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- ItemPhotosensitized production of functionalized and unsaturated organic compounds at the air-sea interface(London : Nature Publishing Group, 2015) Ciuraru, Raluca; Fine, Ludovic; van Pinxteren, Manuela; D’Anna, Barbara; Herrmann, Hartmut; George, ChristianThe sea-surface microlayer (SML) has different physical, chemical and biological properties compared to the subsurface water, with an enrichment of organic matter i.e., dissolved organic matter including UV absorbing humic substances, fatty acids and many others. Here we present experimental evidence that dissolved organic matter, such as humic acids, when exposed to sunlight, can photosensitize the chemical conversion of linear saturated fatty acids at the air-water interface into unsaturated functionalized gas phase products (i.e. saturated and unsaturated aldehydes and acids, alkenes and dienes,…) which are known precursors of secondary organic aerosols. These functionalized molecules have previously been thought to be of biological origin, but here we demonstrate that abiotic interfacial photochemistry has the potential to produce such molecules. As the ocean is widely covered by the SML, this new understanding will impact on our ability to describe atmospheric chemistry in the marine environment.
- ItemEffect of varying experimental conditions on the viscosity of α-pinene derived secondary organic material(München : European Geopyhsical Union, 2016) Grayson, James W.; Zhang, Yue; Mutzel, Anke; Renbaum-Wolff, Lindsay; Böge, Olaf; Kamal, Saeid; Herrmann, Hartmut; Martin, Scot T.; Bertram, Allan K.Knowledge of the viscosity of particles containing secondary organic material (SOM) is useful for predicting reaction rates and diffusion in SOM particles. In this study we investigate the viscosity of SOM particles as a function of relative humidity and SOM particle mass concentration, during SOM synthesis. The SOM was generated via the ozonolysis of α-pinene at < 5 % relative humidity (RH). Experiments were carried out using the poke-and-flow technique, which measures the experimental flow time (τexp, flow) of SOM after poking the material with a needle. In the first set of experiments, we show that τexp, flow increased by a factor of 3600 as the RH increased from < 0.5 RH to 50 % RH, for SOM with a production mass concentration of 121 µg m−3. Based on simulations, the viscosities of the particles were between 6 × 105 and 5 × 107 Pa s at < 0.5 % RH and between 3 × 102 and 9 × 103 Pa s at 50 % RH. In the second set of experiments we show that under dry conditions τexp, flow decreased by a factor of 45 as the production mass concentration increased from 121 to 14 000 µg m−3. From simulations of the poke-and-flow experiments, the viscosity of SOM with a production mass concentration of 14 000 µg m−3 was determined to be between 4 × 104 and 1.5 × 106 Pa s compared to between 6 × 105 and 5 × 107 Pa s for SOM with a production mass concentration of 121 µg m−3. The results can be rationalized by a dependence of the chemical composition of SOM on production conditions. These results emphasize the shifting characteristics of SOM, not just with RH and precursor type, but also with the production conditions, and suggest that production mass concentration and the RH at which the viscosity was determined should be considered both when comparing laboratory results and when extrapolating these results to the atmosphere.
- ItemNitrate radicals and biogenic volatile organic compounds: Oxidation, mechanisms, and organic aerosol(München : European Geopyhsical Union, 2017) Ng, Nga Lee; Brown, Steven S.; Archibald, Alexander T.; Atlas, Elliot; Cohen, Ronald C.; Crowley, John N.; Day, Douglas A.; Donahue, Neil M.; Fry, Juliane L.; Fuchs, Hendrik; Griffin, Robert J.; Guzman, Marcelo I.; Herrmann, Hartmut; Hodzic, Alma; Iinuma, Yoshiteru; Jimenez, José L.; Kiendler-Scharr, Astrid; Lee, Ben H.; Luecken, Deborah J.; Mao, Jingqiu; McLaren, Robert; Mutzel, Anke; Osthoff, Hans D.; Ouyang, Bin; Picquet-Varrault, Benedicte; Platt, Ulrich; Pye, Havala O.T.; Rudich, Yinon; Schwantes, Rebecca H.; Shiraiwa, Manabu; Stutz, Jochen; Thornton, Joel A.; Tilgner, Andreas; Williams, Brent J.; Zaveri, Rahul A.Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO3-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry–climate models. This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO3-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO3-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.
