| Particles Matter(PM) in atmospheric, which is known as "fly ash". PM is not only one of the most important pollutants in the atmosphere, but also the primary air pollutants in urban. There are lots of toxic and harmful ingredients in PM which attached to their surface, such as bacteria, germs, harmful organisms, acidic oxides and heavy metals. PM is not only to make air quality deterioration, but also endanger human health. Research on PM and its composition is not only the first-hand information for the atmospheric monitoring fully, but also the technological support and scientific basis for the control of air pollution, which measure by online analytical technology.Under the auspices of the National High Technology Research and Development Program of China(Grant No. 2012AA061803, the project of high precision spectrum detection instrument development) and the Major Scientific and Technological Transformation Program of Sichuan(Grant No. 2013CC0045, the industrialization project of online analysis instrument for monitoring atmospheric particulate matter and heavy metals), the paper has been studied systematically on the β-X ray on-line analysis techniques for PM. The paper studies on the status of the PM at home and abroad, expounded the β-ray and X-ray measurement principle. The paper derives theoretical formulas of calculating the concentration and composition for PM. The paper simulates them via Monte Carlo method, too. Finally, the paper has designed the β-X rays analyzer for particles matter’s concentration and its elemental composition in atmospheric, and has completed to the test in eastern suburbs of Chengdu. Thesis conclusions are as follows:(1) A mathematical model is established for analysis the concentration of atmospheric particulate matters according to the β-ray attenuation rule. The transmittance of filter materials in the system was calculations by MCNP5, such as PTFE, PVC, glass fiber and PP. So as the transmittance of 14 C, 85 Kr, 147 Pm, 204 Tl and90Sr-90 Y. According to the calculation results and the actual situation, 14 C and glassfiber filter are chosen for the concentration measurement system of atmospheric particulate matters.(2) A mathematical model is established for analysis elements in atmospheric particulate matters according to the principle of energy dispersive X-ray fluorescence analysis. Relative geometric positions of the analyzer’s source, detector and specimen are emphasized, which impacts the analyte’s characteristic X-ray fluorescence counts.The factors(thickness, density, particle size, angle and distance) were simulated by MCNP5. According to the calculation results and the actual situation, the optimal geometric conditions for the design are like those: the distance of excitation source to sample is 20mm; the distance of sample to detector is 20mm; α=45° and β=45°(α⊥β);(3) Using β-ray method for the feedback correction to quantitative analysis of elements in EDXRF, when thickness of samples does not meet the thin conditions.Analysis results of measuring a set of knew Cu samples show that the analysis errors are by more than 5% generally to decrease to below 2%. So the correction effect significantly, reflecting an advantage of the β-X ray spectrometry analysis for atmospheric particulates.(4) A PM analyzer of concentration and its elemental composition in atmospheric has been designed. The analyzer can collect PM automatically, on-line,continuous measurement, and analysis PM’s concentration and its composition. This paper provides a novel atmospheric monitoring instrument for our country.(5) System analysis method by β-X ray technology is established, which is for the concentration and element of particulate matters in atmospheric. Through analysis collected parameters, calibration, atmospheric particles and moisture contents, draw the following conclusions:① Influence of Cu powder sample’s thickness and surface density on the characteristics of X-ray fluorescence counts are considered by MCNP5. The results show that: the moderate thickness range is 0.001mm~0.1mm, the thin range is less than 0.001 mm, and the saturated thickness, whose density is greater than 0.3-2,is greater than 0.1mm. X-ray fluorescence counts and thicknesses are in nonlinear for the moderate thickness samples, otherwise linear. Atmospheric particulate matters have been collected via different acquisition time and observed by SEM. The mostappropriate condition is 110mm2 for sampling area and 2.4m3 for atmospheric volume.② Numerical calculation by MCNP5 for particles shows that particle effect can be ignored in the thin sample(thickness≤0.0002 mm for Ca F samples) or under the condition that sample particle sizes are in a certain size(thickness≥0.08 mm for Ca F samples), otherwise the XRF analysis results will be smaller because of particle effect.Collected samples meet the thin condition to avoid particle effect by controlling sampling air traffic and sampling time.③ Water will enhance matrix effect in the process of sample analysis. Moisture content increases, characteristic X-ray counts decreases. MCNP calculation shows that: in the condition of Cu powder samples’ moisture content is 0%, when environmental moisture content reaches 5%, characteristic peak counts of Cu Kαdecrease to the original 6.7%; when environmental moisture content is more than 10%,the counts decrease to 0%; in the condition of environmental moisture content is 0%,Cu powder samples’ moisture content is raised from 5% to 10%, 20% and 30%, the counts decrease to the original 0.78%, 2.86%, 5.67%. Effects of water must be taken into consideration in measurements. Drying device, heating and dehumidification device, moisture absorption device are used in atmospheric sampling and measurements can reduce the influence of water on the monitoring atmospheric particulate matters.④ The paper prepares element filter standard samples(element of Ti, Ni, Cu, Zn,Fe, Sr and so on), and calibrates the PM analyzer. After testing, performance, stability,precision, resolution, detection limit and other aspects are compliant, which meet the design requirements for online analysis, same time analysis, and continuous measurements for atmospheric particulate matters.(6) In the period from April 6, 2014 to April 21 st, the PM analyzer’s application results show that:① Analysis range of air traffic is 2360.2 L~2455.1 L, mean value is 2396.53 L,the maximum error is 1.66%, the average error is 0.14%. With the fluctuation of temperature and atmospheric pressure, the PM analyzer’s analysis air traffic has some fluctuations, but tends to be stable on the whole.② The concentration of PM2.5 changes in the range of 41 μg·m-3~239 μg·m-3 in the eastern suburbs of Chengdu. It is certain difference comparing with the data from CDEPA. The reason is that the data from CDEPA are mean value in Chengdu, and the data in this paper are a point measurement in the eastern suburbs of Chengdu.③ PM2.5 monitoring results of Pb, Se, Hg, Cr, Cd, Zn, Cu, Ni, Fe, Mn, Ti, Sb,Sn, V, Ba, As, Ca, K, Co, Mo, Ag, Sc, Tl, Pd, Br and Te in the eastern suburbs of Chengdu show that: in the same day’s different periods of time, the content of elements is relative changed in atmospheric particulate matters. Taking elements Ca,Fe and K for example, the content rang of element Ca is 0.277 μg·m-3~13.589 μg·m-3,average value is 4.245 μg·m-3; the content rang of element Fe is 0.000 μg·m-3~7.960μg·m-3, average value is 2.873 μg·m-3; the content rang of element K is 0.337μg·m-3~9.906 μg·m-3, average value is 1.330 μg·m-3.④ Repeated experiment of the same sample test shows the count range of atmospheric particulate matters is 3038~3179, average value is 3114.4. All data were less than one standard deviation. Repeated experiment of Ni, Cu, Zn, Pb samples shows the relative errors are less than 1.39%. The PM analyzer’s working stability is good. It can meet the requirements of on-site monitoring for atmospheric particulate matters.In summary, the paper studies the theory of β-rays and X-rays for PM, calculates them by Monte Carlo method, and designs the analyzer, which is provided for the research on PM as a technical guide. The methods and conclusions can provide technical support for environmental management, which with economic and social benefits substantially. |
PDF Full Text Request