汽车尾气中的固体成分
(2017-01-05 18:24:45)
标签:
pm2.5汽车尾气天然气 |
汽车尾气中不仅有气体,而且有固体成分。这是难免的,因为石油从地下抽出来的之后,虽然经过化工提炼,但是由于过滤装置的局限,200纳米之内的固体颗粒几乎是无法过滤掉的。一般老百姓上街戴口罩更是不可能过滤这种微小颗粒。
上面的这张用电子显微镜拍摄的图片取自2003年美国明尼苏达大学(University of
Minnesota)科学与工程学院的一篇论文。
Park, K., F. Cao, D. B. Kittelson, and P. H. McMurry,
2003“Relationship between particle mass and mobility for diesel
exhaust particles,” Environ. Sci. Technol., 37(3) 577-583.
城里人呼入的固体颗粒60%-70%来自汽车尾气中的固体颗粒。呼入一次,几百万的固体颗粒会吸入人体,大部分这种微小颗粒会在呼出的时候带出来。但是,长时间积累效应会损坏健康。
下面的文章会帮助读者更好的了解汽车尾气:(文章来源:http://phys.org/news/2005-09-traffic-pollution-real.html)。
汽车尾气英文为:traffic fumes, particles in exhaust gas,the particle emissions from
engines 。工业排放的污染气体英文为:industrial gases 。
中国几乎没有天然气,但欧洲和美国有大片大片的天然气田,空气自然非常好。发电,供暖中国只能烧煤。一年四季空气中的固体颗粒非常多。而且烧煤废气的颗粒比汽车尾气的固体颗粒大得多,甚至可以用肉眼就能看到。其主要成分为氧化铁、碳酸钙、硫酸盐等等。
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Traffic pollution -
measuring the real damage
September 21, 2005
Traffic fumes from individual vehicles are decreasing every
year as engines become cleaner, but there are more vehicles on the
road and the number continues to grow. The long term effects of
living in urban areas and breathing in traffic fumes is widely
studied, particularly in cities such as Athens and Los Angeles,
where there is a lot of sunlight and not much air movement,
resulting in photochemical smog from traffic fumes and industrial
gases hanging in the air.
In the 1970s the Harvard Six Cities Study looked at morbidity
and mortality and the correlation with diesel and gasoline particle
levels in the environment and found a correlation which subsequent
studies have born out.
In an urban environment typically 60-70% of the particles that
we breathe in are from diesel or gasoline engines. Millions of
particles are taken into our lungs with every breath we take, most
of these pass back out again when we breathe out. The particles
that are not exhaled travel in the human body, passing from the
"air side" to the "fluid side" very quickly. Research elsewhere is
being carried out to find out more about the tiny diesel particles
that are able to travel through the lung walls into the
bloodstream, what the body does with them and what the long term
damage might be.
Here in the Department Professor Nick Collings and his student
Jason Olfert are working on a new method to measure extremely tiny
particles in exhaust gas. Vehicle engines continue to be designed
to be cleaner and the particles that need to be measured are
extremely small. The old method of analysing vehicle exhaust fumes
would be to pass exhaust gas through a filter, weighing it both
before and after. This method is not relevant for tomorrow's
cleaner engines since there is too little mass collected to be
reliably measured.
The tiny particles are given an electrical charge and they are
then passed through a centrifugal machine that Nick and Jason have
designed and built, that will separate the particles depending on
their mass and the amount of electrical charge that they are
carrying. Particles of the same mass-to-charge ratio can be
separated using the machine and the particles can then be counted
with an optical detector. Being able to measure the number and mass
across the particle size range (approximately 5nm - 200nm) will
help to better characterise, and more reliably measure the quantity
of, the particle emissions from engines. While the precise
mechanisms by which particles damage health remain unclear, it is
important to measure the differentiating characteristics, and thus
help the epidemiologists to disentangle cause and effect, followed
by more cost-effective legislative action.
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