The morphology of mixed organic/inorganic particles can strongly influence the physicochemical properties of aerosols but remains relatively less examined in particle formation studies. The morphologies of inorganic seed particles grown with either -pinene or limonene secondary organic aerosol (SOA) generated in a flow tube reactor were found to depend on initial seed particle water content. Effloresced and deliquesced ammonium sulfate seed particles were generated at low relative humidity (<15% RH, dry) and high relative humidity (~60% RH, wet) and were also coated with secondary organic material under low growth and high growth conditions. Particles were dried and analyzed using SMPS and TEM for diameter and substrate-induced diameter changes and for the prevalence of phase separation for organic-coated particles. Effloresced inorganic seed particle diameters generally increased after impaction, whereas deliquesced inorganic seed particles had smaller differences in diameter, although they appeared morphologically similar to the effloresced seed particles. Differences in the changes to diameter for deliquesced seed particles suggest crystal restructuring with RH cycling. SOA-coated particles showed negative diameter changes for low organic growth, although wet-seeded organic particles changed by larger magnitudes compared to dry-seeded organic particles. High organic growth gave wide ranging diameter percent differences for both dry- and wet-seeded samples. Wet-seeded particles with organic coatings occasionally showed a textured morphology unseen in the coated particles with dry seeds. Using a flow tube reactor with a combination of spectrometry and microscopy techniques allows for insights into the dependence of aerosol particle morphology on formation parameters for two seed conditions and two secondary organic precursors.
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Droplet activation of wet particles: development of the Wet CCN approach
Abstract. Relationships between critical supersaturation required for activation and particle dry diameter have been the primary means for experimentally characterizing cloud condensation nuclei (CCN) activity; however, use of the dry diameter inherently limits the application to cases where the dry diameter can be used to accurately estimate solute volume. This study challenges the requirement and proposes a new experimental approach, Wet CCN, for studying CCN activity without the need for a drying step. The new approach directly measures the subsaturated portion of the Köhler curves. The experimental setup consists of a humidity-controlled differential mobility analyzer and a CCN counter; wet diameter equilibrated at known relative humidity is used to characterize CCN activity instead of the dry diameter. The experimental approach was validated against ammonium sulfate, glucose, and nonspherical ammonium oxalate monohydrate. Further, the approach was applied to a mixture of nonspherical iodine oxide particles. The Wet CCN approach successfully determined the hygroscopicity of nonspherical particles by collapsing them into spherical, deliquesced droplets. We further show that the Wet CCN approach offers unique insights into the physical and chemical impacts of the aqueous phase on CCN activity; a potential application is to investigate the impact of evaporation/co-condensation of water-soluble semivolatile species on CCN activity.
more » « less- Award ID(s):
- 1230395
- PAR ID:
- 10063580
- Date Published:
- Journal Name:
- Atmospheric Measurement Techniques
- Volume:
- 7
- Issue:
- 7
- ISSN:
- 1867-8548
- Page Range / eLocation ID:
- 2227 to 2241
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract. The aerodynamic aerosol classifier (AAC) is a novel instrument that size-selects aerosol particles based on their mechanical mobility. So far, the application of an AAC for cloud condensation nuclei (CCN) activity analysis of aerosols has yet to be explored. Traditionally, a differential mobility analyzer (DMA) is used for aerosol classification in a CCN experimental setup. A DMA classifies particles based on their electrical mobility. Substituting the DMA with an AAC can eliminate multiple-charging artifacts as classification using an AAC does not require particle charging. In this work, we describe an AAC-based CCN experimental setup and CCN analysis method. We also discuss and develop equations to quantify the uncertainties associated with aerosol particle sizing. To do so, we extend the AAC transfer function analysis and calculate the measurement uncertainties of the aerodynamic diameter from the resolution of the AAC. The analysis framework has been packaged into a Python-based CCN Analysis Tool (PyCAT 1.0) open-source code, which is available on GitHub for public use. Results show that the AAC size-selects robustly (AAC resolution is 10.1, diffusion losses are minimal, and particle transmission is high) at larger aerodynamic diameters (≥∼ 85 nm). The size-resolved activation ratio is ideally sigmoidal since no charge corrections are required. Moreover, the uncertainties in the critical particle aerodynamic diameter at a given supersaturation can propagate through droplet activation, and the subsequent uncertainties with respect to the single-hygroscopicity parameter (κ) are reported. For a known aerosol such as sucrose, the κ derived from the critical dry aerodynamic diameter can be up to ∼ 50 % different from the theoretical κ. In this work, we do additional measurements to obtain dynamic shape factor information and convert the sucrose aerodynamic to volume equivalent diameter. The volume equivalent diameter applied to κ-Köhler theory improves the agreement between measured and theoretical κ. Given the limitations of the coupled AAC–CCN experimental setup, this setup is best used for low-hygroscopicity aerosol (κ≤0.2) CCN measurements.more » « less
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Abstract Understanding the formation processes of particles and cloud condensation nuclei (CCN) in pristine environments is a major challenge in assessing the anthropogenic impacts on climate change. Using a state‐of‐the‐art model that systematically simulates the new‐particle formation (NPF) from condensable vapors and multi‐scale transport of chemical species, we find that NPF contributes ∼90% of the particle number and ∼80% of the CCN at 0.5% supersaturation (CCN0.5%) in the pristine Amazon boundary layer during the wet season. The corresponding contributions are only ∼30% and ∼20% during the dry season because of prevalent biomass burning. In both seasons, ∼50% of the NPF‐induced particles and ∼85% of the NPF‐induced CCN0.5% in the boundary layer originate from the long‐range transport of new particles formed hundreds to thousands of kilometers away. Moreover, about 50%–65% of the NPF‐induced particles and 35%–50% of the NPF‐induced CCN0.5% originate from the downward transport of new particles formed aloft.
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Atmospheric aerosols significantly offset positive radiative forcing due to their contributions as cloud condensation nuclei (CCN) and ice nucleating particles (INPs). The cloud-aerosol-precipitation interactions in the atmosphere are determined by physical and chemical properties of aerosol particles, which can undergo many cycles of droplet activation and subsequent drying before dry or wet deposition from the atmosphere. Secondary organic aerosol (SOA) is an abundant class of aerosol and has been previously shown to contribute to aerosol formed from cloud processing. Isoprene-derived secondary organic aerosol SOA (iSOA) is a particularly important class of aerosol involved in cloud processing. iSOA has both soluble and insoluble components, but there has been a measurement gap in characterizing the insoluble components, as most analyses have focused on soluble components. These measurements are needed as previous research has suggested that insoluble components could be important with respect to CCN and INP formation. Herein, we analyze the insoluble components of SOA generated from the reactive uptake of IEPOX onto acidic seed particles (ammonium sulfate + sulfuric acid at different ratios for different pH conditions) in an atmospheric chamber. We characterize the size distributions and chemical composition, using NanoParticle Tracking Analysis (NTA), Raman microspectroscopy and atomic force microscopy infrared (AFM-IR) spectroscopy as a function of sulfate aerosol seed pH. These insights may help understand aerosol properties after cloud cycling in the atmosphere.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/amt-7-2227-2014
