Variabilité spatio-temporelle du CO dans le centre de Limoges : apport des mesures itinérantes

The aim is to show the spatiotemporal variability of a typical urban pollutant: the carbon monoxide (CO). This gas is indeed well representative of car traffic-related pollution and its concentrations are likely to vary in the center of a medium-sized city as Limoges, in both space and time. On a fine temporal scale, spatiotemporal fluctuations of CO can be dependent on atmospheric conditions, road traffic and urban architecture (such as urban street layout and the difference between wide and narrow streets). This paper is based on itinerant measuresʼ series, carried out within the town center of Limoges. This place corresponds to the historical and commercial center, which is particularly frequented by pedestrians and motorists, with a low speed traffic, frequent slowing downs and accelerations. Itinerant measures have been done four times, thanks to a "Testo" sensor with every 5 seconds recordings, along a specific way: a 4 kilometers long and 1 hourʼs walk along various types of streets (pedestrian, narrow and wide ones, squares and crossroads). Those measuresʼ series have been carried out on Sunday 10th and Monday 11th February 2008, during anticyclonic conditions, with low or moderate wind speeds. It is turned out that the upper CO concentrations (until 7,6 ppm) appear during the lowest wind speeds (1,3 m/s), whereas the average lowest pollution (0,9 ppm) is recorded when the average highest wind speeds are present (4,2 m/s). Moreover, it is shown that noticeable pollution increases can be recorded in the case of car traffic increase on a boulevard, stops at red lights and a few carsʼtraffic on a narrow street.