NEW ORLEANS (WVUE) - New York City recorded its most hazardous air on record this week stemming from Canadian wildfire smoke. Many were glued to the air quality map provided by the Environmental Protection Agency (EPA) to see how safe their air was. Millions were told by this map to stay indoors. But what is this map? And how do you read it?

The EPA started monitoring the air quality in the 1940s. Air samples from around the country were sent in every 3 to 6 months for quality control purposes. But this wasn’t adequate enough for short term health dangers the public would need to be notified about. A complex network was built consisting of more than 100 U.S. and Canadian agencies that would send in hourly ozone readings. This network is now a part of the AIRNow program used today.

What is AQI?

Under the Clean Air Act of 1970, the EPA established an index for monitoring air quality. After much research and several updates, the Air Quality Index (AQI) as we know it today was developed in 1999. It’s since been tweaked a few times for better quality. It’s like measuring the air quality with a yard stick that runs from 0 to 500. The lower numbers represent the cleanest air qualities with the higher numbers representing the more hazardous air.

These AQI values were then broken down into six categories to represent levels of concern and who should take action. The green category represents AQI values of 0 to 50. This means the air quality is good and poses little to no risk to the public. The highest level is represented by the maroon color. It has AQI values of 301 and higher. This level would be the most hazardous and is deemed a threat to all who breath it.

What is polluting our air?

We often hear of the term “ozone” when it comes to pollution. This is an all-encompassing term to mean pollutants from cars, power plants, industrial broilers, and many other man-made pollutants that have a chemical reaction with sunlight. This reaction can make the ground-level air unhealthy to breathe. It’s more likely to happen on hot and sunny days and in urban cities.

Another pollutant that can be natural but just as dangerous is wildfire smoke (PM2.5). It’s dangerous because it can be a gaseous mixture of carbon monoxide and other dangerous particulates that are harmful if inhaled.

Reading the primary pollutants of the day

When reading the AIRNow map, you’ll see the primary pollutants listed. Most harmful pollutants are smaller than the width of human hair. Ozone pollution will be labeled “Ozone” while particulate matter like dust, pollen, mold, or smoke are labeled “PM”. When you see the label “PM10″, that will mean the primary pollutants are particulate matter like dust, pollen & mold. The label “PM2.5″ denotes smoke and organic compounds. As you can see in the image below provided by the EPA, the primary pollutant “PM2.5″ poses the largest threat to the public since it’s the smallest and enters the lungs much easier.

EPA image of particulate matter size.(WVUE Fox 8)

When is the air quality warned as harmful?

When the air is particularly harmful (typically an AQI of 101 and higher), the Louisiana Department of Environmental Quality will issue an Air Quality Alert Day. It’s best to monitor the air quality and decide on your individual needs as to what’s best for you. But it’s suggested to stay indoors, close your windows and doors, run your A/C on “recirculating mode”, and pay attention to signs of health problems. Those could include wheezing, coughing with trouble breathing, red and itchy eyes, nose & mouth, or painful breathing,