Modelling ultrafine particle growth in a flow tube reactor
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Published:2022-08-16
Issue:16
Volume:15
Page:4663-4674
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Taylor Jr. Michael S.ORCID, Higgins Devon N., Johnston Murray V.ORCID
Abstract
Abstract. Flow tube reactors are often used to study aerosol
kinetics. The goal of this study is to investigate how to best represent
complex growth kinetics of ultrafine particles within a flow tube reactor
when the chemical processes causing particle growth are unknown. In a
typical flow tube experiment, one measures the inlet and outlet particle
size distributions to give a time-averaged measure of growth, which may
be difficult to interpret if the growth kinetics change as particles transit
through the flow tube. In this work, we simulate particle growth for
secondary organic aerosol (SOA) formation that incorporates both surface-
and volume-limited chemical processes to illustrate how complex growth
kinetics inside a flow tube can arise. We then develop and assess a method
to account for complex growth kinetics when the chemical processes driving
the kinetics are not known. Diameter growth of particles is represented by a
growth factor (GF), defined as the fraction of products from oxidation of
the volatile organic compound (VOC) precursors that grow particles during a
specific time period. Defined in this way, GF is the sum of all non-volatile
products that condensationally grow particles plus a portion of semi-volatile
molecules that react on or in the particle to give non-volatile products that
remain in the particle over the investigated time frame. With respect to
flow tube measurements, GF is independent of wall loss and condensation
sink, which influence particle growth kinetics and can vary from experiment
to experiment. GF is shown to change as a function of time within the flow
tube and is sensitive to factors that affect growth such as gas-phase mixing
ratios of the precursors and the presence of aerosol liquid water (ALW) on
the surface or in the volume of the particle. A method to calculate GF from the
outlet-minus-inlet particle diameter change in a flow tube experiment is
presented and shown to accurately match GFs from simulations of SOA
formation.
Funder
National Science Foundation
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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