Recent studies have shown that large-scale open fires emit a previously unrecognized form of soot particle-superaggregates (SAs), in quantities greater than 70% by number and mass concentration. These particles could have previous unaccounted-for impacts on human health and the environment. The objective of this research is to generate, in a controlled manner, soot SAs that mimic those from large-scale open burns, and investigate the particle formation mechanism and the emitted particle properties. Undergraduate and graduate students will participate in the research effort. The PI will also conduct teachers training workshop for twenty school teachers over the summer.
The conventional view holds that mobility diameter (Dm) less than or equal to 700 nm, aerodynamic diameter (Da) less than or equal to 300 nm, and fractal dimension approximately 1.8 is the end-point morphology of freshly-emitted soot particles. Preliminary investigations indicate that Dm and specific surface areas of soot SAs are ten and three times greater, respectively, than those of conventional soot particles. The unusually large Dm values render soot SAs undetectable using aerosol mobility sizing instruments. Alternatively, Da of these particles, which is used for estimating the probability of deposition within lungs, are similar to those of conventional soot particles. These contradicting observations of soot SA properties have left several fundamental questions unanswered: How does the superaggregate growth kinetics in a flame depend on the process parameters such as particle volume fraction, residence time, sooting index of the fuel, fuel/air flow rates, and temperature? How is the aggregation kinetics different in a positive gravity (upward rising) flame system? How sensitive are the superaggregate particle morphologies and properties to changes in the flame process parameters? This project proposes to answer these questions, which will bring about a potentially transformative understanding of soot SA's growth kinetics and their microphysical properties.
