While the atmosphere's ozone protects us from the sun's rays, ground-level ozone is a pollutant.

大气层中的臭氧保护我们免受阳光的辐射，而地面的臭氧是一种污染物。

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Unlike the protective layer of ozone in the upper atmosphere, excessive ground-level ozone is tied directly to health.

与高空中具有保护能力的臭氧层不同，过量的近地面臭氧直接危害人体健康。

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WMO scientists assess and monitor air pollutants such as ground-level ozone, smog, particulate matter, sulfur dioxide and carbon monoxide.

世界气象组织的科学家对地面臭氧、烟雾、空气悬浮微粒子、二氧化硫、一氧化碳之类的污染物质进行评估监测。

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WMO scientists assess and monitor air pollutants such as ground-level ozone,smog, particulate matter, sulfur dioxide and carbon monoxide.

VOA: standard.2009.03.23

Scientists think they have identified one key reason why ground-level ozone remains stubbornly high in Europe.

BBC: London's clue to stubborn ozone levels

Ms. Jackson late last year delayed a decision on whether to tighten the government's limits on ground-level ozone, a primary ingredient in smog.

WSJ: EPA Tangles With New Critic: Labor

But the traffic increase has slowed progress in reducing emissions further, and people in many areas still suffer from nitrogen-related air pollution, including small particulates that get sucked deep into the lungs, and ground-level ozone - a strongly irritant gas formed by the action of sunlight on reactive nitrogen.

BBC: Nitrogen pollution 'costs EU up to ?280bn a year'