2012年12月14日，老美把PM2.5的标准值降低到12微克每立方米（年均值），并说由此带来的健康收益为40-90多亿美元（原来的值好像是15）。

原文：
On December 14, 2012, EPA updated the national air quality standards for PM 2.5 by revising the annual standard to 12 micrograms per cubic meter (ug/m3). Updated last in 1997, the revised annual standard will have major economic benefits with comparatively low costs. EPA estimates health benefits of the revised standard would range from $4 billion to over $9 billion per year.

原文链接：

http://yosemite.epa.gov/opa/admpress.nsf/bd4379a92ceceeac8525735900400c27/e4cef67086019f9a85257af60059cdbc!OpenDocument

PM2.5也称为苏特（SOOT），意为烟灰、煤烟，就是指小于等于2.5微米的颗粒。苏特是衡量空气污染的重要指标。

苏特能够进入肺的深处，会带来一系列严重的健康危害。这包括死的早、心脏病、中风、急性支气管炎、儿童哮喘加重等。

翻译可能不当，请参照原文：

Soot, also known as fine particle pollution (PM_2.5), can penetrate deep into the lungs and has been linked to a wide range of serious health effects, including premature death, heart attacks, and strokes, as well as acute bronchitis and aggravated asthma among children.

曹相生

2013,1.18