Emission of NO from savanna soils during rainy season

Emission of NO from soil was measured in a woodland savanna of Venezuela during the rainy season. Fluxes obtained using closed chamber and gradient techniques were found to agree to within around 30%. The emission varied by up to a factor 4 from one site to another and increased dramatically after rain. An estimate of the total rainy season (7 months) emission range from 0.2 to 1.2 g N m −2 . Adding to this our earlier estimate, based on measurements during the dry season, gives an annual emission of 0.3–1.3 g N m −2 . These results suggest that NO emission from savanna soils should play an important role in the photochemistry of the tropical region. The NO x concentrations varied diurnally, with up to 20 parts per billion by volume (ppbv) during stable conditions during nighttime. Daytime concentrations, which may be considered representative of a large part of the boundary layer, were found to be around 1 ppbv.