- ItemReal-time detection of highly oxidized organosulfates and BSOA marker compounds during the F-BEACh 2014 field study(München : European Geopyhsical Union, 2017) Brüggemann, Martin; Poulain, Laurent; Held, Andreas; Stelzer, Torsten; Zuth, Christoph; Richters, Stefanie; Mutzel, Anke; van Pinxteren, Dominik; Iinuma, Yoshiteru; Katkevica, Sarmite; Rabe, René; Herrmann, Hartmut; Hoffmann, ThorstenThe chemical composition of ambient organic aerosols was analyzed using complementary mass spectrometric techniques during a field study in central Europe in July 2014 (Fichtelgebirge – Biogenic Emission and Aerosol Chemistry, F-BEACh 2014). Among several common biogenic secondary organic aerosol (BSOA) marker compounds, 93 acidic oxygenated hydrocarbons were detected with elevated abundances and were thus attributed to be characteristic for the organic aerosol mass at the site. Monoterpene measurements exhibited median mixing ratios of 1.6 and 0.8 ppbV for in and above canopy levels respectively. Nonetheless, concentrations for early-generation oxidation products were rather low, e.g., pinic acid (c = 4.7 (±2.5) ng m−3). In contrast, high concentrations were found for later-generation photooxidation products such as 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA, c = 13.8 (±9.0) ng m−3) and 3-carboxyheptanedioic acid (c = 10.2 (±6.6) ng m−3), suggesting that aged aerosol masses were present during the campaign period. In agreement, HYSPLIT trajectory calculations indicate that most of the arriving air masses traveled long distances (> 1500 km) over land with high solar radiation. In addition, around 47 % of the detected compounds from filter sample analysis contained sulfur, confirming a rather high anthropogenic impact on biogenic emissions and their oxidation processes. Among the sulfur-containing compounds, several organosulfates, nitrooxy organosulfates, and highly oxidized organosulfates (HOOS) were tentatively identified by high-resolution mass spectrometry. Correlations among HOOS, sulfate, and highly oxidized multifunctional organic compounds (HOMs) support the hypothesis of previous studies that HOOS are formed by reactions of gas-phase HOMs with particulate sulfate. Moreover, periods with high relative humidity indicate that aqueous-phase chemistry might play a major role in HOOS production. However, for dryer periods, coinciding signals for HOOS and gas-phase peroxyradicals (RO2•) were observed, suggesting RO2• to be involved in HOOS formation.
- ItemEvidence for ambient dark aqueous SOA formation in the Po Valley, Italy(München : European Geopyhsical Union, 2016) Sullivan, Amy P.; Hodas, Natasha; Turpin, Barbara J.; Skog, Kate; Keutsch, Frank N.; Gilardoni, Stefania; Paglione, Marco; Rinaldi, Matteo; Decesari, Stefano; Facchini, Maria Cristina; Poulain, Laurent; Herrmann, Hartmut; Wiedensohler, Alfred; Nemitz, Eiko; Twigg, Marsailidh M.; Collett, Jeffrey L. Jr.Laboratory experiments suggest that water-soluble products from the gas-phase oxidation of volatile organic compounds can partition into atmospheric waters where they are further oxidized to form low volatility products, providing an alternative route for oxidation in addition to further oxidation in the gas phase. These products can remain in the particle phase after water evaporation, forming what is termed as aqueous secondary organic aerosol (aqSOA). However, few studies have attempted to observe ambient aqSOA. Therefore, a suite of measurements, including near-real-time WSOC (water-soluble organic carbon), inorganic anions/cations, organic acids, and gas-phase glyoxal, were made during the PEGASOS (Pan-European Gas-AeroSOls-climate interaction Study) 2012 campaign in the Po Valley, Italy, to search for evidence of aqSOA. Our analysis focused on four periods: Period A on 19–21 June, Period B on 30 June and 1–2 July, Period C on 3–5 July, and Period D on 6–7 July to represent the first (Period A) and second (Periods B, C, and D) halves of the study. These periods were picked to cover varying levels of WSOC and aerosol liquid water. In addition, back trajectory analysis suggested all sites sampled similar air masses on a given day. The data collected during both periods were divided into times of increasing relative humidity (RH) and decreasing RH, with the aim of diminishing the influence of dilution and mixing on SOA concentrations and other measured variables. Evidence for local aqSOA formation was only observed during Period A. When this occurred, there was a correlation of WSOC with organic aerosol (R2 = 0.84), aerosol liquid water (R2 = 0.65), RH (R2 = 0.39), and aerosol nitrate (R2 = 0.66). Additionally, this was only observed during times of increasing RH, which coincided with dark conditions. Comparisons of WSOC with oxygenated organic aerosol (OOA) factors, determined from application of positive matrix factorization analysis on the aerosol mass spectrometer observations of the submicron non-refractory organic particle composition, suggested that the WSOC differed in the two halves of the study (Period A WSOC vs. OOA-2 R2 = 0.83 and OOA-4 R2 = 0.04, whereas Period C WSOC vs. OOA-2 R2 = 0.03 and OOA-4 R2 = 0.64). OOA-2 had a high O ∕ C (oxygen ∕ carbon) ratio of 0.77, providing evidence that aqueous processing was occurring during Period A. Key factors of local aqSOA production during Period A appear to include air mass stagnation, which allows aqSOA precursors to accumulate in the region; the formation of substantial local particulate nitrate during the overnight hours, which enhances water uptake by the aerosol; and the presence of significant amounts of ammonia, which may contribute to ammonium nitrate formation and subsequent water uptake and/or play a more direct role in the aqSOA chemistry.
