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- ItemLong-term cloud condensation nuclei number concentration, particle number size distribution and chemical composition measurements at regionally representative observatories(Katlenburg-Lindau : EGU, 2018) Schmale, Julia; Henning, Silvia; Decesari, Stefano; Henzing, Bas; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Pöhlker, Mira L.; Brito, Joel; Bougiatioti, Aikaterini; Kristensson, Adam; Kalivitis, Nikos; Stavroulas, Iasonas; Carbone, Samara; Jefferson, Anne; Park, Minsu; Schlag, Patrick; Iwamoto, Yoko; Aalto, Pasi; Äijälä, Mikko; Bukowiecki, Nicolas; Ehn, Mikael; Frank, Göran; Fröhlich, Roman; Frumau, Arnoud; Herrmann, Erik; Herrmann, Hartmut; Holzinger, Rupert; Kos, Gerard; Kulmala, Markku; Mihalopoulos, Nikolaos; Nenes, Athanasios; O'Dowd, Colin; Petäjä, Tuukka; Picard, David; Pöhlker, Christopher; Pöschl, Ulrich; Poulain, Laurent; Prévôt, André Stephan Henry; Swietlicki, Erik; Andreae, Meinrat O.; Artaxo, Paulo; Wiedensohler, Alfred; Ogren, John; Matsuki, Atsushi; Yum, Seong Soo; Stratmann, Frank; Baltensperger, Urs; Gysel, MartinAerosol-cloud interactions (ACI) constitute the single largest uncertainty in anthropogenic radiative forcing. To reduce the uncertainties and gain more confidence in the simulation of ACI, models need to be evaluated against observations, in particular against measurements of cloud condensation nuclei (CCN). Here we present a data set - ready to be used for model validation - of long-term observations of CCN number concentrations, particle number size distributions and chemical composition from 12 sites on 3 continents. Studied environments include coastal background, rural background, alpine sites, remote forests and an urban surrounding. Expectedly, CCN characteristics are highly variable across site categories. However, they also vary within them, most strongly in the coastal background group, where CCN number concentrations can vary by up to a factor of 30 within one season. In terms of particle activation behaviour, most continental stations exhibit very similar activation ratios (relative to particles 20nm) across the range of 0.1 to 1.0% supersaturation. At the coastal sites the transition from particles being CCN inactive to becoming CCN active occurs over a wider range of the supersaturation spectrum. Several stations show strong seasonal cycles of CCN number concentrations and particle number size distributions, e.g. at Barrow (Arctic haze in spring), at the alpine stations (stronger influence of polluted boundary layer air masses in summer), the rain forest (wet and dry season) or Finokalia (wildfire influence in autumn). The rural background and urban sites exhibit relatively little variability throughout the year, while short-term variability can be high especially at the urban site. The average hygroscopicity parameter, calculated from the chemical composition of submicron particles was highest at the coastal site of Mace Head (0.6) and lowest at the rain forest station ATTO (0.2-0.3). We performed closure studies based on -Köhler theory to predict CCN number concentrations. The ratio of predicted to measured CCN concentrations is between 0.87 and 1.4 for five different types of . The temporal variability is also well captured, with Pearson correlation coefficients exceeding 0.87. Information on CCN number concentrations at many locations is important to better characterise ACI and their radiative forcing. But long-term comprehensive aerosol particle characterisations are labour intensive and costly. Hence, we recommend operating migrating-CCNCs to conduct collocated CCN number concentration and particle number size distribution measurements at individual locations throughout one year at least to derive a seasonally resolved hygroscopicity parameter. This way, CCN number concentrations can only be calculated based on continued particle number size distribution information and greater spatial coverage of long-term measurements can be achieved.
