Abstract
Hydroxyl radical (OH) oxidation of toluene produces ring-retaining
products: cresol and benzaldehyde, and ring-opening products: bicyclic
intermediate compounds and epoxides. Here, first- and later-generation OH
oxidation products from cresol and benzaldehyde are identified in laboratory
chamber experiments. For benzaldehyde, first-generation ring-retaining
products are identified, but later-generation products are not detected. For
cresol, low-volatility (saturation mass concentration, C* ∼ 3.5 × 104 − 7.7 × 10−3 µg m−3), first- and later-generation ring-retaining products are identified. Subsequent OH addition to the aromatic ring of o-cresol leads to compounds such as hydroxy, dihydroxy, and trihydroxy methyl benzoquinones and dihydroxy, trihydroxy, tetrahydroxy, and pentahydroxy toluenes. These products are detected in the gas phase by chemical ionization mass spectrometry (CIMS) and in the particle phase using offline direct analysis in real-time mass spectrometry (DART-MS). Our data
suggest that the yield of trihydroxy toluene from dihydroxy toluene is
substantial. While an exact yield cannot be reported as authentic standards
are unavailable, we find that a yield for trihydroxy toluene from dihydroxy
toluene of ∼ 0.7 (equal to the reported yield of dihydroxy toluene from
o-cresol; Olariu et al., 2002) is consistent with experimental results
for o-cresol oxidation under low-NO conditions. These results
suggest that even though the cresol pathway accounts for only ∼ 20 % of
the oxidation products of toluene, it is the source of a significant fraction
(∼ 20–40 %) of toluene secondary organic aerosol (SOA) due to the
formation of low-volatility products.
Citation
ID:
135083
Ref Key:
schwantes2017atmosphericformation