- ItemThe Arctic Cloud Puzzle: Using ACLOUD/PASCAL Multiplatform Observations to Unravel the Role of Clouds and Aerosol Particles in Arctic Amplification(Boston, Mass. : ASM, 2019) Wendisch, Manfred; Macke, Andreas; Ehrlich, André; Lüpkes, Christof; Mech, Mario; Chechin, Dmitry; Dethloff, Klaus; Velasco, Carola Barrientos; Bozem, Heiko; Brückner, Marlen; Clemen, Hans-Christian; Crewell, Susanne; Donth, Tobias; Dupuy, Regis; Ebell, Kerstin; Egerer, Ulrike; Engelmann, Ronny; Engler, Christa; Eppers, Oliver; Gehrmann, Martin; Gong, Xianda; Gottschalk, Matthias; Gourbeyre, Christophe; Griesche, Hannes; Hartmann, Jörg; Hartmann, Markus; Heinold, Bernd; Herber, Andreas; Herrmann, Hartmut; Heygster, Georg; Hoor, Peter; Jafariserajehlou, Soheila; Jäkel, Evelyn; Järvinen, Emma; Jourdan, Olivier; Kästner, Udo; Kecorius, Simonas; Knudsen, Erlend M.; Köllner, Franziska; Kretzschmar, Jan; Lelli, Luca; Leroy, Delphine; Maturilli, Marion; Mei, Linlu; Mertes, Stephan; Mioche, Guillaume; Neuber, Roland; Nicolaus, Marcel; Nomokonova, Tatiana; Notholt, Justus; Palm, Mathias; van Pinxteren, Manuela; Quaas, Johannes; Richter, Philipp; Ruiz-Donoso, Elena; Schäfer, Michael; Schmieder, Katja; Schnaiter, Martin; Schneider, Johannes; Schwarzenböck, Alfons; Seifert, Patric; Shupe, Matthew D.; Siebert, Holger; Spreen, Gunnar; Stapf, Johannes; Stratmann, Frank; Vogl, Teresa; Welti, André; Wex, Heike; Wiedensohler, Alfred; Zanatta, Marco; Zeppenfeld, SebastianClouds play an important role in Arctic amplification. This term represents the recently observed enhanced warming of the Arctic relative to the global increase of near-surface air temperature. However, there are still important knowledge gaps regarding the interplay between Arctic clouds and aerosol particles, and surface properties, as well as turbulent and radiative fluxes that inhibit accurate model simulations of clouds in the Arctic climate system. In an attempt to resolve this so-called Arctic cloud puzzle, two comprehensive and closely coordinated field studies were conducted: the Arctic Cloud Observations Using Airborne Measurements during Polar Day (ACLOUD) aircraft campaign and the Physical Feedbacks of Arctic Boundary Layer, Sea Ice, Cloud and Aerosol (PASCAL) ice breaker expedition. Both observational studies were performed in the framework of the German Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC) project. They took place in the vicinity of Svalbard, Norway, in May and June 2017. ACLOUD and PASCAL explored four pieces of the Arctic cloud puzzle: cloud properties, aerosol impact on clouds, atmospheric radiation, and turbulent dynamical processes. The two instrumented Polar 5 and Polar 6 aircraft; the icebreaker Research Vessel (R/V) Polarstern; an ice floe camp including an instrumented tethered balloon; and the permanent ground-based measurement station at Ny-Ålesund, Svalbard, were employed to observe Arctic low- and mid-level mixed-phase clouds and to investigate related atmospheric and surface processes. The Polar 5 aircraft served as a remote sensing observatory examining the clouds from above by downward-looking sensors; the Polar 6 aircraft operated as a flying in situ measurement laboratory sampling inside and below the clouds. Most of the collocated Polar 5/6 flights were conducted either above the R/V Polarstern or over the Ny-Ålesund station, both of which monitored the clouds from below using similar but upward-looking remote sensing techniques as the Polar 5 aircraft. Several of the flights were carried out underneath collocated satellite tracks. The paper motivates the scientific objectives of the ACLOUD/PASCAL observations and describes the measured quantities, retrieved parameters, and the applied complementary instrumentation. Furthermore, it discusses selected measurement results and poses critical research questions to be answered in future papers analyzing the data from the two field campaigns.
