The Accurate Measurement Of Aerosol Number Concentration And Particle Size

Aerosol is a mixed phase composed of gas,solid or liquid particles.It mainly contains six types of aerosol particles such as dust aerosol,black carbon aerosol and various salt aerosols and so on.Because of its unique physical and chemical properties,aerosols are widely applied to meteorological remote sensing,industry and agriculture,nanotechnology and electronics industry.Atmospheric aerosols play important roles in the global climate change and weather pollution.It not only affects global climate but also changes atmospheric radiation and the energy balance between grounds with gas.Besides it has a harm to human health.Concentration and particle size are two important parameters to characterize aerosols.The measurement method is different according to the measurement principle.Therefore,the traceability of the concentration and particle size measurement has not yet reached a uniform understanding.In terms of the concentration,the research at domestic and abroad formed a common traceability chain.Abroad metrology institutions such as the United States,Japan carried out a series of the study;the domestic institutions has established a corresponding measurement standard.But the complete calibration for the system has not been studied;the particle size calibration,especially particle size-related particle density measurement has not yet been carried out.Based on the above,the aerosol particle concentration and particle size were systematically calibrated,including aerosol electrometer concentration calibration and experimental conditions optimization,the detection of the performance parameters of the condensation particle counter and the calibration of the concentration count,the optical particle counter calibration of counting efficiency in full size range and the measurement of particle density.First of all,we designed and set up calibration equipment of the aerosol electrometer and the particle concentration can be traced to the standard current.The experimental conditions were optimized,such as the anti-electromagnetic and external noise shielding box,power supply mode selection and bias current error.Several test points in high current(?20 fA)and low current(<20 fA)were selected.The results showed that the FCAE response current and standard current had a good consistency;the uncertainty(k=2)was better than 2.7%.Secondly,based on the calibration of the aerosol electrometer above,compared to the laboratory condensation particle counter,we built two different devices of high concentration and low concentration.The results showed that in the range of 6/cm~3 to10000/cm~3 particle concentration,the deviation of the two instruments was less than6%.In the full particle size range,the counting efficiency of two optical particle counters in the laboratory was calibrated.The counting efficiency of two optical particle counters in the small particle size range was between 96%and 106%;two optical particle counters count efficiency was reduced in the high particle size range.Finally,we designed a self-calibration electrometer consisting of the Faraday Cup and the KEITHLEY multimeter and compared the measured results with the calibrated aerosol electrometer with or without additional current.The results showed that the bias was between7%.The instrument can be used to instrument verification by further improvement.SMPS was used to measure aerosol particle size distribution in the particle.The response values were in the particle size of 100~600nm respectively.For the measurement of particle density,F547and F556 PSL were measured by saturated NaCl solution and the particle densities were measured to be 1.044~1.045g/cm~3 and1.048~1.049g/cm~3,respectively and the error was less than 0.001g/cm~3.In this paper,we also participated in the FCEA and CPC international comparisons organized by EU.The results of concentration and charge concentration of the FCEA and CPC measurements under the different size and material aerosol sample were evaluated.Calibration results between NPL,FCEA and CPC instrument showed that the detection efficiency bias was less than 3%which proved that the calibration method established in this paper was accurate and reliable.