Distribution of C1 - C2 Aldehydes in the Free Troposphere

Abstract

A sensitive and selective measurement technique for the determination of tropospheric formaldehyde and acetaldehyde in background air is described . The method is based on the derivatization of aldehydes with 2,4 dinitrophenylhydrazine (DNPH) . The derivative aldehyde hydrazones are then separated using high performance liquid chromatography (HPLC) and detected at 355 nm using a conventional HPLC UV/VIS absorbance detector. Aldehydes were collected with Waters Sep-Pak C®18 DNPHcoated cartridges using a portable sampling system . The apparatus proved to be easy and convenient to operate, even in remote clean air locations where aldehyde mixing ratios and their natural variations are likely to be of special interest in air chemistry. The method was used for ground-based measurements of formaldehyde and acetaldehyde during an uninterupted two-week period in August 1990 in Jülich . Ground level measurements in Jülich for formaldehyde and acetaldehyde were shown to vary from 0 .5 to 7 ppb and 0 .1 to 2 .0 ppb, respectively . Diurnal mean mixing ratios of, formaldehyde and acetaldehyde were 2 .8 +/® 1 .5 ppb and 0 .7 -+/® 0 .4 ppb respectively . Significant diurnal patterns were observed with maximum mixing ratios in the early afternoons, and minimum mixing ratios shortly before sunrise . A potential interference from organic hydroperoxides is also discussed. ~n~'r cr ai6~ 9 ~ Lv~ vr.m. $ re measurements up ac .o nearly ~ 8L811 är J=s t he s.~ai ;f ei a•®rs-I an, in z vi av,=-rns, -F ver‘fw { .°174YiF.9'i ®~fl to November 1 9 4 0 showed the potential of cartridge-based methods for aldehyde measurements in the free troposphere . These test flights indicated that formaldehyde vertical profiles can be dependent on inversion height and cloud frequency . In-cloud formaldehyde measurements tended to be lower than gas-phase measurement