I discovered a really interesting article about the Air Quality Index (AQI) titled: “Air Quality Index – time for a rethink?” written by Clive Stott in the Dec. 2017 issue of the Woodsmoke Climate Change News newsletter on pages 14 and 15.
In it, Stott, in effect, asserts PM 2.5 is unsafe regardless of air concentration or level of such. I take that to mean that no matter the concentration in the air, if breathed in, fine particulate matter is unhealthy, period.
So, let’s think about this for a moment.
What we know is, fine particulate matter is released in the air as a result of fossil-fuel combustion or from the burning of wood, for example. But, it can also form in the air when certain chemicals combine and, in addition to being a solid (often referred to as soot) can take liquid form as well.
Speaking to this, and in “Particulates uncovered: Diesel, soot get closer look,” the California Environmental Protection Agency Air Resources Board states: “‘Particulate matter (PM) is a complex mixture of substances ranging from dry solid fragments, solid-cores fragments with liquid coatings, and small droplets of liquid,’ the California Environmental Protection Agency Air Resources Board (ARB) in: ‘Facts About Particulate Matter Mortality: New data revealing greater dangers from PM2.5,’ expressed. ‘These particles vary in shape, size and chemical composition and may include metals, soot, soil and dust.’”
As to size, the particles are less than 2.5 micrometers in diameter (20 to 30 can be placed side-by-side across the width of a human hair) and they can become lodged deep in lung tissue and/or enter the bloodstream.
According to information presented on the “Air Quality Guide for Particle Pollution” page presented on the U.S. Environmental Protection Agency’s (EPA) Web site inhalation of PM 2.5 is linked to: coughing and wheezing; reduced lung function; heart and asthma attacks; strokes and early death.
So, understanding this, the question on the table is: If PM 2.5 is unhealthy or unsafe at any concentration, then why have it listed on the Air Quality Index at all?
Okay, but, wait a minute. What about the National Ambient Air Quality Standards (here in the U.S.) for such – both 24-hour and annual which are 35 and 12 micrograms per cubic meter of air, respectively?
So as to provide a bit more detail, I wrote in the “Making sense of air quality data – PM 2.5” post on Oct. 11, 2014: “For instance, the U.S. Environmental Protection Agency (EPA) assigned a health standard for PM 2.5 of 35 micrograms per cubic meter (35 μg/m3 set by the EPA on Oct. 17, 2006). This particular threshold is in reference to daily ambient PM 2.5 or over a period of 24 hours. So, for every cubic meter of air, if the fine particulate matter concentration is greater than 35 micrograms, the standard is exceeded. This corresponds to an Air Quality Index (AQI) of 101 and places air at the unhealthy-for-sensitive-individuals or populations level.
“Then there is the U.S. EPA annual fine particulate matter standard. This is set at 12 μg/m3 of air and became effective on Dec. 14, 2012.”
So, take PM 2.5 measured over a 24-hour period. In establishing or setting standards, by doing such, does this not suggest that daily air concentration with less than 35 micrograms per cubic meter of PM 2.5 mean air quality is considered good or is in the good range given this standard being in effect? But, if PM 2.5 is unsafe regardless of air concentration or level, then to set or establish a standard or limit for such, would this not be a moot point? In other words, what would be the point? I believe this is Stott’s point exactly.
Speaking of which, Stott does have a point.
So I now turn the matter over to you: I am interested in knowing what you think as I am certain others would be as well.
Article updated on Nov. 25, 2017 at 11:09 a.m. Pacific Standard Time.