Atmospheric formic and acetic acids in Venezuela

Abstract Gas, phase and rain concentrations of HCOOH and CH 3 COOH have been measured at various sites in the savannah climatic region, a cloud forest site and a coastal site in Venezuela. Gas phase and rain water were sampled using the aqueous scrubber technique and a wet only collector, respectively. Analyses were made by ion chromatography. The results indicate that formic and acetic acids are important components of the Venezuelan atmosphere. They are homogeneously distributed, suggesting a widespread source. Boundary layer concentrations during the dry season (HCOOH, 1.8 ppbv; CH 3 COOH, 1.25 ppbv) are higher than in the wet season (HCOOH, 1.0 ppbv; CH 3 COOH, 0.7 ppbv), mainly due to a longer lifetime of the acid during the dry season (∼6 days) compared with the wet season (∼2 days). The overall concentrations in rain are 7.0 and 4.0 μM for formic and acetic acids, respectively. The estimated annual total depositions are: HCOOH, 17 mmol m −2 yr −1 and CH 3 COOH,10 mmol m −2 yr −1 ; around half of the acids are removed by dry deposition. It is established that a larger source (∼1.8 times) of both acids is present during the wet season. We speculate that atmospheric oxidation of hydrocarbons should be the main source of HCOOH and CH 3 COOH in the Venezuelan atmosphere; soil emissions could make a significant contribution during the dry season.