GAW Report No. 205 - IGAC Project

CHAPTER 6 - EUROPEFigure 13 - Number of ozone plumes during summers 1998 and 1999. An ozone plume is defined for days with aphotochemical OX (=O3+NO2) production of more than 10 ppb [Derognat, 2002]Major factors of photooxidant pollution and chemical regimesFrom an observational based approach, using ozone, NOy, and VOC measurements in theplume in conjunction with simulations, Sillman et al. [2003] derived either a VOC or NO X sensitivechemical regime ozone build-up depending on the meteorological conditions for particular days.Using Monte Carlo analysis with an observational constraint, Beekmann and Derognat [2003]showed that using the ESQUIF data set could reduce the uncertainty by a factor of 1.5 to 3 fordifferent days. Extending this type of analysis to summers 1998 and 1999, Deguillaume et al. [2008]showed that the photochemical ozone build-up in the plume was in general VOC sensitive, and thatthe result of an average VOC sensitive regime was robust with respect to model uncertainty.Derognat et al. [2003] showed that biogenic VOC emissions (mainly isoprene) significantlycontribute to photochemical ozone build-up in the region, 9 ppb on the median for ESQUIF IOPdays (a selection of more polluted days), and up to 40 ppb for an exceptionally hot and polluted day.Using the CHIMERE adjoint for sensitivity analysis, Menut et al. [2003] tested the sensitivity ofozone build-up due to a large variety of parameters and found them mainly driven by traffic andsolvent surface emissions and meteorological parameters such as temperature. On average, onlyabout a quarter of the ozone present in the Paris agglomeration plume is formed from localemissions, with the majority of the ozone advected from outside. During high pollution episodes (O 3> 90 ppb), the local fraction is more than 40% [Derognat, 2003]. In extension of results of theESQUIF campaign, the LISAIR campaign (LSCE /IPSL, AirParif) has gathered a large amount ofurban VOC measurements (C2 – C12) during May 2005 in conjunction with aerosol lidarmeasurements (boundary layer height evolution) in order to address the spatial and diurnal VOCvariability for different urban sites [Gros et al., 2007].205