GAW Report No. 205 - IGAC Project

CHAPTER 6 - EUROPEFrom a regulatory point of view, enhanced urban NO 2 levels present the biggest problem.During the last few years, the annual average limit value of 40 µg/m 3 as of 2010 was violated over alarge part of the Paris agglomeration. For ozone, the national air quality standard for protection ofhuman health in 2010 limits exceedances of the daily maximum 8 h average of 120 µg/m 3 at 25times per year, averaged over three years. According to measurements in recent years, the newozone standard is achievable, except for a year with exceptionally hot and anticyclonic conditionslike during the summer of 2003. The information threshold of 180 µg/m 3 (hourly mean) for ozone isexceeded several times a year. For PM 10 , the objective of an annual average below 30 µg/m 3 isviolated in the central region of the agglomeration during some years (e.g. 2003 and 2007).6.3.5 Specific scientific campaignsIn addition to the operational air quality monitoring, a large number of field campaigns andscientific studies have been performed in the last ten years to study the processes of air pollutionbuild-up in the Paris agglomeration. A comprehensive gas phase chemistry experiment wasperformed as part of the ESQUIF campaign during the summers 1998 and 1999. Particulate matterformation in the region has been recently addressed during the very comprehensive MEGAPOLIexperiment campaigns in July 2009 and January-February 2010.A) Photo-oxidant pollution ESQUIF campaign and later studiesThe ESQUIF campaign (IPSL and LISA, Research Centre Jülich, Météo-France, AirParif,Laboratoire d’Aérologie) has allowed a detailed documentation of major gaseous pollutants (O 3 ,NO X , NOy, VOC) and a first characterisation of particulate matter (chemical, size distribution) withinthe Paris agglomeration and its plume during 13 multiday IOP’s (Intensive Observation Periods)between 1998 and 2000 [Menut et al., 2000; Vautard et al., 2003a]. An integrated observationnetwork including ground based in-situ and remote sensing instruments as well as airbornemeasurements were set up. Major outcomes from this campaign are presented in the followingparagraphs.Emission uncertaintyAirborne NOy, CO, and VOC measurements from the ESQUIF campaign were used incombination with the air quality photochemical model CHIMERE in order to diagnose uncertaintiesin the current emission inventory from AirParif for the year 2000 [Vautard et al., 2003b]. There isreasonable consistency between simulated and measured concentrations. NO y simulations agreewith measured concentrations to within 35%. There are significant underestimations andoverestimations in some individual primary hydrocarbons. However, the total mass and reactivity ofthe measured hydrocarbon mixture, which accounts for only about half of the total emitted mass,agree with modelled values to within an estimated uncertainty of 40%. These values give directconstraints for the emission uncertainty, given that uncertainty in model parameters (for exampleboundary layer height) is lower than that of the uncertainty for emissions.This work was later extended by inverse modelling work assessing the uncertainty inregional emission inventories [Pison et al., 2006; Deguillaume et al., 2007]. The latter authorsapplied a Bayesian Monte Carlo analysis using urban and surrounding air quality observations tocorrect average Paris agglomeration with respect to the initial inventory and to derive theiruncertainty: for VOC emissions the result was 0 ± 20 % (1 sigma), and for VOC emissions +16 ± 30%.Ozone plume characteristicsAverage photochemical ozone build-up in the Paris agglomeration plume during summers1998 and 1999 was about 15 ppb [Deguillaume et al., 2008]. During the ESQUIF IOP days, thisvalue was often several tenths of ppb (Figure 13). During summers 1998 and 1999, plumes weremost often encountered in the north-eastern sector, consistent with the climatology of the region ofpredominantly south-westerly winds. However, the plumes with the highest pollution levels wereencountered in the south-western sector, corresponding to anticyclonic situations with stagnantnorth-easterly winds.204