SE Valley Times

Phoenix is grappling with a significant ozone pollution issue, particularly evident during the summer months when a brown haze often hangs over the Valley. This urban emissions problem, exacerbated by high levels of sunlight, has placed metro Phoenix's air quality among the worst in the nation. The region frequently surpasses federal health-based air quality standards, posing serious respiratory health risks.

In response, researchers from Arizona State University’s School of Molecular Sciences and School of Sustainable Engineering and the Built Environment are conducting field research this summer to study natural emission levels in Phoenix. The goal is to better understand and address the city's ozone pollution problem.

"If you enter a forest or smell a flower, the pleasant odors you experience are a mix of naturally occurring emissions called volatile organic compounds (VOCs)," explained Pierre Herckes, an atmospheric chemistry professor at ASU who co-leads the project. "These compounds contribute to summer ozone formation, along with human-caused VOCs from gasoline or solvents."

By measuring these naturally occurring emissions and examining weather conditions that may influence them, ASU researchers aim to improve air quality models and develop more effective strategies for reducing ozone levels. "A big challenge is figuring out the amount of the critical ingredients that make up our ozone," said Herckes. "If we think about regulation based on data, we can begin to determine the best actions to try and address these issues and get lower concentrations of ozone."

The project involves collaboration with the University of Arizona and is funded by the Arizona Board of Regents and the Arizona Department of Environmental Quality.

Ground-level ozone forms through sunlight-driven chemical reactions between pollutants like nitrogen oxides and VOCs. These pollutants originate from sources such as car exhaust, industrial emissions, and some plants. While nitrogen oxide sources are well understood—primarily from energy generation, industry, and vehicles—there remains uncertainty about VOC sources.

VOC emissions occur naturally from plants and forest fires as well as human activities like fueling cars. However, few measurements have been conducted in hot and dry climates like Phoenix to calibrate existing models accurately.

Over the past year, environmental chemistry PhD student Trinity Olguin and civil engineering PhD student Gabrielle Cano have assisted in assembling instruments for field measurements and provided updates to Maricopa County stakeholders involved in the project.

Inside an air-conditioned trailer on-site, ASU researchers Cano and Olguin analyze collected data with hopes that new information will enhance air quality models. They plan further VOC measurements at two additional sites later this summer: one in a natural desert area and another in an agricultural setting. The team will work with the University of Arizona to refine mathematical models predicting air pollution formation.

"No one's proposing cutting down trees to improve air quality," stated Matthew Fraser, professor at ASU’s School of Sustainable Engineering and co-lead on the project. "We need to understand uncontrollable emissions from vegetation so we can determine how to control human sources like industry and vehicles."

Using fast-response sensors atop a 40-foot tower in west Phoenix neighborhoods, researchers measure VOC releases from vegetation coupled with three-dimensional wind field and temperature data to see how weather conditions affect VOC release.

"It is important that we understand biogenic VOC quantities to grasp their impact on air quality," said Olguin. "Tropospheric (ground-level) ozone directly affects human health. Improving air quality benefits everyone because no one chooses what air they breathe."

The project is conducted in collaboration with Maricopa County and ASU's Central Arizona-Phoenix Long-Term Ecological Research Center.

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