Ozone is a gas that occurs both in the Earth's upper atmosphere and at ground level. In the upper atmosphere ozone is “good” and protects us
from the sun’s harmful ultraviolet (UV) rays. At ground level, ozone is “bad” and is an air pollutant that is harmful to breathe and that damages crops, trees and other vegetation. It is a main ingredient of smog.
Hot weather and sunlight interacting with oxides of nitrogen (NOx) and volatile organics (VOC) cause ground-level ozone to form in harmful concentrations in the air. Emissions from oil and gas drilling and motor vehicle exhaust are thought to be the main sources of NOx and VOC, with gasoline vapors and chemical solvents being lesser sources.
Many urban areas tend to have high levels of "bad" ground-level ozone, but even rural areas are subject to increased ozone levels because wind carries the pollutants that form ozone hundreds of miles away from their original sources.
Worsening of bronchitis, emphysema, and asthma
Ground level ozone is a secondary pollutant that forms in the air rather than being directly emitted, such as from a tail pipe. For ozone to become a health issue it requires the right mix of Nitrogen Oxides (NOx) and Volatile Organics (VOC) that get “cooked” by sunlight or UV. Weather patterns play an important role in producing ozone. Wind can transport precursor pollutants to Aspen from where they originate. There are also regional weather events that can cause high levels of ozone, such as warm high pressure systems or large scale air stagnation (an air mass that is parked over the same area for several days causing the pollution to build up).
Both natural and human-made sources contribute to emissions of ground level ozone precursors. Trees emit large amounts of VOCs and lightening releases large amounts of NOx. In Western Colorado, the oil & gas industry and vehicle emissions are the most common human-made sources of VOCs with the combustion of fossil fuels the local source of NOx.
Located near the intersection of Highway 82 and Cemetery Lane, the City’s ozone monitor was installed in December of 2009. This location provides a good indication of the overall ozone levels for Aspen. By monitoring ozone we can determine our compliance with the EPA’s 8-hour standard of 75 ppb. To date, Aspen is in compliance with this standard.
The data from local ozone air quality monitoring also provides information on how Aspen’s air quality is or is not impacted by local sources, weather and regional air quality events, such as wildfires and dust storms. It is also an important public health response tool for staff during regional air quality events. Aspen’s ozone data is available for regional and statewide air quality planning activities.