Impact of Phase State on the Competition between Condensation and Coagulation
KIEUDIEM NGUYEN, Meredith Schervish, Manabu Shiraiwa, University of California, Irvine
Abstract Number: 210
Working Group: Aerosol Physics
Abstract
Particle size distribution is a critical property for radiative forcing and cloud activation of atmospheric aerosol particles. The evolution of particle size distribution is influenced by condensation and coagulation. While condensation drives the growth of secondary organic aerosols (SOA), coagulation leads to scavenging of small particles to reduce particle number concentrations. It has been shown that amorphous semisolid and glassy solid phase states in SOA can cause kinetic limitations for condensational growth, but their influence on competition between condensation and coagulation has not been evaluated. In this work, we implement coagulation into the kinetic multilayer model of gas-particle interactions (KM-GAP) to simulate evolution of particle size distribution by condensation and coagulation for particles with different phase states. Equilibration timescales of SOA partitioning (τeq) and coagulation timescales (τcoag) are calculated for liquid, semisolid, and solid particles with different volatilities of organic compounds for closed and open systems. Our results show that condensation of semi- and low-volatile species mostly leads to the narrowing of particle size distribution, while when coagulation is dominant a reduction in the number of particles with a broader size distribution is observed. Our results also show that τeq is shorter for condensation of lower volatility compounds into viscous particles in a closed system as rapid equilibrium is established between the gas phase and the particle surface. τeq prolongs to hours and days for condensation of semivolatile compounds into semisolid and solid particles (Db ≤ 10-15 cm2s-1), which makes coagulation as a competitive process. We also illustrate that coagulation should be mostly insignificant for chamber experiments for SOA formation in the presence of seed particles, while coagulation becomes important for nucleation events and for biomass burning plumes with high particle concentrations.