Atmospheric formic and acetic acids in Venezuela

Gas phase and rain concentrations of HCOOH and CH3COOH 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; CH3COOH, 1.25 ppbv) are higher than in the wet season (HCOOH, 1.0 ppbv; CH3COOH, 0.7 ppbv), mainly due to a longer lifetime of the acid during the dry season (similar to 6 days) compared with the wet season (similar to 2 days). The overall concentrations in rain are 7.0 acid 4.0 mu M for formic and acetic acids, respectively. The estimated annual total depositions are: HCOOH, 17 mmol m(-2) yr(-1) and CH3COOH, 10 mmol m(-2) yr(-1); around half of the acids are removed by dry deposition. It is established that a larger source (similar to 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 CH3COOH in the Venezuelan atmosphere; soil emissions could make a significant contribution during the dry season.