Mexico City has its worst smog in more than a decade. The government has ordered cars off the street one day a week, but city planners say that isn't a long-term solution.
A human rights group says police in China detained two people for protesting the government's approach to smog. A popular film about the same topic was recently removed from major websites.
The rules would lower the threshold for ozone from 75 parts per billion to between 65 ppb and 70 ppb. They are likely to be opposed by industry groups as well as Republicans.