Air quality differs from place to place and day to day. But about 99 percent of the world’s population breathes air at some point that does not meet pollution guidelines set by the World Health Organization (WHO).

空气质量每天都有不同的位置。 但是，在某个时候，大约99％的人口呼吸着空气不符合世界卫生组织（WHO）制定的污染指南。

Different forms of air pollution kill about 7 million people each year, the U.N. health agency estimates. But health experts say there are some actions individuals can take to protect themselves, even in the world’s most polluted cities.

联合国卫生局估计，每年不同形式的空气污染杀死约700万人。 但是健康专家说，即使在世界上最污染的城市中，个人也可以采取一些行动来保护自己。

The first step is to start with the understanding that air is not only polluted when it looks smoky or smoggy, said Tanushree Ganguly. She is an air quality expert with the Energy Policy Institute of Chicago’s India program.

Tanushree Ganguly说，第一步是从了解空气时不仅在看起来烟熏或烟雾时受到污染的第一步。 她是芝加哥印度能源政策研究所的空中质量专家。

“Blue skies can’t guarantee you clean air,” Ganguly told The Associated Press.

“蓝天不能保证您清洁空气，”甘加利对美联社说。

Air pollutants often come from people burning things. Examples include fuels as well as clearing operations involving crops or trees. Pollutants can also be released from wildfires.

空气污染物通常来自燃烧东西的人。 例子包括燃料以及涉及农作物或树木的清理操作。 污染物也可以从野火中释放出来。

Among the most dangerous particles we can breathe in are called particulate matter. The smallest of these are known as PM 2.5. This is because they are less than 2.5 microns in diameter. These particles can travel deep inside human lungs and are mostly created by burning fuels. Larger particles, known as PM 10, are linked to agriculture, roadways, mining or wind-blown dust.

在我们可以呼吸的最危险的颗粒中，称为颗粒物。 其中最小的被称为PM 2.5。 这是因为它们的直径小于2.5微米。 这些颗粒可以在人类肺部深处传播，并且主要是由燃烧燃料产生的。 较大的颗粒（称为PM 10）与农业，道路，采矿或风吹灰尘有关。

Other dangerous pollutants include gases like nitrogen dioxide or sulfur dioxide, which are also produced from burning fuels. This information comes from Anumita Roychowdhury, an air pollution expert at the Center for Science and Environment in New Delhi.

其他危险污染物包括诸如二氧化氮或二氧化硫等气体，这些气体也是由燃烧燃料产生的。 该信息来自新德里科学与环境中心的空气污染专家Anumita Roychowdhury。

The American-based Health Effects Institute says air pollution is the second-largest risk factor for early death worldwide, behind high blood pressure.

美国的健康影响研究所表示，空气污染是全球早期死亡的第二大危险因素，仅次于高血压。

Short-term exposure can cause asthma attacks and increase the risk of heart attacks and stroke, especially in older people and those with existing medical problems. Long-term exposure can cause serious heart and lung problems that can lead to death.

短期暴露会引起哮喘发作，并增加心脏病发作和中风的风险，尤其是在老年人和现有医疗问题的人中。 长期暴露会导致严重的心脏和肺部问题，导致死亡。