Air Quality in North-Central Colorado: How Has It Changed Over Time?

Colorado's Front Range has long been known for its poor air quality. In recent years, Denver's notorious brown cloud and ground-level ozone have been eliminated. Long-term data sets, collected over multiple years, can provide insight into air quality trends and how levels of toxic substances in the air change over time. These changes may be attributed to new technologies and regulations aimed at reducing air pollution. This type of information is essential to reduce people's exposure to potentially hazardous contaminants.

The Denver and Fort Collins metropolitan areas are consistently ranked higher on a well-known list of the worst cities in the United States. Only the Los Angeles area and parts of California's Central Valley now surpass Colorado's Front Range cities with their ground-level ozone levels, which are linked to hospitalizations, emergency room visits, and thousands of premature deaths. For the second week in a row, residents of the Denver metro area and other cities in the northern Front Range are facing air quality alerts as ozone levels exceed the federal health limit of 70 parts per billion (89 ppb) in Golden, 74 ppb in Rocky Mountain National Park, 81 ppb in the Rocky Flats National Wildlife Refuge, 76 ppb in Fort Collins, and 73 ppb in Chatfield State Park, southwest of Denver. The American Lung Association advocates a health limit for ozone of 60 ppb, which is in line with World Health Organization recommendations. Colorado has failed to meet existing national health standards so frequently over the past decade that Environmental Protection Agency officials reclassified the state as a “serious offender” last year. This placed a nine-county area along the Front Range in the same category as Phoenix, Los Angeles, Dallas, Chicago, Houston, and Salt Lake City.

The Environmental Protection Agency classifies parts of California's Central Valley and the Los Angeles metropolitan area as “extreme offenders”.Ozone pollution is created when chemical gases, including volatile organic compounds and nitrogen oxides, mix with sunlight. It causes respiratory problems and triggers asthma attacks. Doctors from the American Lung Association have been lobbying President Joe Biden's administration to make greater investments to install electric vehicle charging stations and provide sufficient incentives to drivers, including tax credits, rebates, and free use of charging stations and highway express lanes. If Colorado's constant violations of health limits lead the EPA to further downgrade the state to the category of “serious offender”, health officials would be forced to take more drastic measures to reduce air pollution. This would include stricter restrictions on oil and gas installations and other industrial sources. Temperature inversions are meteorological phenomena where cold, contaminated air close to the ground cannot escape into the atmosphere due to a layer of warmer air on top.

This creates a trapping effect. However, these discrepancies reduce confidence in bottom-up inventories and air quality models that are based on these likely unforecasted emissions. In recent weeks, Denver has one of the worst air qualities in the United States and ten worst air qualities among major cities worldwide. Colorado is one of more than 22 states participating in the National Airborne Toxic Trends Station (NATTS) network. The current design of buildings and appliances that run on gas can contribute to poor indoor air quality. This means that Coloradans who have health problems related to air quality and who live in these buildings cannot find relief indoors either. However, population growth and rising temperatures create enormous challenges for clean breathable air in Denver and the Front Range.

Several Western Slope counties experienced terrible air quality last summer and received low ozone ratings from the American Lung Association. Denver's air quality is mainly affected by ozone pollution formed by precursor pollutants emitted by motor vehicles (mobile sources) and oil and gas industry (stationary sources). While wildfires in other states contribute to Denver's poor air quality, elevated ozone levels are mainly due to Denver's unique weather patterns, summer temperatures above 85 degrees F., and a rapidly growing population which attracts more vehicles to Colorado's highways. The arguments presented in the letter did not take into account most of the considerable amount of peer-reviewed literature on the impacts of O&NG industry operations on Colorado's air quality that has been published over the past 10 years. While short-term exposure to smoke poses a health risk to all Coloradans, the combination of existing poor air quality and increased wildfires takes concerns about air quality in the Front Range to a whole new level. This requires concerted efforts to better characterize emissions and air quality impacts from O&NG emissions as well as regulating emissions. Air quality monitoring and sampling are conducted by CDPHE (Colorado Department of Public Health & Environment), NOAA (National Oceanic & Atmospheric Administration), National Park Service, Boulder County, City of Longmont.

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