Tracking a Heavy Pollution Process in Beijing in Winter 2016 Using GRAPES-CUACE Adjoint Model

By using the GRAPES-CUACE (Global-Regional Assimilation and Prediction System coupled with the CMA Unified Atmospheric Chemistry Environmental Forecasting System) adjoint model, the adjoint sensitivity of the heavy pollution process in the winter of 2016 in Beijing is traced, and the key emission sources and periods that impacted this heavy pollution process most seriously are analyzed. The research findings suggest that the peak concentration of PM2.5 has a rapid response to the local emission, and the local hourly sensitivity coefficient, which is 9.31 μg m-3, reaches the peak at the moment 1h before the objective time. From the cumulative sensitivity coefficient, the local emission plays the main theme within 20h before the objective time. The contribution of the surrounding emission is the accumulation of the neighboring sources of Beijing, Tianjin, Hebei and Shanxi, whose cumulative contribution ratios are 34.2%, 3.0%, 49.4% and 13.4% respectively within 72h before the objective time. From the hourly sensitivity coefficient, the major contribution period of Tianjin source is 1-26h before the objective time and its hourly contribution peak value is 0.59 μg m-3, appearing at the moment 4h before the objective time. The main contribution periods of Hebei and Shanxi emission sources are respectively 1-54h and 14-53h before the objective time and their hourly sensitivity coefficients both show periodic fluctuations. The Hebei source shows three peaks of sensitivity coefficients, which are 3.45 μg m-3, 4.27 μg m-3 and 0.71 μg m-3, respectively appearing at the time of 4h, 16h and 38h before the objective time. For the Shanxi source, sensitivity coefficient peaks twice with the values of 1.41 μg m-3 and 0.64 μg m-3, which are seen at the time 24h and 45h before the objective time, respectively.