bluuebunny/crossref_metadata_2025 huggingface dataset:
Detecting charging state of ultra-fine particles: instrumental development and ambient measurements
Authors: Laakso L. , Gagné S. , Petäjä T. , Hirsikko A. , Aalto P. P. , Kulmala M. , Kerminen V.-M.
Published: April 2010

Abstract. The importance of ion-induced nucleation in the lower atmosphere has been discussed for a long time. In this article we describe a new instrumental setup – Ion-DMPS – which can be used to detect contribution of ion-induced nucleation on atmospheric new particle formation events. We performed several laboratory tests to test the operation of the device and then we measured atmospheric new particle formation events with the instrument in a boreal forest. We found that some of the events were clearly dominated by neutral nucleation but in some cases also ion-induced nucleation contributed to the new particle formation. We also found that negative and positive ions behaved in a different manner, days with negative overcharging were more frequent than days with positive overcharging. A simple order of magnitude estimate gave the contribution of ion-induced nucleation on total nucleation approximately 10%. During the neutral-dominated nucleation days ion contribution was close to zero.
MIPAS level 2 operational analysis
Authors: Raspollini P. , Belotti C. , Burgess A. , Carli B. , Carlotti M. , Ceccherini S. , Dinelli B. M. , Dudhia A. , Flaud J.-M. , Funke B. , Höpfner M. , Lopez-Puertas M. , Payne V. , Piccolo C. , Remedios J. J. , Ridolfi M. , Spang R.
Published: April 2010

Abstract. The MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) instrument has been operating on-board the ENVISAT satellite since March 2002. In the first two years, it acquired in a nearly continuous manner high resolution (0.025 cm−1 unapodised) emission spectra of the Earth's atmosphere at limb in the middle infrared region. This paper describes the level 2 near real-time (NRT) and off-line (OL) ESA processors that have been used to derive level 2 geophysical products from the calibrated and geolocated level 1b spectra. The design of the code and the analysis methodology have been driven by the requirements for NRT processing. This paper reviews the performance of the optimised retrieval strategy that has been implemented to achieve these requirements and provides estimated error budgets for the target products: pressure/temperature, O3, H2O, CH4, HNO3, N2O and NO2, in the altitude measurement range from 6 to 68 km. From application to real MIPAS data, it was found that no change was needed in the developed code although an external algorithm was introduced to identify clouds with high opacity and to exclude affected spectra from the analysis. In addition, a number of updates were made to the set-up parameters and to auxiliary data. In particular, a new version of the MIPAS dedicated spectroscopic database was used and, in the OL analysis, the retrieval range was extended to reduce errors due to uncertainties in extrapolation of the profile outside the retrieval range and more stringent convergence criteria were implemented. A statistical analysis on the χ2 values obtained in one year of measurements shows good agreement with the a priori estimate of the forward model errors. On the basis of the first two years of MIPAS measurements the estimates of the forward model and instrument errors are in general found to be conservative with excellent performance demonstrated for frequency calibration. It is noted that the total retrieval error is limited by forward model errors which make useless a further reduction of random errors. However, such a reduction is within the capabilities of MIPAS measurements, which contain many more spectral signatures of the target species than what currently used. Further work is needed to reduce the amplitude of the forward model errors, so that the random error and the total error budget can be reduced accordingly. The importance of the Averaging kernels for a full characterisation of the target products is underlined and the equations are provided for their practical applications.
Changes in background aerosol composition in Finland during polluted and clean periods studied by TEM/EDX individual particle analysis
Authors: Niemi J. V. , Saarikoski S. , Tervahattu H. , Mäkelä T. , Hillamo R. , Vehkamäki H. , Sogacheva L. , Kulmala M.
Published: April 2010

Abstract. Aerosol samples were collected at a rural background site in southern Finland in May 2004. The elemental composition, morphology and mixing state of individual aerosol particles in three size fractions were studied using transmission electron microscopy (TEM) coupled with energy dispersive X-ray (EDX) microanalyses. The TEM/EDX results were complemented with the size-segregated bulk chemical measurements of selected ions and organic and elemental carbon. Many of the particles in PM0.2−1 and PM1−3.3 size fractions were strongly internally mixed with S, C and/or N. The major particle types in all PM0.2−1 samples were ammonium sulphates with/without carbon and dark inclusion(s) (number proportion of particles 54–86%), carbon/sulphate mixture with dark inclusions(s) (4–10%), internally mixed soot/sulphate particles (2–22%), soot (0–12%) and K-rich particles with S and/or C (0–9%). During the pollution episode (PM1.6~18 μg m−3, the proportion of Ca-rich particles was very high (26–48%) in the PM1−3.3 and PM3.3−11 samples, while the PM0.2−1 and PM1−3.3 samples contained elevated proportions of silicates (22–33%, also fly ash particles), metal oxides/hydroxides (1–9%) and tar balls (1–4%). These aerosols originated mainly from polluted areas of Eastern Europe, and some open biomass burning smoke was also brought by long-range transport. During the clean period (PM1.6~2 μg m−3, when air masses arrived from the Arctic Ocean, PM1−3.3 samples contained mainly sea salt particles (67–89%) with a variable rate of Cl substitution (mainly by NO3−. During the intermediate period (PM1.6~5 μg m−3, the PM1−3.3 sample contained porous (sponge-like) Na-rich particles (35%) with abundant S, K and O. They might originate from the burning of wood pulp wastes of paper industry. The proportion of biological particles and C-rich fragments (probably also biological origin) were highest in the PM3.3−11 samples (0–81% and 0–22%, respectively). The origin of different particle types and the effect of aging processes on particle composition and their hygroscopic and optical properties are discussed.
Methane emission from tropical savanna Trachypogon sp. grasses
Authors: Sanhueza E. , Donoso L.
Published: April 2010

Abstract. Methane flux measurements from the soil-grass system were made during the wet season in unperturbed plots and plots where standing dry and green Trachypogon sp. grasses were clipped to just above the soil surface. Results support the surprising discovery that vegetation emits methane. The dry/green mixture of grasses produce methane at a rate of ~10 ng m−2 s−1, which extrapolated to the global savanna would produce an annual emission of ~5 Tg, much lower than the production recently suggested in the literature. On the other hand, during the wet season savanna soil consume CH4 at a rate of ~4.7 ng m−2 s−1, producing a global sink of ~1.3 Tg yr−1. Therefore, the tropical savanna soil-grass system would make a modest contribution to the global budget of methane.
Technical Note: an implementation of the dry removal processes DRY DEPosition and SEDImentation in the Modular Earth Submodel System (MESSy)
Authors: Kerkweg A. , Buchholz J. , Ganzeveld L. , Pozzer A. , Tost H. , Jöckel P.
Published: April 2010

Abstract. We present the submodels DRYDEP and SEDI for the Modular Earth Submodel System (MESSy). Gas phase and aerosol dry deposition are calculated within DRYDEP, whereas SEDI deals with aerosol particle sedimentation. Dry deposition velocities depend on the near-surface turbulence and the physical and chemical properties of the surface cover (e.g. the roughness length, soil pH or leaf stomatal exchange). The dry deposition algorithm used in DRYDEP is based on the big leaf approach and is described in detail within this Technical Note. The sedimentation submodel SEDI contains two sedimentation schemes: a simple upwind zeroth order scheme and a first order approach.
In situ observations of “cold trap" dehydration in the western tropical Pacific
Authors: Hasebe F. , Fujiwara M. , Nishi N. , Shiotani M. , Vömel H. , Oltmans S. , Takashima H. , Saraspriya S. , Komala N.
Published: April 2010

Abstract. Water vapor sonde observations were conducted at Bandung, Indonesia (6.90 S, 107.60 E) and Tarawa, Kiribati (1.35 N, 172.91 E) in December 2003 to examine the efficiency of the "cold trap'' dehydration in the tropical tropopause layer (TTL). Trajectory analysis based on bundles of trajectories suggest that the modification of air parcels' identity due to irreversible mixing by the branching-out and merging-in of nearby trajectories is found to be an important factor, in addition to the routes air parcels are supposed to follow, for interpreting the water vapor concentrations observed by radiosondes in the TTL. Clear correspondence between the observed water vapor concentration and the estimated temperature history of air parcels is found showing that dry air parcels are exposed to low temperatures while humid air parcels do not experience cold conditions during advection, in support of the "cold trap'' hypothesis. It is suggested that the observed air parcel retained the water vapor by roughly twice as much as the minimum saturation mixing ratio after its passage through the "cold trap,'' although appreciable uncertainties remain.
20th Century trends and budget implications of trihalomethanes and dihalomethanes inferred from North GRIP firn air
Authors: Worton D. R. , Sturges W. T. , Schwander J. , Mulvaney R. , Barnola J.-M. , Chappellaz J.
Published: April 2010

Abstract. Four trihalomethane (THM; CHCl3, CHBrCl2, CHBr2Cl and CHBr3) and two dihalomethane (DHM; CH2BrCl and CH2Br2) trace gases have been measured in air extracted from polar firn collected at the North Greenland Icecore Project (NGRIP) site. CHCl3 was also measured in firn air from Devon Island (DI), Canada, Dronning Maud Land (DML), Antarctica and Dome Concordia (Dome C), Antarctica. All of these species are believed to be almost entirely of natural origin except for CHCl3 where anthropogenic sources have been reported to contribute ~10% to the global burden. A 2-D atmospheric model was run for CHCl3 using reported emission estimates to produce historical atmospheric trends at the three firn sites, which were then input into a firn diffusion model to produce concentration depth profiles that were compared against the measurements. The anthropogenic emissions were modified in order to give the best model fit to the firn data at NGRIP, Dome C and DML. As a result, the contribution of CHCl3 from anthropogenic sources, mainly from pulp and paper manufacture, to the total chloroform budget appears to have been considerably underestimated and was likely to have been close to ~40% at the maximum in atmospheric CHCl3 concentrations around 1990, declining to ~19% at the beginning of the 21st Century. We also show that the atmospheric burden of the brominated THM's in the northern hemisphere have increased over the 20th Century while CH2Br2 has remained constant over time implying that it is entirely of natural origin.
The relative importance of competing pathways for the formation of high-molecular-weight peroxides in the ozonolysis of organic aerosol particles
Authors: Mochida M. , Katrib Y. , Jayne J. T. , Worsnop D. R. , Martin S. T.
Published: April 2010

