1 . 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 that up to 60% of the ozone (臭氧) in a city’s air on hot days may have its origin in chemicals released by trees.
City trees offer a host of benefits. They provide cooling shade, absorb carbon dioxide, and also 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(碳氢化合物) that can react with burning pollutants, such as nitrogen oxides (氮氧化合物). The result is the formation of ozone which can cause airway diseases.
Galina Churkina works in Germany at Humboldt University of Berlin. She and her team wanted to explore how much chemicals released by trees could affect city air. To do this, the researchers turned to a computer. They asked it to model the likely reactions between plant chemicals and nitrogen oxides in air throughout the Berlin city area. To do that, the researchers fed in local weather data for two summers. One was 2006, when there was a heat wave. The other was 2014, when temperatures were mild.
An average daily high there in summer tends to be at roughly 25℃. On such a day, chemicals released by area greenery would likely have contributed to making about 6 to 20 percent of the ozone in the city’s air. But during a heat wave, when temperatures are more than 30℃ , tree-chemical emissions (发出物) are also high. As a result, they are now likely to be responsible for up to 60 percent of the ozone in air.
Churkina says her team was not surprised to see the contrary relationship between plants and pollution. The results, Churkina says, suggest city tree-planting programs should not ignore the role this greenery may play in bad summer air pollution. Adding more trees will improve quality of life only if those cities also undertake plans to sharply cut vehicle pollution (汽车污染).
1. What might people think of the new study finding?| A．Reasonable. | B．Intelligent. | C．Surprising. | D．Disappointing. |
| A．It is released by trees and other green plants. |
| B．It directly comes from the burning of oxygen. |
| C．A part of nitrogen oxides results in ozone in the end. |
| D．It is from the chemical reaction between a hydrocarbon and burning pollutants. |
| A．The higher the temperature is, the more ozone forms. |
| B．There’re no emissions of chemicals in spring or autumn. |
| C．Churkina suggests the number of city trees be lessened. |
| D．Churkina was surprised at seeing the contrary finding first. |
2 . Within the environmental movement, the question often arises whether global warming can be mitigated (缓解) by planting more vegetation. The idea is that the plants will consume carbon dioxide (CO2) that is causing the warming, while producing oxygen for us to breathe. This is acceptable on condition that global warming is indeed caused in some way by CO2 in the air.
However, actual scientific debate on the issue has shifted away from CO2 as the probable cause, especially after the findings that the temperatures changed 800 to 1000 years before carbon dioxide changed. In other words, CO2 levels are an indicator of temperature change, not a cause.
While there is nothing we can do to control the global climate, there is still a lot we can do to improve our local climates. Land use is the biggest decisive factor of local temperature and air quality. On clear days, the temperatures in big cities can be 5.6 degrees Centigrade higher than in the countryside around them. This is because the concrete (混凝土) of sidewalks and buildings and the asphalt (沥青) of roads take in sunlight and transform it into heat. Some get so hot, one could cook an egg on them! These vast surfaces of man﹣made stone also store lots of heat, which they radiate (散发) all night long. Just before sunrise, when the earth should be its coolest, roadways are still warm to touch.
If vegetation was blocking the Sun from the sidewalks and roads, the vegetation would absorb the sunlight, fueling the plants’ oxygen-making engines, and the rock would stay at surrounding temperatures. The easiest and most obvious choice is trees, particularly wide-reaching trees like the oak. Another possibility, especially outside the city centre, could be vine-covered trellises (棚架).Covering rooftops with grasses or other short vegetation reduces a building’s cooling cost as sharply as having trees or trellises that provide shade for windows does.
The reason why vegetation does not warm the air like rock does is that plants take water from the ground and evaporate (蒸发) it through their leaves. The Sun’s energy isn’t radiated as heat — it is used to change water into water vapor. The evaporative cooling works so well that the leaves stay 5.6 to 8.33 degrees Centigrade cooler than they would have been without water. While we can’t improve global climate, increased vegetation can help cool local climates.
1. Which of the following is True according to the passage?| A．With some effort, we can still affect global climate. |
| B．We can do a lot to improve the climate where we live. |
| C．Temperatures in big cities are usually lower than in the countryside. |
| D．The asphalt of roads throws back sunlight. |
| A．Planting full and wide-reaching trees. |
| B．Using vehicles that get better gas mileage. |
| C．Using energy-saving equipment. |
| D．Constructing dark-colored roofs on new buildings. |
| A．Darker colors absorb more sunlight and transform it into heat. |
| B．More thick materials store heat and give off it at night. |
| C．Human activity is changing global climate. |
| D．Vegetation is neither dark nor thick; thus, it reduces localized heating. |
| A．Encourage the next generation to increase vegetation. |
| B．Promote rooftop gardening. |
| C．Remove vines and trellises from buildings. |
| D．A and B above. |
