Laboratory Studies of Aerosol Nanocluster Growth

With support from the Environmental Chemical Sciences (ECS) program in the Division of Chemistry, Professor James Smith of the University of California, Irvine is investigating the growth mechanisms of aerosol nanoparticles involving the interactions between organic compounds with inorganic acids and bases. The composition, growth mechanisms, and properties of atmospheric nanoclusters remain unknown and have previously not been directly studied given the analytical challenges.

Professor Smith and his students will perform experiments by first generating low-volatility gas phase precursors and clusters up to 2.5 nm in diameter and then measuring the physical and chemical properties of these clusters as they grow to 10 nm in diameter. Their studies could result in the identification of the major species and processes that lead to nanoparticle growth of atmospheric aerosol and could lead to improved understanding of the role of new particle formation on clouds and climate.

The project will also enhance educational and professional training of undergraduate and graduate students and provide opportunities for science communication to the general public.

The contribution of organics to nanoparticle growth rates will be studied for the following systems: (a) heterogeneous acid-base chemistry of semi-volatile organic acids with sulfuric acid, ammonia and amines; (b) particulate-phase accretion reaction chemistry; (c) direct partitioning of low-volatility gas-phase species. Experiments will be performed using a temperature-controlled flow tube and 560L chamber, and measurements will be made of the size-resolved composition and concentration of nanoclusters over the complete size range (1 – 10 nm).

Two modeling frameworks will be employed to determine the chemical mechanisms responsible for growth. The first is a growth law analysis method that can use measured size distributions to determine whether growth is diffusion-limited or can be attributed to surface- or volume-controlled processes that indicate reactive uptake. The second approach is a chemical closure method, where a model of condensation and reactive uptake will be used to connect measured gas-phase precursor concentrations to the measured composition of nanoclusters.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.