The gradual decline in vehicle emissions in California over the years has been a positive sign for environmentalists and policymakers. However, a new study has shed light on a previously overlooked contributor to air pollution in the state – trees and shrubs. While efforts have been made to reduce emissions from transportation and industry, the rise in ‘secondary sources’ such as botanical emissions poses a new challenge in the fight against air pollution.
A team of US researchers conducted a study over Los Angeles in June 2021 to directly measure volatile organic compounds (VOCs) emitted by plants. Unlike previous methods that relied on estimating emissions or modeling their movement, this study used an airborne approach with an on-board mass spectrometer to measure more than 400 types of emissions in unprecedented detail. The results showed that botanical sources of VOCs contributed significantly to the potential formation of secondary organic aerosols, with compounds like isoprene, monoterpenes, and sesquiterpenes playing a key role.
Ambient air pollution remains a significant health concern with fine solid particles and ozone in the air posing serious risks to human health. VOCs play a crucial role in the formation of these harmful particles and gases, contributing to respiratory illnesses, heart diseases, low birth weights, and increased mortality rates. With an estimated 4.2 million premature deaths per year attributed to ambient air pollution, identifying and mitigating sources of VOCs becomes imperative for public health authorities.
While it may come as a surprise, even the green spaces that define clean living in urban areas can be a significant source of VOC emissions. The study revealed that terpenoids emitted by plants contribute a significant amount to the measured mass flux of VOCs, highlighting the complex relationship between botanical and industrial sources of emissions. The increasing emissions of these compounds with higher temperatures and drought conditions further emphasize the need to better understand the dynamics of biogenic VOC emissions in urban environments.
The findings of the study raise important questions about the role of green spaces in urban air pollution and the need for targeted mitigation strategies. While reducing green spaces is not a viable solution, understanding how different plant species contribute to VOC emissions and identifying lower-emission alternatives can help in minimizing the impact of botanical sources on air quality. Moreover, as global temperatures continue to rise, a proactive approach to managing biogenic VOC emissions becomes crucial for maintaining air quality standards in cities.
The study provides valuable insights into the often overlooked contribution of trees and shrubs to air pollution in urban areas. By acknowledging and addressing the role of botanical emissions in the formation of harmful pollutants, policymakers, urban planners, and environmentalists can work towards sustainable solutions that balance the benefits of green spaces with the need for clean and healthy air.
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