<International Circulation>: I know there are government issued alert days in the US.  How many days cross a threshold where an alert should be issued?

   《国际循环》：我知道美国政府会发布天气污染警报，那么污染超过阈值多少天才发布警报？
 
    Prof. Baccarelli:  If you use the EU or the EPA parameters， almost every day would be above that threshold.  This is a big issue because air pollution is causing an adverse effect in Beijing.  Having that amount of pollution in the air is causing adverse consequences on cardiovascular health， on respiratory health， and on is possibly leading to increases in lung cancer.  The air pollution is not a very strong risk factor individually on someone’s life. Smoking， for instance， increase the risk of lung cancer by 7 or 8-fold.  For someone who smokes 20 cigarettes per day for a lifetime has about an 8-fold increased risk of lung cancer than a non-smoker.  95% of lung cancer cases are among smokers.  Air pollution increases that risk of 10-20%， compared to the increased risk with smoking of 800%.  The difference of air pollution is that it exposes everyone.  People decide whether to smoke or not and take responsibility when they choose to smoke.  With air pollution， although people do decide to move or live there they do not decide to breath or not.  People move to cities for economic reasons and other reasons of opportunity.  There are benefits of urbanization， for instance sanitation might be better.  In general， access to healthcare would be better.   Usually， however， people who live in smaller towns have better health than those in more remote areas.  Air pollution is a problem in the US just as it is in Beijing， the difference being that the pollution levels are about 10 times higher in Beijing than the dirtiest in the US.  In Orlando， Florida for instance， pollution levels are between 10-15 microgram/km， whereas in Beijing the levels are 100-400 microgram/km.

    Baccarelli教授: 倘若按照EU或EPA标准，几乎每天污染都超过阈值。 这是个严重的问题，因为空气污染对北京造成不利影响，空气污染会对居民的心血管系统和呼吸系统的健康造成不良后果，并可能诱导肺癌发生率的增加。空气污染对个人的生活并不是很强的风险因素。相反，吸烟则可令肺癌风险增加7至8倍。每天吸烟20支的个体较不吸烟者，一生中患肺癌的风险高出8倍。约为95%的肺癌患者吸烟。相比于吸烟导致肺癌风险增加800%，空气污染仅增加10-20%。两者的区别在于，每个人都会暴露在空气染污中。人们可以选择是否吸烟并对他们的选择负责。但是空气污染，虽然人们可以决定搬家或继续生活在原处，但他们没有权力选择是否呼吸空气。城市化有它的优点，比如卫生措施可能会更好，可以获得更好的医疗保健。然而，通常生活在小城镇的人们的健康水平较那些偏远地区的人们更好。空气污染不仅仅是美国面临的问题，北京同样面临着，所不同的是北京的空气污染是美国最脏城市的10倍。比如，佛罗里达州的奥兰多的污染水平在10-15微克/公里，而北京竟达到100-400微克/公里。