Photosensitized reactions involving
imidazole-2-carboxaldehyde
(IC) have been experimentally observed to contribute to secondary
organic aerosol (SOA) growth. However, the extent of photosensitized
reactions in ambient aerosols remains poorly understood and unaccounted
for in atmospheric models. Here we use GAMMA 4.0, a photochemical
box model that couples gas-phase and aqueous-phase aerosol chemistry,
along with recent laboratory measurements of the kinetics of IC photochemistry,
to analyze IC-photosensitized SOA formation in laboratory and ambient
settings. Analysis of the laboratory results of Aregahegn et al. (2013)
suggests that photosensitized production of SOA from limonene, isoprene,
α-pinene, β-pinene, and toluene by <sup>3</sup>IC* occurs
at or near the surface of the aerosol particle. Reactive uptake coefficients
were derived from the experimental data using GAMMA 4.0. Simulations
of aqueous aerosol SOA formation at remote ambient conditions including
IC photosensitizer chemistry indicate less than 0.3% contribution
to SOA growth from direct reactions of <sup>3</sup>IC* with limonene,
isoprene, α-pinene, β-pinene, and toluene, and an enhancement
of less than 0.04% of SOA formation from other precursors due to the
formation of radicals in the bulk aerosol aqueous phase. Other, more
abundant photosensitizer species, such as humic-like substances (HULIS),
may contribute more significantly to aqueous aerosol SOA production
