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Tong YK, Ye A. Liquid-Liquid Phase Separation in Single Suspended Aerosol Microdroplets. Anal Chem 2023; 95:12200-12208. [PMID: 37556845 DOI: 10.1021/acs.analchem.2c05605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/11/2023]
Abstract
Liquid-liquid phase separation (LLPS) is ubiquitous in ambient aerosols. This specific morphology exerts substantial impacts on the physicochemical properties and atmospheric processes of aerosols, particularly on the gas-particle mass transfer, the interfacial heterogeneous reaction, and the surface albedo. Although there are many studies on the LLPS of aerosols, a clear picture of LLPS in individual aerosols is scarce due to the experimental difficulties of trapping a single particle and mimicking the suspended state of real aerosols. Here, we investigate the phase separation in individual contactless microdroplets by a self-constructed laser tweezer/Raman spectroscopy system. The dynamic transformation of the morphology of optically trapped droplets over the course of humidity cycles is detected by the time-resolved cavity-enhanced Raman spectra. The impacts of pH and inorganic components on LLPS in aerosols are discussed. The results show that the increasing acidity can enhance the miscibility between the hydrophilic and hydrophobic phases and decrease the separation relative humidity of aerosols. Moreover, the inorganic components also have various impacts on the aerosol phase state, whose influence depends on their different salting-out capabilities. It brings possible implications on the morphology of actual atmospheric particles, particularly for those dominated by internal mixtures of inorganic and organic components.
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Affiliation(s)
- Yu-Kai Tong
- Key Laboratory for the Physics and Chemistry of Nanodevices, School of Electronics, Peking University, Beijing 100871, China
| | - Anpei Ye
- Key Laboratory for the Physics and Chemistry of Nanodevices, School of Electronics, Peking University, Beijing 100871, China
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2
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Mahrt F, Newman E, Huang Y, Ammann M, Bertram AK. Phase Behavior of Hydrocarbon-like Primary Organic Aerosol and Secondary Organic Aerosol Proxies Based on Their Elemental Oxygen-to-Carbon Ratio. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:12202-12214. [PMID: 34473474 DOI: 10.1021/acs.est.1c02697] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A large fraction of atmospheric aerosols can be characterized as primary organic aerosol (POA) and secondary organic aerosol (SOA). Knowledge of the phase behavior, that is, the number and type of phases within internal POA + SOA mixtures, is crucial to predict their effect on climate and air quality. For example, if POA and SOA form a single phase, POA will enhance the formation of SOA by providing organic mass to absorb SOA precursors. Using microscopy, we studied the phase behavior of mixtures of SOA proxies and hydrocarbon-like POA proxies at relative humidity (RH) values of 90%, 45%, and below 5%. Internal mixtures of POA and SOA almost always formed two phases if the elemental oxygen-to-carbon ratio (O/C) of the POA was less than 0.11, which encompasses a large fraction of atmospheric hydrocarbon-like POA from fossil fuel combustion. SOA proxies mixed with POA proxies having 0.11 ≤ O/C ≤ 0.29 mostly resulted in particles with one liquid phase. However, two liquid phases were also observed, depending on the type of SOA and POA surrogates, and an increase in phase-separated particles was observed when increasing the RH in this O/C range. The results have implications for predicting atmospheric SOA formation and policy strategies to reduce SOA in urban environments.
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Affiliation(s)
- Fabian Mahrt
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T1Z1 Canada
- Laboratory of Environmental Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Elli Newman
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T1Z1 Canada
| | - Yuanzhou Huang
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T1Z1 Canada
| | - Markus Ammann
- Laboratory of Environmental Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Allan K Bertram
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T1Z1 Canada
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3
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Yarolimek MR, Bookbinder HR, Coia BM, Kennemur JG. Ring-Opening Metathesis Polymerization of δ-Pinene: Well-Defined Polyolefins from Pine Sap. ACS Macro Lett 2021; 10:760-766. [PMID: 35549097 DOI: 10.1021/acsmacrolett.1c00284] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Well-controlled ring-opening metathesis polymerization (ROMP) of δ-pinene is reported. The monomer is produced through a facile, metal-free, three-step synthesis from highly abundant and sustainable α-pinene. Using Grubbs third-generation catalyst, δ-pinene undergoes ROMP to high conversion (>95%) with molar mass up to 70 kg mol-1 and narrow dispersity (<1.2). A highly regioregular propagation mechanism was concluded by NMR spectroscopic analysis that revealed a head-to-tail (HT, >95%) microstructure and high trans content (>98%). Successful ROMP is corroborated with density functional theory calculations on δ-pinene's ring strain energy (∼35 kJ mol-1). Poly(δ-pinene) has a high glass transition temperature (∼104 °C) and a unique chiral microstructure bearing gem-dimethylcyclobutane rings. Controlled ROMP also allowed the synthesis of block copolymers containing segments of poly(δ-pinene) and polynorbornene which are discussed. Finally, bulk polymerization of δ-pinene is possible, indicating a greener approach to these materials, albeit with some loss of control.
