单颗粒气溶胶质谱仪自动粒径校正方法
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摘要
单颗粒气溶胶质谱仪通常采用空气动力学透镜进样,通过测量透镜出口每一个颗粒物的速度来推算颗粒物的空气动力学直径。然而,颗粒物速度受透镜前端压力的影响较大,该压力发生微小变化就会导致颗粒物粒径检测发生偏差。本研究提出一种适用于单颗粒气溶胶质谱仪的自动粒径校正方法,预先记录几组一定透镜前端压力范围内的粒径校准参数,然后根据进样压力的变化,使软件自动通过插值算法拟合相应的粒径校正方程对颗粒物粒径测量值进行校正,从而保证在指定的压力波动范围内粒径测量结果的准确性。实验结果表明,当透镜前端压力在164.92~352.45Pa范围变化时,该方法对于152~3 100nm颗粒物的测径偏差大部分都在10nm以内。模拟结果表明,该方法能够保证仪器在海拔8km范围内粒径测量的准确性,可以应用到所有采用空气动力学进样及激光颗粒物粒径测量的仪器中,能够极大地增加仪器对外界环境的适应性并提高数据结果的可靠性。
Single particle aerosol mass spectrometer(SPAMS)normally uses aerodynamic lens to introduce the particles from the ambient to vacuum system and focus them into a collimated beam.When exiting from the aerodynamic lens,every particle will get a ve-locity,which is a function of its aerodynamic diameter.Thus,the aerodynamic diameter of each particle can be calculated by measuring the corresponding velocity.However,this particle velocity is greatly influenced by the inlet pressure of the aerodynamic lens,a tiny changes of the pressure will lead to particle size calibration deviation.For the standard 740 nm PSL particles,the calculated size changes from 1 680 nm to 560 nm with the pressure from 164.92 to 352.45 Pa using a fixed size calibration function,that is to say the calculated size deviates about 40-60 nm every 13.3 Pa.The inlet pressure changes from time to time during sampling period.After the long-term sampling,particles will enrich and block at the edge of the injection orifice,thus the operator need to clean the orifice from time to time to ensure the consistent pressure.Such cleaning could be very frequent when the air pollution is serious or the environmental pressure changes frequently.In order to solve this problem,this paper put forward an automatic particle size calibration method for the SPAMS.After embedding several size calibration parameters in different pressure in advance,the software could automatically fit the proper size calibration curve by the interpolation algorithm when the inlet pressure changed.This method ensured the calculated size accuracy within a certain range of pressure fluctuations.Experimental results showed that,for all the PSL particles ranging from152 to 3 100 nm,the calculated size distribution had a peak deviation less than 2%in the range of 164.92-352.45 Pa when using this automatic interpolation algorithm.In addition,It could also be used when the elevation changes from 0 to 8 km.Actually,this method can be applied to all the similar instruments,which use the aerodynamics sampling and laser sizing technologies.In conclusion,the method is simple in operation and does not reguire any hardware to support.It can greatly increase the adaptability to external environmental conditions and improve the reliability of the measurement result of the instrument.
Single particle aerosol mass spectrometer(SPAMS)normally uses aerodynamic lens to introduce the particles from the ambient to vacuum system and focus them into a collimated beam.When exiting from the aerodynamic lens,every particle will get a ve-locity,which is a function of its aerodynamic diameter.Thus,the aerodynamic diameter of each particle can be calculated by measuring the corresponding velocity.However,this particle velocity is greatly influenced by the inlet pressure of the aerodynamic lens,a tiny changes of the pressure will lead to particle size calibration deviation.For the standard 740 nm PSL particles,the calculated size changes from 1 680 nm to 560 nm with the pressure from 164.92 to 352.45 Pa using a fixed size calibration function,that is to say the calculated size deviates about 40-60 nm every 13.3 Pa.The inlet pressure changes from time to time during sampling period.After the long-term sampling,particles will enrich and block at the edge of the injection orifice,thus the operator need to clean the orifice from time to time to ensure the consistent pressure.Such cleaning could be very frequent when the air pollution is serious or the environmental pressure changes frequently.In order to solve this problem,this paper put forward an automatic particle size calibration method for the SPAMS.After embedding several size calibration parameters in different pressure in advance,the software could automatically fit the proper size calibration curve by the interpolation algorithm when the inlet pressure changed.This method ensured the calculated size accuracy within a certain range of pressure fluctuations.Experimental results showed that,for all the PSL particles ranging from152 to 3 100 nm,the calculated size distribution had a peak deviation less than 2%in the range of 164.92-352.45 Pa when using this automatic interpolation algorithm.In addition,It could also be used when the elevation changes from 0 to 8 km.Actually,this method can be applied to all the similar instruments,which use the aerodynamics sampling and laser sizing technologies.In conclusion,the method is simple in operation and does not reguire any hardware to support.It can greatly increase the adaptability to external environmental conditions and improve the reliability of the measurement result of the instrument.
引文
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[2]NASH D G,BAER T,JOHNSTON M V.Aerosol mass spectrometry:an introductory review[J].International Journal of Mass Spectrometry,2006,258(1):2-12.
[3]BI X,ZHANG G,LI L,et al.Mixing state of biomass burning particles by single particle aerosol mass spectrometer in the urban area of PRD,China[J].Atmos Environ,2011,45(20):3 447-3 453.
[4]ZHANG G,BI X,CHAN L Y,et al.Enhanced trimethylamine-containing particles during fog events detected by single particle aerosol mass spectrometry in urban Guangzhou,China[J].Atmospheric Environment,2012,55(Suppl C):121-126.
[5]ZHANG G,BI X,LOU S,et al.Source and mixing state of iron-containing particles in Shanghai by individual particle analysis[J].Chemosphere,2014,95(Suppl C):9-16.
[6]ZELENYUK A,IMRE D,HAN J H,et al.Simultaneous measurements of individual ambient particle size,composition,effective density,and hygroscopicity[J].Anal Chem,2008,80(5):1 401-1 407.
[7]DECARLO P F,SLOWIK J G,WORSNOP D R,et al.Particle morphology and density characterization by combined mobility and aerodynamic diameter measurements.Part 1:theory[J].Aerosol Sci Technol,2005,39(2):1 185-1 205.
[8]LI L,HUANG Z,DONG J,et al.Real time bipolar time-of-flight mass spectrometer for analyzing single aerosol particles[J].Int J Mass Spectrom,2011,303(2/3):118-124.
[9]KAMPHUS M,ETTNER-MAHL M,BRANDS M,et al.Comparison of two aerodynamic lenses as an inlet for a single particle laser ablation mass spectrometer[J].Aerosol Sci Technol,2008,42(11):970-980.
[10]BAHREINI R,JIMENEZ J L,WANG J,et al.Aircraft-based aerosol size and composition measurements during ACE-Asia using an Aerodyne aerosol mass spectrometer[J].Journal of Geophysical Research:Atmospheres,2003,108(D23):8 645-8 666.
[11]BAHREINI R,DUNLEA E J,MATTHEW B M,et al.Design and operation of a pressurecontrolled inlet for airborne sampling with an aerodynamic aerosol lens[J].Aerosol Science and Technology,2008,42(6):465-471.