Clearing the air: Stay-at-home eases Denver’s ‘brown cloud’

Photo of smoggy downtown Denver skyline via the Colorado Department of Public Health and Environment, Air Pollution Control Division, Technical Services Program, Wednesday, March 6, 2019.
Photo of smoggy downtown Denver skyline via the Colorado Department of Public Health and Environment, Air Pollution Control Division, Technical Services Program, Wednesday, March 6, 2019. The EPA downgraded the region to a "serious" violator of the Clean Air Act on Dec. 16, 2019.

As Denver and the state begin to reopen this month, people will emerge from their houses having gotten a taste of some potential new normals:

Wearing masks. Working from home. Fewer traffic jams. A Denver skyline free of haze.

Under a stay-at-home order for about a month and a half, the city’s sudden shift to stiller life led to some unexpected consequences: cleaner air from falling car emissions, streets turned over to walkers and cyclists, more time to consider the connection between public health and the environment. 

“While COVID-19 has helped our air quality, it should serve as a starting point in which we should imagine our world after this,” said Hannah Collazo, the state director of Environment Colorado, a research and policy nonprofit.

For starters, she said, life post-pandemic could include driving less, using public transit more, keeping some roads closed to cars, and regularly working remotely to reduce daily commutes. 

Most importantly, she and other environmental experts say, it could include stronger air pollution protection at the federal and state levels and a harder push toward renewable energy.

“We want to be really clear that we are not taking any joy in COVID-19 leading to healthier air,” she stressed. “We just think it’s a really opportune time for gathering data that we can use — once we are no longer sheltering in place — when we’re crafting legislation or trying to educate the public.”

Increasing levels of particulate matter, a primary ingredient in Denver’s “brown cloud,” is correlated with “more mortality and more health problems … and these include increases in deaths and health problems related to cardiovascular disease and respiratory diseases,” said Lisa McKenzie, a researcher at the University of Colorado Denver who studies the correlation between air pollutants and public health.

Particulate matter is a pollutant that not only causes health problems “at high levels,” according to the Colorado Department of Public Health and Environment, but also can affect air visibility.

A team of researchers at the Harvard University T.H. Chan School of Public Health recently found a preliminary link between higher rates of COVID-19 deaths and diseases associated with long-term exposure to fine particulate matter, also known as PM 2.5. The tiny particles in the air result from complex reactions of chemicals, such as sulfur dioxide and nitrogen dioxide, which are emitted from power plants, refineries and vehicles, according to the Environmental Protection Agency.

Harvard’s nationwide analysis examined data from 3,080 counties, representing 98% of the population, and found that a “small increase” in exposure to PM 2.5 over time leads to a “large increase” in the COVID-19 death rate. The study looked at county data for the past 17 years and coronavirus-related deaths through April 22 from the Coronavirus Resource Center at the Johns Hopkins Center for Systems Science and Engineering.

“Our results underscore the importance of continuing to enforce existing air pollution regulations to protect human health both during and after the COVID-19 crisis,” the researchers wrote.

However, the study’s tentative findings, which have not yet been peer-reviewed, have caused an “uproar” in the nation’s capital, The Washington Post reports, as both the left and right attempt to use the research to advance political agendas.

Denver Traffic. Photo by Jared Tarbell via Flicker Creative Commons.

Clearer skies

The coronavirus is shedding light on other issues related to air quality, too.

Denver’s transportation department reports that shortly after the city went into lockdown on March 24, roadways experienced a reduction of traffic by as much as two-thirds. For about two weeks in April, traffic volume held steady around 50%.

With extra street space, several roads around the city were transformed into “open streets,” which were closed to cars, as well as “shared streets,” which were opened to motorists but designed for residents walking and biking. 

According to the Denver Streets Partnership, a sustainable transportation advocacy group, between April 8 and April 19 an average of 1,026 people sauntered down 16th Avenue in North Capitol Hill and City Park West, which was temporarily closed to drivers except those who lived along that stretch. 

The results showed that, compared with the same time period in 2015, the number of walkers and bikers hitting the pavement had more than doubled on the days when temperatures were above 40 degrees.   

The group and other sustainable transportation advocates say the data, which was collected by a bike and pedestrian counter, makes a strong argument for these kinds of resources to be expanded beyond stay-at-home orders.  

But Tim Jackson, the president of the Colorado Automobile Dealers Association, disagrees. 

“As transit ridership plummets and (the Regional Transportation District) makes drastic cuts, the need for access to personal vehicles is clearer than ever,” he told Colorado Politics in an email. “Exploiting this pandemic to push to keep streets closed after the crisis would deliberately increase traffic congestion, create more pollution and hinder the community’s ability to rebound economically.”

The city’s transportation department has no new plans to expand open and shared streets, especially as Denver’s government prepares to make steep budget cuts due to the economic fallout from the coronavirus pandemic. 

However, Denver opened a permanent “shared street” on 35th Avenue, barred cars from a one-block stretch of Bannock Street and plans to rebuild a recreation area with a bicycle path on 39th Avenue later this year. In December, Mayor Michael Hancock announced the city was also speeding up efforts to install 125 miles of bike lanes by 2023. 

