bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic model framework for aerosol and cloud surface chemistry and gas-particle interactions: Part 2 – exemplary practical applications and numerical simulations
Authors: Ammann M. , Pöschl U.
Published: April 2010

Abstract. A kinetic model framework with consistent and unambiguous terminology and universally applicable rate equations and parameters for aerosol and cloud surface chemistry and gas-particle interactions has been presented in the preceding companion paper by Pöschl, Rudich and Ammann (Pöschl et al., 2005), abbreviated PRA. It allows to describe mass transport and chemical reaction at the gas-particle interface and to link aerosol and cloud surface processes with gas phase and particle bulk processes. Here we present multiple exemplary model systems and calculations illustrating how the general mass balance and rate equations of the PRA framework can be easily reduced to compact sets of equations which enable a mechanistic description of time and concentration dependencies of trace gas uptake and particle composition in systems with one or more chemical components and physicochemical processes. Time-dependent model scenarios show the effects of reversible adsorption, surface-bulk transport, and chemical aging on the temporal evolution of trace gas uptake by solid particles and solubility saturation of liquid particles. They demonstrate, how the transformation of particles and the variation of trace gas accommodation and uptake coefficients by orders of magnitude over time scales of microseconds to days can be explained and predicted from the initial composition and basic kinetic parameters of model systems by iterative calculations using standard spreadsheet programs. Moreover, they show how apparently inconsistent experimental data sets obtained with different techniques and on different time scales can be efficiently linked and mechanistically explained by application of consistent model formalisms and terminologies within the PRA framework. Steady-state model scenarios illustrate characteristic effects of gas phase composition and basic kinetic parameters on the rates of mass transport and chemical reactions. They demonstrate how adsorption and surface saturation effects can explain non-linear gas phase concentration dependencies of surface and bulk accommodation coefficients, uptake coefficients, and bulk solubilities (deviations from Henry's law). Such effects are expected to play an important role in many real atmospheric aerosol and cloud systems involving a wide range of organic and inorganic components of concentrated aqueous and organic solution droplets, ice crystals, and other crystalline or amorphous solid particles. We hope that the presented model systems and simulations clearly demonstrate the universal applicability and consistency of the PRA framework as a tool and common basis for experimental and theoretical studies investigating and describing atmospheric aerosol and cloud surface chemistry and gas-particle interactions.
Comparison of raingauge observations with modeled precipitation over Cyprus using Contiguous Rain Area analysis
Authors: Tartaglione N. , Mariani S. , Accadia C. , Speranza A. , Casaioli M.
Published: April 2010

Abstract. Verification of modeled rainfall with precipitation observed by a rain gauge network has been performed in a case study over the Cyprus Island. Cyprus has a relatively dense rain gauge network. The applied verification method is the Contiguous Rain Area (CRA) analysis. In this work some drawbacks are pointed out when CRA method is applied in such a case study. Impact on CRA results, when considering different dimensions of the compared model domain and different types of indicators (correlation and mean square error) used in the comparison, are discussed. Results indicate that care has to be taken when verification of modeled rainfall is performed over some of islands or hydrological basins.
Stratospheric and tropospheric NO2 variability on the diurnal and annual scale: a combined retrieval from ENVISAT/SCIAMACHY and solar FTIR at the Permanent Ground-Truthing Facility Zugspitze/Garmisch
Authors: Sussmann R. , Stremme W. , Burrows J. P. , Richter A. , Seiler W. , Rettinger M.
Published: April 2010

Abstract. Columnar NO2 retrievals from solar FTIR measurements at the Zugspitze (47.42° N, 10.98° E, 2964 m a.s.l.), Germany were investigated synergistically with columnar NO2 retrieved from SCIAMACHY data by the University of Bremen scientific algorithm UB1.5 for the time span July 2002–October 2004. A new concept to match FTIR data to the time of satellite overpass makes use of the NO2 daytime increasing rate retrieved from the FTIR data set itself (+1.02E+14 cm-2/h). This measured increasing rate shows no significant seasonal variation. SCIAMACHY data within a 200-km selection radius around Zugspitze were considered, and a pollution-clearing scheme was developed to select only pixels corresponding to clean background (free) tropospheric conditions, and exclude local pollution hot spots. The resulting (uncorrected) difference between SCIAMACHY and FTIR columns varies between 0.59–0.95E+15 cm-2 with an average of 0.74E+15 cm-2. A day-to-day scatter of daily means of 7–10% could be retrieved in mutual agreement from FTIR and SCIAMACHY. Both data sets are showing sufficient precisions to make this assessment. Analysis of the averaging kernels gives proof that at high-mountain-site FTIR is a perfect measure for the pure stratospheric column, while SCIAMACHY shows significant tropospheric sensitivity. Based on this finding, we set up a combined a posteriori FTIR-SCIAMACHY retrieval for tropospheric NO
Comparison of the levels of organic, elemental and inorganic carbon in particulate matter in six urban environments in Europe
Authors: Sillanpää M. , Frey A. , Hillamo R. , Pennanen A. S. , Salonen R. O.
Published: April 2010

