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The tunnel module of a rather simple Lagrangian model GRAL (Grazer Langrange model) has been chosen to study air pollutant dispersion around tunnel portals in Nanjing inner ring. Two points have been made to popularize GRAL3.5TM (the tunnel module of a Lagrangian model GRAL; the update was in May 2003) and assure it more suitable for the actual situations in Nanjing. One is to derive a piecewise function of the intermediate parameter ‘stiffness’. Another is to take Romberg NOx-NO2 scheme into account. After these 2 works on GRAL3.5TM, NO2 dispersion from portals of all the 6 tunnels in Nanjing inner ring has been simulated. The importance of limiting urban traffic volume to control air quality around tunnel portals and roadways has been emphasized.

NO-NO2-O3 recycle has been added into model dealing with air pollutant dispersion from tunnel portals-GRAL35TM to improve its performance. A mixed method GRAL-C has been discussed. It has been integrated into GRAL35TM to model dispersion in the street canyon where Tongjimen tunnel northern portal locates. It has been illustrated that GRAL35TM+C simulated NO2 dispersion more precisely than the original GRAL35TM. It requires background O3 concentrations.