PM2.5 specification and air pollution

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PM2.5 refers to particulate matter with a diameter less than or equal to 2.5 microns in the atmosphere , also known as accessible particulate matter. Usually particles larger than 10 microns in diameter will be blocked outside the nose ; particles with a diameter between 2.5 microns and 10 microns can enter the respiratory tract, but are partially excreted with spitting and sneezing ; and the diameter is less than 2.5 microns. The fine particles will pass through the lower respiratory tract and cause diseases including asthma, bronchitis and cardiovascular disease.

Fine particles can adsorb a wide variety of toxic chemicals. At the same mass concentration, the finer the particles, the greater the number of toxic substances in the adsorbed air.

The particulate matter is very small, and this digestion of light is more pronounced. PM2.5 is also a very important pollutant that causes our current visibility to decline.

November 1, 2011 The Ministry of Environmental Protection issued the " Measurement Weight Method for Ambient Air PM10 and PM2.5 ", which is the first to standardize the measurement method of PM2.5 . November 16 , Environmental Protection Department official notification, "Ambient Air Quality Standards" to start from the day the whole of society for public comment a second time, the biggest adjustment is PM2.5, ozone concentration eight hours into the routine air quality assessment, PM2.5 years The 24- hour average concentration limits were set at 0.035 mg per cubic meter and 0.075 mg per cubic meter, respectively .

According to the " Measurement Weight Method for Ambient Air PM10 and PM2.5 ", the sample volume with certain cutting characteristics is used to extract the quantitative volume of air at a constant speed, so that PM2.5 and PM10 in the ambient air are trapped in the filter of known mass. On the membrane, the concentrations of PM2.5 and PM10 were calculated based on the difference in weight of the filter before and after sampling and the sample volume .

Sample collection is first required for testing. When sampling, the weighed filter ( 5.3 ) is placed on the filter screen in the clean sampling clamp with tweezers, and the matte side of the filter should face the intake direction. Firmly press the filter to airtightness. After sampling, remove it with tweezers. The dusty surface is folded in two times, placed in a sample box or paper bag, and the sampling record is made. The sample weight of the filter after sampling was analyzed according to the following analysis procedure.

The filter is placed in a constant temperature and humidity chamber (chamber) for 24 hours . The equilibrium condition is: the temperature is 15 °C~ 30 ° C At any point, the relative humidity is controlled within the range of 45% to 55% , and the equilibrium temperature and humidity are recorded. Under the above equilibrium conditions, the filter was weighed with an analytical balance having a sensitivity of 0.1 mg or 0.01 mg , and the weight of the filter was recorded. The same filter membrane was re-equilibrated for 1 h under the same conditions in a constant temperature and humidity chamber (chamber) and weighed. For the PM10 and PM2.5 particulate sample filters, the difference between the two weights is less than 0.4 mg or 0.04 mg , respectively, to meet the constant weight requirement.

The PM 2.5 and PM 10 concentrations are calculated as follows:

Where: ρ —— PM10 or PM2.5 concentration, mg/m 3 ;

w 2 —— the weight of the filter after sampling, g ;

w 1 - the weight of the blank filter, g ;

V - The sample volume, m 3 , that has been converted to the standard state ( 101.325 kPa, 273K ) .

The choice of sample acquisition object glass fiber filters, silica and other inorganic membrane or membrane of polyvinyl chloride, polypropylene, cellulose mixed organic membrane. Membrane entrapment efficiency 0.3 μ m standard particles is not less than 99%.

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