Evaluation of pollutant outflow and CO sources during TRACE-P using model-calculated, aircraft-based, and Measurements of Pollution in the Troposphere (MOPITT)-derived CO concentrations

Outflow of CO from Asia during March 2001 is evaluated using data from the Transport and Chemical Evolution over the Pacific (TRACE-P) mission and the Measurements of Pollution in the Troposphere (MOPITT) instrument in conjunction with model-calculated CO from the University of Maryland chemistry and transport model (UMD CTM). Comparison of model-calculated CO with aircraft measurements indicates that temporal and spatial variations in CO are well captured by the model ( mean correlation coefficient of 0.78); however, model-calculated mixing ratios are lower than observed especially for pressures >850 hPa where negative biases of similar to60 ppbv were seen. Regression analysis is used to optimize the magnitudes of the bottom-up TRACE-P Asian fossil fuel (FF), biofuel (BF), and biomass burning (BB) CO emission inventories. Resulting Asian scaling factors are 1.59 +/- 0.34 for FF + BF emissions and 0.47 +/- 0.46 for BB emissions. Resulting FF + BF emissions are 27.7 +/- 6.1 Tg for March 2001 (301 +/- 67 Tg for an entire year). Resulting BB emissions for March 2001 are 8.5 +/- 8.3 Tg. These results are consistent with recent inverse modeling studies. Scaling factors are lowest (highest) for experiments that assume a high ( low) CO yield for the oxidation of anthropogenic and natural hydrocarbons and for experiments that use (do not use) an aerosol-modified OH distribution. Comparison of model-calculated CO with MOPITT measurements supports the results from our regression analysis. Without exception, mean March 2001 model-calculated CO profiles in the TRACE-P region from a simulation with adjusted CO sources are within a standard deviation of mean March 2001 MOPITT-sampled profiles.