Air Quality Modeling Working Group developed two models to evaluate effects of automobile emission reduction measures on air quality improvement: Urban Air Quality Simulation Model in which secondary aerosol formation processes have been incorporated, and Roadside Air Quality Simulation Model in which micro-scale traffic flow has been taken into consideration.Concretely, a model has been built up for estimating SPM concentration in ambient air in which high concentrated air pollutants have been contained during summer and winter. The model has been built up by using UAM (Urban Airshed Model) as base model, and the following modification has been made to the base model. First, ISSOROPIA (secondary inorganic aerosol equilibrium model) has been added to the base model, and a secondary organic aerosol formation/reaction model (SOA model) has been incorporated into the model. Therefore, SOA formation rate estimation accuracy varying with temperature and SPM concentration has been improved.As for roadside air quality simulation model, vehicle speed and acceleration per vehicle per second have been estimated by using a micro-scale traffic flow model, and then an approach for estimating high-accurate emission inventory distribution in the vicinity of crossroads has been developed by applying transient emission factors obtained through chassis dynamometer experiments. The emission data have been applied to roadside air quality simulation model developed for estimating air pollutant concentration distribution at roadsides, in which air flow and diffusion have been calculated with LES (Large Eddy Simulation).Effect of New Long-term regulations (to be implemented from 2005) on air quality has been evaluated through air pollutant concentration simulation by using these models. Evaluation results have shown air quality standard attainment rate for NO2 and SPM would be vastly improved. However, the rate of NOx would be remained unattained in some roadsides. Therefore, further reduction of NOx emissions from automobiles (especially from diesel vehicles), factories, and other sources, has been required for air quality improvement.