- ItemThe influence of impactor size cut-off shift caused by hygroscopic growth on particulate matter loading and composition measurements(Oxford [u.a.] : Elsevier, 2018) Chen, Ying; Wild, Oliver; Wang, Yu; Ran, Liang; Teich, Monique; Größ, Johannes; Wang, Lina; Spindler, Gerald; Herrmann, Hartmut; van Pinxteren, Dominik; McFiggans, Gordon; Wiedensohler, AlfredThe mass loading and composition of atmospheric particles are important in determining their climate and health effects, and are typically measured by filter sampling. However, particle sampling under ambient conditions can lead to a shift in the size cut-off threshold induced by hygroscopic growth, and the influence of this on measurement of particle loading and composition has not been adequately quantified. Here, we propose a method to assess this influence based on κ-Köhler theory. A global perspective is presented based on previously reported annual climatological values of hygroscopic properties, meteorological parameters and particle volume size distributions. Measurements at background sites in Europe may be more greatly influenced by the cut-off shift than those from other continents, with a median influence of 10–20% on the total mass of sampled particles. However, the influence is generally much smaller (<7%) at urban sites, and is negligible for dust and particles in the Arctic. Sea-salt particles experience the largest influence (median value ∼50%), resulting from their large size, high hygroscopicity and the high relative humidity (RH) in marine air-masses. We estimate a difference of ∼30% in this influence of sea-salt particle sampling between relatively dry (RH = 60%) and humid (RH = 90%) conditions. Given the variation in the cut-off shift in different locations and at different times, a consistent consideration of this influence using the approach we introduce here is critical for observational studies of the long-term and spatial distribution of particle loading and composition, and crucial for robust validation of aerosol modules in modelling studies.
- ItemContributions of nitrated aromatic compounds to the light absorption of water-soluble and particulate brown carbon in different atmospheric environments in Germany and China(München : European Geopyhsical Union, 2017) Teich, Monique; van Pinxteren, Dominik; Wang, Michael; Kecorius, Simonas; Wang, Zhibin; Müller, Thomas; Močnik, Griša; Herrmann, HartmutThe relative contributions of eight nitrated aromatic compounds (NACs: nitrophenols and nitrated salicylic acids) to the light absorption of aqueous particle extracts and particulate brown carbon were determined from aerosol particle samples collected in Germany and China. High-volume filter samples were collected during six campaigns, performed at five locations in two seasons: (I) two campaigns with strong influence of biomass-burning (BB) aerosol at the TROPOS institute (winter, 2014, urban background, Leipzig, Germany) and the Melpitz research site (winter, 2014, rural background); (II) two campaigns with strong influence from biogenic emissions at Melpitz (summer, 2014) and the forest site Waldstein (summer, 2014, Fichtelgebirge, Germany); and (III) two CAREBeijing-NCP campaigns at Xianghe (summer, 2013, anthropogenic polluted background) and Wangdu (summer, 2014, anthropogenic polluted background with a distinct BB episode), both in the North China Plain. The filter samples were analyzed for NAC concentrations and the light absorption of aqueous filter extracts was determined. Light absorption properties of particulate brown carbon were derived from a seven-wavelength aethalometer during the campaigns at TROPOS (winter) and Waldstein (summer). The light absorption of the aqueous filter extracts was found to be pH dependent, with larger values at higher pH. In general, the aqueous light absorption coefficient (Abs370) ranged from 0.21 to 21.8 Mm−1 under acidic conditions and 0.63 to 27.2 Mm−1 under alkaline conditions, over all campaigns. The observed mass absorption efficiency (MAE370) was in a range of 0.10–1.79 m2 g−1 and 0.24–2.57 m2 g−1 for acidic and alkaline conditions, respectively. For MAE370 and Abs370, the observed values were higher in winter than in summer, in agreement with other studies. The lowest MAE was observed for the Waldstein (summer) campaign (average of 0.17 ± 0.03 m2 g−1), indicating that freshly emitted biogenic aerosols are only weakly absorbing. In contrast, a strong relationship was found between the light absorption properties and the concentrations of levoglucosan, corroborating findings from other studies. Regarding the particulate light absorption at 370 nm, a mean particulate light absorption coefficient babs, 370 of 54 Mm−1 and 6.0 Mm−1 was determined for the TROPOS (winter) and Waldstein (summer) campaigns, respectively, with average contributions of particulate brown carbon to babs, 370 of 46 % at TROPOS (winter) and 15 % at Waldstein (summer). Thus, the aethalometer measurements support the findings from aqueous filter extracts of only weakly absorbing biogenic aerosols in comparison to the more polluted and BB influenced aerosol at TROPOS (winter). The mean contribution of NACs to the aqueous extract light absorption over all campaigns ranged from 0.10 to 1.25 % under acidic conditions and 0.13 to 3.71 % under alkaline conditions. The high variability among the measurement sites showed that the emission strengths of light-absorbing compounds and the composition of brown carbon were very different for each site. The mean contribution of NACs to the particulate brown carbon light absorption was 0.10 ± 0.06 % (acidic conditions) and 0.13 ± 0.09 % (alkaline conditions) during the Waldstein (summer) campaign and 0.25 ± 0.21 % (acidic conditions) and 1.13 ± 1.03 % (alkaline conditions) during the TROPOS (winter) campaign.
