Washington had a code orange air-quality day in 2010. The only days worse are code red and code purple, and we haven’t had the latter since 2006. (Linda Davidson/The Washington Post)

Have you ever run around outside on a hot summer day, and suddenly your lungs feel as though they’re burning? You could be overly tired. Or your lungs may be reacting to pollutants and chemicals in the air. Understanding air pollution can help you avoid it and think about ways you can make the air cleaner.

What’s happening?

Air pollution often refers to two things: ozone and fine particulate matter, both of which are harmful to humans.

Fine particulate matter, or tiny pieces of dustlike substance, is mostly produced from burning fossil fuels, for instance, gasoline in cars and coal in power plants.

Fine particulate matter is much smaller than the kind of dust that you find after you haven’t cleaned your room in a while. The small size is what makes this matter problematic to our health, because it can settle deep in our lungs, making it hard to breathe.

Ozone happens because of a chemical reaction. Sunlight chemically reacts with gases produced from the burning of fossil fuels to form ground-level ozone.

Every little bit helps fight pollution, including taking the bus instead of asking your parents to drive you to school. (Kate Patterson/For The Washington Post)

When ozone is high in the atmosphere, it helps protect life on the ground from harmful radiation from the sun. This radiation causes problems such as skin cancer. Ozone becomes a problem when it’s close to Earth. When ozone gets into our lungs, it becomes harmful to our health.

Kids are at higher risk of the damaging effects of ozone and particulate matter, especially kids with asthma, because their bodies and lungs are developing.

“Children tend to have a higher respiratory rate [inhaling and exhaling more rapidly than adults],” said Janet Phoenix of Clean Air Partners, an organization that educates people about air pollution in the Washington area. “So they’re more exposed to any chemical particles that might be in the air.”

When to go inside

Some of the worst air-quality days are actually the most beautiful days. On hot, sunny days without wind, the air doesn’t move around and pollutants build up.

“Poor air circulation, heat and light kind of help to bake the chemicals into the air,” Phoenix said.

Rain helps wash the bad things out of the air, so the worst time to be outside is when it hasn’t rained in a while.

“It’s like if you don’t take a shower for a few days, you know what happens,” said Ross Salawitch, a professor of atmospheric and oceanic studies at the University of Maryland. “The rain is cleansing like a shower is cleansing.”

In order to help you know when it’s safe to be outside, days are assigned color codes that correspond to numbers, which represent how much of these nasty substances is in the air. When the amount of ozone and particulate matter reaches unsafe levels, the day will be labeled as code orange, code red and on the worst days, code purple.

“When we have air-quality alerts that are either red or purple, even orange, those are the days to stay inside and play video games,” Salawitch said.

According to Phoenix, the worst time of day for air quality is when people are going back and forth from school and work.

“If you can wait until later in the day to do some of these [outdoor] physical activities, especially when in the red or orange zone, then you’re better off,” she said.

A hopeful trend

The good news? Because of stricter pollution regulations, Washington’s air quality is improving, according to Salawitch. There hasn’t been a code red day in the region in the past three summers. The last code purple was in 2006.

But even short exposure to poor air quality can have negative effects on your body. That’s why area residents should limit activities that increase air pollution, Phoenix said.

Try encouraging your family to walk to the pool or the library. When school starts, take the bus instead of having your parents drive you. Keeping your family’s cars off the road means less air pollution — and not just for your neighborhood.

“What you do in one part of D.C. will affect your neighbors,” said Phoenix, adding that area residents are becoming more aware. “I think people are really making an effort, and that’s wonderful.”