Abstract. A series of 7-week sampling campaigns were conducted in urban background sites in the six European cities as follows: Duisburg 4 October–21 November 2002 (autumn), Prague 29 November 2002–16 January 2003 (winter), Amsterdam 24 January–13 March 2003 (winter), Helsinki 21 March–12 May 2003 (spring), Barcelona 28 March–19 May 2003 (spring) and Athens 2 June–21 July 2003 (summer). The campaigns were scheduled to include seasons of local public health concern due to high PM concentrations or findings in previously conducted epidemiological studies. Aerosol samples were collected in parallel with two identical virtual impactors (VI), which divide air PM into two size fractions, PM2.5 and PM2.5-10. The filter samples were analysed with a microbalance, an energy dispersive X-ray fluorescence (ED-XRF), an ion chromatograph (IC) and a thermo-optical carbon analyser (TOA). The PM2.5 and PM2.5-10 campaign means ranged 8.3–29.6 µg m-3 and 5.4–28.7 µg m-3, respectively. The ''wet and cool'' seasons favoured low coarse PM concentration and high fine PM concentration, whereas the spring and summer led to low fine and high coarse PM concentrations. The contribution of particulate organic matter (POM) to PM2.5-10 was highest (27%) in Prague and the lowest (10%) in Barcelona, while those to PM2.5 were generally higher, ranging from 21% in Barcelona to 54% in Prague. The contribution of elemental carbon (EC) to PM2.5-10 were relatively low (1–6%) in all the six European cities but it contributed somewhat higher (5–9%) to PM2.5. The differences are most likely due to variable contributions of local emission sources and seasonal factors such as domestic heating, vehicle exhausts and photochemical reactions. Carbonate, which interferes with carbon analysis by evolving stage at 900°C, was detected in the coarse particles of Athens and Barcelona and it could be separated reliably from OC by a simple integrating method. The calcium carbonate in Athens and Barcelona accounted for 56% and 11% of coarse PM masses, respectively. Carbonate was not found in other cities or in PM2.5. The mean PM2.5 mass portions of five OC thermal fractions (OC1, OC2, OC3, OC4 and OCP) varied in the range 26–33%, 6–10%, 7–10%, 9–22% and 29–50%, respectively, in six cities. The differences in the mass portion profiles were relatively small between the cities.
Water activity and activation diameters from hygroscopicity data – Part I: Theory and application to inorganic salts
Authors: Kreidenweis S. M. , Koehler K. , DeMott P. , Prenni A. J. , Carrico C. , Ervens B.
Published: April 2010

Abstract. A method is described that uses particle hygroscopicity measurements, made with a humidified tandem differential mobility analyzer (HTDMA), to determine solution water activity as a function of composition. The use of derived water activity data in computations 5 determining the ability of aerosols to serve as cloud condensation nuclei (CCN) is explored. Results for sodium chloride and ammonium sulfate are shown in Part I. In Part II (Koehler et al., to be submitted, 2005), results are reported for several atmospherically-relevant dicarboxylic acids: malonic acid, glutaric acid and oxalic acid. The methodology yields solution water activities and critical dry diameters for 10 ammonium sulfate and sodium chloride in good agreement with previously published data. The approach avoids the assumptions required for application of simplified and modified K¨ohler equations to predict CCN activity, most importantly, knowledge of the molecular weight and the degree of dissociation of the soluble species. Predictions of the dependence of water activity on the mass fraction of aerosol species are sensitive 15 to the assumed dry density, but predicted critical dry diameters are not.
The Indian summer monsoon rainfall: interplay of coupled dynamics, radiation and cloud microphysics
Authors: Patra P. K. , Behera S. K. , Herman J. R. , Maksyutov S. , Akimoto H. , Yamagata T.
Published: April 2010

Abstract. The Indian summer monsoon rainfall (ISMR), which has a strong connection to agricultural food production, has been less predictable by conventional models in recent times. Two distinct years 2002 and 2003 with lower and higher July rainfall, respectively, are selected to help understand the natural and anthropogenic influences on ISMR. We show that heating gradients along the meridional monsoon circulation are reduced due to aerosol radiative forcing and the Indian Ocean Dipole in 2002. An increase in the dust and biomass-burning component of the aerosols through the zonal monsoon circulation resulted in reduction of cloud droplet growth in July 2002. These conditions were opposite to those in July 2003 which led to an above average ISMR. In this study, we have utilized NCEP/NCAR reanalyses for meteorological data (e.g. sea-surface temperature, horizontal winds, and precipitable water), NOAA interpolated outgoing long-wave radiation, IITM constructed all-India rainfall amounts, aerosol parameters as observed from the TOMS and MODIS satellites, and ATSR fire count maps. Based on this analysis, we suggest that monsoon rainfall prediction models should include synoptic as well as interannual variability in both atmospheric dynamics and chemical composition.
Observation of 2-methyltetrols and related photo-oxidation products of isoprene in boreal forest aerosols from Hyytiälä, Finland
Authors: Kourtchev I. , Ruuskanen T. , Maenhaut W. , Kulmala M. , Claeys M.
Published: April 2010