- ItemTrends of pollution in rain over East Germany caused by changing emissions(Milton Park : Taylor & Francis, 2016) Marquardt, Wolfgang; Brüggemann, Erika; Auel, Renate; Herrmann, Hartmut; Möller, DetlevLarge changes in emissions also cause a significant change in pollutant concentrations in rain water. The influence of these changes on pollutant concentrations in rain water and wet deposition were investigated in different regions and time periods from 1983 to 1999 in East Germany. Initially, this period is characterized by large emissions of SO2(about 5400 kt a−1), NOx(about 750 kt a−1), and dust (about 2000 kt a−1) at the end of the 1980s. After the reunification of Germany in 1990 and restructuring of industry and agriculture, emissions drastically decreased. For example, from 1990 to 1998 in Saxony emissions of SO2, NOx and dust decreased by 84, 44 and 97%, respectively. Alkaline components also strongly decreased through efficient dust removal, while no desulphurization was used in flue gases of power and heating plants. As a consequence, the mean acidity of precipitation strongly rose by a factor of three from before 1990 up to 1995 (the mean pH value in 1995 was about 3.9, with minimum values down to 3.6). In 1996 desulphurization techniques were established in power plants and resulted in an increase of pH values to the level in the period from 1983 to 1989/1990. The results for ionic composition (Cl−, NO3−, SO42−, Na+, NH4+, K+, Ca2+, and Mg2+, the pH value (acidity), and conductivity) are based on precipitation samples collected in periods > 4 h. The data were classified with backward trajectories and entry sectors which are characterized by similar emissions and/or geographical regions.
- ItemThe ocean's vital skin: Toward an integrated understanding of the sea surface microlayer(Lausanne : Frontiers Media, 2017) Engel, Anja; Bange, Hermann W.; Cunliffe, Michael; Burrows, Susannah M.; Friedrichs, Gernot; Galgani, Luisa; Herrmann, Hartmut; Hertkorn, Norbert; Johnson, Martin; Liss, Peter S.; Quinn, Patricia K.; Schartau, Markus; Soloviev, Alexander; Stolle, Christian; Upstill-Goddard, Robert C.; van Pinxteren, Manuela; Zäncker, BirtheDespite the huge extent of the ocean's surface, until now relatively little attention has been paid to the sea surface microlayer (SML) as the ultimate interface where heat, momentum and mass exchange between the ocean and the atmosphere takes place. Via the SML, large-scale environmental changes in the ocean such as warming, acidification, deoxygenation, and eutrophication potentially influence cloud formation, precipitation, and the global radiation balance. Due to the deep connectivity between biological, chemical, and physical processes, studies of the SML may reveal multiple sensitivities to global and regional changes. Understanding the processes at the ocean's surface, in particular involving the SML as an important and determinant interface, could therefore provide an essential contribution to the reduction of uncertainties regarding ocean-climate feedbacks. This review identifies gaps in our current knowledge of the SML and highlights a need to develop a holistic and mechanistic understanding of the diverse biological, chemical, and physical processes occurring at the ocean-atmosphere interface. We advocate the development of strong interdisciplinary expertise and collaboration in order to bridge between ocean and atmospheric sciences. Although this will pose significant methodological challenges, such an initiative would represent a new role model for interdisciplinary research in Earth System sciences.