| Polycyclic aromatic hydrocarbons(PAHs) are a kind of widely existed organic carcinogen which is very detrimental to the environment as well as the human being. Besides the buming of fossil fuels,PAHs can also be generated from the combustion of bio-related materials.The economy in Tibet is less developed;the pattern of the Tibet people being exposed to polluted air is unique and special compared with other regions.But no relevant research is reported ever before.To reveal the characteristic and the concentration of PAHs in Tibet as well as assess its potential of causing cancer to people.This research,which was carried out during from May 2006 to August 2007,collected sample on site from farming area in both winter and summer,and from pastoral areas in summer(due to limitations of traffic and climate,the sample in winter was not collected).We measured the concentration of PAHs under the indoor condition and analysis the properties of PAHs pollutant generated by each different fuels.We also assess their cancer-causing potential and draw the following conclusions:(1) The concentration of PAHs indoor is significantly season-related.In winter it is 564ng/m~3,which is about 1.5 times as high as that of summer.The 4-,5- and 6-ring PAHs make up to 66%of the total amount of all PAHs,far excess the ratio of 32%in summer.(2) The annual average concentration of PAHs indoor in Tibet village is up to 729ng/m~3,among them,the concentration of BaP is 6 times as high as the maximum tolerable value set by the national standard.Concentration in outdoor is lower;we only detected 7 Low Molecular Weight PAHs of all the 16 PAHs.(3) The indoor PAHs pollution and its cancer-causing potential are highly dependent on the oven.Under the same geologic conditions and taking cow dung as fuel,the stoves generate the highest density of PAHs concentration of 2389 ng/m~3,which is 8 times as high as that produced by the iron oven.People who use stove suffer from a 10-time higher risk than those who use iron oven.(4) After comparing the different concentration of the PAHs and its characteristic generated by cow dung,wood and LPG,it is found that all the three fuels emit sixteen PAHs when burning.LPG emits least amount of PAHs which also contains fewer High Molecular Weight PAHs.Cow dung emits the unique characteristics of PAHs which is not known before.(5) The risk of suffering from cancer is affected by the fuel and the oven.Compare with open stove,iron oven with smoke extraction system can reduce the user's cancer-suffering risk.The Burning natural gas with iron oven brings the cancer-suffering risk which is only 1/2 and 1/3 of burning wood and cow dung. |
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