OZONE LIDAR OBSERVATIONS IN THE CITY OF PARIS: SEASONAL VARIABILITY AND ROLE OF THE NOCTURNAL LOW LEVEL JET

Abstract : Ozone lidar measurements have been carried out in Paris during 4 years to characterize the seasonal variability of the vertical gradient within the urban planetary boundary layer (PBL). The interaction between NOx emission and thermal stability of the PBL is the main driver of the winter strong positive O3 gradient, while summer neutral gradient is related to weaker thermal stability and photochemical ozone production at the regional scale. Simultaneous lidar measurements of ozone and wind vertical profiles during 36 hours in September 2014 also show that the nocturnal low level jet (NLLJ) plays a significant role in the early morning ozone increase.