California has seen a decline in vehicle emissions over the years due to environmental policies and advancing technology. However, since 2010, there has been a stubborn refusal of microscopic airborne particles and ground-level ozone to drop. This is attributed to the rise in ‘secondary sources’, many of which are the trees and shrubs greening up city streets.
In June 2021, a team of US researchers conducted a study over Los Angeles to measure concentrations of volatile organic compounds (VOCs) in the air. Unlike previous methods that estimated emissions based on known sources or modeled the movement of emissions, this approach involved directly measuring airborne pollutants multiple times a second using an on-board mass spectrometer.
The researchers found that botanical sources of VOCs, including compounds like isoprene, monoterpenes, and sesquiterpenes, contributed to around 60 percent of the potential formation of secondary organic aerosols at the beginning of the LA summer. These botanical emissions tend to increase with hot weather and drought, posing a potential problem as the summer progresses.
Ambient air pollution remains a significant health concern globally, despite efforts to reduce toxic emissions in transportation and industry. Fine solid particles and ozone in the air are linked to various health issues such as heart disease, low birth weights, respiratory illnesses, and increased mortality. VOCs play a key role in the formation of these harmful materials.
Health authorities are seeking better ways to identify sources of VOCs that can be mitigated in urban areas, where most premature deaths attributed to ambient airborne pollution occur. Various sources such as pesticides, hair products, car upholstery, and cleaning agents contribute to VOC emissions in industrialized cities.
Debate continues over the significance of biogenic sources, such as trees and shrubs, versus industrial sources of VOC emissions, especially in higher temperatures. The study revealed that terpenoids generated by green spaces contribute to VOC emissions, raising questions about the impact of factors like drought on biogenic emissions.
While trees and shrubs play a role in air pollution through VOC emissions, they also provide cooling effects and other health benefits. Some plants are even capable of removing certain VOCs from the air. Understanding how different plants contribute to VOC emissions and identifying lower-emitting species can help maximize the benefits of green spaces in urban areas.
As global temperatures continue to rise, it is essential to monitor and mitigate sources of VOC emissions, including those from botanical sources. Researching the impact of factors like drought on biogenic emissions and identifying ways to reduce VOC emissions from plants can help address air pollution challenges in urban areas.
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