Light scattering and extinction measurements combined with laser-induced incandescence for the real-time determination of soot mass absorption cross section

Yiyi Wei, Lulu Ma, Tingting Cao, Qing Zhang, Jun Wu, P R Buseck, J. E. Thompson

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

An aerosol albedometer was combined with laser-induced incandescence (LII) to achieve simultaneous measurements of aerosol scattering, extinction coefficient, and soot mass concentration. Frequency doubling of a Nd:YAG laser line resulted in a colinear beam of both λ = 532 and 1064 nm. The green beam was used to perform cavity ring-down spectroscopy (CRDS), with simultaneous measurements of scattering coefficient made through use of a reciprocal sphere nephelometer. The 1064 nm beam was selected and directed into a second integrating sphere and used for LII of light-absorbing kerosene lamp soot. Thermal denuder experiments showed the LII signals were not affected by the particle mixing state when laser peak power was 1.5-2.5 MW. The combined measurements of optical properties and soot mass concentration allowed determination of mass absorption cross section (M.A.C., m2/g) with 1 min time resolution when soot concentrations were in the low microgram per cubic meter range. Fresh kerosene nanosphere soot (ns-soot) exhibited a mean M.A.C and standard deviation of 9.3 ± 2.7 m2/g while limited measurements on dry ambient aerosol yielded an average of 8.2 ± 5.9 m2/g when soot was >0.25 μg/m3. The method also detected increases in M.A.C. values associated with enhanced light absorption when polydisperse, laboratory-generated ns-soot particles were embedded within or coated with ammonium nitrate, ammonium sulfate, and glycerol. Glycerol coatings produced the largest fractional increase in M.A.C. (1.41-fold increase), while solid coatings of ammonium sulfate and ammonium nitrate produced increases of 1.10 and 1.06, respectively. Fresh, ns-soot did not exhibit increased M.A.C. at high relative humidity (RH); however, lab-generated soot coated with ammonium nitrate and held at 85% RH exhibited M.A.C. values nearly double the low-humidity case. The hybrid instrument for simultaneously tracking soot mass concentration and aerosol optical properties in real time is a valuable tool for probing enhanced absorption by soot at atmospherically relevant concentrations.

Original languageEnglish (US)
Pages (from-to)9181-9188
Number of pages8
JournalAnalytical Chemistry
Volume85
Issue number19
DOIs
StatePublished - Oct 1 2013

Fingerprint

Soot
Light extinction
Light scattering
Lasers
Aerosols
Nanospheres
Atmospheric humidity
Kerosene
Ammonium Sulfate
Glycerol
Optical properties
Nephelometers
Scattering
Coatings
Electric lamps
Light absorption

ASJC Scopus subject areas

  • Analytical Chemistry

Cite this

Light scattering and extinction measurements combined with laser-induced incandescence for the real-time determination of soot mass absorption cross section. / Wei, Yiyi; Ma, Lulu; Cao, Tingting; Zhang, Qing; Wu, Jun; Buseck, P R; Thompson, J. E.

In: Analytical Chemistry, Vol. 85, No. 19, 01.10.2013, p. 9181-9188.

Research output: Contribution to journalArticle

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abstract = "An aerosol albedometer was combined with laser-induced incandescence (LII) to achieve simultaneous measurements of aerosol scattering, extinction coefficient, and soot mass concentration. Frequency doubling of a Nd:YAG laser line resulted in a colinear beam of both λ = 532 and 1064 nm. The green beam was used to perform cavity ring-down spectroscopy (CRDS), with simultaneous measurements of scattering coefficient made through use of a reciprocal sphere nephelometer. The 1064 nm beam was selected and directed into a second integrating sphere and used for LII of light-absorbing kerosene lamp soot. Thermal denuder experiments showed the LII signals were not affected by the particle mixing state when laser peak power was 1.5-2.5 MW. The combined measurements of optical properties and soot mass concentration allowed determination of mass absorption cross section (M.A.C., m2/g) with 1 min time resolution when soot concentrations were in the low microgram per cubic meter range. Fresh kerosene nanosphere soot (ns-soot) exhibited a mean M.A.C and standard deviation of 9.3 ± 2.7 m2/g while limited measurements on dry ambient aerosol yielded an average of 8.2 ± 5.9 m2/g when soot was >0.25 μg/m3. The method also detected increases in M.A.C. values associated with enhanced light absorption when polydisperse, laboratory-generated ns-soot particles were embedded within or coated with ammonium nitrate, ammonium sulfate, and glycerol. Glycerol coatings produced the largest fractional increase in M.A.C. (1.41-fold increase), while solid coatings of ammonium sulfate and ammonium nitrate produced increases of 1.10 and 1.06, respectively. Fresh, ns-soot did not exhibit increased M.A.C. at high relative humidity (RH); however, lab-generated soot coated with ammonium nitrate and held at 85{\%} RH exhibited M.A.C. values nearly double the low-humidity case. The hybrid instrument for simultaneously tracking soot mass concentration and aerosol optical properties in real time is a valuable tool for probing enhanced absorption by soot at atmospherically relevant concentrations.",
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