Abstract. Oxidation products of isoprene including 2-methyltetrols (2-methylthreitol and 2-methylerythritol), 2-methylglyceric acid and triol derivatives of isoprene (2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene) have been detected in boreal forest PM1 aerosols collected at Hyytiälä, southern Finland, during a 2004 summer period, at significant atmospheric concentrations (in total 51 ng m-3 in summer versus 0.46 ng m-3 in fall). On the basis of these results, it can be concluded that photo-oxidation of isoprene is an important atmospheric chemistry process that contributes to secondary organic aerosol formation during summer in this conifer forest ecosystem. In addition to isoprene oxidation products, malic acid, which can be regarded as an end-oxidation product of unsaturated fatty acids, was also detected at high concentrations during the summer period (46 ng m-3 in summer versus 5.2 ng m-3 in fall), while levoglucosan, originating from biomass burning, became relatively more important during the fall period (29 ng m-3 in fall versus 10 ng m-3 in summer). Pinic acid, a major photo-oxidation product of α-pinene in laboratory experiments, could only be detected at trace levels in the summer PM1 aerosol samples from Hyytiälä, suggesting that further oxidation of pinic acid occurs and/or that different oxidation pathways are followed. We hypothesize that photo-oxidation of isoprene may participate in the early stages of new particle formation, a phenomenon which has been well documented in the boreal forest environment.
Retrieving the vertical distribution of stratospheric OClO from Odin/OSIRIS limb-scattered sunlight measurements
Authors: Krecl P. , Haley C. S. , Stegman J. , Brohede S. M. , Berthet G.
Published: April 2010

Abstract. The first vertical profiles of stratospheric OClO retrieved from Odin/OSIRIS limb-scattered sunlight radiances are presented. The retrieval method is based on a two-step approach, using differential optical absorption spectroscopy combined with the maximum a posteriori estimator. The details of the spectral window selection, spectral corrections and inversion technique are discussed. The results show that OClO can be detected inside the South polar vortex region between about 12 and 20 km altitude with a 2–5 km height resolution and an estimated retrieval error better than 60% at the peak. OClO concentrations are consistent with chemical transport model simulations and show the expected relation to the atmospheric conditions in the lower stratosphere in the austral spring 2002. This unique data set of OClO profiles is very promising to study the stratospheric chlorine activation in both polar regions.
Tropospheric O3 over Indonesia during biomass burning events measured with GOME (Global Ozone Monitoring Experiment) and compared with trajectory analysis
Authors: Ladstätter-Weißenmayer A. , Meyer-Arnek J. , Richter A. , Wittrock F. , Burrows J. P.
Published: April 2010

Abstract. Tropospheric ozone columns of up to 50 DU were observed by GOME (Global Ozone Monitoring Experiment) above Indonesia in September 1997, while only background amounts were measured in September 1998. The Traj.x trajectory model along with BRemen's Atmospheric PHOtochemical model (BRAPHO) were used to investigate the higher than average ozone columns above Indonesia. The transport analysis reveals that biomass burning over central Africa and northern Australia does not significantly influence ozone columns over Indonesia in September 1997. El Niño conditions, leading to extreme dryness and uncontrolled fires in Indonesia, produced ozone precursors, which are initially only slowly advected westwards to the central Indian Ocean. Joint transport and chemistry modelling was able to reproduce the spatial distribution and amounts of ozone, NO2 and formaldehyde columns over Indonesia. The chemistry modelling shows a net production of 3.1 Tg of ozone produced by biomass burning in Indonesia in September 1997. Transport analysis further reveals that ozone columns over the Indian Ocean, between 10 and 20° S can be accounted for by the mixing of air masses containing NOx from lightning over the Congo Basin with air masses containing volatile organic compounds from biomass burning.
Dry and wet deposition of inorganic nitrogen compounds to a tropical pasture site (Rondônia, Brazil)
Authors: Trebs I. , Lara L. L. , Zeri L. M. M. , Gatti L. V. , Artaxo P. , Dlugi R. , Slanina J. , Andreae M. O. , Meixner F. X.
Published: April 2010

Abstract. The input of nitrogen (N) to ecosystems has increased dramatically over the past decades. While total N deposition (wet + dry) has been extensively determined in temperate regions, only very few data sets exist about wet N deposition in tropical ecosystems, and moreover, experimental information about dry N deposition in tropical environments is lacking. In this study we estimate dry and wet deposition of inorganic N for a remote pasture site in the Amazon Basin based on in-situ measurements. The measurements covered the late dry (biomass burning) season, a transition period and the onset of the wet season (clean conditions) (12 September to 14 November 2002, LBA-SMOCC). Ammonia (NH3), nitric acid (HNO3), nitrous acid (HONO), nitrogen dioxide (NO2), nitric oxide (NO), ozone (O3), aerosol ammonium (NH4+) and aerosol nitrate (NO3-) were measured in real-time, accompanied by simultaneous (micro-)meteorological measurements. Dry deposition fluxes of NO2 and HNO3 are inferred using the ''big leaf multiple resistance approach'' and particle deposition fluxes are derived using an established empirical parameterization. Bi-directional surface-atmosphere exchange fluxes of NH3 and HONO are estimated by applying a ''canopy compensation point model''. Dry and wet N deposition is dominated by NH3 and NH4+, which is largely the consequence of biomass burning during the dry season. The grass surface appeared to have a strong potential for daytime NH3 (re-)emission, owing to high canopy compensation points, which are related to high surface temperatures and to direct NH3 emissions from cattle excreta. NO2 also significantly accounted for dry N deposition, whereas HNO3, HONO and N-containing aerosol species were only minor contributors. We estimated a total (dry + wet) N deposition of 7.3–9.8 kgN ha-1 yr-1 to the tropical pasture site, whereof 2–4.5 kgN ha-1 yr-1 are attributed to dry N deposition and ~5.3 kgN ha-1 yr-1 to wet N deposition. Our estimate exceeds total (wet + dry) N deposition to tropical ecosystems predicted by global chemistry and transport models by at least factor of two.
Systematic errors in global air-sea CO2 flux caused by temporal averaging of sea-level pressure
Authors: Kettle H. , Merchant C. J.
Published: April 2010

