A development of ozone abatement strategies for the Grenoble area using modeling and indicators

The Grenoble metropolitan area, located in the French Alps, regularly has periods of high ozone concentrations during the summertime. Grenoble is located in a Y shaped convergence of three deep valleys, some 3000 m above sea level, with typical wind pattern. During the summer of 1999, a major field campaign GRENOble PHOTochemistry (GRENOPHOT) was held in order to obtain measurements necessary for air quality model validation. The air quality model METeorological PHOtochemistry MODel (METPHOMOD) is used to investigate the dynamic characteristics of air pollution in the Grenoble area during the GRENOPHOT field campaign. The meteorological and atmospheric chemistry simulations were validated using both ground and vertical profile measurements (e.g. lidar) performed during the observation period (25–27 July) when the measured ozone concentrations reached 95 ppb. Both the spatial as well as the temporal variability of the simulated ozone concentrations were in good agreement with the measured values. The highest ozone values were found, in the southern zone, some 20 km downwind of the city center. It was found that about 32 ppb of fresh ozone are generated in the Grenoble plume. For developing ozone abatement strategies it is important to know whether in a specific area the ozone production is limited by VOC or NOx. Several indicators were proposed for distinguishing between VOC and NOx limitation. The morning Θ=τHOVOC/τHONOx (the ratio of the lifetimes of OH against losses by reacting with VOC and NOx) was applied and the afternoon indicator was κ=[H2O2]/[HNO3]. The Θ indicator gives information about the effect of changes in the emissions on the ozone formation in the air parcel which passes there, whereas κ provides information about the sensitivity of ozone formation in the aging plume. A combination of both indicators can be used to obtain a comprehensive view of the ozone formation in the Grenoble area. These results are confirmed by the investigation of the air mass regime with the time evolution of the ozone isopleths at the maximums locations (south and north west valleys).