Quantitative IR spectrum and vibrational assignments for glycolaldehyde vapor: glycolaldehyde measurements in biomass burning plumes.

Glycolaldehyde (GA, 2-hydroxyethanal, C2H4O2) is a semivolatile molecule of atmospheric importance, recently proposed as a precursor in the formation of aqueous-phase secondary organic aerosol (SOA). There are few methods to measure GA vapor, but infrared spectroscopy has been used successfully. Using vetted protocols we have completed the first assignment of all fundamental vibrational modes and also derived quantitative IR absorption band strengths using both neat and pressure-broadened GA vapor. Even though GA is problematic due to its propensity to both dimerize and condense, our intensities agree well with the few previously published values. Using the ν10 band Q-branch at 860.51 cm(-1), we have also determined GA mixing ratios in biomass burning plumes generated by field and laboratory burns of fuels from the southeastern and southwestern United States, including the first IR field measurements of GA in smoke. The GA emission factors were anti-correlated with modified combustion efficiency confirming release of GA from smoldering combustion. The GA emission factors (grams of GA emitted per kilogram of biomass burned on a dry mass basis) had a low dependence on fuel type consistent with the production mechanism being pyrolysis of cellulose. GA was emitted at 0.23 ± 0.13% of CO from field fires, and we calculate that it accounts for ∼18% of the aqueous-phase SOA precursors that we were able to measure.