Abstract. High-molecular-weight (HMW) organic compounds are an important component of atmospheric particles, although their origins, possibly including in situ formation pathways, remain incompletely understood. This study investigates the formation of HMW organic peroxides through reactions involving stabilized Criegee intermediates (SCI's). The model system is methyl oleate (MO) mixed with dioctyl adipate (DOA) and myristic acid (MA) in submicron aerosol particles. Criegee intermediates are formed by the ozonolysis of the double bond in methyl oleate. An aerosol flow tube coupled to an Aerodyne quadrupole aerosol mass spectrometer is employed for the studies. The relative importance of different HMW organic peroxides, including secondary ozonides (SOZ's), α-acyloxyalkyl hydroperoxides and α-acyloxyalkyl alkyl peroxides (αAAHP-type compounds), diperoxides, and monoperoxide oligomers, is determined for the ozonolysis of different mixing mole fractions of MO in DOA and MA. Two SOZ's are identified as the HMW products of the ozonolysis of pure methyl oleate. Changes in the mobility and vacuum aerodynamic diameters of the particles indicate that up to 67% of the product mass remains in the particles, with the balance evaporating. In mixed particles, SOZ's form within an inert matrix of DOA to as low as 0.04 mole fraction MO. In comparison, in mixed particles of MO and MA, αAAHP-type compounds form in high yields for initial MO mole fractions under 0.5, suggesting that SCI's efficiently attack the carboxylic acid group of myristic acid. The reactions of SCI's with carboxylic acid groups to form αAAHP-type compounds therefore compete with those of SCI's with aldehydes to form SOZ's, provided that both types of functionalities are present at significant concentrations. The results suggest that SCI's formed by the ozonolysis of unsaturated organic molecules in atmospheric particles could lead to the transformation of carboxylic acids and other protic groups into HMW organic peroxides.
Processes controlling the concentration of hydroperoxides at Jungfraujoch Observatory, Switzerland
Authors: Walker S. J. , Evans M. J. , Jackson A. V. , Steinbacher M. , Zellweger C. , McQuaid J. B.
Published: April 2010

Abstract. An automated, ground-based instrument was used to measure gas-phase hydroperoxides at the Jungfraujoch High Altitude Research Station as part of the Free Tropospheric EXperiment (FREETEX) during February/March 2003. A nebulising reflux concentrator sampled ambient air twice hourly, prior to on-site analysis by HPLC speciation, coupled with post-column peroxidase derivatisation and fluorescence detection. Hydrogen peroxide (H2O2) concentrations reached up to 1420 pptv over the 13-day period with a mean of 206±261 pptv (± one standard deviation). Methyl hydroperoxide (CH3OOH) reached up to 921 pptv with a mean of 76±96 pptv. No other organic hydroperoxides were detected. The lack of an explicit diurnal cycle suggests that hydroperoxide concentrations are chiefly influenced by transport processes rather than local photochemistry at this mountainous site. We find elevated concentrations of H2O2 in air masses originating from the south-west indicative of higher concentrations of HOx due to more active photochemistry. Air which has been recently polluted exhibits low H2O2 concentration due to a combination of suppression of HO2 by NOx and deposition. We also conclude that despite being at a high alpine site, the vast majority of the air observed was extensively influence by the boundary layer during our campaign (diagnosed from high CO concentrations and the high NOx to NOy ratio) resulting in deposition of H2O2 to the surface and hence reduced H2O2 concentrations. The concentrations of H2O2 sampled here are consistent with previous box modelling studies of hydroperoxides which invoked a depositional sink.
What does reflection from cloud sides tell us about vertical distribution of cloud droplet sizes?
Authors: Marshak A. , Martins J. V. , Zubko V. , Kaufman Y. J.
Published: April 2010

Abstract. Cloud development, the onset of precipitation and the effect of aerosol on clouds depend on the structure of the cloud profiles of droplet size and phase. Aircraft measurements of cloud profiles are limited in their temporal and spatial extent. Satellites were used to observe cloud tops not cloud profiles with vertical profiles of precipitation-sized droplets anticipated from CloudSat.  The recently proposed CLAIM-3D satellite mission (cloud aerosol interaction mission in 3-D) suggests to measure profiles of cloud microphysical properties by retrieving them from the solar and infrared radiation reflected or emitted from cloud sides. Inversion of measurements from the cloud sides requires rigorous understanding of the 3-dimentional (3-D) properties of clouds. Here we discuss the reflected sunlight from the cloud sides and top at two wavelengths: one nonabsorbing to solar radiation (0.67 μm) and one with liquid water efficient absorption of solar radiation (2.1 μm). In contrast to the plane-parallel approximation, a conventional approach to all current operational retrievals, 3-D radiative transfer is used for interpreting the observed reflectances. General properties of the radiation reflected from the sides of an isolated cloud are discussed. As a proof of concept, the paper shows a few examples of radiation reflected from cloud fields generated by a simple stochastic cloud model with the prescribed vertically resolved microphysics. To retrieve the information about droplet sizes, we propose to use the probability density function of the droplet size distribution and its first two moments instead of the assumption about fixed values of the droplet effective radius. The retrieval algorithm is based on the Bayesian theorem that combines prior information about cloud structure and microphysics with radiative transfer calculations.
Seasonal dependence of peroxy radical concentrations at a northern hemisphere marine boundary layer site during summer and winter: evidence for photochemical activity in winter
Authors: Fleming Z. L. , Monks P. S. , Rickard A. R. , Bandy B. J. , Brough N. , Green T. J. , Reeves C. E. , Penkett S. A.
Published: April 2010

Abstract. Peroxy radicals (HO2+ΣRO2) were measured at the Weybourne Atmospheric Observatory (52° N, 1° E), Norfolk using a PEroxy Radical Chemical Amplifier (PERCA) during the winter and summer of 2002. The peroxy radical diurnal cycles showed a marked difference between the winter and summer campaigns with maximum concentrations of 12 pptv at midday in the summer and maximum concentrations as high as 30 pptv (10 min averages) in winter at night. The corresponding nighttime peroxy radical concentrations were not as high in summer (3 pptv). The peroxy radical concentration shows a distinct anti-correlation with increasing NOx during the daylight hours. At night, peroxy radicals increase with increasing NOx indicative of the role of NO3 chemistry. The average diurnal cycles for net ozone production, N(O3) show a large variability in ozone production, P(O3), and a large ozone loss, L(O3) in summer relative to winter. For a daylight average, net ozone production in summer than winter (1.51±0.5 ppbv h−1 and 1.11±0.47 ppbv h−1 respectively) but summer shows more variability of (meteorological) conditions than winter. The variability in NO concentration has a much larger effect on N(O3) than the peroxy radical concentrations. Photostationary state (PSS) calculations show an NO2 lifetime of 5 min in summer and 21 min in the winter, implying that steady-state NO-NO2 ratios are not always attained during the winter months. The results show an active peroxy radical chemistry at night and the ability of winter to make oxidant. The net effect of this with respect to production of ozone in winter is unclear owing to the breakdown in the photostationary state.
PM measurement campaign HOVERT in the Greater Berlin area: model evaluation with chemically specified particulate matter observations for a one year period
Authors: Beekmann M. , Kerschbaumer A. , Reimer E. , Stern R. , Möller D.
Published: April 2010

Abstract. The HOVERT (Horizontal and VERtical Transport of Ozone and particulate matter) campaign held in the Berlin Brandenburg area in Eastern Germany from September 2001 to September 2002 allowed to collect a unique data set of the aerosol chemical speciation (daily averages) at traffic, urban and rural sites. These observations are used for a thorough evaluation of the aerosol part in the REM-CALGRID model (RCG) developed at the Free University of Berlin (FUB). For inorganic ions (sulphate, nitrate and ammonium), simulated annual averages agree to observations within ±30% at more than half of the sites and always within a factor of two. Correlation coefficients are larger than in previous studies for SO42- and NH4+ (>0.7). For nitrate, less elevated correlations, 0.4–0.7 in the cold season, 0.2–0.4 in the warm season, are encountered. To our knowledge, this is one of the first comparisons of air quality model simulated elemental carbon (EC and OC) with daily observations for a whole year. It suggests an overestimation of EC and OC emissions in the Berlin area (through a scaling techniques between EC, OC and NOx and when assuming correct NOx emissions), and an underestimation of EC and OC at rural sites. Secondary organic aerosol (SOA) formation, recently introduced into the model (SORGAM module, Schell et al., 2001), is simulated as a very variable process, SOA levels varying from close to zero for most days to more than 5 µg/m3. Correlation between simulated SOA to observed OC is about 0.6, indicating that simulated variability partly corresponds to reality.
Evaluation of linear ozone photochemistry parametrizations in a stratosphere-troposphere data assimilation system
Authors: Geer A. J. , Lahoz W. A. , Jackson D. R. , Cariolle D. , McCormack J. P.
Published: April 2010

Abstract. This paper evaluates the performance of various linear ozone photochemistry parametrizations using the stratosphere-troposphere data assimilation system of the Met Office. A set of experiments were run for the period 23 September 2003 to 5 November 2003 using the Cariolle (v1.0 and v2.1), LINOZ and Chem2D-OPP (v0.1 and v2.1) parametrizations. All operational meteorological observations were assimilated, together with ozone retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Experiments were validated against independent data from the Halogen Occultation Experiment (HALOE) and ozonesondes. It is shown that the LINOZ scheme is unsuitable for use above 10 hPa, but below this level it works as well as the other schemes. The Cariolle v1.0 scheme shows excessive sensitivity in the term related to overlying column ozone, and this results in erroneous ozone production in the ozone hole. The other three schemes (Cariolle v2.1 and Chem2D-OPP v0.1 and v2.1) all perform well through most of the atmosphere. Exceptions were the troposphere, where modelling and observing ozone remains a substantial challenge, and the upper stratosphere and mesosphere, where the main problems come from biases in the schemes' climatology coefficients. Cariolle v2.1 analyses showed biases of up to 20% against HALOE at levels above 1 hPa. These biases could be partially corrected by substituting the Fortuin and Kelder (1998) ozone climatology into the scheme. Chem2D-OPP v2.1 analyses showed biases up to 20% and unrealistic ozone patterns in the southern hemisphere upper stratosphere, likely due to discrepancies between analysed temperatures and the temperature climatology supplied with the scheme. Future developments should include a better treatment of the troposphere, and a parametrization of the diurnal cycle of ozone above 0.5 hPa.
Accuracy of analyzed temperatures, winds and trajectories in the Southern Hemisphere tropical and midlatitude stratosphere as compared to long-duration balloon flights
Authors: Knudsen B. M. , Christensen T. , Hertzog A. , Deme A. , Vial F. , Pommereau J.-P.
Published: April 2010