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Affiliation(s)
- Mark R. Yarolimek
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States
| | - Heather R. Bookbinder
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States
| | - Brianna M. Coia
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States
| | - Justin G. Kennemur
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States
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Ault AP. Aerosol Acidity: Novel Measurements and Implications for Atmospheric Chemistry. Acc Chem Res 2020; 53:1703-1714. [PMID: 32786333 DOI: 10.1021/acs.accounts.0c00303] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The pH of a solution is one of its most fundamental chemical properties, impacting reaction pathways and kinetics across every area of chemistry. The atmosphere is no different, with the pH of the condensed phase driving key chemical reactions that ultimately impact global climate in numerous ways. The condensed phase in the atmosphere is comprised of suspended liquid or solid particles, known as the atmospheric aerosol, which are differentiated from cloud droplets by their much smaller size (primarily <10 μm). The pH of the atmospheric aerosol can enhance certain chemical reactions leading to the formation of additional condensed phase mass from lower volatility species (secondary aerosol), alter the optical and water uptake properties of particles, and solubilize metals that can act as key nutrients in nutrient-limited ecosystems or cause oxidative stress after inhalation. However, despite the importance of aerosol acidity for climate and health, our fundamental understanding of pH has been limited due to aerosol size (by number >99% of particles are <1 μm) and complexity. Within a single atmospheric particle, there can be hundreds to thousands of distinct chemical species, varying water content, high ionic strengths, and different phases (liquid, semisolid, and solid). Making aerosol analysis even more challenging, atmospheric particles are constantly evolving through heterogeneous reactions with gases and multiphase chemistry within the condensed phase. Based on these challenges, traditional pH measurements are not feasible, and, for years, indirect and proxy methods were the most common way to estimate aerosol pH, with mixed results. However, aerosol pH needs to be incorporated into climate models to accurately determine which chemical reactions are dominant in the atmosphere. Consequently, experimental measurements that probe pH in atmospherically relevant particles are sorely needed to advance our understanding of aerosol acidity.This Account describes recent advances in measurements of aerosol particle acidity, specifically three distinct methods we developed for experimentally determining particle pH. Our acid-conjugate base method uses Raman microspectroscopy to probe an acid (e.g., HSO4-) and its conjugate base (e.g., SO42-) in individual micrometer-sized particles. Our second approach is a field-deployable colorimetric method based on pH indicators (e.g., thymol blue) and cell phone imaging to provide a simple, low-cost approach to ensemble average (or bulk) pH for particles in distinct size ranges down to a few hundred nanometers in diameter. In our third method, we monitor acid-catalyzed polymer degradation of a thin film (∼23 nm) of poly(ε-caprolactone) (PCL) on silicon by individual particles with atomic force microscopy (AFM) after inertially impacting particles of different pH. These measurements are improving our understanding of aerosol pH from a fundamental physical chemistry perspective and have led to initial atmospheric measurements. The impact of aerosol pH on key atmospheric processes, such as secondary organic aerosol (SOA) formation, is discussed. Some unique findings, such as an unexpected size dependence to aerosol pH and kinetic limitations, illustrate that particles are not always in thermodynamic equilibrium with the surrounding gas. The implications of our limited, but improving, understanding of the fundamental chemical concept of pH in the atmospheric aerosol are critical for connecting chemistry and climate.
