Inversion of CO emissions over Beijing and its surrounding areas with ensemble Kalman filter

Inversion of the carbon monoxide (CO) emissions over Beijing and surrounding areas in the summer of 2010 is carried on the Nested Air Quality Prediction Modeling System (NAQPMS) in coupling with an ensemble Kalman filter. CO emission is estimated through integration of observations data obtained from 25 sites in Beijing and surrounding areas of which 13 sites selected as assimilation sites are used to perform a joint adjustment of both CO concentrations and emissions with hourly surface CO observations, and 12 other sites selected to validate the inversion emission inventory. As a result, estimated CO emissions (Tg year−1) for Beijing, Tianjin, Tangshan and Baoding are 4.11, 3.75, 3.17 and 4.08, respectively; higher than the a priori estimates in the Regional Emission inventory in Asia Version 1.1 (REAS V1.1) by 50%, 80%, 120% and 150% respectively. Obviously, the regional CO emissions are underestimated in REAS1.1, especially over Beijing and surrounding areas. Use of the inverse emission inventory reduces the bias of CO simulation by 64% at assimilation sites and 48% at validation sites.