es9b07051_si_001.pdf (1.6 MB)
Photolysis Controls Atmospheric Budgets of Biogenic Secondary Organic Aerosol
journal contribution
posted on 2020-03-19, 19:14 authored by Maria
A. Zawadowicz, Ben H. Lee, Manish Shrivastava, Alla Zelenyuk, Rahul A. Zaveri, Connor Flynn, Joel A. Thornton, John E. ShillingSecondary organic aerosol (SOA) accounts
for a large fraction of
the tropospheric particulate matter. Although SOA production rates
and mechanisms have been extensively investigated, loss pathways remain
uncertain. Most large-scale chemistry and transport models account
for mechanical deposition of SOA but not chemical losses such as photolysis.
There is also a paucity of laboratory measurements of SOA photolysis,
which limits how well photolytic losses can be modeled. Here, we show,
through a combined experimental and modeling approach, that photolytic
loss of SOA mass significantly alters SOA budget predictions. Using
environmental chamber experiments at variable relative humidity between
0 and 60%, we find that SOA produced from several biogenic volatile
organic compounds undergoes photolysis-induced mass loss at rates
between 0 and 2.2 ± 0.4% of nitrogen dioxide (NO2)
photolysis, equivalent to average atmospheric lifetimes as short as
10 h. We incorporate our photolysis rates into a regional chemical
transport model to test the sensitivity of predicted SOA mass concentrations
to photolytic losses. The addition of photolysis causes a ∼50%
reduction in biogenic SOA loadings over the Amazon, indicating that
photolysis exerts a substantial control over the atmospheric SOA lifetime,
with a likely dependence upon the SOA molecular composition and thus
production mechanisms.