Development Of The Adjoint Of GRAPES-CUACE Aerosol Module And Model Application To Air Pollution Optimal Control Problems

Sensitivity analysis is more and more important in the air quality numerical simulation field. Based on the concept of inverse modeling, the adjoint method is an efficient sensitivity analysis approach. Only through one simulation can it work out the sensitivities of the objective function to all the model parameters. First, the adjoint theory was introduced, then, the adjoint of GRAPES-CUACE aerosol module was developed and applied to emission sensitivity analysis in one high BC concentration episode occurred in Beijing. In addition, the Models-3/CMAQ modeling system was used in evaluating emission-sources reduction time periods, rates and regions on air quality control effect. In selecting different reduction regions, the demand to guarantee air quality during important activities was considered, and the FLEXPART model was implemented to inverse model sensitive emission-sources regions. At last, from the present situation that China is an agricultural country, Beijing-Tianjin-Hebei and its surrounding regions’ biomass burning effects on Beijing air quality was quantified. Main results are presented as followings:The newly built GRAPES-CUACE aerosol module adjoint has the capability to conduct reliable adjoint simulation. In this study, the more influential emission-sources regions(regions with relatively larger sensitivity coefficients) do not necessarily correspond to the administrative regions, with the former have higher control efficiency. When implementing air quality control measures, we can use the adjoint model to inverse model influential emission-sources regions and time periods, then, the limitation of administrative divisions can be broken through, and effective emission sources reduction time periods can be selected, accordingly, the control efficiency will be increased. When reducing emission-sources at a set rate, the most effective way is to take control measures 2~3 days ahead of the possible severe pollution day. In this way, substantial decrease of peak PM2.5 concentration can be achieved with less economic cost. At a fixed overall emission-sources reduction amount, reducing a moderate rate of emission-sources ahead of the peak day can take pollutants transport processes into account, and is more effective for Beijing to reach the air quality standard than reducing a large rate of emission-sources on the peak day. In summary, before possible severe pollution event, besides cooperating with surrounding regions, the adjoint method(or theFLEXPART model) can be used to narrow emission reduction regions to a smaller area, and the control cost can be lessened and the controllability can be improved. Biomass burning’s impacts on rural Shangdianzi station were relatively larger than on urban Haidian station.