While stay-at-home orders kept most people off the roadways, the speed of traffic flow during Denver’s morning rush hour traffic also increased by an average of 13%, according to an April 28 report from INRIX, a transportation analytics company.

Vehicles moved even more freely during the 5 p.m. rush-hour, with an increase in travel speeds by about a quarter.

“These gains in travel speeds help employees and caretakers continue their essential work without delay and allow local fleets of commercial companies the ability to speed up delivery and achieve a higher number of deliveries,” the INRIX report stated.

A May 1 analysis of Denver’s air quality amid the stay-at-home order found “significant drops” in all air pollutants evaluated. The study, conducted by CDPHE, evaluated PM 2.5 and nitrogen dioxide at the air quality monitor at 2105 Broadway in Denver during mid-March through mid-April between 2010 and 2020.  

PM 2.5 levels dropped by 10.4%, according to the analysis. Levels of nitrogen dioxide — a pollutant formed from emissions of motor vehicles, power plants and off-road equipment — decreased by 28%.  

The CDPHE report explained that Denver likely saw smaller decreases in PM 2.5 because of the variability of natural sources that contribute to the pollutant. In dry, windy years, for example, there is likely to be more dust kicked up in the air. During colder years, more smoke blows about from wood-burning.

The state health department estimates that natural sources, like smoke and dust, contribute roughly 10% to particulate matter, but that percentage “can be much higher” — it all depends on the weather.

Still, Robert Spotts, the transportation planning supervisor for the Denver Regional Council of Governments (DRCOG), said impacts shown from the analysis are “intuitively much less than you might think.

“It points to how much human activity is still kind of happening, even though we’re cooped up in our houses. There is still power being generated, there are still delivery trucks traveling all over,” he said. “It’s not a ghost town out there.”

Ongoing construction in Denver, which went largely unhalted under public health orders — and for some projects, including those on Interstates 70 and 25, even ramped up due to less people on the roads — also “definitely” has “an influence” on air quality, Scott Landes, supervisor of CDPHE’s meteorology and prescribed fire unit, said during a virtual Electric Vehicle Coalition meeting in April. 

“While there has definitely been some significant air quality improvements, depending on where you live, you might not actually be experiencing the same kind of pollution reduction,” said Sophia Mayott-Guerrero, an energy and transportation advocate at Conservation Colorado, an environmental advocacy group.

“Everyone’s experiencing that benefit differently,” including people who live along Denver’s “inverted L,” she said, which is a stretch of precincts that runs northeast along the I-70 corridor and south along Federal Boulevard. Those precincts also include where many of Denver’s lowest-income residents live.

“The current health crisis has really pointed out and demonstrated the health outcomes associated with air pollution and some of those disparities,” Mayott-Guerrero said, “and it’s really critical, as we see several federal rules get rolled back on some air pollution protections, that the state steps up and takes leadership, recognizing that it is something contributing to public health.”

In many cities across the country and around the world, data has shown that traffic and pollution improved while stay-at-home orders kept most cars in park.

For example, The New York Times reported that major U.S. cities, such as Atlanta, Chicago, Los Angeles, New York and Seattle, saw air pollution “plummet” between March 2019 and 2020.  

However, the data — which the Descartes Lab compiled from satellites that detect traffic-related emissions in the atmosphere — has been questioned by some scientists.

Europe’s atmosphere monitoring service, for example, said the mapping was “flawed” because differences in weather conditions, specifically cloud cover, between the two years weren’t taken into account.

Still, there is no doubt that people were driving less under public health orders.

Nationwide, personal vehicle miles traveled dropped by 46% between March 14 and April 17, according to the INRIX report.

Denver became known for its problematic air more than a century ago. In 1889, The Denver Times reported that “disease had started to spread to the entire population” and “bad air was hurting the city’s reputation.”

By the mid-1950s, health officials “really became concerned about air quality,” said Lisa Devore, an environmental engineer at CDPHE. Denver logged 1,250 air pollution complaints in 1956 from residents concerned about excessive smoke and other problems in the air.

Public pressure led to action at both the state and federal level. The Colorado legislature adopted the Air Pollution Control Act in 1970. That same year, Congress amended the Clean Air Act, which authorized the EPA to establish new national standards on air pollution from vehicles and factories.

Not long after this time, Denver’s looming air pollution came to be known as the “brown cloud.”

The brown cloud peaked in the 1970s and ‘80s before cleaner fuel and sustainable emissions technology had been fully utilized. Although pollution in the air has improved, environmental experts say it still poses a threat as more people, and their cars, continue to make Denver home. 

“It’s worse in the winter because of something called temperature inversion,” Devore explained, when cold air gets trapped under a layer of warmer air.

“In Denver, because we’re actually in somewhat of a bowl, where we’re bounded on one side by the mountains and the Platte River Valley on the other side, which actually rises up a little bit, so we become trapped.”   

