The creation of carbon dioxide “domes” by heat-trapping greenhouse gas emissions over urban areas makes CO2 emissions a greater health risk for city-dwellers than people who live in rural areas, according to a new study. Increased concentrations of CO2 over city areas cause local temperatures to rise, which in turn increases levels of air pollution and ground-level ozone, said Mark Z. Jacobson, director of the Atmosphere/Energy Program at Stanford and author of the study published in the journal Environmental Science and Technology. In addition, the more stable air column over cities tends to slow the dispersal of pollutants. According to Jacobson, the existence of the CO2 domes above urban areas exposes a fundamental flaw in the cap-and-trade legislation passed last year by the U.S. House of Representatives, which allows carbon emitters to trade emissions allowances regardless of location. “Not all carbon dioxide emissions are equal,” Jacobson said. “As in real estate, location matters.” His study suggests that emitters of CO2 in urban areas should pay a higher price for their pollution than emitters in rural areas.