HR: 0800h
AN: A11A-0024    [Abstracts]
TI: Photochemical Cycling of Humic-Like Substances in Atmospheric Aerosols
AU: * Rincon, A G
EM: agrincon@caltech.edu
AF: California Institute of Technology, 1200 E. California Blv. 138-78 Caltech, Pasadena, CA 91125, United States
AU: Guzman, M I
EM: mig@seas.harvard.edu
AF: Harvard School of Engineering and Applied Sciences, 40 Oxford Street, Cambridge, MA 02138, United States
AU: Hoffmann, M R
EM: mrh@caltech.edu
AF: California Institute of Technology, 1200 E. California Blv. 138-78 Caltech, Pasadena, CA 91125, United States
AU: Colussi, A J
EM: ajcoluss@caltech.edu
AF: California Institute of Technology, 1200 E. California Blv. 138-78 Caltech, Pasadena, CA 91125, United States
AB: Colored, humic-like substances (HULIS) arising from the biodegradation of organic detritus are widespread in natural surface waters, where they ultimately undergo solar photolysis into small alpha-dicarbonylic species, such as glyoxal, glyoxylic and pyruvic acids. Diversely generated and chemically dissimilar HULIS are also found in the atmospheric aerosol. How are significant levels of colored HULIS produced and sustained in the concentrated aerosol phase under intense solar irradiation? Here, this issue is tackled by investigating the solar photolysis of aqueous pyruvic acid (PA) solutions at concentrations representative of the atmospheric aerosol using UV-absorption, high resolution electrospray mass, and nuclear magnetic resonance spectrometries. Under such conditions, PA is not photodegraded but yields polyfunctional polymers, whose mass and UV-absorption spectra remain unaffected after 3, 8 and 22 h photolysis. Unless diluted, these polymers undergo condensation/polymerization in the post-photolysis period into mass < 700 Da species that absorb in the visible, and are bleached upon resuming irradiation. The re- photolyzed solutions recover the mass and UV-absorption spectra of first photolyzed solutions. Whereas initial pH has no effect on the mechanism of reaction, ammonium bisulfate, a major component of the aerosol, markedly influences these processes. These findings suggest that the chemical identity and concentration levels of complex organic substances in the aerosol are the result of dynamic photochemical processing in the condensed phase.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0322 Constituent sources and sinks
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting