How you affect the air, and it affects you.
Simple Science Behind Ground-Level Ozone
Ozone is three oxygen atoms stuck together in a molecule known as “O3.” High up in the atmosphere, ozone serves an important purpose: it protects us from the sun’s ultraviolet radiation.
But at ground level, high concentrations of ozone are toxic to people and plants: irritating our throats and lungs, making it difficult to breathe, increasing our susceptibility to respiratory infections, and exacerbating ailments such as asthma.
Ground-level ozone is formed when two chemicals, volatile organic compounds (VOC) and nitrogen oxides (NOx), react in the abundance of sunshine and heat that build up on Colorado summer days — effectively “baking” in the sun to form ozone. You can’t see it, smell it, or taste it. This invisible pollutant even accumulates the most on hot and sunny blue-sky days, when the Colorado air appears clear.
Nitrogen Oxides are highly reactive and poisonous gases formed by the combustion of fuels. Volatile Organic Compounds are any compound of carbon (except those excluded by EPA or with very little reactivity) that participates in photochemical reactions in the atmosphere. These emissions come mainly from our gas-powered vehicles, lawn equipment, and oil and gas production.
Other Air Pollution Coloradans Breathe
Another type of air pollution in Colorado is what’s called particulate matter, or PM2.5. This is also found in wildfire smoke, it harmful to breathe, and can make ozone pollution even worse. However, both colorless and odorless, ozone is different than wildfire smoke and PM2.5.
Denver’s “brown cloud” typically occurs in the wintertime, when denser, heavier cold air gets trapped under a blanket of warm air, in part due to the unique geography of our area. This temperature inversion concentrates pollutants closer to the ground, and results in the yellow-brown strip visible along the horizon. The pollution that creates this unsightly color is mainly from oxides of nitrogen and sulfur, as well as tiny particles of grit and dust. While it also gets trapped by this phenomenon, ground-level ozone is actually colorless and odorless—and mainly an issue in the summertime, as it is the result of a chemical reaction with emissions that requires sunlight and heat.
How Ground-Level Ozone Affects Coloradans
You can’t see or smell ground-level ozone, but it’s harmful to breathe. You can stay indoors to protect yourself from higher levels of summer ozone, or avoid or reduce outdoor activites between noon and 8 p.m. That makes it different from PM2.5 pollution, such as wildfire smoke, which can infiltrate buildings. You can protect yourself from wildfire smoke by using indoor air purifiers with HEPA filters and wearing N95 masks. However, masks are not recommended for ozone, as while filtering ozone out of the air through a mask is possible, it requires a specific, higher-quality mask that is quite expensive.
Where Ground-Level Ozone Comes from in Colorado
NITROGEN OXIDES (NOx)
During an average summer day, approximately 164 tons of NOx pollutes our air. People who drive gas-powered vehicles, that’s everything from cars to large construction equipment, make up 33% of those emissions.
NITROGEN OXIDES (NOx)
During an average summer day, approximately 164 tons of NOx pollutes our air. People who drive gas-powered vehicles, that’s everything from cars to large construction equipment, make up 33% of those emissions.
VOLATILE ORGANIC COMPOUNDS (VOC)
During an average summer day, approximately 292 tons of VOC emissions pollute our air. People who drive gas-powered vehicles, that’s everything from cars to large construction equipment, make up 17% of those emissions.
VOLATILE ORGANIC COMPOUNDS (VOC)
During an average summer day, approximately 292 tons of VOC emissions pollute our air. People who drive gas-powered vehicles, that’s everything from cars to large construction equipment, make up 17% of those emissions.
*Data from the 2020 anthropogenic inventory developed for nine-county Denver Metro/North Front Range ozone nonattainment area’s Serious Area Ozone State Implementation Plan.