PASSIVE SAMPLING OF SUMMER CONCENTRATIONS OF NO2 AND O-3 IN AN ALPINEVALLEY, CHAMONIX, FRANCE

Passive sampling of summer concentrations of NO2 and O-3 in an alpine valley, Chamonix, France. Ground measurements of NO2 and O-3 were cond ucted in summer 1995 in an alpine valley at Chamonix, in France, durin g three weekly sequences from July 17th to August 7th. The concentrati on of gases were estimated using a passive method from the bottom of t he valley (altitude: 1020 m) to the timberline (2200 m) over 42 sites distributed merely at the junction of every square kilometre. Two samp le sites were also selected at the two valley's ends to estimate the l ongitudinal fluxes of gases. Active continuous measuments were simulta neously collected at Chamonix and helped to calibrate the concentratio ns of gases obtained by the passive method. The results indicated that NO2 concentrations augment along the NE-SW axis of the valley, from 9 .9 to 50.3 mu g/m(3), but damp gradually with altitude (from 27.3 mu g /m(3) in the valley to 3.2 mu g/m(3) at 2000 m). Maximum concentration s were found at the position of the main road traffic: main road (26 0 00 vehicles per day), Mont Blanc tunnel road (7000 v/d) and parking lo ts. O-3 concentrations are maximum in altitude (125 mu g/m(3)) in the northeastern part of the valley and damp toward the lower south-wester n area (67.1 mu g/m(3)). The geographical patterns of pollution are ex plained by the local climatic conditions (air turbulence and temperatu re gradient), associated with the valley geomorphic configuration and the geographic and temporal distribution of road traffic.