportionment of oxygenated VOCs to direct emission sources vs. secondary reaction products, improved correlation of oxygenated aerosol factors with photochemical age, and increased detail regarding the composition of oxygenated organic aerosol factors. This analysis represents the first application of PMF to a unified AMS/PTR-MS dataset.