HCHO and HCOOH in Tropical Rains

Formic acid is the major contributor to acidity of tropical rains. In this work, formic acid and formaldehyde were measured in rain collected at two rural savannah sites, a suburban location, and in the city of Caracas. Higher concentrations of both compounds were recorded in the first rains at the end of the dry season, when vegetation burning occurs throughout Venezuela. From the samples at all four sites, a significant statistical correlation was found between HCHO and HCOOH. The HCOOH/HCHO ratio in heavy rains ( > 10 mm) is 1.2, and in fairly good agreement with predictions from theoretical models. The results suggest that in-cloud oxidation of formaldehyde plays a major role in controlling the concentration of formic acid in