Ground based gas phase measurements in Surinam during the LBA-Claire 98 experiment

As part of the LBA-CLAIRE-98 experiment, ground level atmospheric concentra tions of O-3, CO, hydroperoxides and organic acids were measured in the rai nforest region in Surinam. Measurements of CO and O-3 were also made at a c oastal site. The results suggest that a significant consumption of 'boundary layer' ozon e occurs over the forested region of Surinam, with an estimated net ozone c onsumption of about 5% hr(-1) during daytime. This would be mainly explaine d by a low photochemical production and high dry deposition to the forest v egetation. Compared to other tropical sites, lower levels of H2O2 were obse rved at the rainforest site, with an average boundary layer concentration o f 0.55 +/- 0.2 nmol mol(-1). Also acetic and formic acids showed relatively low average boundary layer mixing ratios; 1.1 +/- 0.4 nmol mol(-1) and 1.4 +/- 0.5 nmol mol(-1), respectively. Significant correlations were found be tween both acids and between the acids and hydrogen peroxide, suggesting an atmospheric source for the acids. From the available observations we discuss possible implications of our mea surements for the O-3, HO2, and NOx budgets and concentrations in the bound ary layer. We conclude that, despite the high solar irradiation, relatively low levels of O-3, H2O2, HCOOH and CH3COOH are observed in the boundary la yer of the rainforest of Surinam, probably due to low levels of NOx and hig h levels of VOCs, which leads to loss of OH and HO2 radicals. Additionally, high deposition rates of these gases occur to the forest vegetation.