Temporal variations in formaldehyde, acetaldehyde and acetone and budget of formaldehyde at a rural site in Southern Germany

Formaldehyde was measured at the TOR station, Schauinsland, (48°N, 6°E, 1250 m asl) in September 1992 during the TRACT intensive field campaign, using concurrently a continuous enzymatic/fluorometric technique and the DNPH cartridge method, which also allowed the concentrations of CH3CHO and CH3COCH3 to be determined. The DNPH method gave, on an average, 0.84 ppb higher CH2O concentrations than the fluorometric technique, which was most likely due to contamination during sampling and HPLC analysis. The average relative mole fractions of the carbonyl compounds measured by the DNPH method were 37% CH2O, 14% CH3CHO and 49% CH3COCH3. Mixing ratios of formaldehyde (measured fluorometrically) ranged from 0.2 to 2.8 ppb. They were highest during the daytime when polluted air from the Rhine valley was advected. Lower mixing ratios were usually found during the night or early morning when the site was situated above the nocturnal inversion. Comparison of the diurnal variation of CH2O with the concentrations of O3, NO, NO2, NOy, and PAN and with meteorological data indicated that both transport and photochemical formation contributed to the observed CH2O levels. Budget for CH2O was estimated using covariance of CH2O with NOx, and PAN.