2018-2019 Air Quality Study Results

When the D&SNGR starts a wildfire, it has a tremendous impact on local and regional air quality. Smoke from the 416 Fire daily filled the Animas River Valley, blanketed the Weminuche Wilderness and traveled to impact communities dozens of miles to the east and south into New Mexico. In Durango and La Plata County, residents woke each morning to smoke heavy enough to obscure the views less than a block away. The local health authority, San Juan Basin Public Health, issued warnings advising people to limit their outdoor activity or remain indoors during the daily bouts of heavy smoke. The graph below shows readings of particulate matter of 2.5 microns size (PM2.5) at two air monitors in downtown Durango, during and after the fire.

416 Fire to Startup pm2.5

Moderate – Air quality is acceptable; however, for some pollutants there may be moderate health concern for a small number of people.
Unhealthy for Sensitive Groups – Persons with heart and lung disease, older adults, children and people active outdoors are at greater risk from the presence of particles in the air.

During this time, several citizens in La Plata County obtained PurpleAir PA-II particulate matter (PM) air quality monitors to assess conditions for themselves and their neighbors in real time. These low-cost monitors only recently become available to provide people with information on air quality beyond what is available from state and tribal federal reference method (FRM) air quality monitors, which are few and far between in western Colorado. While low-cost monitors are not as accurate as the FRMs used by state agencies to regulate air quality, independent testing found the PurpleAir PA-II’s accuracy was acceptable for identifying and characterizing hotspots of poor air quality.

In the map below, the PurpleAir monitors used in this study are shown as blue dots. The Durango and Silverton Narrow Gauge Railroad (D&SNGR) roundhouse, a source of PM pollution, is shown as a red dot.

This is a summary of what we found in the first full year of monitoring particulate matter in the 2.5 micron size range (PM2.5).

  • The color-coded graphs on this website represent the U.S. Environmental Protection Agency’s Air Quality Index (AQI) levels. The AQI focuses on health effects people may experience within a few hours or days after breathing polluted air. The AQI is different than the National Ambient Air Quality Standards (NAAQS) which provide regulatory limits for air pollution in the United States. The NAAQS will be discussed later on this page.
  • The graph above shows the train has the greatest impact on air quality when it starts a fire. The hot cinders from coal combustion emitted from the trains’ smokestacks cause an elevated risk of fire. Running the trains on other fuels, such as diesel, bio-diesel, natural gas or battery power would greatly reduce the risk of fire caused by the D&SNGR.
  • The graph below shows the impact the train has in the neighborhood downwind of the D&SNGR roundhouse. Before 9/20/18, during a period the trains were not downtown due to being trapped up north after 416 Fire-related mudslides blocked the tracks for several weeks, PM2.5 levels at both Canary 1 and Ouzel 1 were similar and remained in the Good Air Quality Index (AQI) zone. When the train began running again, PM2.5 levels at Canary 1 became substantially degraded in the evening and night hours.

Because the coal-fired trains must be idled all night at the roundhouse, those who live and sleep on the south side of Durango’s downtown get a big hit of PM air pollution each night. It results in the annual averages of PM2.5 air pollution on the south side of downtown Durango being two times greater than the parts of Durango where the train the just passes through a couple times a day. This is a level that in 2018 – 2019 was just 0.1 ug/m3 short of the World Health Organization’s (WHO) 10 ug/m3 guideline.

  • The graph below shows the impact the train has on areas near the D&SNGR roundhouse (Canary 1 and Durango monitors) is much greater than the impact it has on downtown areas where the train just passes through (Ouzel 1 monitor). The Durango monitor came online in April 2019. This graph of hourly averages shows PM2.5 levels are in the Unhealthy Air Pollution Index zone most nights during the D&SNGR peak season.

The graph below, shows the majority of the PM2.5 impact from the roundhouse at the Canary 1 monitor during the peak train operating season occurs at night, when people are at home, and in the summer when having windows open is critical to cooling homes.

