Surface ozone concentrations and deposition to a deforested site in Rondonia, Brazil

Surface ozone concentrations over a deforested pasture site near Ji Parana, Rondonia, Brazil were measured during the NASA/TRMM field campaign, January-February, 1999. Two-minute averages of ozone concentration were measured continuously for 38 days using an ozone analyzer with an intake located approximately 2.5 m from the surface. This study places specific emphasis on diurnal variation of ozone and uses a one-dimensional resistance analog model to calculate deposition velocity and ozone flux to the site. The diurnal variations indicate ozone concentrations often near zero at night and maximum average concentrations between 12 and 25 ppb between 14:00 and 15:00 LST. Diurnal maxima at this site are usually much higher than average maximum ozone concentrations over forested sites during the wet season (reported after the ABLE 2B experiment in 1987). In several instances, abnormal increases in ozone concentration, often at night, correspond with heavy rain activity. Increases in ozone to daytime levels occur before sunrise in several cases. Ozone deposition velocity and flux tends to be strongly dependent on mechanical turbulence (friction velocity) and tended to be lower than values calculated for rain forest sites.