Abstract. Eight super-pressure balloons floating at constant level between 50 and 80 hPa and three Infra-Red Montgolfier balloons of variable altitude (15 hPa daytime, 40–80 hPa night time) have been launched at 22° S from Brazil in February–May 2004 in the frame of the HIBISCUS project. The flights lasted for 7 to 79 days residing mainly in the tropics, but some of them passed the tropical barrier and went to southern midlatitudes. Compared to the balloon measurements just above the tropical tropopause the ECMWF operational temperatures show a systematic cold bias of 0.9 K and the easterly zonal winds are too strong by 0.7 m/s. This bias in the zonal wind adds to the ECMWF trajectory errors, but they still are relatively small with e.g. about an error of 700 km after 5 days. The NCEP/NCAR reanalysis trajectory errors are substantially larger (1300 km after 5 days). In the southern midlatitudes the cold bias is the same, but the zonal wind bias is almost zero. The trajectories are generally more accurate than in the tropics, but for one balloon a lot of the calculated trajectories end up on the wrong side of the tropical barrier and this leads to large trajectory errors.
Consecutive reactions of aromatic–OH adducts with NO, NO2 and O2: benzene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline
Authors: Koch R. , Knispel R. , Elend M. , Siese M. , Zetzsch C.
Published: April 2010

Abstract. Consecutive reactions of adducts, resulting from OH radicals and aromatics, with the tropospheric scavenger molecules O2, NO and NO2 have been studied for benzene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline by observing decays of OH at temperatures where the thermal back-decomposition to OH is faster than 3 s−1, typically between 300 and 340 K. The experimental technique was resonance fluorescence with flash photolysis of water as source of OH. Biexponential decays were observed in the presence of either O2 or NO, and triexponential decays were obtained in the presence of NO2. The kinetic analysis was performed by fitting the relevant rate constants of the reaction mechanism to whole sets of decays obtained at various concentrations of aromatic and scavenger. In the case of hexamethylbenzene, the biexponential decays suggest the existence of the ipso-adduct, and the slightly higher necessary temperatures show that it is even more stable. In addition, smog chamber experiments at O2 concentrations from atmospheric composition down to well below 100 ppm have been carried out for benzene, toluene and p-xylene. The drop of the effective rate constant of removal by OH occurs at reasonable O2 levels, given the FP/RF results. Comparison of the adduct reactivities shows for all aromatics of this study that the reaction with O2 predominates over that with NO2 under all tropospheric conditions, and that a reaction with NO may only occur after the reaction with O2.
A mass spectrometric study of secondary organic aerosols formed from the photooxidation of anthropogenic and biogenic precursors in a reaction chamber
Authors: Alfarra M. R. , Paulsen D. , Gysel M. , Garforth A. A. , Dommen J. , Prévôt A. S. H. , Worsnop D. R. , Baltensperger U. , Coe H.
Published: April 2010

Abstract. An Aerodyne Aerosol Mass Spectrometer (AMS) has been utilised to provide on-line measurements of the mass spectral signatures and mass size distributions of the oxidation products resulting from irradiating 1,3,5-trimethylbenzene (1,3,5-TMB) and α-pinene, separately, in the presence of nitrogen oxide, nitrogen dioxide and propene in a reaction chamber. Mass spectral results indicate that both precursors produce SOA with broadly similar chemical functionality of a highly oxidised nature. However, significant differences occur in the minor mass spectral fragments for the SOA in the two reaction systems, indicating that they have different molecular composition. Nitrogen-containing organic compounds have been observed in the photooxidation products of both precursors, and their formation appeared to be controlled by the temporal variability of NOx. Although the overall fragmentation patterns of the photooxidation products in both systems did not change substantially over the duration of each experiment, the contribution of some individual mass fragments to total mass appeared to be influenced by the irradiation time. The effective densities of the 1,3,5-TMB and α-pinene SOA particles were determined for various particle sizes using the relationship between mobility and vacuum aerodynamic diameters. The effective density for the TMB-SOA ranged from 1.35–1.40 g/cm3, while that for α-pinene SOA ranged from 1.29–1.32 g/cm3. The determined effective densities did not show dependence on irradiation time. Results suggest that further chemical processing of SOA takes place in the real atmosphere, as neither the α-pinene nor the 1,3,5-TMB experimental results reproduce the right relative product distribution between carbonyl-containing and multifunctional carboxylic acid species measured at ambient locations influenced by aged continental organic aerosols.
Investigations of the photochemical isotope equilibrium between O2, CO2 and O3
Authors: Shaheen R. , Janssen C. , Röckmann T.
Published: April 2010

