Most Americans breath dirty air -- in many places, levels of pollutants like nitrogen dioxide and ozone are in violation of federal air quality standards. And now, those standards are getting even stronger, which will put even more of the country out of compliance: EPA recently upped standards for nitrogen dioxide and is working on strengthening limits for other pollutants. But to make real improvements in air quality without breaking the bank, what is called for is not another round of top-down regulation, but an update of the Clean Air Act to allow strong market-based solutions.   Progress on cleaning our …