While air pollution and chemicals are believed to pose a major threat, our analysis determined that tourism served as the silent killer.

虽然空气污染和化学物质被确认为是主要的威胁，但我们的分析认定，旅游业也是一个无声的杀手。

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Poor indoor air quality may pose a risk to the health of over half of the world’s population.

室内空气质量恶劣可对全球一半以上人口健康构成风险。

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For example, visible and invisible chemicals spewed into the air or water from a plant nearby pose a danger to the people nearby and other animals and plants.

例如，有形和无形的化学原料从附近的工厂排放到空气或水中，这对于附近的人们和其他的生物构成危害。

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The study was actually conducted in and reported on air pollution in Boston, but it pointed out that air quality levels even below current standards set by the Environmental Protection Agency still pose risks to people who breathe particulate air pollution.

FORBES: Los Angeles Pollution From Car Exhaust Is Down 98%

Researchers at Southampton University say metal in the air thrown up by trains running on metal tracks could pose a health risk.

BBC: Railway tracks