[Exposure of urban bus drivers to traffic pollution]

Two measurement campaigns aimed at measuring the air pollutant emissions of vehicles (carbon monoxide, nitrogen oxides, lead, benzo[a]pyrene and formaldehyde) have been carried out using on-board sampling or analysis equipment in public buses in two major French towns. The study had a double objective: (i) to assess the occupational exposure through pollutant measurements in the breathing zone of the drivers at their working posts, (ii) to compare the quality of the air sampled outside, either at the bus front (current position of the ventilation air intake), or on the vehicle roof. Carbon monoxide measurements were performed with several Ecolyser (electrochemical detection) standardized with a Mahiak Unor 6N infra-red non-dispersive analyser and nitrogen mono- and dioxide with AC 30 M Environment S.A. analysers (chemiluminescent detection), with a data-logger recording the '5-min weighted average concentrations'. Lead on dust was sampled on cellulose acetate or quartz filters and analysed by atomic absorption, benzo[a]pyrene (as a tracer of polynuclear hydrocarbons) on quartz filters and by HPLC/UV fluorescence detector and formaldehyde (as a tracer of aldehydes) on 2,4-DNPH-impregnated silicagel tubes by HPLC/UV. Recording and sampling were performed for 18 single and return routes in the center of Paris (for 1.5-2 h each) and for 25 routes in the center of Bordeaux (for 35-60 min). The results clearly indicate that the occupational exposures of urban bus drivers for the six pollutants are lower than the exposure limit values in the working place (French Labour Department or A.C.G.I.H. standards). In particular, levels for benzopyrene, associated with carcinogenic hazard, do not increase 5% of the standard from Russian origin (150 ng/m3). On the contrary, concentrations reached the levels recommended by international air quality standards (OMS, US or European standards) for carbon monoxide, nitrogen dioxide and lead. When CO mean concentration values by bus lines in the driver's breathing zone are compared with the measurement results provided for the same sample days by the Air-Parif control network (in Paris), or the Gertrude traffic management system (in Bordeaux), it may be assumed that they are at the level of the most polluted surveillance stations. The CO concentrations are significantly lower in the outdoor air coming from the roof than in that coming from the front of the bus, so that better indoor air quality at the driving post can be found with air intake from an upper than a lower part.