Estimation of regional VOC contribution of CO comparing the use of a full chemistry and a simplified tracer regional chemical transport model for the Trace-P period

CO is an important species in the atmosphere due to its relatively high concentration and widespread existence. Its atmospheric concentration is determined by primary emissions, and by secondary formation due to VOC oxidation. VOC also reacts with OH, otherwise a CO removal agent. The present work explores this dual role of VOC during the Trace-P period. Full chemistry runs were carried out with and without the presence of VOC in the emissions inventory. Tracer runs were carried out using constant OH fields and considering complete oxidation of VOC to CO. These runs allowed evaluating the role of VOC in the formation of CO. In the full chemistry runs, VOC contribution to CO was maximal in areas downwind to the sources. For March 2001, the tracer model estimates the VOC contributed CO in the domain to be 1.676 x 10^6 ton, and the full chemistry model estimates a formation of 1.061 x 10^6 ton. This shows the importance of using variable OH fields as VOC impacts both the formation of CO, and the reduction of CO by OH oxidation. The March averaged cross section of VOC contributed CO over the East boundary of the domain shows a higher outflow flux for the full chemistry model in comparison to the tracer model (1.70 tons/s vs 1.22 tons/s, respectively). The flux values, extrapolated to a yearly basis (simply as an example) correspond to a formation of 53.7 Tg/year and 38.6 Tg/year of CO, for the full chem and tracer runs, respectively. In comparison, the CO emissions from China are about 116 Tg in 2000. This study indicates that VOC is an important chemical source of CO on a regional and global scale.