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Photochemistry of formaldehyde during the 1993 Tropospheric OH Photochemistry Experiment

1997; American Geophysical Union; Volume: 102; Issue: D5 Linguagem: Inglês

10.1029/96jd03249

2156-2202

Alan Fried, S. A. McKeen, Scott Sewell, Jerry Harder, Bruce Henry, P. D. Goldan, W. C. Kuster, E. J. Williams, Karsten Baumann, R. E. Shetter, C. A. Cantrell,

Atmospheric and Environmental Gas Dynamics

The present study examines in detail the photochemistry of the important hydrocarbon intermediate HCHO during the 1993 Fritz Peak/Idaho Hill OH Photochemistry Experiment. Measurement‐model relationships for HCHO were studied employing a box model with input measurements of hydrocarbons, photolysis frequencies, NO x , and HO x measured at the Idaho Hill sampling site during clean westerly flow. Tunable diode laser absorption and long‐path UV‐visible absorption spectroscopic techniques provided the high‐quality time‐resolved ambient HCHO database necessary for this study. For clear sky conditions during clean westerly flow, midday HCHO measurements and model calculations were in agreement to within 12% under various realistic model scenarios. This is significant since it places constraints on the OH concentrations as well as the characteristics of potential missing hydrocarbons necessary to balance measured and modeled OH. Measurement relationships between HCHO and CH 3 CHO were also investigated; polluted air from the Denver‐Boulder front range resulted in the following linear regression: [HCHO] = (0.62±0.20) ppbv + (1.83±0.15) CH 3 CHO. The slope reflects the large if not dominant influence of primary and biogenic emissions, and the intercept reflects the existence of HCHO sources which are not sources of CH 3 CHO. Clean westerly flow produced a significantly different relationship with no obvious correlation, and this is consistent with smaller biogenic sources of CH 3 CHO compared with the much larger known biogenic sources of HCHO.