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- ItemOrganic aerosol components derived from 25 AMS data sets across Europe using a consistent ME-2 based source apportionment approach(München : European Geopyhsical Union, 2014) Crippa, M.; Canonaco, F.; Lanz, V.A.; Äijälä, M.; Allan, J.D.; Carbone, S.; Capes, G.; Ceburnis, D.; Dall'Osto, M.; Day, D.A.; DeCarlo, P.F.; Ehn, M.; Eriksson, A.; Freney, E.; Hildebrandt Ruiz, L.; Hillamo, R.; Jimenez, J.L.; Junninen, H.; Kiendler-Scharr, A.; Kortelainen, A.-M.; Kulmala, M.; Laaksonen, A.; Mensah, A.A.; Mohr, C.; Nemitz, E.; O'Dowd, C.; Ovadnevaite, J.; Pandis, S.N.; Petäjä, T.; Poulain, L.; Saarikoski, S.; Sellegri, K.; Swietlicki, E.; Tiitta, P.; Worsnop, D.R.; Baltensperger, U.; Prévôt, A.S.H.Organic aerosols (OA) represent one of the major constituents of submicron particulate matter (PM1) and comprise a huge variety of compounds emitted by different sources. Three intensive measurement field campaigns to investigate the aerosol chemical composition all over Europe were carried out within the framework of the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) and the intensive campaigns of European Monitoring and Evaluation Programme (EMEP) during 2008 (May–June and September–October) and 2009 (February–March). In this paper we focus on the identification of the main organic aerosol sources and we define a standardized methodology to perform source apportionment using positive matrix factorization (PMF) with the multilinear engine (ME-2) on Aerodyne aerosol mass spectrometer (AMS) data. Our source apportionment procedure is tested and applied on 25 data sets accounting for two urban, several rural and remote and two high altitude sites; therefore it is likely suitable for the treatment of AMS-related ambient data sets. For most of the sites, four organic components are retrieved, improving significantly previous source apportionment results where only a separation in primary and secondary OA sources was possible. Generally, our solutions include two primary OA sources, i.e. hydrocarbon-like OA (HOA) and biomass burning OA (BBOA) and two secondary OA components, i.e. semi-volatile oxygenated OA (SV-OOA) and low-volatility oxygenated OA (LV-OOA). For specific sites cooking-related (COA) and marine-related sources (MSA) are also separated. Finally, our work provides a large overview of organic aerosol sources in Europe and an interesting set of highly time resolved data for modeling purposes.
- ItemTreatment of non-ideality in the SPACCIM multiphase model - Part 1: Model development(München : European Geopyhsical Union, 2016) Rusumdar, A.J.; Wolke, R.; Tilgner, A.; Herrmann, H.Ambient tropospheric deliquesced particles generally comprise a complex mixture of electrolytes, organic compounds, and water. Dynamic modeling of physical and chemical processes in this complex matrix is challenging. Thus, up-to-date multiphase chemistry models generally do not consider non-ideal solution effects. Therefore, the present study was aimed at presenting further development of the SPACCIM (Spectral Aerosol Cloud Chemistry Interaction Model) through treatment of solution non-ideality, which has not been considered before. The present paper firstly describes the model developments including (i) the implementation of solution non-ideality in aqueous-phase reaction kinetics in the SPACCIM framework, (ii) the advancements in the coupling scheme of microphysics and multiphase chemistry and (iii) the required adjustments of the numerical schemes, especially in the sparse linear solver and the calculation of the Jacobian. Secondly, results of sensitivity investigations are outlined, aiming at the evaluation of different activity coefficient modules and the examination of the contributions of different intermolecular forces to the overall activity coefficients. Finally, first results obtained with the new model framework are presented. The SPACCIM parcel model was developed and, so far, applied for the description of aerosol–cloud interactions. To advance SPACCIM also for modeling physical and chemical processes in deliquesced particles, the solution non-ideality has to be taken into account by utilizing activities in reaction terms instead of aqueous concentrations. The main goal of the extended approach was to provide appropriate activity coefficients for solved species. Therefore, an activity coefficient module was incorporated into the kinetic model framework of SPACCIM. Based on an intercomparison of different activity coefficient models and the comparison with experimental data, the AIOMFAC approach was implemented and extended by additional interaction parameters from the literature for mixed organic–inorganic systems. Moreover, the performance and the capability of the applied activity coefficient module were evaluated by means of water activity measurements, literature data and results of other activity coefficient models. Comprehensive comparison studies showed that the SpactMod (SPACCIM activity coefficient module) is valuable for predicting the thermodynamic behavior of complex mixtures of multicomponent atmospheric aerosol particles. First simulations with a detailed chemical mechanism have demonstrated the applicability of SPACCIM-SpactMod. The simulations indicate that the treatment of solution non-ideality might be needed for modeling multiphase chemistry processes in deliquesced particles. The modeled activity coefficients imply that chemical reaction fluxes of chemical processes in deliquesced particles can be both decreased and increased depending on the particular species involved in the reactions. For key ions, activity coefficients on the order of 0.1–0.8 and a strong dependency on the charge state as well as the RH conditions are modeled, implying a lowered chemical processing of ions in concentrated solutions. In contrast, modeled activity coefficients of organic compounds are in some cases larger than 1 under deliquesced particle conditions and suggest the possibility of an increased chemical processing of organic compounds. Moreover, the model runs have shown noticeable differences in the pH values calculated with and without consideration of solution non-ideality. On average, the predicted pH values of the simulations considering solution non-ideality are −0.27 and −0.44 pH units lower under 90 and 70 % RH conditions, respectively. More comprehensive results of detailed SPACCIM-SpactMod studies on the multiphase processing in organic–inorganic mixtures of deliquesced particles are described in a companion paper.
