I am not surprised that the latest science blames asthma problems on indoor rather than outdoor pollution. I complained of the questionable asthma science behind the American Lung Association ad, Red Carriage Advertisement III, in 2011. According to Cato,  Asthma Justification for EPA Regulations Gutted by the Latest Science, a recent scientific paper in the Journal of Asthma and Clinical Immunology says somewhat cryptically:

Taking the United States as a whole, living in an urban neighborhood is not associated with increased asthma prevalence.

Cato then defers to Dr. Joseph Perrone, chief science officer at the Center for Accountability in Science, to explain why this research is important to the Clean Air Standards in this article on The Hill:

It’s a radical finding. The study upends more than half a century of research that assumed outdoor air pollution in cities was to blame for higher asthma rates—a hypothesis repeatedly used by EPA regulators to justify the agency’s regulations.

…

For years, environmentalists and regulators have cited childhood asthma as an excuse for ever-stricter pollution rules. The U.S. Environmental Protection Agency (EPA), for instance, uses asthma as a pretext for nearly every “clean air” regulation issued since the 1970s.

But what if the assumed link between air pollution and childhood asthma doesn’t actually exist?

New research questions the long-held wisdom on asthma and air pollution, casting doubt over the scientific basis for EPA’s expansive regulatory agenda….

The study still points to air pollution as a cause for asthma, only it’s indoor air pollution—think second hand smoke, rodents, mold, etc.—that may be the main culprit.