Factors controlling the correlation between ozone and CO in the North American continental boundary layer

Abstract:

Previous research has reported good correlation between O₃ and CO over continental outflow regions. The correlation is often considered as an indication of anthropogenic emissions. In this study, a Regional chEmical trAnsport Model (REAM) was used to study the correlation between boundary layer O₃ and CO. The observed correlation during the DISCOVER-AQ 2011 campaign was reproduced in the model and revealed that biogenic emissions made a significant contribution to the observed correlation and slope between O₃ and CO in that experiment. In order to quantify source contributions to the observed linear correlation of O₃ and CO in the continental boundary layer, CO sources were separated into four different categories: anthropogenic emission, chemical production from anthropogenic VOC oxidation, production of biogenic isoprene oxidation, and transport from lateral boundaries. The tagged tracer simulations reveal that biogenic isoprene is the main factor determining the correlation and slope between O₃ and CO and those between O₃ and CH₂O near the surface and in the continental boundary layer. In the outflow region (western North Atlantic), both biogenic isoprene and anthropogenic emissions are significant factors. This finding implies that estimate of continental O₃ export on the basis of O₃ and CO correlation must account for the biogenic contribution and that satellite observations of CH₂O and CO can be applied to provide observational constraints on the distribution of surface O₃.