- ItemDoppler lidar studies of heat island effects on vertical mixing of aerosols during SAMUM-2(Milton Park : Taylor & Francis, 2017) Engelmann, Ronny; Ansmann, Albert; Horn, Stefan; Seifert, Patric; Althausen, Dietrich; Tesche, Matthias; Esselborn, Michael; Fruntke, Julia; Lieke, Kirsten; Freudenthaler, Volker; Gross, SilkeA wind Doppler lidar was deployed next to three aerosol lidars during the SAMUM–2 campaign on the main island of Cape Verde. The effects of the differential heating of the island and the surrounding ocean and the orographic impact of the capital island Santiago and the small island on its luv side, Maio, are investigated. Horizontal and vertical winds were measured in the disturbed maritime boundary layer and compared to local radiosoundings. Lidar measurements from the research aircraft Falcon and a 3-D Large Eddy Simulation (LES) model were used in addition to study the heating effects on the scale of the islands. Indications are found that these effects can widely control the downward mixing from greater heights to the surface of African aerosols, mainly Saharan dust and biomass-burning smoke, which were detected in a complex layering over the Cape Verde region.
- ItemModelling lidar-relevant optical properties of complex mineral dust aerosols(Milton Park : Taylor & Francis, 2017) Gasteiger, Josef; Wiegner, Matthias; Groß, Silke; Freudenthaler, Volker; Toledano, Carlos; Tesche, Matthias; Kandler, KonradWe model lidar-relevant optical properties of mineral dust aerosols and compare the modelling results with optical properties derived from lidar measurements during the SAMUM field campaigns. The Discrete Dipole Approximation is used for optical modelling of single particles. For modelling of ensemble properties, the desert aerosol type of the OPAC aerosol dataset is extended by mixtures of absorbing and non-absorbing irregularly shaped mineral dust particles. Absorbing and non-absorbing particles are mixed to mimic the natural mineralogical inhomogeneity of dust particles. A sensitivity study reveals that the mineralogical inhomogeneity is critical for the lidar ratio at short wavelengths; it has to be considered for agreement with the observed wavelength dependence of the lidar ratio. The amount of particles with low aspect ratios (about 1.4 and lower) affects the lidar ratio at any lidar wavelength; their amount has to be low for agreement with SAMUM observations. Irregularly shaped dust particles with typical refractive indices, in general, have higher linear depolarization ratios than corresponding spheroids, and improve the agreement with the observations.
- ItemRegional modelling of Saharan dust and biomass-burning smoke, Part 2: Direct radiative forcing and atmospheric dynamic response(Milton Park : Taylor & Francis, 2017) Heinold, Bernd; Tegen, Ina; Bauer, Stefan; Wendisch, ManfredThe direct radiative forcing and dynamic atmospheric response due to Saharan dust and biomass-burning aerosol particles are presented for a case study during the SAMUM-2 field campaign in January and February 2008. The regional model system COSMO-MUSCAT is used. It allows online interaction of the computed dust and smoke load with the solar and terrestrial radiation and with the model dynamics. Model results of upward solar irradiances are evaluated against airborne radiation measurements in the Cape Verde region. The comparison shows a good agreement for the case of dust and smoke mixture. Dust and smoke particles influence the atmospheric dynamics by changing the radiative heating rates. The related pressure perturbations modify local and synoptic scale air-flow patterns. In the radiative feedback simulations, the Hadley circulation is enhanced and convergence zones occur along the Guinea coast. Thus, the smoke particles spread more than 5◦ further north and the equatorward transport is reduced. Within the convergence zones, Saharan dust and biomass-burning material are more effectively advected towards the Cape Verdes. Given the model uncertainties, the agreement between the modelled and observed aerosol distribution is locally improved when aerosol–radiation interaction is considered.
- ItemA modelling study on the activation of small Aitken-mode aerosol particles during CIME 97(Milton Park : Taylor & Francis, 2016) Gérémy, Guiléne; Wobrock, Wolfram; Flossmann, Andrea I.; Schwarzenböck, Alfons; Mertes, StephanDuring February 1997, one of the 2 observational periods of CIME (cloud ice mountain experiment), a joint field experiment funded by the European Commission, took place on the summit of the Puy de Doˆme in the centre of France. During this experiment the droplet spectra were measured with an FSSP and the aerosol particles in the drops and in the interstitial particle phase were measured with a counterflow virtual impactor and a round jet impactor inside a windtunnel. Very low aerosol particle and drop concentrations were observed and particles as small as 25 nm in diameter were found to activate. Two datasets obtained on 15 February and 17 February were used to study the activation of the small Aitken-mode particles and the spectral form of the droplet spectrum and the scavenging fraction. Numerous sensitivity studies were performed investigating the roˆ le of the number density and chemical composition of the aerosol particles. The roˆ le of mixing inside the orographic cloud was studied by using a new technique. It considers the fact that the air arriving on the summit of the Puy de Doˆme is a mixture of air of different origins. Thus, it weighs the results of a spectral scavenging model (DESCAM or EXMIX) calculated along a number of individual trajectories. The weighing function is derived from tracer and trajectory studies with a 3-dimensional mesoscale model. The model was able to reproduce the activation of aerosol particles as small as 25 nm. It was caused by the low aerosol particle number concentrations. In general, we can conclude that the variability found in the sensitivity tests of the dynamical and chemical factors allows to reproduce the shape of the observed results. As too many free parameters exit at the moment we cannot quantify the contribution of each factor studied to the observed scavenging fraction, however, it seems that dynamics dominates.