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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 100, NO. D5, PAGES 9325–9333, 1995

Formaldehyde, glyoxal, and methylglyoxal in air and cloudwater at a rural mountain site in central Virginia

J. William Munger

Division of Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge


D. J. Jacob

Division of Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge


B. C. Daube

Division of Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge


L. W. Horowitz

Division of Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge


W. C. Keene

Department of Environmental Sciences, University of Virginia, Charlottesville


B. G. Heikes

Center for Atmospheric Chemistry Studies, Graduate School of Oceanography, University of Rhode Island, Narragansett


Abstract

As part of the Shenandoah Cloud and Photochemistry Experiment (SCAPE), we measured formaldehyde (HCHO), glyoxal (CHOCHO), and methylglyoxal (CH3C(O)CHO) concentrations in air and cloudwater at Pinnacles (elevation 1037 m) in Shenandoah National Park during September 1990. Mean gas-phase concentrations of HCHO and CHOCHO were 980 and 44 pptv, respectively. The concentration of CH3C(O)CHO rarely exceeded the detection limit of 50 pptv. Mean cloudwater concentrations of HCHO and CHOCHO were 9 and 2 μM, respectively; the mean CH3C(O)CHO concentration was below its detection limit of 0.3 μM. The maximum carbonyl concentrations were observed during stagnation events with high O3, peroxides, and CO. Outside of these events the carbonyls did not correlate significantly with O3, CO, or NOy. Carbonyl concentrations and concentration ratios were consistent with a major source for the carbonyls from isoprene oxidation. Oxidation of CH4 supplies a significant background of HCHO. The carbonyl concentrations were indistinguishable in two size fractions of cloudwater having a cut at d=18 μm. Gas- and aqueous-phase concentrations of HCHO from samples collected during a nighttime cloud event agree with thermodynamic equilibria within a factor of 2. Samples collected during a daytime cloud event show HCHO supersaturation by up to a factor of 4. Positive artifacts in the cloudwater samples due to hydrolysis of hydroxymethylhydroperoxide (HOCH2OOH) could perhaps account for this discrepancy.

Received 18 April 1994; accepted 12 January 1995.

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Citation: Munger, J. W., D. J. Jacob, B. C. Daube, L. W. Horowitz, W. C. Keene, and B. G. Heikes (1995), Formaldehyde, glyoxal, and methylglyoxal in air and cloudwater at a rural mountain site in central Virginia, J. Geophys. Res., 100(D5), 9325–9333.