Abstract. Long-term temporal averaging of meteorological data, such as wind speed and air pressure, can cause large errors in air-sea carbon flux estimates. Other researchers have already shown that time averaging of wind speed data creates large errors in flux due to the non-linear dependence of the gas transfer velocity on wind speed (Bates and Merlivat, 2001). However, in general, wind speed is negatively correlated with air pressure, and a given fractional change in the pressure of dry air produces an equivalent fractional change in the atmospheric partial pressure of carbon dioxide (pCO2air). Thus low pressure systems cause a drop in pCO2air, which together with the associated high winds, promotes outgassing/reduces uptake of CO2 from the ocean. Here we quantify the errors in global carbon flux estimates caused by using monthly or climatological pressure data to calculate pCO2air (and thus ignoring the covariance of wind and pressure) over the period 1990–1999, using two common parameterisations for gas transfer velocity (Wanninkhof, 1992 (W92) and Wanninkhof and McGillis, 1999 (WM99)). Results show that on average, compared with estimates made using 6 hourly pressure data, the global oceanic sink is systematically overestimated by 7% (W92) and 10% (WM99) when monthly mean pressure is used, and 9% (W92) and 12% (WM99) when climatological pressure is used.
The structure of the haze plume over the Indian Ocean during INDOEX: tracer simulations and LIDAR observations
Authors: Forêt G. , Flamant C. , Cautenet S. , Pelon J. , Minvielle F. , Taghavi M. , Chazette P.
Published: April 2010

Abstract. Three-dimensional nested tracer simulations of a pollution plume originating from the Indian sub-continent over the Indian Ocean in the framework of the Indian Ocean Experiment (INDOEX) between 5 and 9 March 1999 were performed with the Regional Atmospheric Modeling System (RAMS) to provide insight into the transport patterns of the pollutants as well as investigate the dynamical mechanisms controlling the vertical structure of the plume and its evolution in the vicinity of the Maldives Islands. Airborne and ground-based LIDAR observations of the structure of the haze plume made on 7 March 1999 were used to assess the quality of the simulations as well as the impact of grid resolution on the vertical structure of the simulated plume. It is shown that, over the Arabian Sea, in the vicinity of the Maldives Islands, the pollutants composing the plume observed by the airborne LIDAR essentially originated from the city of Madras and that the vertical structure of the plume was controlled by the diurnal cycle of the continental boundary layer depth. A combination of tracer simulations and remote sensing observations (airborne LIDAR, ship-borne photometer, ground-based LIDAR in Goa) was used to analyse the diurnal evolution of the haze plume over the sea. We find evidence that the sea breeze circulation and orographic lifting taking place in the southern part of the Indian sub-continent during the day time play a crucial role in the modulation of the continental boundary layer depth, and in turn, the haze plume depth. The dynamical processes, as well as entrainment at the top of the marine atmospheric boundary layer, also play a crucial role in re-circulating a fraction of the tracers transported over ocean by the monsoon flow above the marine atmospheric boundary layer in the landward (southwesterly) branch of breeze circulation during the next day. This in turn leads to pollutant accumulation in the vicinity of the Indian coastline. Nevertheless, this contribution to the total aerosol load observed during the INDOEX intensive field phase is shown to small compared to that related to massive advection of aerosol from the continent. The nesting of a high horizontal resolution domain (5 km, with 39 vertical levels below 4000 m above mean seal level), allows a better representation of local dynamics, sea and mountains breezes circulations, and therefore a noticeable improvement in the representation of the pollutants plume in the simulation.
Evidence of systematic errors in SCIAMACHY-observed CO2 due to aerosols
Authors: Houweling S. , Hartmann W. , Aben I. , Schrijver H. , Skidmore J. , Roelofs G.-J. , Breon F.-M.
Published: April 2010