Abstract. Contrary to tropospheric CO2 whose oxygen isotopic composition follows a standard mass dependent relationship, i.e. δ17O~0.5 δ18O, stratospheric CO2 is preferentially enriched in 17O, leading to a strikingly different relation with δ17O~1.7δ18O. The isotope anomaly is likely inherited from O3 via photolytically produced O(1D) that undergoes isotope exchange with CO2 and the anomaly may well serve as a tracer of stratospheric chemistry if details of the exchange mechanism are understood. We have studied the photochemical isotope equilibrium in UV-irradiated O2-CO2 and O3-CO2 mixtures to quantify the transfer of the anomaly from O3 to CO2 at room temperature. By following the time evolution of the oxygen isotopic compositions of CO2 and O2 under varying initial isotopic compositions of both, O2/O3 and CO2, the isotope equilibria between the two reservoirs were determined. A very strong dependence of the isotope equilibrium on the O2/CO2-ratio was established. Equilibrium enrichments of 17O and 18O in CO2 relative to O2 diminish with increasing CO2 content, and this reduction in the equilibrium enrichments does not follow a standard mass dependent relation. When molecular oxygen exceeds the amount of CO2 by a factor of about 20, 17O and 18O in equilibrated CO2 are enriched by (142±4) and (146±4), respectively, at room temperature and at a pressure of 225 hPa, independent of the initial isotopic compositions of CO2 and O2 or O3. From these findings we derive a simple and general relation between the starting isotopic compositions and amounts of O2 and CO2 and the observed slope in a three oxygen isotope diagram. Predictions from this relation are compared with published laboratory and atmospheric data.
Satellite monitoring of different vegetation types by differential optical absorption spectroscopy (DOAS) in the red spectral range
Authors: Wagner T. , Beirle S. , Grzegorski M. , Platt U.
Published: April 2010

Abstract. A new method for the satellite remote sensing of different types of vegetation and ocean colour is presented. In contrast to existing algorithms, our method analyses weak narrow-band reflectance structures (i.e. "fingerprint" structures) of vegetation in the red spectral range. It is based on differential optical absorption spectroscopy (DOAS), which is usually applied for the analysis of atmospheric trace gas absorptions. Since the spectra of atmospheric absorption and vegetation reflectance are simultaneously included in the analysis, the effects of atmospheric scattering and absorption are automatically corrected. The inclusion of the vegetation spectra also significantly improves the results of the trace gas retrieval. The global maps of the fitting coefficients for the vegetation spectra (indicating the fraction of the observed ground scene covered by vegetation) illustrate the seasonal cycle of different vegetation types. In addition to the vegetation distribution on land, they also show patterns of biological activity in the oceans. Our results indicate that improved sets of vegetation spectra might lead to more accurate and more specific identification of vegetation type in the future.
Process-based estimates of terrestrial ecosystem isoprene emissions
Authors: Arneth A. , Niinemets Ü. , Pressley S. , Bäck J. , Hari P. , Karl T. , Noe S. , Prentice I. C. , Serça D. , Hickler T. , Wolf A. , Smith B.
Published: April 2010

Abstract. In recent years evidence has emerged that the amount of isoprene emitted from a leaf is affected by the CO2 growth environment. Many – though not all – laboratory experiments indicate that emissions increase significantly at below-ambient CO2 concentrations and decrease when concentrations are raised to above ambient levels. A small number of process-based leaf isoprene emission models can reproduce this CO2-stimulation and -inhibition. These models are briefly reviewed, and their performance in standard conditions compared with each other and to an empirical algorithm. One of the models was judged particularly useful to be incorporated into a dynamic vegetation model framework, LPJ-GUESS, aiming to develop a tool that allows the interactive effects of climate and increasing CO2 concentration on vegetation distribution, productivity, and leaf and ecosystem isoprene emissions to be explored. The coupled vegetation dynamics-isoprene model is described and used here in a mode particularly suited for the ecosystem scale, but it can be employed at the global level as well. Annual and/or daily isoprene emissions simulated by the model were evaluated against flux measurements (or model estimates that had previously been evaluated with flux data) from a wide range of environments, and agreement between modelled and simulated values was generally good. By using a dynamic vegetation model, effects of canopy composition, disturbance history, or trends in CO2 concentration can be assessed. We show here for five model test sites that the suggested CO2-inhibition of leaf-isoprene metabolism can be large enough to offset increases in emissions due to CO2-stimulation of vegetation productivity and leaf area growth. When effects of climate change are considered atop the effects of atmospheric composition the interactions between the relevant processes will become even more complex. The CO2-isoprene inhibition may have the potential to significantly dampen the expected steep increase of ecosystem isoprene emission in a future warmer atmosphere with higher CO2 levels; this effect raises important questions for projections of future atmospheric chemistry and its connection to the terrestrial vegetation and carbon cycle.
In-situ measurement of reactive hydrocarbons at Hohenpeissenberg with comprehensive gas chromatography (GCxGC-FID): use in estimating HO and NO3
Authors: Bartenbach S. , Williams J. , Plass-Dülmer C. , Berresheim H. , Lelieveld J.
Published: April 2010

