A new study by Chinese researchers sheds new light on the issue -- and it has implications for breathers in the United States.
The study, published this month in Environmental Health Perspectives (a monthly journal of peer-reviewed research and news published with support from the National Institute of Environmental Health Sciences, National Institutes of Health, U.S. Department of Health and Human Services), found that the smaller a soot particle is, the more deadly. http://ehp.niehs.nih.gov/wp-content/uploads/121/10/ehp.1206398.pdf
To quote from the study's conclusions:
Our findings suggest that particles < 0.5 μm in diameter may be most responsible for adverse health effects of particulate air pollution and that adverse health effects may increase with decreasing particle size.
Why should those of in the U.S. care? There is evidence that these really tiny "ultrafine" particles aren't being adequately controlled.
For example, as noted in a recent report by emission control makers bit.ly/1bvhefU , current strategies aimed at simply reducing the overall mass of particle soot from diesel and gasoline engines may be missing the most deadly soot agents:
While the body of epidemiological and toxicological studies on [ultrafine particles] is not as robust as the body of literature on the health impacts of overall PM mass, we see emerging trends in the research that suggest evidence of potential health impacts. In light of these trends, Europe has adopted first-ever limits on particle number (PN) as a way to ensure that diesel particulate filters (DPFs) are used and UFPs are reduced. In addition, Europe will soon begin implementation of a PN limit for gasoline-fueled cars that are equipped with direct injection, which will accelerate the introduction of PM reduction technologies such as gasoline particulate filters (GPFs), high pressure spray guided injectors and other combustion control technologies for PM in the European car market. This is a topic that deserves additional research and attention in the U.S.
In this context, the new research from China is something our regulators need to be aware of, so we're not letting too many deadly soot particles slip through the cracks.