Experimental studies on aerosol size spectroscopy with multijet low-pressure inertial impactors: Dissertation

Esko Kauppinen

Research output: ThesisDissertationCollection of Articles

Abstract

Factors associated with the determination of continuous aerosol size distribution functions with compressible flow low pressure impactors, including the determination of the kernel functions for the submicron stages, data inversion and the validity of the determined continuous submicron size distribution functions, were studied. Methods to determine mass and composition size distributions of aerosols emitted from combustion processes with low pressure impactors were developed. Impactors were used to characterize aerosols emitted from the real scale hospital refuse incineration and pulverized coal combustion processes. Collection efficiency curves for the submicron stages of the modified University of Washington Mark 5 low pressure impact (KLPI) and Berner type low pressure impactor (BLPI HAUKE 25/0.015) were determined experimentally with singly charged, monodispersed liquid di octyl phtalate aerosol particles. Calibration results indicate that the steepness of the efficiency curve and the square root value of the cut Stokes number of compressible flow impactor stages depend on the stage pressure ratio as well as on the distance between the jet and collection plates. This behaviour is contradictory to the collection characteristics of the ambient pressure, incompressible flow impactor stages. Collection efficiency curves for stages operating at the pressure ratios from 0.45-0.65 and at upstream stage absolute stagnation pressures of 7-35 kPa are very sharp for both impactors. Stages operating at pressure ratios of 0.65-0.95 and at upstream stage absolute stagnation pressures of 51-87 kPa have curves with reduced sharpness of cut, with the detoriation of the size resolution being pronounced for KLPI. This is due to the larger distance between the jet and collection plates of KLPI. Errors due to data inversion with the method based on constrained regularization were studied by inverting multiple sets of both error free and noisy unimodal submicron aerosol data sets simulated for BLPI, KLPI and LLPI (the impactor designed at the University of Florida) low pressure impactors. Inverted results for error free data with small (2.5 %) error estimate were very close to input distributions. When the normally distributed random error level and data error estimates were equal to or smaller than 10 % of the stage mass concentrations, the majority of inverted spectra were unimodal close to the input distributions. The inversion of impactor data from laboratory instrument comparison experiments using experimental stage mass error estimate indicates that only BLPI kernel functions are sufficiently accurate to yield unimodal distributions close to those determined with the differential electrical mobility (DMA) method. When the stage mass error estimate was increased beyond the experimental error, unimodal spectra were also found for KLPI and LLPI. Mass and Na, K, S, Cd, Zn and Pb size distributions of aerosols emitted from the hospital refuse incineration process equipped with a cleaning cyclone were bimodal, with the fine mode at about 0.1 to 0.2 ~m and the coarse mode between 6 and 10 ~m. Mg, Al, Cl, Ca, Ti and Fe size distributions were unimodal, with these elements found only in coarse mode particles. Bimodal distributions indicate partial vaporization and nucleation of inorganic compounds. Significant fractions of toxic trace metals were vaporized, i.e. 23-80 % of particle bound Zn, 62-77 % of Cd and 7-74 % of Pb were found in the fine mode particles. Mass and Na, Mg, Al, Si, S, K, Ca, Ti, Fe, V, Mn, Cu, Zn, Sr, Cd and Pb size distributions of aerosols emitted from the combustion of pulverized, bituminous coal from Poland were bimodal. When samples were collected after the electrostatic precipitator, geometric mass mean diameters of fine and coarse modes were about 0.05 and 2 ~m, respectively. About 5 % of particle mass and particlebound Na, Mg, Al, Si, Ti, Fe, Mn and Zn were found in the fineparticle mode. S, Ca, V, Cu, Sr, Cd and Pb were enriched in the fine mode particles, i.e. about 80 % of the particlebound S, 17 % of Ca, 23 % of V, 22 % of Cu, 11 % of Sr, 23 % of Cd and 9 % of Pb were in the submicron fine mode particles. The flatness of the Mg, Al, Si and Ti mass fraction size distributions suggests vaporization and subsequent nucleation of the fraction of these ash components during the combustion of single pulverized coal particles.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • University of Helsinki
Award date1 Feb 1992
Place of PublicationEspoo
Publisher
Print ISBNs951-38-4064-6
Publication statusPublished - 1992
MoE publication typeG5 Doctoral dissertation (article)

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Keywords

  • aerosols
  • impactors
  • low pressure
  • spectroscopy
  • combustion products
  • particle size distribution
  • size determination
  • air pollution
  • flue gases
  • coal
  • environmental protection
  • compressible flow
  • experimentation
  • methods
  • refuse
  • incinerators
  • hospitals

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