Modelling chemistry in the nocturnal boundary layer above tropical rainforest and a generalised effective nocturnal ozone deposition velocity for sub-ppbv NOx conditions

Measurements of atmospheric composition have been made over a remote rainforest landscape. A box model has previously been demonstrated to model the observed daytime chemistry well. However the box model is unable to explain the nocturnal measurements of relatively high [NO] and [O3], but relatively low observed [NO2]. It is shown that a onedimensional (1-D) column model with simple O3-NOx chemistry and a simple representation of vertical transport is able to explain the observed nocturnal concentrations and predict the likely vertical profiles of these species in the nocturnal boundary layer (NBL). Concentrations of tracers carried over from the end of the night can affect the atmospheric chemistry of the following day. To ascertain the anomaly introduced by using the box model to represent the NBL, vertically-averaged NBL concentrations at the end of the night are compared between the 1-D model and the box model. It is found that, under low to medium [NOx] conditions ∗Lancaster Environment Centre, Lancaster University, Lancaster, U.K. †correspondence to: [email protected] ‡Centre for Ecology and Hydrology, Penicuik, Midlothian, U.K. and University of Manchester, Manchester, U.K. §Department of Chemistry, University of York, York, U.K. ¶National Centre for Atmospheric Science, University of York, York, U.K. ‖Centre for Ecology and Hydrology, Penicuik, Midlothian, U.K. ∗∗University of Manchester, Manchester, U.K.