Ehhalt, D. H.FZJ* ; Schmidt, U.FZJ* ; Schubert, B. (Corresponding author)FZJ*

1988
Kernforschungsanlage Jülich GmbH Zentralbibliothek, Verlag Jülich

Report No.: Juel-2257

Abstract: A method for determining formaldehyde mixing ratios in tropospheric air has been modified for the additional measurement of acetaldehyde. The technique is based on stripping of the aldehydes from the air into an aqueous 2,4-dinitrophenylhydrazine solution. The reaction products, the 2,4-dinitrophenzlhydrazones of the respective aldehydes, are separated using high performance liquid chromatography and quantified by UV absorption. In clean air, measurements can be performed with a time resolution of two hours. An interference of the formaldehyde determination performed with the modified technique is discussed . It was noticed only in continental air in summer and led to increased formaldehyde mixing ratios. For the detection of acetaldehyde, no interference has been observed. Formaldehyde and acetaldehyde mixing ratios were determined in continental air and over the Atlantic ocean during two cruises of the German research vessel "Polarstern" from 30 $^\circ$S and 50 $^\circ$N. In slightly polluted continental air, the mean mixing ratios of formaldehyde and acetaldehyde were 1.53 $\pm$ 0.76 ppb and 0.52 $\pm$ 0.61 ppb, much higher than the mean values of 0.4 $\pm$ 0.19 ppb for formaldehyde and 0.19 $\pm$ 0.13 ppb for acetaldehyde observed in marine air. Simultaneous measurements of ethene and propene concentrations showed a similar latitudinal distribution as formaldehyde mixing ratios, confirming the importance of alkenes for the aldehyde production predicted by models. The influence of nonmethane hydrocarbons is further indicated by the fact that the formaldehyde mixing ratios are correlated with the sum of the C$_{2}$ - C$_{4}$ hydrocarbon concentrations in both, marine and continental air. On sunny days, diurnal variations with maxima during the early afternoon and nocturnal minima were observed for both aldehydes in continental air as well as in maritime air. The diurnal profiles of the measurements in maritime air are compared to the results of a 1 D boundary layer model. In continental air during the day the measured ozone and formaldehyde concentrations showed a positive correlation, while the diurnal variations were anticorrelated in marine air. This anticorrelation indicates photochemical estruction of ozone.

1. Troposphäre (ICG-2)