Photo by Natabico, Wikimedia Commons
There was a term that we used when I was at Texas Tech in Lubbock to describe the sky on a really beautiful, sunny day: Colorado Blue! Since moving to Colorado, I have looked forward to days highlighted by this stunning sky-blue color! Unfortunately, much of my first summer and fall here had skies of a very different nature.
Smoke from last summer and fall’s wildfires up in the mountains along with the summer haze from Denver oscillating up and around the mountains dampened the intensity of our blue skies. The fires even made the sky orange on a few occasions along with dumping inches of ash on our yards and streets. Throughout the winter, though, we have had blue-skies of great depth and quality all along the Front Range.
Photo by Josieshowaa, Flickr
The “Front Range” of Colorado, by the way, consists of a line of cities and towns along the eastern edge of the Rocky Mountains. Denver, of course, is the largest of these cities which includes Golden, Boulder, Fort Collins, Loveland, Longmont, Pueblo, Colorado Springs and also Greeley. The population of Colorado has greatly increased in the past 60 years. In 1960 there were 1.75 million people living in the state, while in 2021 there were 5.9 million people living here. About 80% of these 5.9 million people live in the cities and towns of the Front Range!
One growing casualty of this population explosion just might be the quality of our Colorado Blue skies!
The color-coded air quality alert system that we used back in Pennsylvania is also use here in Colorado: (Green (good), Yellow (moderate), Orange (unhealthy for select groups), Red (unhealthy), Maroon (very unhealthy) and Purple (hazardous)). The Air Quality Indices (AQI’s) underlying these color levels are based on the measured amounts of ozone, particulates, sulfur dioxide, carbon monoxide and nitrogen dioxide in ground-level air.
Photo by J. St. John, Wikimedia Commons
The pollutants in the AQI come from a variety of sources including cars, trucks, power plants, factories, construction sites, incinerators and other types of fires. Ozone is especially formed in the summer when high temperatures and sunlight drive the conversion of some of these gaseous pollutants into ozone-rich soup, but it and most of the other pollutants (especially the particulates) are present all year round.
When half of the air monitors in an area report Yellow levels (or above) AQI’s in a day, that day is then classified as a “poor air quality day.” Back in the 1960’s, 1970’s and into the 1980’s Denver’s air and the air along most of the Front Range was even worse than “poor” and regularly violated EPA standards often as frequently as 200 days a year!
By the year 2000, Denver and the rest of the Front Range had made considerable progress to cleaning up their air. According to an E.P.A. report published in 2000, Denver had had no violations of Ozone (1-hour standard) since 1985, no violations of carbon monoxide since 1995 and no violations of particulate matter (10 micrometers or smaller) (“PM-10”) since 1993.
The whole system, though, was straining under the pressure of the growing crush of people and the exhaust fumes from all of their cars and trucks and all of the smokestack pollution from energy generating plants and industry. The system was stretched to a new tipping point, and air quality began to decline.
Photo by N. Hartmann, Wikimedia Commons
In 2016 Denver and the Front Range had 98 poor air quality days, and in 2018, 131 poor air quality days (with 99 days of elevated ozone levels and 51 days of elevated particulates). A news report the other evening announced that Denver’s “brown cloud” (a dome of polluted air that dominated the skies over Denver back in the “bad-old-decades” of severe air pollution) was back! An unusually warm, sunny, January day triggered an atmospheric inversion that trapped the air over the city and energized the synthesis of smog and ozone.
Ozone levels in our lower atmosphere are particularly worrisome and have regularly caused Denver to be listed among the ten worst cities in the country for ozone pollution. Ozone is not a chemical being emitted from any of the pollution sources along the Front Range. Instead, it is synthesized in nitrogen dioxide-rich clouds of pollution by a photochemical process driven by sunlight and heat. Ozone can aggravate lung diseases like emphysema and can cause chronic obstructive pulmonary disease (COPD). It may also be the cause of the rising numbers of asthma cases in our population. Ozone is a colorless gas, so even on a Colorado Blue sky day, ozone levels can be dangerously high.
Why are ozone levels so high in Denver and the rest of the Front Range? The high levels of nitrogen oxides and volatile organics from car and truck exhaust are one reason. These chemicals are the reactants that sunlight and heat then cook into ozone. Colorado’s extensive array of oil and gas industries also contribute high levels of these ozone generating chemicals into our air and may even be more of a factor in ozone generation than vehicular pollution! Most studies agree that vehicular exhaust and the oil and gas industries each cause 35 to 40% of the Front Range ozone pollution problem.
The energetic driver for these ozone reactions is, of course, sunlight and heat, and both of these factors are also changing. Rising temperatures associated with Climate Change and the reduction in cloud formation, cloud cover and rainfall from an increasingly dry atmosphere generates more and more hot, sunny days that are optimal for the formation of ozone. Almost each passing year becomes Denver’s (and the world’s) “hottest year on record,” and ozone levels continue to rise along with these rising temperatures!
It seems paradoxical that the air here on the wide open plains, at the very edge of the Rocky Mountains might be even more polluted that it was back in Pennsylvania in the shadow of all of those old steel mills and factories! I do love the blue skies here, though!