Check out this information from the American Lung Association on new soot standards from the EPA:
Particulate matter, also known as particle pollution or soot, is a mixture of liquid droplets and solid particles made of toxic chemicals, metals and smoke. These particles are small enough to penetrate deep into the lungs and even into the bloodstream, leading to tens of thousands of premature deaths, heart attacks and asthma attacks every year. Particles come from wide-ranging sources, including coal-fired power plants, industrial boilers, diesel vehicles and woodstoves.
The EPA tightened the limit, called the national ambient air quality standards, for the annual average level of fine particulate matter (PM 2.5) to 12 micrograms per cubic meter (µg/m3) from the outdated standard set in 1997 of 15 µg/m3. EPA made no changes to the 24-hour fine particle standard or the coarse particle standard (PM 10) despite evidence that both standards need strengthening.
Click the link above to read the whole press release.