Planning Trips – All about the Air Quality Index

When I plan trips, I have specific steps I follow.

I look at maps, see what permits I need to procure, plan out my supplies, etc.

And as I get closer to the trip, Joan and I have a “nuts and bolts” checklist we follow to ensure we don’t forget some essential items and for last-minute checks we like to do.

Checking the weather via NOAA features prominently.

However, because we are now in the Anthropocene, there are two items I now check:

  • Inciweb for fires since about 2016 or so.
  • And new for 2021, I now see if I am going to suck in the equivalent of a pack of unfiltered Camels; I now check the Air Quality Index (AQI).

What is the Air Quality Index? 

To quote Wikipedia:

An air quality index is used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. Public health risks increase as the AQI rises.

To put it briefly, the higher the AQI, the worse the air conditions for breathing.

There is no worldwide standard for AQI; different countries use different criteria.  Since I base myself in the land of Freedom UnitsTM , I’m going to the US-based system for comparison.

However, a word of note the US system is more stringent with its rating scale (that’s good!) than some other countries. Many other countries make use of the US scale because it is stringent. Yeah, America!

And another word of note:  The AQI is based primarily on PM2.5 measurements, but not entirely as other pollutants potentially make up the AQI scale. However, PM2.5 is the measurement that tends to lead to a higher AQI index.

First, AQI is separately calculated for each pollutant by converting the pollutant’s concentration into a number between 0 to 500. Then, the AQI is determined by the pollutant with the highest index.

For example, if the PM2.5 AQI is 125, the PM10 AQI is 50, SO2 is 30, NOx is 50, and all other pollutants are less than 125, then the AQI is 125–determined ONLY by the concentration of PM2.5.

And what is PM2.5? Particulate Matter; 2.5 micrometers or less in diameter.

Or in more detail:

Particulate matter, or PM2.5, is very small particles in air that are 2.5 micrometers (about 1 ten-thousandth of an inch) or less in diameter. This is less than the thickness of a human hair. Particulate matter, one of six U.S. EPA criteria air pollutants, is a mixture that can include organic chemicals, dust, soot and metals. These particles can come from cars and trucks, factories, wood burning, and other activities.

In layperson terms with my non-science background, the higher the AQI, regardless of the scale, the worse the air.

And the worse the PM2.5, in particular, the worse the air and the larger the scale. Scientists, medical personnel, and engineers tend to towards PM2.5 since it is a universal measurement with no worries about which scale you use.  On the other hand, the AQI is the measurement often given and easy to understand for many.

This handy graphic from IQAir sums it up rather well:


Enough science. Where do I find this info?

If you are typing on a Windows 10 machine, I noticed that the AQI became very mainstream this year. Every day, I see the weather and now my local AQI in the taskbar:

A temperate desert evening with some moderately bad air quality.

Convenient. And another example of how easily we normalize crappy things.  But that’s another discussion!

For more detailed information, I’ve been making use of IQAir. 

I enjoy their worldwide scope, the easy-to-use map, extended forecasts, the way the information gets presented, and the fact that they include the PM2.5 levels.

And I do like the extended forecast. It looks like a clearer weekend:

And you can zoom to other monitoring stations:

IQAir also makes an app for iOS and Android platforms.

Of course, these forecasts get based on monitoring stations. More remote areas don’t have monitoring stations. And it would be best if you used an educated hunch to apply AQI to a more mountainous area or something nearby.

Or, you can let the US tax dollars do some of this work for you.

The best way to get an overall feel for a region is at the EPA’s and their interactive map in particular.

I see if I wanted to hike in some of my old stomping grounds, it might be OK if not particularly scenic or pleasant:

In summary, I find that IQAir works best for specific places as a starting point as I like their interface. But if I need a broader view of where there’s no monitoring station,’s interactive map proves helpful. 

Why do I care about this crap?

Friends of mine hiked the Great Divide Trail the same year I did and hit some awful smoke in the Banff area.

I am in excellent shape and love to go hiking and backpacking as much as I can.  However, I do spend a lot of time outside regularly and often with Joan.  If we want to continue excellent health into our 50s, 60s, 70s, and hopefully beyond, we need to pay attention to what we’re exposing to our bodies when we hike up the mountain.

Mucho-macho-hotdogs, as a high school teacher used to say, may take a cavalier attitude to their long-term health. I suspect medical people have a term for these folks – FUTURE PATIENTS.

I kept an N95 mask in my first aid kit due to a previous volunteer role and now keep it in there if I find myself in red conditions AQI as well.

It’s a new reality. And one that’s not going away anytime soon.

Checking the AQI is an easy task to perform. And I think a needed part of trip planning in 2021. And in the years ahead.

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Colorado Jones
2 years ago

Thanks for compiling this information, Paul! Following AQI is a bit frustrating because of the wildly different numbers posted by different sources. For example, the readings here in Aurora, CO as of a few minutes ago are: IQAir, 70 AQI; AirNow, 100 AQI; and, 73 AQI. While IQAir and AirNow both indicate that their readings are moderate (51-100), Accuweather designates 73 as “poor.” I’m not entirely sure what to make of these descrepancies. Perhaps a more productive question is this: At what level AQI should I consider calling off a hike? I did a 12 mile mountain hike today… Read more »

Colorado Jones
2 years ago
Reply to  Paul Mags

Thanks, Paul! Very helpful!


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