Abstract. SCIAMACHY CO2 measurements show a large variability in total column CO2 over the Sahara desert of up to 10% that is not anticipated from in situ measurements and cannot be explained by results of atmospheric models. Comparisons with colocated aerosol measurements by TOMS and MISR over the Sahara indicate that the seasonal variation of SCIAMACHY-observed CO2 strongly resembles seasonal variations of windblown dust. Correlation coefficients of monthly datasets of colocated MISR aerosol optical depth and SCIAMACHY CO2 vary between 0.6 and 0.8, indicating that about half of the CO2 variance is explained by aerosol optical depth. Radiative transfer model calculations confirm the role of dust and can explain the size of the errors. Sensitivity tests suggest that the remaining variance may largely be explained by variations in the vertical distribution of dust. Further calculations for a few typical aerosol classes and a broad range of atmospheric conditions show that the impact of aerosols on SCIAMACHY retrieved CO2 is by far the largest over the Sahara, but may also reach significant levels elsewhere. Inverse modelling calculations indicate that continental scale source and sink estimation on the basis of SCIAMACHY CO2 data without aerosol correction leads to significant errors. To improve terrestrial CO2 flux estimates by inverse modelling using SCIAMACHY measurements at 1.6μm, aerosol correction will be needed. Methods for correcting aerosol-induced errors exist, but so far mainly on the basis of theoretical considerations. As demonstrated by this study, SCIAMACHY may contribute to a verification of such methods using real data.
SCIAMACHY Absorbing Aerosol Index – calibration issues and global results from 2002–2004
Authors: de Graaf M. , Stammes P.
Published: April 2010

Abstract. The validity of the Absorbing Aerosol Index (AAI) product from the SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY (SCIAMACHY) is discussed. The operational SCIAMACHY AAI product suffers from calibration errors in the reflectance as measured by SCIAMACHY and design errors. Therefore, the AAI product was recalculated, compensating for the errors, with reflectance data from the start of measurements of SCIAMACHY until December 2004. Appropriate correction factors were determined for the UV to correct for the radiometric error in the SCIAMACHY reflectances. The algorithm was provided with LookUp Tables in which a good representation of polarisation effects was incorporated, as opposed to the LookUp Tables of the operational product, in which polarisation effects were not accounted for. The results are presented, their validity discussed, and compared to the operational product. The AAI is very sensitive to calibration errors and can be used to monitor calibration errors and changes. From 2004 onwards, the new SCIAMACHY AAI is suitable to add to the continuation of the long-term AAI record. Recommendations are given for improvement of the operational AAI product.
3-D microphysical model studies of Arctic denitrification: comparison with observations
Authors: Davies S. , Mann G. W. , Carslaw K. S. , Chipperfield M. P. , Kettleborough J. A. , Santee M. L. , Oelhaf H. , Wetzel G. , Sasano Y. , Sugita T.
Published: April 2010

Abstract. Simulations of Arctic denitrification using a 3-D chemistry-microphysics transport model are compared with observations for the winters 1994/1995, 1996/1997 and 1999/2000. The model of Denitrification by Lagrangian Particle Sedimentation (DLAPSE) couples the full chemical scheme of the 3-D chemical transport model, SLIMCAT, with a nitric acid trihydrate (NAT) growth and sedimentation scheme. We use observations from the Microwave Limb Sounder (MLS) and Improved Limb Atmospheric Sounder (ILAS) satellite instruments, the balloon-borne Michelsen Interferometer for Passive Atmospheric Sounding (MIPAS-B), and the in situ NOy instrument on-board the ER-2. As well as directly comparing model results with observations, we also assess the extent to which these observations are able to validate the modelling approach taken. For instance, in 1999/2000 the model captures the temporal development of denitrification observed by the ER-2 from late January into March. However, in this winter the vortex was already highly denitrified by late January so the observations do not provide a strong constraint on the modelled rate of denitrification. The model also reproduces the MLS observations of denitrification in early February 2000. In 1996/1997 the model captures the timing and magnitude of denitrification as observed by ILAS, although the lack of observations north of ~67° N make it difficult to constrain the actual timing of onset. The comparison for this winter does not support previous conclusions that denitrification must be caused by an ice-mediated process. In 1994/1995 the model notably underestimates the magnitude of denitrification observed during a single balloon flight of the MIPAS-B instrument. Agreement between model and MLS HNO3 at 68 hPa in mid-February 1995 was significantly better. Sensitivity tests show that a 1.5 K overall decrease in vortex temperatures or a factor 4 increase in assumed NAT nucleation rates produce the best statistical fit to MLS observations. Both adjustments would be required to bring the model into agreement with the MIPAS-B observations. The agreement between the model and observations suggests that a NAT-only denitrification scheme (without ice), which was discounted by previous studies, must now be considered as one mechanism for the observed Arctic denitrification. The timing of onset and the rate of denitrification remain poorly constrained by the available observations.
A broadband cavity ringdown spectrometer for in-situ measurements of atmospheric trace gases
Authors: Bitter M. , Ball S. M. , Povey I. M. , Jones R. L.
Published: April 2010

