01-14-2013, 04:41 AM
More info
http://news.yahoo.com/beijing-warns-resi...40614.html
By Monday levels had declined to 245 micrograms on the Beijing government scale — down from a high above 700 — but still way above the level of 25 considered safe by the World Health Organization.
PM2.5 are tiny particulate matter less than 2.5 micrometers in size, or about 1/30th the average width of a human hair. They can penetrate deep into the lungs, and measuring them is considered a more accurate reflection of air quality than other methods.
http://news.yahoo.com/beijing-warns-resi...40614.html
By Monday levels had declined to 245 micrograms on the Beijing government scale — down from a high above 700 — but still way above the level of 25 considered safe by the World Health Organization.
PM2.5 are tiny particulate matter less than 2.5 micrometers in size, or about 1/30th the average width of a human hair. They can penetrate deep into the lungs, and measuring them is considered a more accurate reflection of air quality than other methods.