Investigation of the Impacts of “Seed” and “Ambient” Particles on the Formation and Characteristics of Secondary Organic Aerosols

The formation of aerosols is a key component in understanding cloud formation in the context of radiative forcing and global climate modeling. A majority of the studies of aerosol properties are done by creating aerosols, formed from the reaction of ozone with volatile organic compounds (VOCs), in a laboratory setting.

However, this research investigates the final properties of aerosols that grow on “seed” and “ambient” particles that more realistically exist in the natural environment. The goals of this project were to design and generate aerosol particles on seed as well as ambient particles in a laboratory setting and to explore the differences between the properties of these aerosols. 

Experiments were conducted in a Teflon “smog chamber” in which aerosols were generated on existing particles. Because sodium chloride particles are so abundant in the atmosphere, they were first added to the smog chamber to act as seed particles. Once the seed particles were thought to be evenly distributed, ozone and VOCs were added to prompt nucleation. The second part of this research studies the effect of ambient particles on aerosol formation. These experiments were conducted in a smaller, portable Teflon “smog chamber” that was used to collect ambient outside air. Once enough ambient particles were in the chamber, ozone and VOCs were added and aerosol formation was measured. Measurements were made using a Scanning Mobility Particle Sizer (SMPS) and a Cloud Condensation Nuclei Counter (CCNC). The use of these two instruments together as well as the Aerosol Instrument Manager (AIM) program allowed for a comparison of the concentration of particles created to particle size. Results were compared across samples to determine the relationship between the physical properties of the original particles to the properties of the resulting aerosols.

The results of this research suggest that the presence of a seed particle allows for an increased growth of particles, but limits the total concentration. The concentration of the original seed particles also affects the growth and concentration of the resulting aerosols thus suggesting that there is an optimal solution concentration that can be used to get the largest concentration of particles formed. Furthermore, it was also found that the order in which ozone and VOCs are added and the concentration of the salt solution have a measurable effect on these properties. Interestingly, this variance did not seem to have a large effect on the aerosol formed in the “ambient” trials.