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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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