Laboratory investigation of mixing states and physical and optical properties of soot-containing aerosols 
Renyi Zhang, Texas A & M University
Abstract
Soot particles released from fossil fuels combustion and biomass burning have a large impact on the regional/global climate by altering the radiative properties of the atmosphere or by serving as cloud condensation nuclei (CCN). However, the exact forcing is affected by the mixing state of soot with other aerosol constituents, such as sulfate and organics. The purpose of this project is to investigate the interaction between soot and inorganic and organic acids and the aerosol mixing states under controlled laboratory conditions, and to quantify the impact of the mixing state of soot on their hygroscopic and optical properties. A low-pressure laminar-flow reactor, coupled to ion drift-chemical ionization mass spectrometry (ID-CIMS) detection, will be used to study uptake coefficients of inorganic (e.g., H2SO4) and organic (e.g., anthropogenic and biogenic) acids on the surface of soot produced by combustion of various fuels. The uptake coefficient will be measured at various ambient conditions (i.e., temperature and RH). A tandem differential mobility analyzer (TDMA) system will be employed to determine the sized distribution, mixing state and hygroscopicity of freshly generated soot in the presence of other aerosol constituents. In addition, the morphology of the mixed particles will be examined using transmission electron microscopy (TEM). The extinction coefficient of the various soot-containing aerosols will be measured using a multipath optical cell. A photoacoustic system will be employed to measure the absorption coefficients and a three-wave nephelometer will be utilized to determine the scattering coefficients. The proposed research will provide critical information concerning the relationship between mixing state and hygroscopic and optical properties of soot-containing aerosols, which is largely unknown. 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.
Publications
Levitt, N. P., R. Zhang, H. Xue, and J. Chen. 2007. Heterogeneous chemistry of organic acids on soot surfaces, J. Phys. Chem. A 111: 4804-4814.
Levitt, N. P., J. Zhao, and R. Zhang. 2006. Heterogeneous chemistry of butanol and decanol with sulfuric acid: Implications for secondary organic aerosol formation, J. Phys. Chem. A 110: 13215-13220.
Zhang, R., A.F. Khalizov, J. Pagels, D. Zhang, H. Xue, J. Chen, and P.H. McMurry. 2007. Remarkable variability in morphology, hygroscopic and optical properties of soot aerosols during internal mixing in the atmosphere, Nature Geoscience, under revision.
