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  3. People often recommend planting trees to make cities greener, cleaner and healthier. But during heat waves, city trees can actua

People often recommend planting trees to make cities greener, cleaner and healthier. But during heat waves, city trees can actua

admin2019-04-22  0
问题    People often recommend planting trees to make cities greener, cleaner and healthier. But during heat waves, city trees can actually increase air pollution. Indeed, a new study finds, up to 60 percent of the smoggy ozone in a city’s air on hot days may trace to chemicals emitted by trees. Galina Churkina, who works at Humboldt University of Berlin, and her team confirmed it.
   The findings might seem the opposite of what you would expect, notes Robert Young, an expert in city planting at the University of Texas at Austin. Indeed, he notes, " everything has multiple effects. " The new findings do not mean cities should discourage tree planting, he says. Instead, cities may need stricter controls on other sources of pollution, such as tailpipe emissions from cars and trucks.
   City trees soak up carbon dioxide, and at the same time they release oxygen into the air. But oxygen is far from the only gas that trees and certain other green plants release into the air. One of these chemicals is a hydrocarbon known as isoprene (异戊二烯). It can react with combustion (氧化)pollutants, such as nitrogen oxides(氧化氮) emitted by cars and trucks in cities. The result is the formation of ozone. A component of smog, ozone can irritate the lungs and aggravate airway diseases.
   Churkina says her team was not surprised to see the seemingly contrary relationship between plants and pollution. She adds that " its importance was, however, quite amazing. " The results, Churkina says, suggests that city tree plantings programs should not ignore the role this greenery may play in aggravating summer air pollution. Adding more trees will improve quality of life only if those cities also undertake plans to sharply cut vehicle pollution in summer and to increase their reliance on clean energy sources for electric power, she says.
What is the third paragraph mainly about?
选项 A、The harm ozone does to people in cities.
B、The way trees help the formation of ozone.
C、The chemicals green plants release into the air.
D、The benefits trees bring to the city environment.
答案B
解析 第三段主要讲述了树木帮助形成臭氧的方式。故选B。
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