Abstract. During a field campaign at the Meteorological Observatory Hohenpeissenberg (MOHp) in July 2004, VOCs were measured using GCxGC-FID. Comparison to routinely made GC-MS measurements showed good agreement for a variety of anthropogenic and biogenic ambient VOCs ranging in concentration from below the detection limit (0.1 pmol mol−1) to 180 pmol mol−1. Pronounced diurnal cycles were found for both the biogenic and anthropogenic compounds, driven for the most part by the daily rise and fall of the boundary layer over the station. For the reactive compounds (lifetimes <2 days), a significant, non-zero dependency of the variability on lifetime was found, indicating that chemistry (as opposed to transport alone) was playing a role in determining the ambient VOC concentrations. The relationship was exploited using a single-variate analysis to derive a daytime mean value of HO (5.3±1.4×106 molecules cm−3), which compares well to that measured at the site, 3.2±2.3×106 molecules cm−3. The analysis was extended to the night time data to estimate concentrations for NO3 (1.47±0.2×108 molecules cm−3), which is not measured at the site. The feasibility of this approach for environments dominated by emissions of short-lived VOCs to estimate ambient levels of radical species is discussed.
Technical note: The MESSy-submodel AIRSEA calculating the air-sea exchange of chemical species
Authors: Pozzer A. , Jöckel P. , Sander R. , Ganzeveld L. , Lelieveld J.
Published: April 2010

Abstract. The new submodel AIRSEA for the Modular Earth Submodel System (MESSy) is presented. It calculates the exchange of chemical species between the ocean and the atmosphere with a focus on organic compounds. The submodel can be easily extended to a large number of tracers, including highly soluble ones. It is demonstrated that application of explicitly calculated air-sea exchanges with AIRSEA can induce substantial changes in the simulated tracer distributions in the troposphere in comparison to a model version in which this process is neglected. For example, the simulations of acetone, constrained with measured oceanic concentrations, shows relative changes in the atmospheric surface layer mixing ratios over the Atlantic Ocean up to 300%.
Mesoscale modelling of water vapour in the tropical UTLS: two case studies from the HIBISCUS campaign
Authors: Marécal V. , Durry G. , Longo K. , Freitas S. , Rivière E. D. , Pirre M.
Published: April 2010

Abstract. In this study, we evaluate the ability of the BRAMS mesoscale model compared to ECMWF global analysis to simulate the observed vertical variations of water vapour in the tropical upper troposphere and lower stratosphere (UTLS). The observations are balloon-borne measurements of water vapour mixing ratio and temperature from micro-SDLA (Tunable Diode Laser Spectrometer) instrument. Data from two balloon flights performed during the 2004 HIBISCUS field campaign are used to compare with the mesoscale simulations and to ECMWF analysis. The mesoscale model performs significantly better than ECMWF analysis for water vapour in the upper troposphere and similarly or slightly worse for temperature. The improvement provided by the mesoscale model for water vapour comes mainly from (i) the enhanced vertical resolution in the UTLS (250 m for BRAMS and ~1 km for ECMWF model) and (ii) the more detailed microphysical parameterization providing ice supersaturations as in the observations. The ECMWF vertical resolution (~1 km) is too coarse to capture the observed fine scale vertical variations of water vapour in the UTLS. In near saturated or supersaturated layers, the mesoscale model relative humidity with respect to ice saturation is close to observations provided that the temperature profile is realistic. For temperature, ECMWF analysis gives good results partly thanks to data assimilation. The analysis of the mesoscale model results showed that in undersaturated layers, the water vapour profile depends mainly on the dynamics. In saturated/supersaturated layers, microphysical processes play an important role and have to be taken into account on top of the dynamical processes to understand the water vapour profiles. In the lower stratosphere, the ECMWF model and the BRAMS model give very similar water vapour profiles that are significantly dryer than micro-SDLA measurements. This similarity comes from the fact that BRAMS is initialised using ECMWF analysis and that no mesoscale process acts in the stratosphere leading to no modification of the BRAMS results with respect to ECMWF analysis.
Improved ozone profile retrievals from GOME data with degradation correction in reflectance
Authors: Liu X. , Chance K. , Kurosu T. P.
Published: April 2010

Abstract. We present a simple method to perform degradation correction to Global Ozone Monitoring Experiment (GOME) reflectance spectra by comparing the average reflectance for 60° N–60° S with that at the beginning of GOME observations after removing the dependences on solar zenith angle and seasonal variation. The results indicate positive degradation of up to ~15–25% in the wavelength range 289–370 nm during 2000–2002; the degradation also exhibits significant dependence on wavelength and view zenith angle. These results are consistent with previous studies using radiative transfer models and ozone observations or climatology. The degradation causes retrieval biases of up to ~3% (10 DU, 1 DU=2.69×1016 molecules cm−2), 30% (10 DU), 10%, and 40% in total column ozone, tropospheric column ozone, stratospheric ozone and tropospheric ozone, respectively, from our GOME ozone profile retrieval algorithm. The application of this degradation correction generally improves the retrievals relative to Dobson and ozonesonde measurements during 2000–2003 and improves the retrieval consistency during 1996–2003.
Reflection and transmission of solar light by clouds: asymptotic theory
Authors: Kokhanovsky A. A. , Nauss T.
Published: April 2010

