In an unexpected scientific twist, Los Angeles trees have landed in the dock for air pollution. At the center of attention are the terpenoids, organic compounds that, when released into the air, could be more harmful than previously thought. How is it possible? Let's see better.
The study on terpenoids and urban pollution
A new study published in the journal Science (I link it here) highlighted the potentially negative role of terpenoids in the urban environment of Los Angeles. This multi-institutional research challenges traditional conceptions of the positive role of trees in urban ecosystems. What drove researchers to suspect the unsuspected? How can we think of the "blasphemous" hypothesis that trees can even promote pollution?
Despite efforts to reduce the harmful traffic emissions and increase environmental protections, levels of ground-level ozone and the fine particulate matter that make up Los Angeles' smog have remained stable. This situation has pushed researchers to investigate possible "secondary" sources of pollution. And a surprising twist has arrived.
Terpenoids: from “good” to “bad”
Terpenoids, as mentioned, are organic compounds present in plants that generally act as antioxidants. However, when released into the atmosphere, they can combine with other pollutants. And transform into volatile organic compounds (VOC) and reacting with existing pollution to create ozone and fine particulate matter.
To study this phenomenon, the researchers used an aircraft equipped with a mass spectrometer to measure VOC concentrations over Los Angeles over several days in June 2021. They also took 3D measurements of wind speeds to determine where the pollutants were coming from.
Key findings
The study revealed that terpenoids they were even the largest source of VOCs, with effects more evident in areas rich in vegetation and on warmer days. I repeat: when temperatures exceeded 30°C, terpenoids were the cause of the worst emissions even in areas with more people and fewer plants.
A crucial aspect that emerged from the research is that plants emit more VOCs due to rising temperatures and drought, conditions that particularly afflict Los Angeles. This suggests that climate change could exacerbate the problem.
Not just terpenoids
The study also found that as temperatures rise, so does pollution from human-related VOCs, including personal hygiene products such as deodorants.
Eye: The authors of the study highlight the importance of correctly interpreting these results. Eva Pfannerstill, first author of the paper, was clear: “Because it is difficult to control plant emissions, it is even more important to control the human-caused part.”
Future implications
To the researcher's clarification I allow myself to humbly add my own. This research does not suggest that trees are harmful, but highlights how climate warming could dramatically alter the quantities and composition of emissions. This highlights the need to consider these factors in urban air pollution mitigation strategies.
The “terpenoid phenomenon in Los Angeles” offers a new perspective on the complex interaction between urban vegetation and air pollution. Anthropic sources of pollution, this is the moral of the story, risk producing unwanted effects even in urban vegetation, transforming trees into boomerangs that turn against us.