- ItemThe impact of biomass burning and aqueous-phase processing on air quality: A multi-year source apportionment study in the Po Valley, Italy(Katlenburg-Lindau : EGU, 2020) Paglione, Marco; Gilardoni, Stefania; Rinaldi, Matteo; Decesari, Stefano; Zanca, Nicola; Sandrini, Silvia; Giulianelli, Lara; Bacco, Dimitri; Ferrari, Silvia; Poluzzi, Vanes; Scotto, Fabiana; Trentini, Arianna; Poulain, Laurent; Herrmann, Hartmut; Wiedensohler, Alfred; Canonaco, Francesco; Prévôt, André S.H.; Massoli, Paola; Carbone, Claudio; Facchini, Maria Cristina; Fuzzi, SandroThe Po Valley (Italy) is a well-known air quality hotspot characterized by particulate matter (PM) levels well above the limit set by the European Air Quality Directive and by the World Health Organization, especially during the colder season. In the framework of Emilia-Romagna regional project "Supersito", the southern Po Valley submicron aerosol chemical composition was characterized by means of high-resolution aerosol mass spectroscopy (HR-AMS) with the specific aim of organic aerosol (OA) characterization and source apportionment. Eight intensive observation periods (IOPs) were carried out over 4 years (from 2011 to 2014) at two different sites (Bologna, BO, urban background, and San Pietro Capofiume, SPC, rural background), to characterize the spatial variability and seasonality of the OA sources, with a special focus on the cold season. On the multi-year basis of the study, the AMS observations show that OA accounts for averages of 45 ± 8 % (ranging from 33 % to 58 %) and 46 ± 7 % (ranging from 36 % to 50 %) of the total non-refractory submicron particle mass (PM1-NR) at the urban and rural sites, respectively. Primary organic aerosol (POA) comprises biomass burning (23±13 % of OA) and fossil fuel (12±7 %) contributions with a marked seasonality in concentration. As expected, the biomass burning contribution to POA is more significant at the rural site (urban / rural concentration ratio of 0.67), but it is also an important source of POA at the urban site during the cold season, with contributions ranging from 14 % to 38 % of the total OA mass. Secondary organic aerosol (SOA) contributes to OA mass to a much larger extent than POA at both sites throughout the year (69 ± 16 % and 83 ± 16 % at the urban and rural sites, respectively), with important implications for public health. Within the secondary fraction of OA, the measurements highlight the importance of biomass burning aging products during the cold season, even at the urban background site. This biomass burning SOA fraction represents 14 %-44 % of the total OA mass in the cold season, indicating that in this region a major contribution of combustion sources to PM mass is mediated by environmental conditions and atmospheric reactivity. © 2020 Author(s).
- ItemDevelopment of a protocol for the auto-generation of explicit aqueous-phase oxidation schemes of organic compounds(Katlenburg-Lindau : EGU, 2019) Bräuer, Peter; Mouchel-Vallon, Camille; Tilgner, Andreas; Mutzel, Anke; Böge, Olaf; Rodigast, Maria; Poulain, Laurent; van Pinxteren, Dominik; Wolke, Ralf; Aumont, Bernard; Herrmann, HartmutThis paper presents a new CAPRAM-GECKOA protocol for mechanism auto-generation of aqueous-phase organic processes. For the development, kinetic data in the literature were reviewed and a database with 464 aqueousphase reactions of the hydroxyl radical with organic compounds and 130 nitrate radical reactions with organic compounds has been compiled and evaluated. Five different methods to predict aqueous-phase rate constants have been evaluated with the help of the kinetics database: gas-aqueous phase correlations, homologous series of various compound classes, radical reactivity comparisons, Evans-Polanyi-type correlations, and structure-activity relationships (SARs). The quality of these prediction methods was tested as well as their suitability for automated mechanism construction. Based on this evaluation, SARs form the basis of the new CAPRAM-GECKO-A protocol. Evans-Polanyi-type correlations have been advanced to consider all available H atoms in a molecule besides the H atoms with only the weakest bond dissociation enthalpies (BDEs). The improved Evans- Polanyi-type correlations are used to predict rate constants for aqueous-phase NO3 and organic compounds reactions. Extensive tests have been performed on essential parameters and on highly uncertain parameters with limited experimental data. These sensitivity studies led to further improvements in the new CAPRAM-GECKO-A protocol but also showed current limitations. Biggest uncertainties were observed in uptake processes and the estimation of Henry's law coefficients as well as radical chemistry, in particular the degradation of alkoxy radicals. Previous estimation methods showed several deficits, which impacted particle growth. For further evaluation, a 1,3,5-trimethylbenzene oxidation experiment has been performed in the aerosol chamber "Leipziger Aerosolkammer" (LEAK) at high relative humidity conditions and compared to a multiphase mechanism using the Master Chemical Mechanism (MCMv3.2) in the gas phase and using a methylglyoxal oxidation scheme of about 600 reactions generated with the new CAPRAM-GECKO-A protocol in the aqueous phase. While it was difficult to evaluate single particle constituents due to concentrations close to the detection limits of the instruments applied, the model studies showed the importance of aqueous-phase chemistry in respect to secondary organic aerosol (SOA) formation and particle growth. The new protocol forms the basis for further CAPRAM mechanism development towards a new version 4.0. Moreover, it can be used as a supplementary tool for aerosol chambers to design and analyse experiments of chemical complexity and help to understand them on a molecular level. © 2019 Author(s).