Abstract. This paper describes a broadband cavity ringdown spectrometer and its deployment during the 2002 North Atlantic Marine Boundary Layer Experiment (NAMBLEX) to measure ambient concentrations of NO3, N2O5, I2 and OIO at the Mace Head Atmospheric Research Station, Co. Galway, Ireland. The effective absorption path lengths accessible with the spectrometer generally exceeded 10 km, enabling sensitive localised ''point'' measurements of atmospheric absorbers to be made adjacent to the other instruments monitoring chemically related species at the same site. For the majority of observations, the spectrometer was used in an open path configuration thereby avoiding surface losses of reactive species. A subset of observations targeted the N2O5 molecule by detecting the additional NO3 formed by the thermal dissociation of N2O5. In all cases the concentrations of the atmospheric absorbers were retrieved by fitting the differential structure in the broadband cavity ringdown spectra using a methodology adapted from long path differential optical absorption spectroscopy. The uncertainty of the retrieval depends crucially on the correct treatment and fitting of the absorption bands due to water vapour, a topic that is discussed in the context of analysing broadband cavity ringdown spectra. The quality of the measurements and the retrieval method are illustrated with representative spectra acquired during NAMBLEX in spectral regions around 660 nm (NO3 and N2O5) and 570 nm (I2 and OIO). Typical detection limits were 1 pptv for NO3 in an integration time of 100 s, 4 pptv for OIO and 20 pptv for I2 in an integration time of 10 min. Additionally, the concentrations of atmospheric water vapour and the aerosol optical extinction were retrieved in both spectral regions. A companion paper in this issue presents the time series of the measurements and discusses their significance for understanding the variability of short lived nitrogen and iodine compounds in the marine boundary layer.
Characterization and source apportionment of atmospheric organic and elemental carbon during fall and winter of 2003 in Xi'an, China
Authors: Cao J. J. , Chow J. C. , Lee S. C. , Li Y. , Chen S. W. , An Z. S. , Fung K. , Watson J. G. , Zhu C. S. , Liu S. X.
Published: April 2010

Abstract. Continuous observation of atmospheric organic and elemental carbon (OC, EC) were conducted at Xi'an during high pollution seasons from September 2003 to February 2004. PM2.5 samples were collected on pre-fired quartz-fiber filters with battery-powered mini-volume samplers every day and PM10 samples were collected every third days. Three types of source samples (i.e., coal-combustion, motor vehicle exhaust, and biomass burning) were also collected during ambient sampling period. Ambient and source samples were analyzed for OC and EC by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. The average PM2.5 OC concentrations in fall and winter were 34.1±18.0 µg m-3 and 61.9±33.2 µg m-3, respectively, while EC were 11.3±6.9 µg m-3 and 12.3±5.3 µg m-3, respectively. Most of OC and EC were associated with fine particle (PM2.5) mode. The OC and EC levels at Xi'an are higher than most urban cities in Asia. The OC and EC in fall were found to be strongly correlated (R2>0.9), with moderate correlation in winter (R2=0.66). The carbonaceous aerosol accounted for 48.8±10.1% of the PM2.5 during fall and 45.9±7.5% during winter. Average OC/EC ratio was 3.3 in fall and 5.1 in winter with individual OC/EC ratios constantly exceeding 2.0. Elevated OC/EC ratios were found during heating seasons with increased coal combustion. The contribution of secondary organic carbon was not significant during winter. The time series of OC and EC showed periodic variability. Traffic contributes 5 and 7 day peaks in the spectrum, precipitation appears as a 10 day periodicity and biomass burning can be identified as a 24 day periodicity. Total carbon (TC) was apportioned by absolute principal component analysis (APCA) using the 8 carbon fraction data (OC1, OC2, OC3, OC4, EC1, EC2, EC3, and OP [a pyrolyzed carbon fraction]). TC attributes 73% to gasoline exhaust, 23% to diesel exhaust, and 4% to biomass burning during fall. However, TC attributes 44% each to gasoline exhaust and coal burning, 9% to biomass burning, and 3% to diesel exhaust during winter.
Application of several activity coefficient models to water-organic-electrolyte aerosols of atmospheric interest
Authors: Raatikainen T. , Laaksonen A.
Published: April 2010

Abstract. In this work, existing and modified activity coefficient models are examined in order to assess their capabilities to describe the properties of aqueous solution droplets relevant in the atmosphere. Five different water-organic-electrolyte activity coefficient models were first selected from the literature. Only one of these models included organics and electrolytes which are common in atmospheric aerosol particles. In the other models, organic species were solvents such as alcohols, and important atmospheric ions like NH4+ could be missing. The predictions of these models were compared to experimental activity and solubility data in aqueous single electrolyte solutions with 31 different electrolytes. Based on the deviations from experimental data and on the capabilities of the models, four predictive models were selected for fitting of new parameters for binary and ternary solutions of common atmospheric electrolytes and organics. New electrolytes (H+, NH4+, Na+, Cl−, NO3− and SO42−) and organics (dicarboxylic and some hydroxy acids) were added and some modifications were made to the models if it was found useful. All new and most of the existing parameters were fitted to experimental single electrolyte data as well as data for aqueous organics and aqueous organic-electrolyte solutions. Unfortunately, there are very few data available for organic activities in binary solutions and for organic and electrolyte activities in aqueous organic-electrolyte solutions. This reduces model capabilities in predicting solubilities. After the parameters were fitted, deviations from measurement data were calculated for all fitted models, and for different data types. These deviations and the calculated property values were compared with those from other non-electrolyte and organic-electrolyte models found in the literature. Finally, hygroscopic growth factors were calculated for four 100 nm organic-electrolyte particles and these predictions were compared to experimental data and to predictions from other models. All of the newly fitted models show good agreement with experimental water activity data in binary and ternary solutions. One of the models is for activities of non-electrolytes only, but the other three models show quite small deviations from measured electrolyte activities. Because there were not enough experimental data for organic and electrolyte activities, some models show bigger deviation for mutual deliquescence relative humidities of organic-electrolyte particles, but calculated growth factors for liquid droplets are quite close to the experimental data. Even in cases with somewhat bigger deviations, the results can be considered satisfactory, because they were calculated based mainly on the predictive properties of the models.
Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation
Authors: Twohy C. H. , Poellot M. R.
Published: April 2010

