AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Atmospheric Soot Superaggregates: Implications for Health and Radiative Forcing
NICHOLAS D BERES, Li Liu, Michael I Mishchenko, Rajan K. Chakrabarty, Desert Research Institute
Abstract Number: 300 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The conventional view holds that fractal dimension (D$_f) 1.8-2.5, mobility diameter (D$_f) ≤ 1 microns, and aerodynamic diameter (D$_a) ≤ 300 nanometers are the end-point physical characteristics of soot aggregates emitted from combustion sources. Recent observations of soot emissions from heavily sooting (10–100 parts per million) anthropogenic fires, such as open-air agricultural residue burning and oil pool fires, contradict this view. Last year, findings from three recent independent investigations showed soot superaggregates (SAs) – aggregates of soot aggregates having D$_f ≈ 2.6, D$_m ≥ 3 microns, and D$_a ≤ 300 nm being emitted in quantities greater than 70% in number and mass from large-scale, open-burning emissions. Average D$_m and specific surface areas of these soot SAs are ten and three times greater, respectively, than those of conventional soot particles. These unusually large D$_m values render these aerosols undetectable using conventional mobility sizing instruments (such as the SMPS). Alternatively, the aerodynamic diameters – used for estimating the probability of deposition within lungs – of these aerosols are similar to those of diesel soot. These observations suggest that soot SAs could be a large component of open burning emissions with the potential to have deleterious effects on human health and the environment, and previously unaccounted-for impacts on climate forcing. In this talk, we will present our findings on the microphysical properties of soot SAs, and discuss their potential impacts on climate and human health.