- ItemThe second ACTRIS inter-comparison (2016) for Aerosol Chemical Speciation Monitors (ACSM): Calibration protocols and instrument performance evaluations(Philadelphia, Pa.: Taylor & Francis, 2019) Freney, Evelyn; Zhang, Yunjiang; Croteau, Philip; Amodeo, Tanguy; Williams, Leah; Truong, François; Petit, Jean-Eudes; Sciare, Jean; Sarda-Esteve, Roland; Bonnaire, Nicolas; Arumae, Tarvo; Aurela, Minna; Bougiatioti, Aikaterini; Mihalopoulos, Nikolaos; Coz, Esther; Artinano, Begoña; Crenn, Vincent; Elste, Thomas; Heikkinen, Liine; Poulain, Laurent; Wiedensohler, Alfred; Herrmann, Hartmut; Priestman, Max; Alastuey, Andres; Stavroulas, Iasonas; Tobler, Anna; Vasilescu, Jeni; Zanca, Nicola; Canagaratna, Manjula; Carbone, Claudio; Flentje, Harald; Green, David; Maasikmets, Marek; Marmureanu, Luminita; Cruz Minguillon, Maria; Prevot, Andre S.H.; Gros, Valerie; Jayne, John; Favez, OlivierThis work describes results obtained from the 2016 Aerosol Chemical Speciation Monitor (ACSM) intercomparison exercise performed at the Aerosol Chemical Monitor Calibration Center (ACMCC, France). Fifteen quadrupole ACSMs (Q_ACSM) from the European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases (ACTRIS) network were calibrated using a new procedure that acquires calibration data under the same operating conditions as those used during sampling and hence gets information representative of instrument performance. The new calibration procedure notably resulted in a decrease in the spread of the measured sulfate mass concentrations, improving the reproducibility of inorganic species measurements between ACSMs as well as the consistency with co-located independent instruments. Tested calibration procedures also allowed for the investigation of artifacts in individual instruments, such as the overestimation of m/z 44 from organic aerosol. This effect was quantified by the m/z (mass-to-charge) 44 to nitrate ratio measured during ammonium nitrate calibrations, with values ranging from 0.03 to 0.26, showing that it can be significant for some instruments. The fragmentation table correction previously proposed to account for this artifact was applied to the measurements acquired during this study. For some instruments (those with high artifacts), this fragmentation table adjustment led to an “overcorrection” of the f44 (m/z 44/Org) signal. This correction based on measurements made with pure NH4NO3, assumes that the magnitude of the artifact is independent of chemical composition. Using data acquired at different NH4NO3 mixing ratios (from solutions of NH4NO3 and (NH4)2SO4) we observe that the magnitude of the artifact varies as a function of composition. Here we applied an updated correction, dependent on the ambient NO3 mass fraction, which resulted in an improved agreement in organic signal among instruments. This work illustrates the benefits of integrating new calibration procedures and artifact corrections, but also highlights the benefits of these intercomparison exercises to continue to improve our knowledge of how these instruments operate, and assist us in interpreting atmospheric chemistry. © 2019, © 2019 Author(s). Published with license by Taylor & Francis Group, LLC.