Vapor Condensation and Coating Evaporation Are Both Responsible for Soot Aggregate Restructuring

Document Type

Article

Publication Date

7-6-2021

Abstract

Fresh soot is made of fractal aggregates, which often appear collapsed in atmospheric samples. A body of work has concluded that the collapse is caused by liquid shells when they form by vapor condensation around soot aggregates. However, some recent studies argue that soot remains fractal even when engulfed by the shells, collapsing only when the shells evaporate. To reconcile this disagreement, we investigated soot restructuring under conditions ranging from capillary condensation to full encapsulation, also including condensate evaporation. In these experiments, airborne fractal aggregates were exposed to vapors of wetting liquids, and particle size was measured before and after coating loss, allowing us to isolate the contribution from condensation toward restructuring. We show the existence of three distinct regions along the path connecting the initial fractal and final collapsed aggregates, where minor restructuring occurs already at zero vapor supersaturation due to capillary condensation. Increasing supersaturation increases the amount of condensate, producing a more notable aggregate shrinkage. At even higher supersaturations, the aggregates become encapsulated, and subsequent condensate evaporation leaves behind fully compacted aggregates. Hence, for wetting liquids, minor restructuring begins already during capillary condensation and significant restructuring occurs as the coating volume increases. However, at this time, we cannot precisely quantify the contribution of condensate evaporation to the full aggregate compaction.

Identifier

85110057393 (Scopus)

Publication Title

Environmental Science and Technology

External Full Text Location

https://doi.org/10.1021/acs.est.1c02391

e-ISSN

15205851

ISSN

0013936X

PubMed ID

34128645

First Page

8622

Last Page

8630

Issue

13

Volume

55

Grant

AGS-1463702

Fund Ref

National Science Foundation

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