Tiny Particles In Air Pollution May Pose Greater Danger Than Once Thought


While the negative health effects of air pollution are no secret, recent discoveries have shed light on some previously unknown facts about fine air particles. Now, new research findings are raising the question of whether or not current standards for air quality control are adequate. Researchers have found that a type of fine particles known as secondary organic aerosols are in greater quantities, and therefore pose a greater risk to health, than previously assumed.

Particulate matter, abbreviated PM, encompasses all particles in the air. This can include substances such as smoke, dirt and soot. Naturally, these particles can vary widely in size. Fine particulate matter (PM2.5) is categorized as being less than 2.5 micrometers in diameter while course particles (PM10) range from 2.5 to 10 micrometers in diameter. Both fine and course particles pose potential health risks because they can become trapped in the respiratory system when inhaled. Fine particles, however, are known to be more dangerous because their small size allows them to become trapped deep within the lungs. Fine particles can originate from various sources of combustion. Secondary organic aerosol particles are formed through chemical interactions that occur after, rather than during, combustion. Because the secondary compounds have a greater total mass, they are a greater threat.

The new findings have a significant effect on what was previously known about gaseous byproducts. Previously, it was assumed that the gaseous byproduct from internal combustion engines clung to drops of moisture in the air and disperses upon evaporation. Recent studies, two of which were conducted at the University of California, Irvine and at the Pacific Northwest National Laboratory located in Richland, Washington lead scientists to believe that this may not be the case. The findings suggest that these particles actually cling on more tightly, producing a polluted air particles that evaporate slower and persist longer than previously assumed. A professor of analytical and atmospheric chemistry at Purdue University and a reviewer of the Irvine study indicated that that study’s results point to a concentration of particles that is significantly higher than once thought. Current models underestimate the amount of secondary organic aerosols “sometimes by as much as a factor of 10”, Shepson said to the New York Times.

These discoveries lead the public health community to question and possibly revise current standards. Bill Becker, an affiliate of the National Association of Clean Air Agencies, told the New York Times, “If the authors’ analysis is correct, the public is now facing a false sense of security in knowing whether the air they breathe is indeed safe,” The U.S. Environmental Protection Agency (EPA) is reconsidering their current national ambient air quality standards with regards to fine particles. Under the Clean Air Act, PM2.5 is considered a criteria pollutant; standards are put in place in attempt to ensure air quality and health. Currently, the agency has set a standard of 35 micrograms per cubic meter of air for short-term (daily) exposure and 15 micrograms per cubic meter for long-term (annual) exposure. Until the newest findings are incorporated into the latest review, it is unclear how much the standards will change, if at all.