GAW Report No. 205 - IGAC Project

CHAPTER 6 - EUROPEFigure 3 - The percentage change in the global surface July O3 mixing ratio due to megacity emissionsunder four scenarios [Butler and Lawrence, 2009]6.2 LONDON6.2.1 City introductionLondon is located in the southeast of England, UK. Greater London, which includes the Cityof London as well as 32 London boroughs in the surrounding area has a population ofapproximately 7.5 million (as of mid-2005). The entire London metropolitan area is just under 14million people. Greater London covers an area of 1,570 sq km and sits on either side of theThames River, approximately 40 km west of the coast of the North Sea. The minimum andmaximum temperatures range from 2.4 to 13.7°C and 7.2 to 22.3°C in January and July,respectively.6.2.2 Emissions sources, trends and dataThe large majority of nitrogen oxides (NO X ), carbon monoxide (CO), particulate matter withan aerodynamic diameter less than or equal to 10 µm (PM 10 ) and certain volatile organic compound(VOC) emissions in London are from mobile sources [Mattai and Hutchinson, 2008]. In an estimatefrom 1997, road emissions of NO X , CO, and PM 10 were found to contribute 76%, 97%, and 77% tototal emissions for all of London, respectively [Crabbe et al., 2000]. Correspondingly, a significantnumber of studies monitoring roadside pollution throughout London have been conducted. Thetrends in NO 2 and NO X from 1997 to 2003 from 36 sites in London have been documented by[Carslaw, 2005] as shown in Figure 4. While NO X concentrations decreased, the NO 2concentrations have remained basically the same from 1997 to 2003. These may have been due tochanges in the vehicle fleet composition, changes in traffic management in London and/or controltechnologies applied to diesel vehicles [Carslaw, 2005]. Changes in the concentration of PM inLondon have also been linked to traffic. Annual mean PM 10 from 1994 to 2004 at different types oflocations throughout London were documented by [Fuller and Green, 2006], and are shown inFigure 5. [Fuller and Green, 2006] found that secondary and natural sources of PM 10 declinedfrom 1997 to 2003, whereas primary sources increased from 1998 to 2003; the largest increases inprimary PM were observed at roadside sites. It should also be noted that long-term transport of airmasses, primarily from mainland Europe, can contribute significantly to PM concentrations in theLondon metropolitan area, especially episodes of elevated concentrations [Charron et al., 2007].197