Sensitivity of the simulated PM2.5 concentrations over Northeast Asia to different secondary aerosol modules during KORUS-AQ

Abstract:

Secondary aerosol formation is one of the highly uncertain process for the PM_2.5 prediction by regional air quality models. To investigate the uncertainty about secondary aerosol formation process in chemical transport model, this study employed different secondary aerosol modules: MADE/VBS and MADE/SORGAM, and carried out WRF-Chem (Weather Research and Forecasting-Chemistry) model simulations of the surface PM_2.5 mass concentration and its relevant chemical compositions: SO₄^-2, NO₃^-, NH₄⁺, and OC for KORUS-AQ campaign period (May 1–June, 2016). This models’ large inconsistencies in the surface PM_2.5 concentrations between two modules over Korean Peninsula were attributed to the differences in the treatments of VOC volatilities. Compared to observations over the Korean Peninsula domain, MADE/VBS showed over-prediction in OC by 125~130% while MADE/SORGAM under-prediction by 75~80%. OC and Sulfate via MADE/VBS was simulated greatly higher than that by MADE/SORGAM by a factor of 1.5~2.0 and 1.4, respectively, but relatively closer to observations. Model verification against KORUS-AQ aircraft measurements also showed big discrepancies in OC between two modules, and MADE/VBS simulated higher OC than MADE/SORGAM by a factor of 5 in long range transport case, but showed much closer to KORUS-AQ aircraft measurement. Based on both ground and aircraft measurement, the disaggregated bias (sum of 4 components) for PM_2.5 mass concentrations from MADE/VBS module showed much closer to the measurements. Our findings suggest that the significant aerosol modules’ prediction inconsistencies should be considered with a great caution in the PM_2.5 forecasts and policy support over the Northeast Asian region.