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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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Effect of dry or wet substrate deposition on the organic volume fraction of core–shell aerosol particles
Abstract. Understanding the impact of sea spray aerosol (SSA) on theclimate and atmosphere requires quantitative knowledge of their chemicalcomposition and mixing states. Furthermore, single-particle measurements areneeded to accurately represent large particle-to-particle variability. Toquantify the mixing state, the organic volume fraction (OVF), defined as therelative organic volume with respect to the total particle volume, ismeasured after generating and collecting aerosol particles, often usingdeposition impactors. In this process, the aerosol streams are either driedor kept wet prior to impacting on solid substrates. However, the atmosphericcommunity has yet to establish how dry versus wet aerosol depositioninfluences the impacted particle morphologies and mixing states. Here, weapply complementary offline single-particle atomic force microscopy (AFM)and bulk ensemble high-performance liquid chromatography (HPLC) techniquesto assess the effects of dry and wet deposition modes on thesubstrate-deposited aerosol particles' mixing states. Glucose and NaClbinary mixtures that form core–shell particle morphologies were studied asmodel systems, and the mixing states were quantified by measuring the OVF ofindividual particles using AFM and compared to the ensemble measured byHPLC. Dry-deposited single-particle OVF data positively deviated from thebulk HPLC data by up to 60 %, which was attributed to significantspreading of the NaCl core upon impaction with the solid substrate. This ledto underestimation of the core volume. This problem was circumvented by (a) performing wet deposition and thus bypassing the effects of the solid corespreading upon impaction and (b) performing a hydration–dehydration cycle ondry-deposited particles to restructure the deformed NaCl core. Bothapproaches produced single-particle OVF values that converge well with thebulk and expected OVF values, validating the methodology. These findingsillustrate the importance of awareness in how conventional particledeposition methods may significantly alter the impacted particlemorphologies and their mixing states.
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- Award ID(s):
- 1801971
- PAR ID:
- 10090723
- Date Published:
- Journal Name:
- Atmospheric Measurement Techniques
- Volume:
- 12
- Issue:
- 3
- ISSN:
- 1867-8548
- Page Range / eLocation ID:
- 2033 to 2042
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/amt-12-2033-2019
