How do I interpret air quality numbers?
December 21, 2014 9:41 AM Subscribe
If an air monitoring station near me says
Ambient Air Quality Standard for PM 2.5:
Annual Standard: 12 µg/m3
Daily Standard: 35 µg/m3
My question: what constitutes the "Annual Standard"? Is that the amount it's okay to breathe, day in an day out? If your year averages out to about 12 µg/m3 per day or less, you're probably okay?
(If anyone's interested, I'm looking at the PM 2.5 that's on the backside tab of each of those tables. PM 2.5 is extra fine particulate matter. And apparently that "µg/m3" means micrograms per cubic meter. )
My question: what constitutes the "Annual Standard"? Is that the amount it's okay to breathe, day in an day out? If your year averages out to about 12 µg/m3 per day or less, you're probably okay?
(If anyone's interested, I'm looking at the PM 2.5 that's on the backside tab of each of those tables. PM 2.5 is extra fine particulate matter. And apparently that "µg/m3" means micrograms per cubic meter. )
Those are the legal allowable limits defined by EPA for that type of air pollutant.
The EPA lists two standards for most air pollution metrics, the annual (averaged over 12 months) and the daily (averaged over 24 hours). The numbers you have in your question are the limits allowed by the EPA, and are not necessarily correlated with any kind of health risk. I'm not sure offhand what, if anything, the EPA does if those limits get busted - they may use it to fine polluters via the Clean Air Act, but I don't know for certain.
posted by backseatpilot at 9:55 AM on December 21, 2014
The EPA lists two standards for most air pollution metrics, the annual (averaged over 12 months) and the daily (averaged over 24 hours). The numbers you have in your question are the limits allowed by the EPA, and are not necessarily correlated with any kind of health risk. I'm not sure offhand what, if anything, the EPA does if those limits get busted - they may use it to fine polluters via the Clean Air Act, but I don't know for certain.
posted by backseatpilot at 9:55 AM on December 21, 2014
Response by poster: Thanks. The numbers keep hanging out between 7 & 11 though in the last hour it switched to "nothing detectible." It's hard to tell how seriously to take it- does it mean a truck drove by and kicked up dust? Who knows?
EDIT: These are posted because they're on the perimeter of a huge Chevron refinery, in case anyone was wondering.
posted by small_ruminant at 10:11 AM on December 21, 2014
EDIT: These are posted because they're on the perimeter of a huge Chevron refinery, in case anyone was wondering.
posted by small_ruminant at 10:11 AM on December 21, 2014
According to that page, the lowest number that the instrument can detect is 6 ug/m3, so nothing detectible could mean anything from 0 to 6.
posted by ssg at 10:18 AM on December 21, 2014
posted by ssg at 10:18 AM on December 21, 2014
The PM2.5 concentration values that you're seeing are probably one-hour averages. That's generally enough so they won't spike due to brief influence from transient sources such as a passing truck. Also, most dust is larger than 2.5 microns, so it doesn't affect PM2.5 readings much. However, if a truck parks next to a monitor site and idles for an hour, the diesel exhaust can definitely affect it. Usually the monitors are sited to avoid that kind of influence.
The National Ambient Air Quality Standards are intended to protect health, but it is true that there is no specific PM2.5 level below which it can be said that there is no health risk.
posted by jkent at 11:08 AM on December 21, 2014
The National Ambient Air Quality Standards are intended to protect health, but it is true that there is no specific PM2.5 level below which it can be said that there is no health risk.
posted by jkent at 11:08 AM on December 21, 2014
This thread is closed to new comments.
These standards are a little higher than the WHO's (10/25), but in line with some national standards. In general, I don't think there is strong evidence to say that there is a particular threshold below which PM2.5 is safe.
posted by ssg at 9:53 AM on December 21, 2014