GAW Report No. 205 - IGAC Project

CHAPTER 8 – KEY ISSUES AND OUTLOOKas possible in the growth of vehicle fleets in emerging megacities. Over the three decadescovered by the US data sets, the hydrocarbon emissions decreased by a significant factor(approximately an order of magnitude), while the ratios of the individual hydrocarbons remainednearly constant (Figure 8a). Differences in the hydrocarbon patterns between cities provideinformation regarding secondary sources. The ambient CO to NO X concentration ratio reported forthe three non-US megacities are higher than present US ratios (Figure 8b), but lower than thoseobserved in the 1980s in the US (not shown). The one exception to the preceding statement is thevery high concentrations of CO observed in Beijing, which apparently have a large regionalcontribution.Figure 7 - Comparison of evolution of ambient ozone (solid and dotted heavy lines) and PM10 (light lines shaded to zero)concentrations in three megacities of similar populations. Through the time period shown each of the three cities had apopulation within ± 40% of the 3-city average (dashed black line). The solid lines are polynomial fits to tabulated air qualitydata. The ozone for each city is the statistic that is used for the US NAAQS (3-year running mean of 4 th highest dailymaximum 8-hr average.) the dotted line is a fit to the maximum 8-hr average ozone observed in the limited research datasets that are available for Beijing. For Los Angeles PM10 is the annual average for the station measuring the highestconcentrations; for the other two cities the annual average over all stations in the city’s network is givenFigure 8 - Comparison of relationships between ambient concentrations of primary pollutants in three megacities.[Parrish et al., 2009a]290