1 research outputs found
Maillard Chemistry in Clouds and Aqueous Aerosol As a Source of Atmospheric Humic-Like Substances
The reported optical,
physical, and chemical properties of aqueous
Maillard reaction mixtures of small aldehydes (glyoxal, methylglyoxal,
and glycolaldehyde) with ammonium sulfate and amines are compared
with those of aqueous extracts of ambient aerosol (water-soluble organic
carbon, WSOC) and the humic-like substances (HULIS) fraction of WSOC.
Using a combination of new and previously published measurements,
we examine fluorescence, X-ray absorbance, UV/vis, and IR spectra,
complex refractive indices, <sup>1</sup>H and <sup>13</sup>C NMR spectra,
thermograms, aerosol and electrospray ionization mass spectra, surface
activity, and hygroscopicity. Atmospheric WSOC and HULIS encompass
a range of properties, but in almost every case aqueous aldehyde-amine
reaction mixtures are squarely within this range. Notable exceptions
are the higher UV/visible absorbance wavelength dependence (Angström
coefficients) observed for methylglyoxal reaction mixtures, the lack
of surface activity of glyoxal reaction mixtures, and the higher N/C
ratios of aldehyde-amine reaction products relative to atmospheric
WSOC and HULIS extracts. The overall optical, physical, and chemical
similarities are consistent with, but not demonstrative of, Maillard
chemistry being a significant secondary source of atmospheric HULIS.
However, the higher N/C ratios of aldehyde-amine reaction products
limits the source strength to ≤50% of atmospheric HULIS, assuming
that other sources of HULIS incorporate only negligible quantities
of nitrogen