关于雾霾, 我刚刚发了一个综合的阐述， 柴静没有回答的问题，我来试试(二), 但是，朋友们仍然有许多人有疑问与争论，说肺癌与吸烟的关系比较密切, 与雾霾无关, 或者关系不大.

http://news.sciencenet.cn/htmlnews/2015/3/314617.shtm

雾霾会否致癌？钟南山说，以科学的态度说，目前尚不能得出“空气污染直接导致肺癌”的结论，没有数据能够说明除去吸烟等因素之外，目前这种浓度的PM2.5对肺癌的发病率有多大影响。2009年，国家发布过一份关于肿瘤方面的流行病学报告指出，大气污染物质中与肺癌有明确关系的是二氧化氮，二氧化硫则会引发哮喘和慢性支气管炎，至于其他物质如PM2.5等与疾病之间的关系都不明确。因此，“雾霾与肺癌关系几何，需要一个长期的科研调查、采样、跟踪过程”。

首先，吸烟是个人的一个选择，许多人明知吸烟有害，但仍然吸烟。这里有个烟瘾的问题，也有侥幸心态（丘吉尔长期吸烟却很长寿），还有就是对长寿的预期与态度。第二，香烟企业是税收大户，地方政府对此心知肚明，心照不宣。 这两个恐怕是为什么吸烟在中国没受太多关注的原因吧。

不吸烟的人觉得我可以选择不吸烟，我可以尽量避免吸二手烟，但雾霾我却逃不掉。所以雾霾是过街老鼠，人人喊打。人们的热情被柴静误导了吗？没有.

根据世界卫生组织所属的International Agency for Research on Cancer （IARC)，雾霾比吸二手烟更有害，雾霾可以导致肺癌。

http://www.cbc.ca/news/health/air-pollution-causes-lung-cancer-who-agency-decides-1.2100862

What many commuters choking on smog have long suspected has finally been scientifically validated: air pollution causes lung cancer.

The International Agency for Research on Cancer declared on Thursday that air pollution is a carcinogen, alongside known dangers such as asbestos, tobacco and ultraviolet radiation. The decision came after a consultation by an expert panel organized by IARC, the cancer agency of the World Health Organization, which is based in Lyon, France.

"We consider this to be the most important environmental carcinogen, more so than passive smoking," said Kurt Straif, head of the IARC department that evaluates cancer-causing substances.  

IARC had previously deemed some of the components in air pollution such as diesel fumes to be carcinogens, but this is the first time it has classified air pollution in its entirety as cancer causing.

The risk to the individual is low, but Straif said the main sources of pollution are widespread, including transportation, power plants, and industrial and agricultural emissions.

Air pollution is a complex mixture that includes gases and particulate matter, and IARC said one of its primary risks is the fine particles that can be deposited deep in the lungs of people.

"These are difficult things for the individual to avoid," he said, observing the worrying dark clouds from nearby factories that he could see from his office window in Lyon. "When I walk on a street where there's heavy pollution from diesel exhaust, I try to go a bit further away," he said. "So that's something you can do."

The fact that nearly everyone on the planet is exposed to outdoor pollution could prompt governments and other agencies to adopt stricter controls on spewing fumes. Straif noted that WHO and the European Commission are reviewing their recommended limits on air pollution.

Previously, pollution had been found to boost the chances of heart and respiratory diseases.

The expert panel's classification was made after scientists analyzed more than 1,000 studies worldwide and concluded there was enough evidence that exposure to outdoor air pollution causes lung cancer.

In 2010, IARC said there were more than 220,000 lung cancer deaths worldwide connected to air pollution. The agency also noted a link with a slightly higher risk of bladder cancer.

Straif said there were dramatic differences in air quality between cities around the world and that the most polluted metropolises were in China and India, where people frequently don masks on streets to protect themselves. China recently announced new efforts to curb pollution after experts found the country's thick smog hurts tourism. Beijing only began publicly releasing data about its air quality last year.

Cleaning the air

"I assume the masks could result in a reduction to particulate matter, so they could be helpful to reduce personal exposure," Straif said. But he said collective international action by governments was necessary to improve air quality. "People can certainly contribute by doing things like not driving a big diesel car, but this needs much wider policies by national and international authorities."

Other experts emphasized the cancer risk from pollution for the average person was very low — but virtually unavoidable.

"You can choose not to drink or not to smoke, but you can't control whether or not you're exposed to air pollution," said Francesca Dominici, a professor of biostatics at Harvard University's School of Public Health. "You can't just decide not to breathe," she said. Dominici was not connected to the IARC expert panel.

A person's risk for cancer depends on numerous variables, including genetics, exposure to dangerous substances and lifestyle choices regarding issues such as drinking alcohol, smoking and exercising.

Dominici said scientists are still trying to figure out which bits of pollution are the most lethal and called for a more targeted approach.

"The level of ambient pollution in the U.S. is much, much lower than it used to be, but we still find evidence of cancer and birth defects," she said. "The question is: How are we going to clean the air even further?"