Abstract. The authors introduce the radiative transfer model CLOUD for reflection, transmission, and absorption characteristics of terrestrial clouds and discuss the accuracy of the approximations used within the model. A Fortran implementation of CLOUD is available for download. This model is fast, accurate, and capable of calculating multiple raditiative transfer characteristics of cloudy media including the spherical and plane albedo, reflection and transmission functions, absorptance as well as global and diffuse transmittance. The approximations are based on the asymptotic solutions of the radiative transfer equations. While the analytic part of the solutions is treated in the code in an approximate way, the correspondent reflection function (RF) of a semi-infinite water cloud R∞ is calculated using numerical solutions of the radiative transfer equations in the assumption of Deirmendjian's cloud C1 model. In the case of ice clouds, the fractal ice crystal model is used. The resulting values of R∞ with respect to the viewing geometry are stored in a look-up table (LUT).
Reevaluation of mineral aerosol radiative forcings suggests a better agreement with satellite and AERONET data
Authors: Balkanski Y. , Schulz M. , Claquin T. , Guibert S.
Published: April 2010

Abstract. Modelling studies and satellite retrievals do not agree on the amplitude and/or sign of the direct radiative perturbation from dust. Modelling studies have systematically overpredicted mineral dust absorption compared to estimates based upon satellite retrievals. In this paper we first point out the source of this discrepancy, which originates from the shortwave refractive index of dust used in models. The imaginary part of the refractive index retrieved from AERONET over the range 300 to 700 nm is 3 to 6 times smaller than that used previously to model dust. We attempt to constrain these refractive indices using a mineralogical database and varying the abundances of iron oxides (the main absorber in the visible). We first consider the optically active mineral constituents of dust and compute the refractive indices from internal and external mixtures of minerals with relative amounts encountered in parent soils. We then compute the radiative perturbation due to mineral aerosols for internally and externally mixed minerals for 3 different hematite contents, 0.9%, 1.5% and 2.7% by volume. These amounts represent low, central and high content of iron oxides in dust determined from the mineralogical database. Based upon values of the refractive index retrieved from AERONET, we show that the best agreement between 440 and 1020 nm occurs for mineral dust internally mixed with 1.5% volume weighted hematite. This representation of mineral dust allows us to compute, using a general circulation model, a new global estimate of mineral dust perturbation between −0.40 and −0.21 Wm−2. This range is determined from both optical properties and varying dust size distribution. The broadband shortwave effect varies from −0.78 to −0.53 Wm−2 and the longwave effect between +0.29 and +0.38 Wm−2. The 24-h average atmospheric heating by mineral dust during summer over the tropical Atlantic region (15° N–25° N; 45° W–15° W) is in the range +22 to +32 Wm−2 τ−1 which compares well with the 30±4 Wm−2 τ−1 measured by Li et al. (2004) over that same region. The refractive indices from Patterson et al. (1977) and from Volz (1973) overestimate by a factor of 2 the energy absorbed in the column during summer over the same region.
Rapid ventilation of the Mexico City basin and regional fate of the urban plume
Authors: de Foy B. , Varela J. R. , Molina L. T. , Molina M. J.
Published: April 2010

Abstract. Urban areas can be large emitters of air pollutants leading to negative health effects and environmental degradation. The rate of venting of these airsheds determines the pollutant loading for given emission levels, and also determines the regional impacts of the urban plume. Mexico City has approximately 20 million people living in a high altitude basin with air pollutant concentrations above the health limits most days of the year. A mesoscale meteorological model (MM5) and a particle trajectory model (FLEXPART) are used to simulate air flow within the Mexico City basin and the fate of the urban plume during the MCMA-2003 field campaign. The simulated trajectories are validated against pilot balloon and radiosonde trajectories. The residence time of air within the basin and the impacted areas are identified by episode type. Three specific cases are analysed to identify the meteorological processes involved. For most days, residence times in the basin are less than 12 h with little carry-over from day to day and little recirculation of air back into the basin. Very efficient vertical mixing leads to a vertically diluted plume which, in April, is transported predominantly towards the Gulf of Mexico. Regional accumulation was found to take place for some days however, with urban emissions sometimes staying over Mexico for more than 6 days. Knowledge of the residence times, recirculation patterns and venting mechanisms will be useful in guiding policies for improving the air quality of the MCMA.
Sub-micron atmospheric aerosols in the surroundings of Marseille and Athens: physical characterization and new particle formation
Authors: Petäjä T. , Kerminen V.-M. , Dal Maso M. , Junninen H. , Koponen I. K. , Hussein T. , Aalto P. P. , Andronopoulos S. , Robin D. , Hämeri K. , Bartzis J. G. , Kulmala M.
Published: April 2010

Abstract. The properties of atmospheric aerosol particles in Marseille and Athens were investigated. The studies were performed in Marseille, France during July 2002 and in Athens Greece during June 2003. The aerosol size distribution and the formation and growth rates of newly formed particles were characterized using Differential Mobility Particle Sizers. Hygroscopic properties were observed using a Hygroscopic Tandem Differential Mobility Analyzer setup. During both campaigns, the observations were performed at suburban, almost rural sites, and the sites can be considered to show general regional background behavior depending on the wind direction. At both sites there were clear pattern for both aerosol number concentration and hygroscopic properties. Nucleation mode number concentration increased during the morning hours indicating new particle formation, which was observed during more than 30% of the days. The observed formation rate was typically more than 1 cm−3 s−1, and the growth rate was between 1.2–9.9 nm h−1. Based on hygroscopicity measurements in Athens, the nucleation mode size increase was due to condensation of both water insoluble and water soluble material. However, during a period of less anthropogenic influence, the growth was to a larger extent due to water insoluble components. When urban pollution was more pronounced, growth due to condensation of water soluble material dominated.