Standing on the roof of a small rectangular building among instruments and sensors, CU Boulder chemistry PhD student Seonsik Yun tinkers with shiny scientific equipment and sample air inlets that lead to instruments inside below. The air quality sampling site, La Casa, houses instruments that have collected gas and particle samples from Denver’s hazy skies for years. Every couple of weeks, Yun drives in his EV from Boulder to maintain instruments at the research site — he comes prepared with a checklist and looks over each piece of tubing and instrument from top to bottom. 

The instruments are part of the National Science Foundation-funded Atmospheric Science and Chemistry mEasurement NeTwork, or ASCENT. Since 2021, CIRES researchers in Jose-Luis Jimenez’s research group have helped lead the new program, made up of 12 sites scattered across the U.S., in setting up a suite of instruments that collect high-resolution air samples day and night. The project will run indefinitely to advance understanding of air quality in different regions of the country.

“Getting everything set up and working with other sites was pretty monumental,” said CIRES research scientist Doug Day, who provides guidance and hands-on support in all aspects of the planning, operation, and analysis at La Casa and the broader ASCENT program. “We set up and characterized and calibrated instruments while developing operating procedures and checklists to ensure the data we are collecting is uniform and high quality.”

ASCENT locations span urban to rural: from national parks like Yellowstone and Joshua Tree to densely populated cities like Denver and Houston, and the data will reflect the air quality of these locations. Research groups in each location set up four aerosol-measuring instruments to take real-time measurements of trace metals, black and brown carbon, organic and inorganic fractions, aerosol number, size, distribution, and concentration along with their sources. The machines run day and night, taking in new data from the air every second, minute, and hour of each day — providing quality data with a chemical specificity at a frequency that is rarely done on a longer-term basis. 

ASCENT sites piggyback on existing monitoring stations that have been collecting air quality samples for years. La Casa is managed by the Colorado Department of Public Health and Environment (CDPHE). Northeast of downtown Denver, the site sits in the middle of a neighborhood with homes, shops, and industrial activity near the intersection of three interstate freeways. The site also hosts the Environmental Protection Agency (EPA), both agencies measure PM2.5 concentrations, gas pollutants, ozone levels, and meteorology. 

“This network may help push forward the next generation of air quality measuring," said Day. "Governments may adopt these instruments in the future if these efforts show the value of measurements."

After inspecting the hardware on the roof, Yun and Day descend the steep ladder back to the ground and step inside the tiny building. In a crowded corner, ASCENT instruments hum as they sort and digest the air from outside. Yun turns to a visual graph sorting the chemical compositions in real-time: green lines on the graph indicate organics and blue highlights nitrate. 

“Monitoring the chemical composition of aerosols is crucial for air quality management, as it helps to understand different sources,” said Yun. “Organic aerosols originate from both natural sources and anthropogenic activities, including vehicle emissions, food cooking, and industrial processes, such as refineries. In urban areas, these aerosols are particularly significant.”

The Jimenez Group typically embarks on shorter projects that measure air quality for weeks rather than years, often in international locations. Day says everyone is excited to be involved in a project that will span years here in Colorado’s Front Range. Three years in, the scientists have worked out the kinks related to instrument operations, and now are diving into the science to understand what it all means.

Day estimates about 80 percent of the data will contribute to research related to health, specifically air quality impacts. The other 20 percent will further scientific understanding of particles’ effects on clouds, climate, and visibility. 

“Aerosol sources and pollution in Denver consists of a complex and changing mixture from different sources — such as industry, vehicles, wildfires, oil and gas extraction, agriculture, cooking, fireworks, and vegetation sources,” said Day. “We are excited to leverage this novel combination of chemical specificity, high time resolution, and long-term record, to help get a better handle on the sources that control Denver and Front Range air quality.”