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Affiliation(s)
- Andrew P. Ault
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
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Schmedding R, Rasool QZ, Zhang Y, Pye HOT, Zhang H, Chen Y, Surratt JD, Lopez-Hilfiker FD, Thornton JA, Goldstein AH, Vizuete W. Predicting secondary organic aerosol phase state and viscosity and its effect on multiphase chemistry in a regional-scale air quality model. ATMOSPHERIC CHEMISTRY AND PHYSICS 2020; 20:8201-8225. [PMID: 32983235 PMCID: PMC7510956 DOI: 10.5194/acp-20-8201-2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Atmospheric aerosols are a significant public health hazard and have substantial impacts on the climate. Secondary organic aerosols (SOAs) have been shown to phase separate into a highly viscous organic outer layer surrounding an aqueous core. This phase separation can decrease the partitioning of semi-volatile and low-volatile species to the organic phase and alter the extent of acid-catalyzed reactions in the aqueous core. A new algorithm that can determine SOA phase separation based on their glass transition temperature (T g), oxygen to carbon (O : C) ratio and organic mass to sulfate ratio, and meteorological conditions was implemented into the Community Multiscale Air Quality Modeling (CMAQ) system version 5.2.1 and was used to simulate the conditions in the continental United States for the summer of 2013. SOA formed at the ground/surface level was predicted to be phase separated with core-shell morphology, i.e., aqueous inorganic core surrounded by organic coating 65.4 % of the time during the 2013 Southern Oxidant and Aerosol Study (SOAS) on average in the isoprene-rich southeastern United States. Our estimate is in proximity to the previously reported ~ 70 % in literature. The phase states of organic coatings switched between semi-solid and liquid states, depending on the environmental conditions. The semi-solid shell occurring with lower aerosol liquid water content (western United States and at higher altitudes) has a viscosity that was predicted to be 102-1012 Pa s, which resulted in organic mass being decreased due to diffusion limitation. Organic aerosol was primarily liquid where aerosol liquid water was dominant (eastern United States and at the surface), with a viscosity < 102 Pa s. Phase separation while in a liquid phase state, i.e., liquid-liquid phase separation (LLPS), also reduces reactive uptake rates relative to homogeneous internally mixed liquid morphology but was lower than aerosols with a thick viscous organic shell. The sensitivity cases performed with different phase-separation parameterization and dissolution rate of isoprene epoxydiol (IEPOX) into the particle phase in CMAQ can have varying impact on fine particulate matter (PM2.5) organic mass, in terms of bias and error compared to field data collected during the 2013 SOAS. This highlights the need to better constrain the parameters that govern phase state and morphology of SOA, as well as expand mechanistic representation of multiphase chemistry for non-IEPOX SOA formation in models aided by novel experimental insights.
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Affiliation(s)
- Ryan Schmedding
- Department of Environmental Science and Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27516, USA
| | - Quazi Z. Rasool
- Department of Environmental Science and Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27516, USA
| | - Yue Zhang
- Department of Environmental Science and Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27516, USA
- Aerodyne Research, Inc., Billerica, MA 01821, USA
| | - Havala O. T. Pye
- Department of Environmental Science and Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27516, USA
- Office of Research and Development, Environmental Protection Agency, Research Triangle Park, Durham, NC 27709, USA
| | - Haofei Zhang
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Yuzhi Chen
- Department of Environmental Science and Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27516, USA
| | - Jason D. Surratt
- Department of Environmental Science and Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27516, USA
| | | | - Joel A. Thornton
- Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA
| | - Allen H. Goldstein
- Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA
- Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA
| | - William Vizuete
- Department of Environmental Science and Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27516, USA
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Pye HOT, Nenes A, Alexander B, Ault AP, Barth MC, Clegg SL, Collett JL, Fahey KM, Hennigan CJ, Herrmann H, Kanakidou M, Kelly JT, Ku IT, McNeill VF, Riemer N, Schaefer T, Shi G, Tilgner A, Walker JT, Wang T, Weber R, Xing J, Zaveri RA, Zuend A. The Acidity of Atmospheric Particles and Clouds. ATMOSPHERIC CHEMISTRY AND PHYSICS 2020; 20:4809-4888. [PMID: 33424953 PMCID: PMC7791434 DOI: 10.5194/acp-20-4809-2020] [Citation(s) in RCA: 147] [Impact Index Per Article: 36.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Acidity, 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 semi-volatile 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 indicates acidity may be relatively constant due to the semi-volatile 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.
