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How do plants become invisible killers of air pollution? Reveal the secrets of their volatile organic compounds!
As global climate change becomes increasingly severe, the role of plants seems not to be fully understood. Many people think of plants as natural filters that purify the air, but the truth may be more complicated. Plants not only release oxygen, but also volatile organic compounds (VOCs), which can become invisible killers of air pollution. Among them, non-methane volatile organic compounds (NMVOCs) have become a topic of concern.
Non-methane volatile organic compounds are a large class of organic compounds that are photochemically active in the atmosphere. Their emission sources include plants, burning biomass, geological sources and human activities.
These compounds range from benzene to ethanol to acetone. Importantly, the activity of these compounds affects the production of atmospheric ozone. Ground-level ozone is not emitted directly but is formed through the reaction of sunlight with various emitting compounds, including NMHCs and nitrogen oxides. This process makes the study of NMVOCs particularly important in atmospheric chemistry.
The role of plants
Plants play both important and contradictory roles in nature. It is estimated that the amount of NMVOCs released by plants may match or exceed the amount released by human activities. The influence of these compounds, such as terpenoids, aldehydes and ketones, on the composition of the atmosphere cannot be ignored.
NMVOCs released by plants can be classified into multiple sources, including chloroplast activity, emissions from special defense tissues, and the effects of plant growth hormones.
Soil microorganisms
In addition to plants, soil microorganisms also produce many NMVOCs. Although these compounds may be metabolized by other soil microorganisms, NMVOC emissions from soil still attract attention from the scientific community.
Impact of biomass burning
As one of the biological sources, the NMVOCs emissions caused by biomass burning cannot be underestimated. During different combustion stages, different chemical components are released. It is estimated that burning every kilogram of organic matter releases about 4.5 grams of carbon as NMVOCs.
Main NMVOCs emissions include ethane, propane and propylene, etc. These components in the environment can pose potential threats to air quality.
The challenge of anthropogenic sources
Human activities are another important source of NMVOCs, such as electricity generation, industrial manufacturing, automobile transportation and other aspects, which add burden to the atmosphere. According to the European Database for Global Atmospheric Research (EDGAR), emissions of NMVOCs from six major sectors reached 120 million tons in 2015.
Between 1970 and 2010, the total global NMVOCs emissions increased. With the promotion of green fuels and changes in emission standards in various places, emissions in the United States and Europe decreased significantly, while Africa and Asia showed an upward trend. This regional difference reflects the effectiveness of local environmental protection policies.
Summary
Non-methane volatile organic compounds in the atmosphere not only come from human activities, these compounds released by plants also play an important role in complex environments. Regarding current environmental issues, we need to rethink the role of plants. Are their natural emissions also exacerbating air pollution to a certain extent?
