Tourists taking photo in front of the Tian Anmen Square by wearing masks
The term PM2.5 stands for Particulate Matter which are air pollutants with a diameter of less or equal to 2.5 micrometers. PM2.5 particles come from nature as well as human activities such as transportation, burning fossil fuel, and the human activities are the major source resulting in harmful damages in the human history. PM2.5 due to its tiny body can be harmful to human body has it can carry virus as well as other harmful matters and travel a long distance before it can be inhaled by human beings. Researches have confirmed that high level of PM2.5 is positively associated with increasing of outpatient visits for many respiratory and cardiovascular diseases.
There is still no formal publication of the PM2.5 in China and the relevant environmental department is working on the measuring and standard setting of the widely concerned PM2.5 and at present the monitored pollutants do not include the PM2.5 . Some believed that the PM2.5 ranges from 100 to 200 micrograms per cubic meter in Beijing largly exceeding the standard accepted in the US as the U.S. Environmental Protection Agency has adhered the standards requiring that the maximum daily PM2.5 level at any location to be less than 65 micrograms per cubic meter while the annual average of the daily PM2.5 maximums at any location should not be more than 15 micrograms per cubic meter.