If you’ve lived in the Mile High City for several years or even months, you probably breathe normally. But think back to when you first moved to Denver (or for natives, when out-of-town guests first visited you here), and you’ll likely recall the times when you—or your friends—lost your breath from walking up a flight of stairs, or began to pant after only a few minutes of a morning run.

Thanks to our high altitude, that low level of oxygen is never going to improve much, but our bodies can adapt to it. What’s more worrisome is that Denver’s air quality may actually be getting worse, thanks to an increase in ozone (a toxic gas formed when light and heat react with things like fossil fuel emissions) and soot, according to last month’s 2015 “State of the Air” Report, published by the American Lung Association. In fact, the Denver-Aurora area now ranks as the 13th most ozone-polluted city in the country. (The Los Angeles-Long Beach region tops the list.)

The ideal conditions for ozone production include warm temperatures, a lot of sunlight, and faint winds (sound familiar?), but Denver’s air has mostly improved since the first “State of the Air” report was published 16 years ago. It’s difficult to determine exactly why the trend reversed, but it’s possible that the influx of people into the area in the past few years—10,300 people moved to Denver County in 2011 alone compared to 3,550 in 2010—put enough cars (and their potentially deadly fumes) on the road to make an impact. (The data for this year’s report dates from 2011 to 2013.)

Colorado did pass the first regulations in the country for methane and other chemicals released from oil and gas development last February, which will hopefully improve air quality in future years. Since drilling tends to take place outside urban areas, the Mile High City itself may not benefit at all.

In November, the EPA also proposed stronger national ozone regulations, but here are some ways that you can clean up the air around you before they make their decision in October:

  • Take the bus, walk, or ride your bike whenever possible
  • Buy Energy Star products and low-polluting vehicles
  • Turn down the thermostat on your water heater to 120 degrees
  • Get rid of old wood stoves in favor of newer models that have been EPA-certified

The Daniels & Fisher Tower will glow turquoise today in honor of National Women’s Lung Health Week (May 10-16). For more information, visit lungcolorado.org, and visit epa.gov for more ways to decrease air pollution.

Follow editorial assistant Mary Clare Fischer on Twitter at @mc_fischer.