Red Air by the Numbers

Apr 29, 2013

The EPA has designated this week Air Quality Awareness Week. As part of UPR’s community engagement project, Jennifer Pemberton has been talking to Cache County residents about the experience of living with some of the nation’s worst air pollution. This week, she’s taking their questions and comments to local experts. In today’s report, she enlists Dr. Randy Martin to define Red Air by the numbers.

A red air day just sounds bad. When you hear a report that involves a code red or red alert, you know that something’s wrong. In January of this year we had 16 red air days in Cache County. That’s 16 days over the federal limit -- up to 3 times over the federal limit on some days. Something was wrong.

Residents of Utah have 2 places to go for air quality monitoring. The EPA has a site called Airnow. A Red Air day using the EPA’s Air Quality Index is when pollution levels are at 151 on a weighted scale that goes from 0 - 500. That’s  when “everyone may begin to experience health effects.”

The EPA's AirNow Air Quality Index uses the "measuring stick" approach to describing air quality. The scale goes from 0 - 500. A "red air day" is 151 - 200.

The Utah Department of Environmental Quality’s Division of Air Quality, here on referred to as the DAQ, has a website,,  that features current conditions by county and a 3-day forecast. They measure particulate pollution using its actual scientific unit of measure which is micrograms per cubic meter. A Red Air Action Alert is issued when particulate levels are more than 35 micrograms. This is when wood burning prohibitions go into effect and the division “requests that people drive less by combining trips or using mass transit.”

The Utah Division of Air Quality uses a thermometer to show the PM2.5 level in micrograms per cubic meter. On January 9, 2013, the PM2.5 level surpassed the 70 microgram mark well into "red air day" territory.

In the winter months, PM2.5 is the pollution that matters. It’s the one that kicks out the red air alerts. PM2.5 is a household term in Cache County. I wanted to know what the big deal was about these microscopic flecks, so I went to talk to Utah State University’s Dr. Randy Martin, Associate Professor of Civil & Environmental Engineering. He has a joint appointment at the water lab and climate center.

“2.5, what it means is 2.5 microns and smaller. It’s a collection of particles. PM10 is 10 microns and smaller. The reason those numbers are important is, back in 1987 EPA used to just regulate all the dust in the air, it was called TSP. They went to PM10 because research has shown that’s really the size that’s most of a health concern because you can can breathe it into the respiratory system. As research went on after 1987 up through the next decade, we found out that it was really the PM2.5 that can get down into the small lungs. The stuff 2.5 microns and smaller can go all the way down in the alveoli. If it’s actually smaller than 1, it can cross directly into the capillaries, which is where you start to see the cardio effects.”

So 35 micrograms of this stuff in a cubic meter of air is what defines a red air day. And that number isn’t arbitrary. That’s the level we know causes human health problems. And most of the experts agree that this number is too high.

“Those standards are based on the best available health information. They’re not arbitrary numbers. They are numbers that are health based. I fully expect as more health studies become available the standards could even lower. But to our best available knowledge this 35 is going to offer the best public health that we know of right now.”

The Air Quality Index was designed for the public. And there are all these nice maps and charts and color scales for us to understand some very complicated atmospheric chemistry. But how are we supposed to know what to do with that information? What does the DAQ want us to know?

“What do they want us to know? I think it’s when do they want us to know too. One of the things we argued for in the valley,  if you hit 35 and it turns to red, it’s too late. It needs to go red or a strong strong message when it’s yellow that now is the time to start cutting down on your driving, not when it’s already red.”

Utah’s state climatologist, Dr. Robert Gillies, developed a model that was tested this winter to predict pollution-concentration episodes that result from temperature inversions. I should say that part of the air quality problem in Cache Valley is due to weather and climate patterns that we absolutely have no control over.

Randy Martin helped test Dr. Gillies’ inversion prediction models this winter.

“This last year when we were paying more attention to those forecasts, they were generally pretty good...But it’s still a forecast and people tend to put that stuff in the back of their minds...Am I planning 4 weeks out how I’m going to drive on a particular day? Not likely...It’s amazing how well the model is working. I hope it keeps the public aware but any time you’re doing any kind of forecasting and you don’t get it right, then you look pretty bad and you lose public confidence.”

We did start to hear air quality forecasts in the media this winter. And as a community we started to do a few things in reaction to red air days.

“We aren’t going to clean up the air with what we’re doing. We’re going to make it better. But we’re still going to have bad air days. If we can convince people to drive less particularly during bad air, that will have a big effect.”

The air quality monitoring information published by the EPA and the DAQ every day is the scientific community’s way of communicating to us what they’ve spent years discovering in labs. There is a lot of calculation and a lot of passion that goes into those numbers, but what we do with that information is entirely up to us.