close
Alex Guenther
Abstract
Hydrocarbon emissions from living vegetation are thought to be harmful to the atmosphere. But the latest study suggests that the negative impact of these emissions in pristine environments is less than expected.
Do trees produce more pollution than cars? Terrestrial vegetation produces copious quantities of hydrocarbons and other volatile organic compounds (VOCs) that dominate global gas emissions. The largest component of emissions from vegetation is the hydrocarbon isoprene. Current models suggest that isoprene emissions in pristine environments can overwhelm the ability of atmospheric oxidants to remove 'greenhouse' gases (such as methane) and toxic gases (such as carbon monoxide). Furthermore, in a polluted atmosphere, isoprene emissions can substantially increase the amount of smog. But on page 737, Lelieveld et al. propose that isoprene emitted by terrestrial ecosystems into unpolluted atmospheres is much less deleterious than was previously thought. Only when it comes into contact with air tainted by human activities does it exert a negative influence.
Some VOCs are known to attract pollinators and repel pests, but the function of isoprene remains a mystery, despite its prevalence in biogenic emissions. What was thought to be known was the dramatic negative impact of isoprene on chemical reactions in the troposphere — the lowest part of Earth's atmosphere. The first speculation that abundant hydrocarbon emissions could modify atmospheric composition appeared almost 50 years ago. Modern atmospheric-chemistry model (ACM) simulations now suggest that, in unpolluted air, isoprene depletes the levels of hydroxyl radicals ( OH). Although these radicals are present in the atmosphere in minuscule amounts (less than 1 part per trillion), they are extremely reactive and serve as the primary cleansing agent for the atmosphere. In an atmosphere depleted of OH, many trace gases would build up to dangerous levels.
1. pristine 原始的
2. terrestrial 陸生的
3. copious 大量的
4. volatile 易揮發的
5. isoprene 異戊二烯
6. methane 甲烷
7. toxic 有毒的
8. ecosystems 自然生態系統
9. deleterious 有害的
10. tainted 污染的
11. exert 發揮
12. pollinator 傳粉媒介
13. repel 驅逐
14. pests 有害的東西
15. prevalence 盛行
16. troposphere 對流層
17. speculation 沉思
18. deplete 用盡
19. radicals 基本的
全站熱搜
留言列表