Abstract. A counterflow virtual impactor was used to collect and analyze residual particles from anvil cirrus clouds generated over the state of Florida in the southern United States. A wide variety of particle types were found, including salts, crustal material, industrial metals, carbonaceous particles, and sulfates. Ambient aerosol particles near the anvils were found to have similar compositions, indicating that anvils act to redistribute particles over large regions of the atmosphere. Sampling occurred at a range of altitudes spanning temperatures from –21 to –56°C. More insoluble (crustal and metallic) particles typical of heterogeneous ice nuclei were found in ice crystals at warmer temperatures, while more soluble salts and sulfates were present at cold temperatures. At temperatures below about –35 to –40°C, soluble nuclei outnumbered insoluble nuclei, reflecting the transition from primarily heterogeneous to primarily homogeneous freezing as a source of anvil ice.
Kinetic isotope effects in the gas phase reactions of OH and Cl with CH3Cl, CD3Cl, and 13CH3Cl
Authors: Gola A. A. , D’Anna B. , Feilberg K. L. , Sellevåg S. R. , Bache-Andreassen L. , Nielsen C. J.
Published: April 2010

Abstract. The kinetic isotope effects in the reactions of CH3Cl, 13CH3Cl and CD3Cl with OH radicals and Cl atoms were studied in relative rate experiments at 298±2K and 1013±10mbar. The reactions were carried out in a smog chamber using long path FTIR detection and the spectroscopic data analyzed employing a non-linear least squares spectral fitting method using measured high-resolution infrared spectra as well as absorption cross sections from the HITRAN database. The reaction rates of 13CH3Cl and CD3Cl with OH and Cl were determined relative to CH3Cl as: kOH + CH3Cl/kOH + 13CH3Cl=1.059±0.008, kOH + CH3Cl/kOH + CD3Cl=3.9±0.4, kCl + CH3Cl/kCl + 13CH3Cl=1.070±0.010 and kCl + CH3Cl/kCl + CD3Cl=4.91±0.07. The uncertainties given are 2σ from the statistical analyses and do not include possible systematic errors. The unusually large 13C kinetic isotope effect in the OH reaction of CH3Cl has important implications for the global emission inventory of CH3Cl.
Evidences of thin cirrus clouds in the stratosphere at mid-latitudes
Authors: Keckhut P. , Hauchecorne A. , Bekki S. , Colette A. , David C. , Jumelet J.
Published: April 2010

Abstract. This study is devoted to the possible presence of cirrus clouds in the stratosphere. Three months of lidar data collected in the south of France (44° N) for detection of stratospheric cirrus are carefully analyzed. Most of the cirrus clouds appear to be located in the troposphere below the dynamical tropopause even when the cloud top is close to the thermal tropopause. Two cirrus are found to be unambiguously located well above the local dynamical tropopause. According to high-resolution PV advection calculations, these two clouds are observed inside air masses that originate from the tropical regions and are then transported rapidly to mid-latitudes through isentropic transport. The air mass history for one case is investigated with a 3-D trajectory model. The back-plumes indicate that the air mass, moist with respect to typical stratospheric air, was transported from the subtropical troposphere to the lowermost stratosphere in 4 days before detection above France. A continuous cooling of 5–10° along the trajectory took place during its transit. This cooling could have been partly responsible for the thin cirrus layer detected.
Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry – Part I: quantification, shape-related collection efficiency, and comparison with collocated instruments
Authors: Salcedo D. , Dzepina K. , Onasch T. B. , Canagaratna M. R. , Zhang Q. , Huffman A.. R. , DeCarlo P. F. , Jayne J. T. , Mortimer P. , Worsnop D. R. , Kolb C. E. , Johnson K. S. , Zuberi B. , Marr L. C. , Molina L. T. , Molina M. J. , Bernabé R. M. , Cardenas B. , Márquez C. , Gaffney J. S. , Marley N. A. , Laskin A. , Shutthanandan V. , Jimenez J. L.
Published: April 2010

Abstract. An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at the CENICA Supersite, while another was deployed in the Aerodyne Mobile Laboratory (AML) during the Mexico City Metropolitan Area field study (MCMA-2003) from 31 March–4 May 2003 to investigate particle concentrations, sources, and processes. This is the first of a series of papers reporting the AMS results from this campaign. The AMS provides real time information on mass concentration and composition of the non-refractory species in particulate matter less than 1 µm (NR-PM1) with high time and size-resolution. For the first time, we report field results from a beam width probe, which was used to study the shape and mixing state of the particles and to quantify potential losses of irregular particles due to beam broadening inside the AMS. Data from this probe show that no significant amount of irregular particles was lost due to excessive beam broadening. A comparison of the CENICA and AML AMSs measurements is presented, being the first published intercomparison between two quadrupole AMSs. The speciation, and mass concentrations reported by the two AMSs compared relatively well. The differences found are likely due to the different inlets used in both instruments. In order to account for the refractory material in the aerosol, we also present measurements of Black Carbon (BC) using an aethalometer and an estimate of the aerosol soil component obtained from Proton-Induced X-ray Emission Spectrometry (PIXE) analysis of impactor substrates. Comparisons of AMS + BC + soil mass concentration with other collocated particle instruments (a LASAIR Optical Particle Counter, a Tapered Element Oscillating Microbalance (TEOM) and a DustTrak Aerosol Monitor) are also presented. The comparisons show that the AMS + BC + soil mass concentration during MCMA-2003 is a good approximation to the total PM2.5 mass concentration.
The mean meridional circulation and midlatitude ozone buildup
Authors: Nikulin G. , Karpechko A.
Published: April 2010

