By: Renee Madden, Bureau of Air Quality

Last summer, I received a call from my daughter who was concerned because she had heard that the Air Quality Index (also known as the AQI) expected a Yellow flag day. Since I work with air quality data, she wanted to know if it was safe to take my 3-year-old granddaughter outside to play or was it dangerous?

I understand her concern. We live in a State that enjoys clean air. In fact, as the graph below shows, the average ozone design value has fallen over the last 18 years and has been below the National Ambient Air Quality Standard since 2010.

So, what’s the deal with all of the colors? As you all know, the AQI is a color-coded air quality guide that lets people know how healthy the air is expected to be - kind of like an air quality shortcut. Each color is associated with a certain level of ozone in the air that lets people know the level of pollution. The Green flag and the Yellow flag are the first two colors that occur in the AQI when the ozone is below the Standard and the air is healthy for normal activities. The Green flag means it’s a Great day and the Yellow flag means it’s a Good day. I know-the color Yellow usually means caution. But, the Yellow flag in air quality means that the air is acceptable except for a small number of people that are unusually sensitive to air pollutants and may need to take some precautions. For those people, it is important to know if there are any pollutants in the air. But, for most of the general population, the Yellow flag means it is safe to go outside and play. So, don’t be scared away by seeing the Yellow flag. This is one time that “Yellow” means, “Go, play and have fun!”

Another statement that I often hear is there seems to be more Yellow flag days now than before-and that’s right! But how can that be if the air quality is better than it was 10 years ago? Good question! The answer is-(drum-roll please)-when the air standards were lowered in 2015, they also change the AQI numbers. To be a Green day in 2008, the ozone level could be up to 0.059 parts per million (ppm). Now, it can only be up to 0.054 ppm. Also, in 2008, the Yellow flag started when the ozone level was 0.060 ppm and went up to 0.075 ppm. Now the Yellow flag starts when the ozone level is 0.055 ppm and goes up to 0.070 ppm (see Table and Graphs below).

So, before 2015, we DID have more Green flag days.

Now, we see more Yellow flag days. But remember, Yellow flag days are good days to be outside, too!