Carbon-monoxide levels seem to be steadily decreasing over the eastern U.S., signaling that polices to reduce pollution may be succeeding, according to University of Maryland scientists who published their findings in Geophysical Research Letters. Still, air quality in East Coast cities this summer has ranked among the worst in the 1990s, with levels of ground-level ozone, the primary component of smog, surging above the federal threshold on a number of days, according to preliminary EPA figures.