Zhang, Dan (2003-05). Laboratory investigation of chemical and physical properties of soot-containing aerosols. Doctoral Dissertation. | Thesis individual record

Soot particles released from fossil fuel combustion and biomass burning have a
large impact on the regional/global climate by altering the atmospheric radiative
properties and by serving as cloud condensation nuclei (CCN). However, the exact
forcing is affected by the mixing of soot with other aerosol constituents, such as sulfuric
acid. In this work, experimental studies have been carried out focusing on three integral
parts: (1) heterogeneous uptake of sulfuric acid on soot; (2) hygroscopic growth of
H2SO4-coated soot aerosols; (3) effect of H2SO4 coating on scattering and extinction
properties of soot particles. A low-pressure laminar-flow reactor, coupled to ion driftchemical
ionization mass spectrometry (ID-CIMS) detection, is used to study uptake
coefficients of H2SO4 on combustion soot. The results suggest that uptake of H2SO4
takes place efficiently on soot particles, representing an important route to convert
hydrophobic soot to hydrophilic aerosols. A tandem differential mobility analyzing
(TDMA) system is employed to determine the hygroscopicity of freshly generated soot
in the presence of H2SO4 coating. It is found that fresh soot particles are highly
hydrophobic, while coating of H2SO4 significantly facilitates water uptake on soot even
at sub-saturation relative humidities. The results indicate that aged soot particles in the atmosphere can potentially be an efficient source of CCN. Scattering and extinction
coefficient measurements of the soot-H2SO4 mixed particles are conducted using a threewavelength
Nephelometer and a multi-path extinction cell. Coating of H2SO4 is found to
increase the single scattering albedo (SSA) of soot particles which has impact on the
aerosol direct radiative effect. Other laboratory techniques such as transmission electron
microscopy (TEM) and Fourier transform infrared spectrometry (FTIR) are utilized to
examine the morphology and chemical composition of the soot-H2SO4 particles.
This work provides critical information concerning the heterogeneous interaction
of soot and sulfuric acid, and how their mixing affects the hygroscopic and optical
properties of soot. The results will improve our ability to model and assess the soot
direct and indirect forcing and hence enhance our understanding of the impact of
anthropogenic activities on the climate.

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