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Urban Areas 277Atmospheric CO 2concentrations in urban areas are usually much higher than annualglobal averages because of the local sources of emissions. For example, measurementsin Phoenix showed peak CO 2ambient concentrations that were up to 75% higherthan in its rural areas (Idso, Idso, and Balling 2001). In Salt Lake City, Pataki, Bowlingand Ehleringer (2003) found peak CO 2ambient concentrations during wintertime atmosphericinversions that were around 60% higher than in its rural areas, while summertimeafternoon values were very close to background levels. Jacobson’s 2010(a) LosAngeles study of the potential implications of these “urban domes” of CO 2, found thathigher ambient CO 2concentrations result in small but important increases in air pollution(ozone and particulate matter; see Figure 13.9). viii This is in addition to potentialincreases in air pollution from a global increase of GHGs in the atmosphere reported byothers (e.g., EPA 2009; Jacobson and Street 2009; Zhao et al. 2011). Local control of CO 2emissions would provide a means of improving urban air quality conditions in cities ifthe urban “dome effect” is confirmed.Figure 13.9 Changes of ozone (O 3) concentrations due to the “CO 2dome” effect in LosAngeles. Modeled differences in ozone concentration in parts per billion from two simulations (with andwithout CO 2emissions in Los Angeles); August-October. Contour lines indicate topography. The darkerareas inland, to the south and west of the San Gabriel and Santa Ana Mountains (e.g., at approximately33.7°N, 117.2°W), show increases in surface ozone, due to increased CO 2aloft. Increased ozone isimplicated in air pollution-related deaths. Adapted with permission from the American Chemical Society(Jacobson 2010a, 2501).Climate change will affect Southwest cities differently, due to their unique geographicallocations, settlement histories, population growth rates, shapes and infrastructure,economies, and socio-demographic characteristics. Impacts to residents will in turndepend on where they live and their own capacities and incomes. Southwestern cities—especiallythe largest metropolitan areas in each of the Southwestern states—haveshared characteristics that may cause climate to impact them differently than cities inother regions of the country. Historic development paths of cities continue to influence