A new USC Dornsife study has discovered that Los Angeles’ urban trees absorb more carbon dioxide than expected, providing valuable data that could guide future environmental initiatives and urban planning.
The trees of Los Angeles are more powerful allies in the fight against climate change than previously believed, according to a study from USC Dornsife College of Letters, Arts and Sciences. The research, conducted under the auspices of USC Dornsife’s Public Exchange, reveals that certain trees in central Los Angeles absorb substantially more carbon dioxide (CO₂) than anticipated, especially during the warmer months.
Published in the journal Environmental Science & Technology, the study offers one of the most detailed analyses to date on the role of urban trees in improving air quality.
The findings show that vegetation within the study area absorbed up to 60% of daytime fossil fuel CO₂ emissions in spring and summer, and approximately 30% annually, positioning Los Angeles among cities with the highest recorded rates of CO₂ uptake.
The Study
The research team employed the Carbon Census array, a set of 12 high-resolution BEACO₂N sensors, to track CO₂ levels in real time. These sensors were installed across a 15-by-6-mile section of Los Angeles’ Mid-City, mapping CO₂ concentrations as they shifted throughout the urban environment.
This allowed researchers to account for wind patterns, urban density and other factors crucial in understanding how local greenery mitigates emissions.
“You can think of emissions like passengers on a train,” Will Berelson, who led the research and is a professor of earth sciences, environmental studies and spatial sciences at USC Dornsife, said in a news release. “As the wind moves pollution through the city, some gets picked up and some gets dropped off. These sensors let us see that process in real time.”
In contrast to models that estimate CO₂ based on fuel sales or static traffic data, this study monitored emissions directly over an extended period, from July 2021 to December 2022.
By differentiating CO₂ from fossil fuels from that produced by living organisms through carbon monoxide (CO), a byproduct of fossil fuel combustion, the researchers obtained a more precise and localized estimation of emissions.
Implications
While the study focused on a specific section of Los Angeles, its implications extend to urban areas globally, offering a template for improving air quality through strategic planting and other green initiatives.
Notably, the research identified that trees absorb the most CO₂ in the summer, despite the season’s dryness in Los Angeles. This unexpected result likely owes to irrigation, groundwater from leaky pipes and resilient tree species.
However, the study also emphasized that urban vegetation alone cannot fully counterbalance emissions from vehicles, buildings and industrial activity.
This research forms a cornerstone for the USC Urban Trees Initiative, a collaborative effort between USC, the City of Los Angeles and local community organizations aimed at expanding urban greenery in under-served neighborhoods.
By pinpointing where trees most effectively absorb carbon, the findings provide actionable data to steer future planting projects.
“Nature is helping us, but we can’t rely on it to do all the work,” Berelson added.
The study estimates urban vegetation absorbs about 30% of annual fossil fuel emissions in the study area, underscoring the need for comprehensive measures such as clean energy adoption, improved public transportation and broader emissions cuts.
Looking Ahead
Encouraged by this study’s success, the USC team has broadened its sensor network, adding eight more BEACO₂N sensors to cover areas east of the original site and extending into Santa Monica.
These sensors, developed through the University of California, Berkeley’s BEACO₂N project, supply urban areas with high-resolution emissions data that were previously inaccessible.
“Our goal is to monitor more areas of L.A. to define baseline values of CO₂ emissions and identify where vegetation is making the biggest impact and where more greenery is needed,” concluded Berenson.
As Los Angeles aims to reach carbon neutrality by 2050, this research indicates that while urban greenery can significantly aid in reducing CO₂ levels, the critical step remains cutting fossil fuel use. The data-driven approach exemplified by the Carbon Census array provides a promising pathway for cities worldwide to better monitor and reduce their carbon footprints.