Those inversions can last between a day, sometimes even a couple of weeks, she said, and when those happen, the air is stagnant.

“You don’t have much wind, and the air is circulating within our bowl … and people continue to operate as usual, so they drive their cars, companies operate as they always would, and all of that pushes stuff inside the bowl until we see a change in weather conditions,” Devore said.

The term describes the dark haze that hovers over Denver as a result of a mix of various fine particulates and gases. Two types of particles can create haze: primary particles — think organic and soot particles in smoke plumes or soil dust — and secondary particles, such as sulfates and nitrates.

Haze was historically worse in the wintertime due to wood-burning and road sanding during construction, as well as in summer, because of road sanding and forest fires.

Usually the haze is local, particularly in winter, although for other seasons it can depend on meteorology and regional weather patterns.

In 1987, CDPHE began implementing a high pollution advisory “action day” program for the Denver metro area during the winter months between Oct. 31 and March 31.

“The primary goal of the advisory program is to provide useful information on air quality to area residents during the high pollution season,” according to the department.

“Action days” were issued when air quality conditions could lead to air pollution levels above federal and/or state standards. Those days trigger mandatory burning restrictions and voluntary driving reductions. CDPHE also implemented in 1990 visibility metrics directly correlated with the brown cloud.

Data shows that frequency of exceedances over the urban visibility standard are decreasing. From the early 1990s to the early 2000s, exceedances decreased from 70% to about 50%.

In recent years, data from the transmissometer, which had begun being used in the 1990s to monitor visibility metrics, is no longer being tracked “due to technical issues,” according to CDPHE, but the Continuous Air Monitoring Program has since been adopted as a substitute.

Since the late 1990s, there has been an approximate 33% decrease in particulate matter in Denver’s air, the department reports.

The improvements reflect control strategies that state and local health departments have established to clean up Denver’s air, including reducing street sanding by half, implementing restrictions and standards on wood-burning, installing low-nitrogen oxide burners at power plants, expanding the bus system and more.

Where we stand

Denver’s brown cloud issue hasn’t gone away, experts say, but rather evolved into a thick smog that’s seen when ozone levels spike.

In December, the EPA announced it was changing the Denver area’s classification from “Moderate” to “Serious” under the Clean Air Act for failing to meet federal 2008 ozone standards in a “timely” manner.

“EPA is taking this action based on monitoring data showing that ozone remains a challenge in Denver and northern Front Range communities,” EPA Regional Administrator Gregory Sopkin stated in the December news release. “We thank our partners at the State of Colorado in working with EPA to strengthen air quality plans and implement these measures to further reduce ozone-forming emissions from sources across the region.”

In 2018, the Denver metro area logged 131 days of degraded air quality, meaning half or more of its monitoring stations reported elevated levels of PM 2.5 and/or elevated ozone.

“We know as ozone levels increase, so does the risk for worsening of asthma and our respiratory diseases,” said Lisa McKenzie, the researcher from the University of Colorado Denver.

The latest report from the American Lung Association ranked Denver as the 10th-most ozone-polluted city in the country. Los Angeles landed at No. 1. 

“Coronavirus is a respiratory disease that is wreaking havoc on the lungs of those infected,” U.S. Democratic Rep. Diana DeGette of Denver said in an email. “Second to eliminating the virus altogether, one of the most important things we can do right now to improve the public health is improve air quality.”

DeGette is preparing to introduce new legislation that would create a federal clean energy standard to help cut carbon emissions from the power sector by 2050. Meanwhile, the Trump administration is working to roll back Obama-era air pollution regulations on toxins provided by oil and coal power plants.

“The science is clear. If we are going to avoid the worst effects of our climate crisis, the U.S. has to take drastic steps now to cut our carbon emissions. The problem is that all of the technology we need to do that does not yet exist,” DeGette said. “By creating a national clean-energy standard that all U.S. power companies will have to adhere to, we will be able to spur the innovation and deployment of the new technologies we’ll need to solve this crisis.”

Democratic state Rep. Dominique Jackson of Aurora introduced a bill in January that would significantly increase fines for air and water quality violations, which currently max out at $15,000 per day. If passed, daily fines per violation would be as high as $47,357. 

While still an issue, ozone from vehicles has primarily decreased due to new technology and cleaner fuel standards, transportation experts say.

“Even though more people are driving in our region, emissions from vehicles keep going down,” said Spotts, DRCOG’s transportation planning supervisor. “We estimate that, even though we’ve had a lot of population growth over the last 10 years, our emissions have reduced by about 50% of what they were in 2010.

“And we anticipate them to continue to decrease all the way up to 2040, which is our current planning horizon here.”

Hancock plans to transition Denver to 100% renewable energy by 2030. Colorado Gov. Jared Polis aims to get the entire state there by 2040.

Air pollution experts agree that we have a ways to go on both the federal and local level.

“I don’t think it’s a problem that’s ever going to be fully solved as long as we’re an industrial society,” CDPHE’s Devore said, “but we continue to make improvements.”