The National Ambient Air Quality Standards (NAAQS) for PM2.5 are both based on annual exposures. One is compared against the annual mean of daily values at a monitor. The other is based on a ranking (the 98th percentile) of the 24-hour values measured at a monitor in a year. The NAAQS are reviewed every 5 years. This includes taking advice from the Clean Air Scientific Advisory Commitee (CASAC). The CASAC has seven members, all of whom are political appointees. CASAC must include at least one member of the National Academy of Sciences, one physician, and one person representing State air pollution control agencies. The remainder are often scientists, regulators and technical representatives of industries whom would be affected by any new regulations resulting from changes in the NAAQS. CASAC advises the EPA Administrator of any adverse public health, welfare, social, economic, or energy effects which may result from various strategies for attainment and maintenance of such national ambient air quality standards. Therefore, while scientific and health research is strongly taken into account, other factors are also considered when setting the NAAQS levels.

The World Health Organization (WHO) sets guidelines for air quality. These are not legally enforceable and focus on what levels of ambient air pollution are harmful to human health. They are usually somewhat lower than the legally enforceable standards set by national governments.

After a full year of monitoring at the Canary1 and Ouzel1 locations, the calculated values for the Canary1 and Ouzel1 monitors are as shown in the tables below.


PM2.5 NAAQS annual mean, ug/m3


World Health Organization PM2.5 Guideline,  annual mean, ug/m3


Canary 1


Ouzel 1



PM2.5 NAAQS 98th percentile 24-hr mean, ug/m3


World Health Organization PM2.5 Guideline, 98th percentile 24-hr mean, ug/m3


Canary 1


Ouzel 1



While the levels measured do not exceed the PM2.5 NAAQS, they do exceed or closely approach the WHO guidelines. The annual average WHO guideline value of 10 μg/m3 for PM2.5 was chosen to represent the lower end of the range over which significant effects on survival have been observed in an American Cancer Society (ACS) Study. For more information on the WHO guidelines visit https://www.who.int/phe/health_topics/outdoorair/outdoorair_aqg/en/

According the EPA:

The size of particles is directly linked to their potential for causing health problems. Small particles less than 10 micrometers in diameter pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream.

Exposure to such particles can affect both your lungs and your heart. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including:

  • premature death in people with heart or lung disease
  • non-fatal heart attacks
  • decreased lung function
  • increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing.
  • irregular heartbeat

People with heart or lung diseases, children, and older adults are the most likely to be affected by particle pollution exposure.

Sustain the Train expresses its appreciation for the efforts of Dr. Christie Chatterley’s Fort Lewis College (FLC) 2019 senior engineering class for their work in considering the best ways to compile and interpret the large amount of data provided through Durango’s Purple Air monitors. Very special thanks goes to 2019 FLC Engineering graduate Andre Bos. Without his work on the core build for our data analysis tool, this work would not have been possible.

I’m a recent Engineer graduate from Fort Lewis College who has been living in Durango for the past 4 years. I was first introduced to this project by my Professor Dr. Chatterley in an environmental principles class. I really enjoyed the project because we were analyzing Air Quality Sensor around Durango and comparing the Air Quality to EPA standards. As I emerged myself into the project, I realized that the results of the project meant a whole lot the community. Working on the project I learned how to code on Python, an open source coding platform, to analyze the data from various Purple Air sensors around town. My drive for this project was sparked by giving back to the community. As a cyclist and a community member, I really enjoyed being outside and I wanted to make sure it was a healthy choice. I learned that particulate matter smaller than 2.5 microns can enter the respiratory system and cause various health effects. These particles are emitted into the air by vehicles, fires, and smoke stacks among other sources. I believe by providing a means to analyze the data from the current sensors and potentially future sensors in the area is the first step to ensuring a healthy community and pinpointing sources of high emissions in the area.

Andre Bos, 2019 Fort Lewis College Engineering graduate