The Research On Indoor PM_2.5Purification Strategies Of Office Building

In recent years,air pollution has becoming seriously in China.To protect human health,it is important to investigate indoor PM_2.5 levels and chemical compositions in different buildings,the purification measures is of great significance to safeguard.Taking office building as the research object,on the basis of the transmission mechanism of indoor and outdoor PM_2.5,indoor PM_2.5 mass balance models for four ventilation purification strategies were set up.?A:infiltration ventilation system without purification facilities and with the doors and windows closed;B1:fresh air supply system combined with filter purification;B2:fresh air supply system combined with filter purification + electrostatic precipitator;C:fresh air supply system combined with filter purification;B2:fresh air supply system combined with filter purification + electrostatic precipitator + filter for indoor recirculated air?PM_2.5 samplings were collected for the chemical analysis.The concentrations of PM_2.5,O3 were monitored hourly for both indoor and ambient air.The results show that,the indoor PM_2.5 mass concentration in strategy C was significantly lower than that in strategy A,B1 and B2?T test,p<0.05?.The mean indoor PM_2.5 mass concentration and infiltration factor were the lowest in strategy C as well,21.07 ?g/m3 and 0.193,respectively.The use of filter for indoor recirculated air can significantly reduce the permeability of outdoor particulate matter and is the most effective way to improve the indoor environment quality.T test results show that the indoor PM_2.5 mass concentration difference was not significant among strategy A,B1 and B2?T test,p>0.05?.The average indoor O3 concentration in strategy B2 was 4.8 ppb which was 1.8 ppb higher than that in strategy B1.With the usage of filter for indoor recirculated air in strategy C,the mean indoor O3 concentration decreased to 0.7 ppb.Field emission scanning electron microscopy?FESEM?was used to characterize the morphological structure of PM_2.5 samplers.The results show that the indoor PM_2.5 mostly centered around 5 microns in strategy A with the form from the smaller chain to thick and fluffy.Fluffy and chain particles were reduced in strategy B1 and B2 compared to strategy A.No massive particles in indoor PM_2.5 samples were found in strategy C.Only in strategy C5 small clumps and chain particles were observed and the proportion of particles equal to or less than 1 ?m in aerodynamic diameter was increased.The contents of 12 kinds of metal elements in PM_2.5 were detected?As,Co,Cd,Cr,Fe,Cu,Mn,Ni,Pb,P,and V?.The analysis results illustrated that 12 kinds of heavy metals in indoor PM_2.5 were lower than that in ambient air.The average value of 12 heavy metal element contents for indoor PM_2.5 in strategy C was the lowest as 63.55 ng/m3,which was 0.48 times of the corresponding value of outdoor PM_2.5.The average value of 12 heavy metal element contents for indoor PM_2.5 in strategy A was the highest as 115.43 ng/m3,which was 0.87 times of the corresponding value of outdoor PM_2.5.Nevertheless,according to the results of element enrichment?EF?method,the EF values of Cd,Pb,and Zn were increased significantly in strategy C,which indicated that these elements were significantly affected by the activities of the human sources.The results of source apportionment with Principle Component Analysis?PCA?showed that the major sources of indoor PM_2.5 in the four ventilation and purification strategies were coal dust source and traffic dust source.The usage of filter for indoor recirculated air had higher purification effect for industrial smelting dust source.