The Japan Clean Air Program (JCAP) is a joint research project sponsored by the Japan Petroleum Energy Center, conducted by automobile manufacturers and oil companies in Japan, and supported by the Ministry of Economy, Trade and Industry of Japan, with the aim of improving ambient air quality. Phase 1 of the project, JCAP I, was conducted from FY 1997 through FY 2001, Phase 2, JCAP II, from FY 2002 through FY 2006, and now New-JCAP (tentative name) program is undertaken (planned as from FY2007 through FY2011).

In Japan, the average air quality of the regions monitored by background monitoring stations has improved recently, partly due to efforts to reduce automobile and industrial emissions. Meanwhile, air quality along urban main roads, monitored by roadside monitoring stations, still shows some high concentration points, representing problems yet to be solved. Therefore, research and development of Roadside Air Quality Simulation Model (RsAQSM), which is capable to represent and analyze air quality conditions in real urban situation, has been settled as one of main columns in JCAP activities.

In the JCAP I, basic structure of RsAQSM was established, in which simplified representation of urban structures and emission estimation were employed. In the following phase, JCAP II, the RsAQSM was made advanced to a sophisticated model system, in which detailed urban structures, accurate traffic flow, and elaborated emission estimation method were involved, as well as easy user interface system were developed so that the RsAQSM to be distributed for use in public.

Following is the abstract of the RsAQSM established in JCAP II. The JCAP II RsAQSM consists of (1) micro-scale traffic model, (2) transient emission estimation model, and (3) CFD model. As for micro-scale traffic model (1), a software with high accuracy and versatility, “Paramics” is employed, and method for generation of road network data from digital road map data. Paramics simulates instantaneous detailed behavior of every vehicle on the road network. In transient emission estimation model (2), instantaneous vehicular emissions corresponding to vehicular behavior are estimated through newly developed transient emission map database obtained from more than 100 types of vehicles on roads. Along with (1) and (2), distribution of vehicular emission gases on the road network is estimated. In (3), software “Star-CD” is employed to simulate wind flow and diffusion of the emission gases, in which detailed configuration of construction objects along roadside is represented in the calculation grid. Comparison with tracer gas diffusion experiment in the real urban roads shows applicability of JCAP II RsAQSM to real urban roadside situation. RsAQSM can simulate “hot spots” where concentration becomes relatively very high in the local area as well as detail distribution of emission gases in the narrow roads in the background areas from the main road. Comparison with measurement of official monitoring stations shows accuracy of RsAQSM prediction of real emission gases.

Now, in the third phase of the project, New-JCAP, the RsAQSM is planned to advance further to be applicable to update roadside air quality issues, such as concentration of nitrogen di-oxides (NO2) and small size particles. Also, extension of the model to sub-regional scale and close linkage with urban regional scale air quality models is planned, which will incorporate air quality models in various scales into unified model system. These studies are on-going, and will be presented in coming years.