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Suncor Energy’s Commerce City plant is seen Feb. 17, 2023. (Olivia Sun, The Colorado Sun via Report for America)

The Suncor refinery in Commerce City sent potentially dangerous spikes of sulfur dioxide into the surrounding neighborhood early Wednesday after an equipment failure, though the state health department’s notice didn’t go out until Wednesday evening. 

Sulfur dioxide detected from Suncor leapt to 155 parts per billion and 186 parts per billion, while the EPA’s National Ambient Air Quality Standards are 75 parts per billion. But to reach an official exceedance, the sulfur dioxide levels must be that high for over an hour. By 9 a.m. Wednesday, a state news release said, the levels had “dropped significantly.”

The state release at 6:23 p.m. said the spike readings “were verified a short time ago.” Despite the drop in the monitored sulfur dioxide levels, the Colorado Department of Public Health and Environment urged families in the future to limit outdoor exercise, keep windows closed and consider an air purifier. 

“The short exposures to sulfur dioxide that occurred earlier could have exacerbated asthma and made breathing difficult, especially during exercise or physical activity,” the health department said.

The state release said that early Wednesday, “the Suncor facility reported that #2 Sulfur Recovery Unit and associated Tail Gas Unit in Plant 1 briefly tripped offline due to a level indicator issue, resulting in: excess sulfur dioxide from the Tail Gas Unit Incinerator (H-25); flaring of acid gas (gas with elevated hydrogen sulfide) in the Plant 1 Flare; elevated hydrogen sulfide in the Plant 1 fuel gas system.”

Neighbors and environmental advocacy groups have been expanding independent monitoring of emissions from Suncor, and amplifying calls for a complete shutdown or at least far tougher state regulation of the refinery. The only refinery in Colorado, Suncor supplies a large portion of vehicle gasoline for the Denver metro area and airplane fuel for Denver International Airport. 

A fire in December damaged equipment at Suncor and forced a weekslong shutdown of the complex, followed by a series of emissions notifications to neighbors as Suncor worked to bring the facility back online. The shutdown also significantly raised gas prices for Colorado drivers during the winter. 

Multiple monitors around Suncor check for dangerous emissions, including some run by a neighborhood nonprofit Cultivando through a state environmental justice project. Cultivando released a report from Boulder atmospheric scientist Detlev Helmig in March warning of exactly what happened Monday: Short-term emissions from Suncor that endanger health but do not officially break EPA limits. 

Helmig’s instruments identified temporary local spikes in levels of pollutants like benzene or harmful particulate matter. Cultivando’s monitoring program can identify spikes that are short-lived but impactful on human health, Helmig said.

“Pollution levels go up and down, up and down very dynamically all the time,” he said at a Cultivando community briefing. “If you happen to go out there at a certain time when levels are low, it may look not too concerning and pretty clean. But you come back just half an hour later and conditions might have changed very dramatically.”

In an email Thursday afternoon, state health department spokesperson Leah Schleifer offered this explanation for the timing of the Wednesday announcement:

“Releasing this type of information is always a balance between providing accurate information, timely information, and assessing the potential of an ongoing problem. We decided to do this notification because we have heard from the community that they would like more information – and we are making a concerted effort to be as transparent as possible. In addition, we wanted to provide the information since Suncor didn’t send a notification.  

“We continuously monitor the area using community monitors, stationary monitors, and the department’s Colorado Air Monitoring Mobile Lab. When we noticed the higher-than-normal readings, we contacted the operators of Cultivando’s monitors. They informed us that they were performing maintenance on their monitors the day before, which can sometimes result in data anomalies. They worked to check the data to make sure it was accurate, then we notified the public. 

“In the time we were checking the data, the higher-than-normal (but below federal standards) levels subsided because they occurred for a short period. Because the elevated emissions had subsided, we took time to translate the full notification into Spanish to be able to reach more of the community.”

Suncor did not respond to a request for further comment.

This story was updated Thursday afternoon, April 13, with additional comments from the Colorado Department of Public Health and Environment.

Michael Booth is The Sun’s environment writer, and co-author of The Sun’s weekly climate and health newsletter The Temperature. He and John Ingold host the weekly Sun-Up podcast on The Temperature topics every Thursday. He is co-author with...