Air quality alerts issued for many things, not just wildfire smoke

Dense wildfire smoke from Canada has once again covered large portions of the northern Midwest. This is leading to hazy skies, reduced visibility, and unhealthy air quality. Due to these factors, an air quality alert has been issued by The Wisconsin Department of Natural Resources through noon on Thursday, June 29.


Southeast Wisconsin has experienced an unusual number of air quality alerts this year. But did you know that an air quality alert can be issued for different reasons? That’s right, wildfire smoke may not always be the culprit. There can be a lot of confusion in terms of why one was issued. This article should give you a better understanding of what may be the hazard(s) on a given day.  Let’s break it down science-style.

Alerts issued for variety of reasons

The Environmental Protection Agency (EPA) has an air quality index for five major air pollutants. These include: 

  • Ground-level ozone
  • Particle pollution (or particulate matter- PM2.5 & PM 10)
  • Carbon monoxide
  • Sulfur dioxide
  • Nitrogen dioxide

We will mainly focus on ground-level ozone and particle pollution since this is what our air quality alerts have been issued for.

Ground-Level Ozone

90% of the good ozone in the atmosphere is in the Stratosphere. This helps absorb harmful ultraviolet radiation from the Sun as it enters the atmosphere. Even though ozone is good, it can be hazardous to come in contact with. The bad ozone, near the surface, is harms humans, animals, and plant life. 

The Milwaukee area has had several air quality alerts issued earlier this month, on June 15 and 19, due to higher ground-level ozone. This is different from smoke because the poor air quality is coming from ground-ozone levels, not particulate matter from smoke.  When air is more stagnant, vehicles and industrial emissions are released into the warm and stable air. Bad ozone is formed when emission gasses and volatile organic compounds (VOC) interact with sunlight. This is more prominent in larger metropolitan areas, and it can cause throat and lung irritation and worsen asthma. 

Particulate matter (PM2.5 & PM10)

This is what we typically look for when smoke is a concern near the surface. Particle pollutions, also known as particulate matter, are a combination of solid particles and liquid droplets in the air. Solid particles could be smoke, dust, or dirt that vary in size. Scientists break the size (micrometers) down in two categories: 

  • PM10: Diameters that are 10 micrometers or smaller
  • PM2.5: Diameters that are 2.5 micrometers or smaller-smaller particles

Both can be inhaled. But since PM2.5 is a lot smaller, it can travel further into the lungs and even the bloodstream. Let’s take a look at an example using M&M’s.

On average, the diameter of an M&M is about ½". Remember that PM (particulate matter) is smoke, dust, dirt. You would need at least 1,355 PM10 particles in a row to go across an M&M.
You would need at least 5,424 PM2.5 particles in a row to go across an M&M. This shows that a lot more PM2.5 particles are needed to go across the diameter of an M&M because they are significantly smaller.

Wisconsin the next few days

The current air quality alert has been issued due to Canada wildfire smoke near Earth’s surface. Breathing this in can be unhealthy and harmful. In fact, the air quality is expected to be poorer than any other day this year making it unhealthy for everyone to breathe on Tuesday, June 27 and Wednesday, June 28.

The same low-pressure system that brought rain from Saturday, June 24 through Monday, June 26, is responsible for bringing Wisconsin this large plume of smoke. Strong northeasterly winds wrapped around the back side of this low are pulling it down from Canada. Ironically, once the smoke begins to push south of the Milwaukee, winds will change direction, out of the south, and bring the smoke back into our area on Wednesday, June 28.

Smoke will still be around on Thursday, June 29, but air quality should slightly improve and more so impact sensitive groups of people that has respiratory issues, heart issues, older adults, children and teenagers, pregnant individuals, and people that work outdoors.

What can you do to stay safe