Alison Davis of the EPA says the agency has reviewed the science of fine particle air pollution and it shows current standards aren't adequately protecting public health.
DAVIS: "More than 300 new epidemiological studies that were reporting adverse health effects even in areas that were meeting the current annual standard."
The EPA recently proposed tightening the annual standard for fine particle pollution so there's less soot in the air.
But Robert McClernon of the California Construction Trucking Association says air quality standards put him out of business years ago. He thinks new ones would mean loss of jobs, and more people without health insurance.
MCCLERNON: "They require us to retrofit our trucks to the tune of $40,000 per truck, or buy a new truck which costs upwards of $200,000. We can't afford such costs."
But health and environmental groups say the new EPA's proposed standards are not stringent enough. Paul Cort is with Earthjustice.
CORT: "I think people have the sense and understand that obviously bad air affects our breathing, you know, it makes our eyes water and all that. But I don't think that people understand that particulate matter - in particular - is killing people."
The EPA proposes to leave other air quality standards unchanged, and it wants a new standard to control haze in urban areas. The public comment period on the EPA's proposed changes runs through the end of August.