MOTOR-VEHICLE POLLUTION IN PARIS AFFECTIN G TRAFFIC AND WEATHER CONDITIONS

The improvement of urban air quality is a major challenge namely for N O2 (nitrogen dioxide), a toxic pollutant controlled by the European Re gulation EEC n degrees 85-203. We now know that catalytic converters r educe car emissions and we believe that a reduction in traffic (alread y enforced in some cities) and the restriction of vehicle road traffic , applied to some European towns, is an area for further research. In Paris, the existance of periods of serious pollution (essentially due to NO2 levels reaching > 200 mu g/m(3) in periods of several hours) ha s made the public and public administration aware of the importance of this problem. Thus, a commitment has been made to reduce these period s of severe pollution. The study being presented deals with the search for a correlation between vehicle traffic (vehicle flow/hour) and mea sured concentrations of NO, NO2 and CO at two sites in Paris, in 1992. This relation has been established by plotting the traffic levels aga inst concentrations of each gaseous effluent. When the pollutants are well dispersed it is possible to plot the concentrations of NO and NO2 . The slope is much steeper for NO than for NO2. On the other hand, wh en meterological conditions are unfavourable (high pressure zone, stab ility of the atmosphere, temperature inversion or strong solar radianc e) no significant correlation could be observed. This proves the predo minance of meteorological conditions on NO2 levels during high polluti on periods. The study also confirmed that NO is a very good indicator of car pollution, taking into account the increasing number of diesel powered vehicles in France.