The vertical distribution of NO3 in the atmospheric boundary layer

Recent urban measurements suggest that NO3 concentrations vary significantl y with altitude in the lowest few hundred metres of the atmosphere. Calcula tions using a one-dimensional boundary layer model show that NO3 concentrat ions are small near the ground and increase with altitude to a maximum near the top of the nocturnal boundary layer (NBL). These results show that the NBL is not well mixed, and that where there are surface sources and sinks two-box models of the NBL are inadequate, and surface measurements are not representative and may lead to an underestimate of the oxidising capacity o f the atmosphere. (C) 1999 Elsevier Science Ltd. All rights reserved.