Sensitivity analyses of factors influencing CMAQ performance for fine particulate nitrate

摘要

Improvement of air quality models is required so that they can be utilized to design effective control strategies for fine particulate matter (PM_(2.5)). The Community Multiscale Air Quality modeling system was applied to the Greater Tokyo Area of Japan in winter 2010 and summer 2011. The model results were compared with observed concentrations of PM_(2.5) sulfate (SO_4~(2-)), nitrate (NO_3~-) and ammonium, and gaseous nitric acid (HNO_3) and ammonia (NH_3). The model approximately reproduced PM_(2.5) SO_4~(2-) concentration, but clearly overestimated PM_(2.5) NO_3~- concentration, which was attributed to overestimation of production of ammonium nitrate (NH_4NO_3). This study conducted sensitivity analyses of factors associated with the model performance for PM_(2.5)NO_3~- concentration, including temperature and relative humidity, emission of nitrogen oxides, seasonal variation of NH_3 emission, HNO_3 and NH_3 dry deposition velocities, and heterogeneous reaction probability of dinitrogen pentoxide. Change in NH_3 emission directly affected NH_3 concentration, and substantially affected NH_4NO_3 concentration. Higher dry deposition velocities of HNO_3 and NH_3 led to substantial reductions of concentrations of the gaseous species and NH_4NO_3. Because uncertainties in NH3 emission and dry deposition processes are probably large, these processes may be key factors for improvement of the model performance for PM_(2.5) NO_3~-. Implications: The Community Multiscale Air Quality modeling system clearly overestimated the concentration of fine particulate nitrate in the Greater Tokyo Area of Japan, which was attributed to overestimation of production of ammonium nitrate. Sensitivity analyses were conducted for factors associated with the model performance for nitrate. Ammonia emission and dry deposition of nitric acid and ammonia may be key factors for improvement of the model performance.