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近几日北京持续被浓重雾霾(fog and haze)笼罩，市场上防尘口罩(anti-dust mask)和空气净化器(air purifier)的销量剧增。部分地区的空气质量指数(air quality index, AQI)可能达到极重污染水平，北京多地PM2.5(particulate matter)浓度“爆表”。本文新东方网
请看《中国日报》的报道：
Longtime exposure to particulate matter especially the particulate matter smaller than 2.5 micrometers (PM2.5) which can go directly to the alveoli of the lungs, is a major health hazard.
专家称，长时间呼吸空气中的颗粒物，特别是直径小于2.5微米的可入肺颗粒物(PM2.5)对人体健康危害很大。
文中的PM2.5就是指“可入肺颗粒物”，PM的英文全称为particulate matter(微粒物、悬浮微粒)，PM2.5就是指大气中直径小于或等于2.5微米的颗粒物，可直接进入人体的alveoli of the lungs(肺泡)，也称为“可入肺颗粒物”，它的直径还不到人头发丝粗细的1/20。PM2.5主要来自vehicle exhaust(机动车尾气尘)、燃油尘、硫酸盐、餐饮油烟尘、建筑水泥尘、煤烟尘和硝酸盐等。
PM2.5粒径小，这种fine particles(细微颗粒)富含大量的toxic and harmful substance(有毒、有害物质)且在大气中的停留时间长、输送距离远，因而对人体健康和大气环境质量的影响更大。今后，使用PM2.5 measurement(PM2.5标准)进行air quality monitoring(空气质量监测)正成为全球趋势。
近来很火的词PM2.5是指大气中直径小于或等于2.5微米的颗粒物，也称为可入肺颗粒物。我们希望更加严格的空气标准将揭示更多的环境危害，提高公众的意识。
China’s environmental authorities are to implement new air quality standards which will now measure some of the smallest and most damaging particles in the air. In many cities, the public are being consulted over the introduction of the new standards ，which will find out just how clean the air really is.
中国的环境部门将执行新的空气质量标准，将测量空气中一些最小、伤害最大的颗粒。在许多城市，民众正被询问到新标准的引进，这将了解到空气实际上有多纯净。
Smog in Beijing. Smog in Shanghai. Smog in Hangzhou - During recent months, dense pollution has frequently blanketed many cities in China. Sometimes visibility drops to less than 1 kilometer, causing serious traffic jams, flight delays and highway closures.
北京的烟雾。上海的烟雾。杭州的烟雾——最近几个月，浓度大的污染经常笼罩着中国的城市。有时，能见度下降到1千米以下，引发了严重的交通阻塞，航班延误和公路关闭。
It has also raised public awareness of the issue. Ma Jun has been conducting environmental research since the mid 1990s and in 2006, he founded his own NGO in Beijing.
它也提高了这个问题的公共意识。马军从上个实际90年代中期就开始进行环境研究，2006年，他在北京成立自己的非政府组织。
The Ministry of Environmental Protection’s newly published air quality standard includes monitoring of PM2.5 - a kind of air particle with a diameter of 2.5 microns or less. These particulates are small enough to penetrate human lung tissue, causing severe health problems. The revised standard is now open for public input and will take effect from 2016.
环保局新近发布的空气质量标准包括了PM2.5的监测——PM2.5是一种直径等于或小于2.5微米的空气颗粒。这些颗粒足够小，能进入人的肺组织，引发严重的健康问题。新修改的标准现在开放公众投入，从2016年开始生效。
Responding to the new air quality standard, several cities, including Shanghai and Nanjing, announced that they are preparing pilot programs that will start to monitor and publish PM 2.5 levels soon. Experts believe that the monitoring results in some cities might not initially meet international standards.
作为对新的空气质量标准的响应，包括上海、南京在内的一些城市宣布，他们正在准备试点计划，很快将开始监测、发布PM2.4水平。专家认为，一些城市的监测结果开始可能达不到国际标准。
Stricter air standards will reveal more environmental hazards and raise public awareness, which should certainly help the government’s aim of providing cleaner, healthier air.
更加严格的空气标准将揭示更多的环境危害，提高公众的意识，这无疑有助于政府提供更清洁、更健康的空气的目标。