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- ItemHigh number concentrations of transparent exopolymer particles in ambient aerosol particles and cloud water – a case study at the tropical Atlantic Ocean(Katlenburg-Lindau : EGU, 2022) van Pinxteren, Manuela; Robinson, Tiera-Brandy; Zeppenfeld, Sebastian; Gong, Xianda; Bahlmann, Enno; Fomba, Khanneh Wadinga; Triesch, Nadja; Stratmann, Frank; Wurl, Oliver; Engel, Anja; Wex, Heike; Herrmann, HartmutTransparent exopolymer particles (TEPs) exhibit the properties of gels and are ubiquitously found in the world oceans. TEPs may enter the atmosphere as part of sea-spray aerosol. Here, we report number concentrations of TEPs with a diameter >4.5 μm, hence covering a part of the supermicron particle range, in ambient aerosol and cloud water samples from the tropical Atlantic Ocean as well as in generated aerosol particles using a plunging waterfall tank that was filled with the ambient seawater. The ambient TEP concentrations ranged between 7×102 and 3×104 #TEP m-3 in the aerosol particles and correlations with sodium (Na+) and calcium (Ca2+) (R2=0.5) suggested some contribution via bubble bursting. Cloud water TEP concentrations were between 4×106 and 9×106 #TEP L-1 and, according to the measured cloud liquid water content, corresponding to equivalent air concentrations of 2-4 × 103 #TEP m-3. Based on Na+ concentrations in seawater and in the atmosphere, the enrichment factors for TEPs in the atmosphere were calculated. The tank-generated TEPs were enriched by a factor of 50 compared with seawater and, therefore, in-line with published enrichment factors for supermicron organic matter in general and TEPs specifically. TEP enrichment in the ambient atmosphere was on average 1×103 in cloud water and 9×103 in ambient aerosol particles and therefore about two orders of magnitude higher than the corresponding enrichment from the tank study. Such high enrichment of supermicron particulate organic constituents in the atmosphere is uncommon and we propose that atmospheric TEP concentrations resulted from a combination of enrichment during bubble bursting transfer from the ocean and a secondary TEP in-situ formation in atmospheric phases. Abiotic in-situ formation might have occurred from aqueous reactions of dissolved organic precursors that were present in particle and cloud water samples, whereas biotic formation involves bacteria, which were abundant in the cloud water samples. The ambient TEP number concentrations were two orders of magnitude higher than recently reported ice nucleating particle (INP) concentrations measured at the same location. As TEPs likely possess good properties to act as INPs, in future experiments it is worth studying if a certain part of TEPs contributes a fraction of the biogenic INP population.
- ItemThe acidity of atmospheric particles and clouds(Katlenburg-Lindau : EGU, 2020) Pye, Havala O.T.; Nenes, Athanasios; Alexander, Becky; Ault, Andrew P.; Barth, Mary C.; Clegg, Simon L.; Collett Jr, Jeffrey L.; Fahey, Kathleen M.; Hennigan, Christopher J.; Herrmann, Hartmut; Kanakidou, Maria; Kelly, James T.; Ku, I-Ting; McNeill, V. Faye; Riemer, Nicole; Schaefer, Thomas; Shi, Guoliang; Tilgner, Andreas; Walker, John T.; Wang, Tao; Weber, Rodney; Xing, Jia; Zaveri, Rahul A.; Zuend, AndreasAcidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semivolatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine-particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicate acidity may be relatively constant due to the semivolatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale. © 2020 Author(s).
- ItemChemical characteristics of cloud water and the impacts on aerosol properties at a subtropical mountain site in Hong Kong SAR(Katlenburg-Lindau : EGU, 2020) Li, Tao; Wang, Zhe; Wang, Yaru; Wu, Chen; Liang, Yiheng; Xia, Men; Yu, Chuan; Yun, Hui; Wang, Weihao; Wang, Yan; Guo, Jia; Herrmann, Hartmut; Wang, TaoTo investigate the cloud water chemistry and the effects of cloud processing on aerosol properties, comprehensive field observations of cloud water, aerosols, and gasphase species were conducted at a mountaintop site in Hong Kong SAR in October and November 2016. The chemical composition of cloud water including water-soluble ions, dissolved organic matter (DOM), carbonyl compounds (refer to aldehydes and acetone), carboxylic acids, and trace metals was quantified. The measured cloud water was very acidic with a mean pH of 3.63, as the ammonium (174 μeq L-1) was insufficient for neutralizing the dominant sulfate (231 μeq L-1) and nitrate (160 μeq L-1). Substantial DOM (9.3 mgC L-1) was found in cloud water, with carbonyl compounds and carboxylic acids accounting for 18% and 6% in carbon molar concentrations, respectively. Different from previous observations, concentrations of methylglyoxal (19.1 μM; μM is equal to μmol L-1) and glyoxal (6.72 μM) were higher than that of formaldehyde (1.59 μM). The partitioning of carbonyls between cloud water and the gas phase was also investigated. The measured aqueous fractions of dicarbonyls were comparable to the theoretical estimations, while significant aqueous-phase supersaturation was found for less soluble monocarbonyls. Both organics and sulfate were significantly produced in cloud water, and the aqueous formation of organics was more enhanced by photochemistry and under less acidic conditions. Moreover, elevated sulfate and organics were measured in the cloudprocessed aerosols, and they were expected to contribute largely to the increase in droplet-mode aerosol mass fraction. This study demonstrates the significant role of clouds in altering the chemical compositions and physical properties of aerosols via scavenging and aqueous chemical processing, providing valuable information about gas-cloud-aerosol interactions in subtropical and coastal regions. © 2020 Author(s). This work is distributed under the Creative Commons Attribution 4.0 License.