Glycolaldehyde (GAld) is a C
2
water-soluble
aldehyde
produced during the atmospheric oxidation of isoprene and many other
species and is commonly found in cloudwater. Previous work has established
that glycolaldehyde evaporates more readily from drying aerosol droplets
containing ammonium sulfate (AS) than does glyoxal, methylglyoxal,
or hydroxyacetone, which implies that it does not oligomerize as quickly
as these other species. Here, we report NMR measurements of glycolaldehyde’s
aqueous-phase reactions with AS, methylamine, and glycine. Reaction
rate constants are smaller than those of respective glyoxal and methylglyoxal
reactions in the pH range of 3–6. In follow-up cloud chamber
experiments, deliquesced glycine and AS seed particles were found
to take up glycolaldehyde and methylamine and form brown carbon. At
very high relative humidity, these changes were more than 2 orders
of magnitude faster than predicted by our bulk liquid NMR kinetics
measurements, suggesting that reactions involving surface-active species
at crowded air–water interfaces may play an important role.
The high-resolution liquid chromatography–electrospray ionization–mass
spectrometric analysis of filter extracts of unprocessed AS + GAld
seed particles identified sugar-like C
6
and C
12
GAld oligomers, including proposed product 3-deoxyglucosone, with
and without modification by reactions with ammonia to diimine and
imidazole forms. Chamber exposure to methylamine gas, cloud processing,
and simulated sunlight increased the incorporation of both ammonia
and methylamine into oligomers. Many C
4
–C
16
imidazole derivatives were detected in an extract of chamber-exposed
aerosol along with a predominance of
N
-derivatized
C
6
and C
12
glycolaldehyde oligomers, suggesting
that GAld is capable of forming brown carbon SOA.
