8.4.1.4 Urban air quality
Background levels of ground-level ozone have risen since pre-industrial times because of increasing emissions of methane, carbon monoxide and nitrogen oxides; this trend is expected to continue over the next 50 years (Fusco and Logan, 2003; Prather et al., 2003). Changes in concentrations of ground-level ozone driven by scenarios of future emissions and/or weather patterns have been projected for Europe and North America (Stevenson et al., 2000; Derwent et al., 2001; Johnson et al., 2001; Taha, 2001; Hogrefe et al., 2004). Future emissions are, of course, uncertain, and depend on assumptions of population growth, economic development, regulatory actions and energy use (Syri et al., 2002; Webster et al., 2002a). Assuming no change in the emissions of ozone precursors, the extent to which climate change affects the frequency of future ‘ozone episodes‘ will depend on the occurrence of the required meteorological conditions (Jones and Davies, 2000; Sousounis et al., 2002; Hogrefe et al., 2004; Laurila et al., 2004; Mickley et al., 2004). Table 8.4 summarises projections of future morbidity and mortality based on current exposure–mortality relationships applied to projected ozone concentrations. An increase in ozone concentrations will affect the ability of regions to achieve air-quality targets. There are no projections for cities in low- or middle-income countries, despite the heavier pollution burdens in these populations.
Table 8.4. Projected impacts of climate change on ozone-related health effects.
| Area | Health effect | Model | Climate scenario, time slices | Temperature increase and baseline | Population projections and other assumptions | Main results | Reference |
|---|
| New York metropolitan region, USA | Ozone-related deaths by county | Concentration response function from published epidemiological literature. Gridded ozone concentrations from CMAQ (Community Multiscale Air Quality model). | GISS driven by SRES A2 emissions scenario downscaled using MM5 2050s | 1.6 to 3.2°C in 2050s compared with 1990s | Population and age structure held constant at year 2000. Assumes no change from United States Environmental Protection Agency (USEPA) 1996 national emissions inventory and A2-consistent increases in NOx and VOCs by 2050s. | A2 climate only: 4.5% increase in ozone-related deaths. Ozone elevated in all counties. A2 climate and precursors: 4.4% increase in ozone-related deaths. (Ozone not elevated in all areas due to NOx interactions.) | Knowlton et al., 2004 |
| 50 cities, eastern USA | Ozone-related hospitalis-ations and deaths | Concentration response function from published epidemiological literature. Gridded ozone concentrations from CMAQ. | GISS driven by SRES A2 emissions scenario downscaled using MM5 2050s | 1.6 to 3.2°C in 2050s compared with 1990s | Population and age structure held constant at year 2000. Assumes no change from USEPA 1996 national emissions inventory and A2-consistent increases in NOx and VOCs by 2050s. | Maximum ozone concentrations increased for all cities, with the largest increases in cities with currently higher concentrations. 68% increase in average number of days/summer exceeding the 8-hour regulatory standard, resulting in 0.11 to 0.27% increase in non-accidental mortality and an average 0.31% increase in cardiovascular disease mortality. | Bell et al., 2007 |
| England and Wales | Exceedance days (ozone, particulates, NOx) | Statistical, based on meteorological factors for high-pollutant days (temperature, wind speed). | UKCIP scenarios 2020s, 2050s, 2080s | 0.57 to 1.38°C in 2020s; 0.89 to 2.44°C in 2050s; 1.13 to 3.47°C in 2080s compared with 1961-1990 baseline | Emissions held constant. | Over all time periods, large decreases in days with high particulates and SO2, small decrease in other pollutants except ozone, which may increase. | Anderson et al., 2001 |
There are few models of the impact of climate change on other pollutants. These tend to emphasise the role of local abatement strategies in determining the future levels of, primarily, particulate matter, and tend to project the probability of air-quality standards being exceeded instead of absolute concentrations (Jensen et al., 2001; Guttikunda et al., 2003; Hicks, 2003; Slanina and Zhang, 2004); the results vary by region. The severity and duration of summertime regional air pollution episodes (as diagnosed by tracking combustion carbon monoxide and black carbon) are projected to increase in the north-eastern and Midwest USA by 2045-2052 because of climate-change-induced decreases in the frequency of surface cyclones (Mickley et al., 2004). A UK study projected that climate change will result in a large decrease in days with high particulate concentrations due to changes in meteorological conditions (Anderson et al., 2001). Because transboundary transport of pollutants plays a significant role in determining local to regional air quality (Holloway et al., 2003; Bergin et al., 2005), changing patterns of atmospheric circulation at the hemispheric to global level are likely to be just as important as regional patterns for future local air quality (Takemura et al., 2001; Langmann et al., 2003).