Can a global model chemical mechanism reproduce NO, NO sub(2), and O sub(3) measurements above a tropical rainforest?

• Published in: Atmospheric chemistry and physics discussions 2009-12, Vol.9 (6), p.27611-27648
• Main Authors: Pike, R C, Lee, J D, Young, P J, Moller, S, Carver, G D, Yang, X, Misztal, P, Langford, B, Stewart, D, Reeves, CE, Hewitt, C N, Pyle, JA
• Format: Article
• Language: English
• ISSN: 1680-7367; 1680-7375

A cross-platform field campaign, OP3, was conducted in the state of Sabah in Malaysian Borneo between April and July of 2008. Among the suite of observations recorded, the campaign included measurements of NO sub(x) and O sub(3)-crucial outputs of any model chemistry mechanism. We describe the measurements of these species made from both the ground site and aircraft. We examine the output from the global model p-TOMCAT at two resolutions for this location during the April campaign period. The models exhibit reasonable ability in capturing the NO sub(x) diurnal cycle, but ozone is overestimated. We use a box model containing the same chemical mechanism to explore the weaknesses in the global model and the ability of the simplified global model chemical mechanism to capture the chemistry at the rainforest site. We achieve a good fit to the data for all three species (NO, NO sub(2), and O sub(3)), though the model is much more sensitive to changes in the treatment of physical processes than to changes in the chemical mechanism. Indeed, without some parameterization of the nighttime boundary layer-free troposphere mixing, a time dependent box model will not reproduce the observations. The final simulation uses this mixing parameterization for NO and NO sub(2) but not O sub(3), as determined by the vertical structure of each species, and matches the measurements well.