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Affiliation(s)
- Havala O. T. Pye
- Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - Athanasios Nenes
- School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, CH-1015, Switzerland
- Institute for Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, GR-26504, Greece
| | - Becky Alexander
- Department of Atmospheric Science, University of Washington, Seattle, WA, 98195, USA
| | - Andrew P. Ault
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109-1055, USA
| | - Mary C. Barth
- National Center for Atmospheric Research, Boulder, CO, 80307, USA
| | - Simon L. Clegg
- School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Jeffrey L. Collett
- Department of Atmospheric Science, Colorado State University, Fort Collins, CO, 80523, USA
| | - Kathleen M. Fahey
- Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - Christopher J. Hennigan
- Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland Baltimore County, Baltimore, MD, 21250, USA
| | - Hartmut Herrmann
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Leipzig, 04318, Germany
| | - Maria Kanakidou
- Department of Chemistry, University of Crete, Voutes, Heraklion Crete, 71003, Greece
| | - James T. Kelly
- Office of Air Quality Planning & Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - I-Ting Ku
- Department of Atmospheric Science, Colorado State University, Fort Collins, CO, 80523, USA
| | - V. Faye McNeill
- Department of Chemical Engineering, Columbia University, New York, NY, 10027, USA
| | - Nicole Riemer
- Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana-Champaign, Illinois, 61801, USA
| | - Thomas Schaefer
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Leipzig, 04318, Germany
| | - Guoliang Shi
- State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, Nankai University, Tianjin, 300071, China
| | - Andreas Tilgner
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Leipzig, 04318, Germany
| | - John T. Walker
- Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - Tao Wang
- Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
| | - Rodney Weber
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Jia Xing
- School of Environment, Tsinghua University, Beijing, 100084, China
| | - Rahul A. Zaveri
- Atmospheric Sciences & Global Change Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA
| | - Andreas Zuend
- Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, H3A 0B9, Canada
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Brüggemann M, Xu R, Tilgner A, Kwong KC, Mutzel A, Poon HY, Otto T, Schaefer T, Poulain L, Chan MN, Herrmann H. Organosulfates in Ambient Aerosol: State of Knowledge and Future Research Directions on Formation, Abundance, Fate, and Importance. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:3767-3782. [PMID: 32157872 DOI: 10.1021/acs.est.9b06751] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Organosulfates (OSs), also referred to as organic sulfate esters, are well-known and ubiquitous constituents of atmospheric aerosol particles. Commonly, they are assumed to form upon mixing of air masses of biogenic and anthropogenic origin, that is, through multiphase reactions between organic compounds and acidic sulfate particles. However, in contrast to this simplified picture, recent studies suggest that OSs may also originate from purely anthropogenic precursors or even directly from biomass and fossil fuel burning. Moreover, besides classical OS formation pathways, several alternative routes have been discovered, suggesting that OS formation possibly occurs through a wider variety of formation mechanisms in the atmosphere than initially expected. During the past decade, OSs have reached a constantly growing attention within the atmospheric science community with evermore studies reporting on large numbers of OS species in ambient aerosol. Nonetheless, estimates on OS concentrations and implications on atmospheric physicochemical processes are still connected to large uncertainties, calling for combined field, laboratory, and modeling studies. In this Critical Review, we summarize the current state of knowledge in atmospheric OS research, discuss unresolved questions, and outline future research needs, also in view of reductions of anthropogenic sulfur dioxide (SO2) emissions. Particularly, we focus on (1) field measurements of OSs and measurement techniques, (2) formation pathways of OSs and their atmospheric relevance, (3) transformation, reactivity, and fate of OSs in atmospheric particles, and (4) modeling efforts of OS formation and their global abundance.
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Affiliation(s)
- Martin Brüggemann
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstrasse 15, 04318 Leipzig, Germany
| | - Rongshuang Xu
- Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Andreas Tilgner
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstrasse 15, 04318 Leipzig, Germany
| | - Kai Chung Kwong
- Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Anke Mutzel
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstrasse 15, 04318 Leipzig, Germany
| | - Hon Yin Poon
- Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Tobias Otto
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstrasse 15, 04318 Leipzig, Germany
| | - Thomas Schaefer
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstrasse 15, 04318 Leipzig, Germany
| | - Laurent Poulain
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstrasse 15, 04318 Leipzig, Germany
| | - Man Nin Chan
- Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
- The Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kong, Hong Kong, China
| | - Hartmut Herrmann
- Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstrasse 15, 04318 Leipzig, Germany
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Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation. ATMOSPHERE 2019. [DOI: 10.3390/atmos10110666] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Chemical processing of organic material in aqueous atmospheric aerosols and cloudwater is known to form secondary organic aerosols (SOA), although the extent to which each of these processes contributes to total aerosol mass is unclear. In this study, we use GAMMA 5.0, a photochemical box model with coupled gas and aqueous-phase chemistry, to consider the impact of aqueous organic reactions in both aqueous aerosols and clouds on isoprene epoxydiol (IEPOX) SOA over a range of pH for both aqueous phases, including cycling between cloud and aerosol within a single simulation. Low pH aqueous aerosol, in the absence of organic coatings or other morphology which may limit uptake of IEPOX, is found to be an efficient source of IEPOX SOA, consistent with previous work. Cloudwater at pH 4 or lower is also found to be a potentially significant source of IEPOX SOA. This phenomenon is primarily attributed to the relatively high uptake of IEPOX to clouds as a result of higher water content in clouds as compared with aerosol. For more acidic cloudwater, the aqueous organic material is comprised primarily of IEPOX SOA and lower-volatility organic acids. Both cloudwater pH and the time of day or sequence of aerosol-to-cloud or cloud-to-aerosol transitions impacted final aqueous SOA mass and composition in the simulations. The potential significance of cloud processing as a contributor to IEPOX SOA production could account for discrepancies between predicted IEPOX SOA mass from atmospheric models and measured ambient IEPOX SOA mass, or observations of IEPOX SOA in locations where mass transfer limitations are expected in aerosol particles.
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