Abstract. The development of wintertime ozone buildup over the Northern Hemisphere (NH) midlatitudes and its connection with the mean meridional circulation in the stratosphere are examined statistically on a monthly basis from October to March (1980–2002). The ozone buildup begins locally in October with positive ozone tendencies over the North Pacific, which spread eastward and westward in November and finally cover all midlatitudes in December. During October–January a longitudinal distribution of the ozone tendencies mirrors a structure of quasi-stationary planetary waves in the lower stratosphere and has less similarity with this structure in February–March when chemistry begins to play a more important role. From November to March, zonal mean ozone tendencies (50°–60° N) show strong correlation (|r|=0.7) with different parameters used as proxies of the mean meridional circulation, namely: eddy heat flux, the vertical residual velocity (diabatically-derived) and temperature tendency. The correlation patterns between ozone tendency and the vertical residual velocity or temperature tendency are more homogeneous from month to month than ones for eddy heat flux. A partial exception is December when correlation is strong only for the vertical residual velocity. In October zonal mean ozone tendencies have no coupling with the proxies. However, positive tendencies averaged over the North Pacific correlate well, with all of them suggesting that intensification of northward ozone transport starts locally over the Pacific already in October. We show that the NH midlatitude ozone buildup has stable statistical relation with the mean meridional circulation in all months from October to March and half of the interannual variability in monthly ozone tendencies can be explained by applying different proxies of the mean meridional circulation.
Validation of the Martilli’s Urban Boundary Layer Scheme with measurements from two mid-latitude European cities
Authors: Hamdi R. , Schayes G.
Published: April 2010

Abstract. The Martilli's urban parameterization scheme is improved and implemented in a mesoscale model in order to take into account the typical effects of a real city on the air temperature near the ground and on the surface exchange fluxes. The mesoscale model is run on a single column using atmospheric data and radiation recorded above roof level as forcing. Here, the authors validate the Martilli's urban boundary layer scheme using measurements from two mid-latitude European cities: Basel, Switzerland and Marseilles, France. For Basel, the model performance is evaluated with observations of canyon temperature, surface radiation, and energy balance fluxes obtained during the Basel urban boundary layer experiment (BUBBLE). The results show that the urban parameterization scheme is able to reproduce the generation of the Urban Heat Island (UHI) effect over urban area and represents correctly most of the behavior of the fluxes typical of the city center of Basel, including the large heat uptake by the urban fabric and the positive sensible heat flux at night. For Marseilles, the model performance is evaluated with observations of surface temperature, canyon temperature, surface radiation, and energy balance fluxes collected during the field experiments to constrain models of atmospheric pollution and transport of emissions (ESCOMPTE) and its urban boundary layer (UBL) campaign. At both urban sites, vegetation cover is less than 20%, therefore, particular attention was directed to the ability of the Martilli's urban boundary layer scheme to reproduce the observations for the Marseilles city center, where the urban parameters and the synoptic forcing are totally different from Basel. Evaluation of the model with wall, road, and roof surface temperatures gave good results. The model correctly simulates the net radiation, canyon temperature, and the partitioning between the turbulent and storage heat fluxes.
Chemical ozone loss in the Arctic winter 2002/2003 determined with Match
Authors: Streibel M. , Rex M. , von der Gathen P. , Lehmann R. , Harris N. R. P. , Braathen G. O. , Reimer E. , Deckelmann H. , Chipperfield M. , Millard G. , Allaart M. , Andersen S. B. , Claude H. , Davies J. , De Backer H. , Dier H. , Dorokov V. , Fast H. , Gerding M. , Kyrö E. , Litynska Z. , Moore D. , Moran E. , Nagai T. , Nakane H. , Parrondo C. , Skrivankova P. , Stübi R. , Vaughan G. , Viatte P. , Yushkov V.
Published: April 2010

Abstract. The Match technique was used to determine chemically induced ozone loss inside the stratospheric vortex during the Arctic winter 2002/2003. From end of November 2002, which is the earliest start of a Match campaign ever, until end of March 2003 approximately 800 ozonesondes were launched from 30 stations in the Arctic and mid latitudes. Ozone loss rates were quantified from the beginning of December until mid of March in the vertical region of 400–550 K potential temperature. In December ozone destruction rates varied between 10–15 ppbv/day depending on height. Maximum loss rates around 35 ppbv/day were reached during late January. Afterwards ozone loss rates decreased until mid-March when the final warming of the vortex began and measurements for the campaign were no longer possible. In the period of 2 December 2002 to 16 March 2003 the accumulated ozone loss reduced the partial ozone column of 400–500 K potential temperature by 56±4 DU. The sensitivity of the results on recent improvements of the approach has been tested.