Researchers claim they have discovered a surprising amount of harmful ozone in the supposedly "fresh" air of the Colorado mountains, showing just how far urban pollutants can travel.

Atmospheric investigators recently collected data from aircraft, balloons and ground stations along northern Colorado's front range as part of a survey of pollutant concentrations from the south Denver area to Fort Collins.

They concluded a month's worth of work last week, and are hesitant to jump to any conclusions. Still, they were willing to share a few of their surprising results, citing the importance of the work.

"People [are] thinking you go into the mountains and you breathe the fresh air - that's not always the case," researcher Gabriele Pfister, from the National Center for Atmospheric Research in Boulder, told the Associated Press (AP).

Pfister, who was one of the study's principle investigators (PIs), explained that they found harmful ozone pollution and chemicals that cause ozone "all the way up to the Continental Divide."

Ozone (O3) isn't always bad. In the upper regions of our atmosphere, it acts as a protective layer, shielding the Earth from the Sun's more harmful rays. However, ground level ozone can be harmful.

Heavy and difficult to breath, ground level ozone can incite asthma attacks, exacerbate lung disease, and even hamper lung development in newborns. It has also been seen to adversely affect sensitive vegetation - namely trees - during growing seasons.

According to the Environmental Protection Agency (EPA), this kind of pollution is created by chemical reactions between oxides of nitrogen and volatile organic compounds. It's most commonly seen in urban environments, where nitrogen can be heavily concentrated.

The city of Denver, for instance, has been known to exceed federal standards for ozone.

Thanks to Pfister's team, we now know that north-bound wind currents can even carry this heavy urban pollution far into the mountains, where it can cause more harm.

"We view Rocky Mountain National Park as a refuge," added PI James Crawford, from NASA's Langley Research Center. "To learn there are days when it's not as safe as we think of it as, it's something people should know."

NOTE: It is recommended that these results be viewed as preliminary until officially published in a peer-reviewed journal.