Impacts of phase state on secondary organic aerosol partitioning and amine uptake by particles
Authors
Manabu Shiraiwa — University of California, Irvine
Annmarie G Carlton — University of California, Irvine
James Smith — University of California, Irvine
Sergey Nizkorodov — University of California, Irvine
Ying Li — University of California, Irvine
Wing-Sy DeRieux — University of California, Irvine
Hayley Glicker — University of California, Irvine
Ryan Dempsey — University of California, Irvine
Lauren Fleming — University of California, Irvine
Julia MontoyaAguilera — University of California, Irvine
Category
Secondary organic aerosol
Description
Secondary organic aerosols (SOA) account for a substantial fraction of air particulate matter and SOA formation is often modeled assuming rapid establishment of gas-particle equilibrium. We estimated the characteristic timescale for SOA to achieve gas−particle equilibrium under a wide range of temperatures and relative humidities using a state-of-the-art kinetic flux model. Equilibration timescales were calculated by varying particle phase state, size, mass loadings, and volatility of organic compounds. Model simulations suggest that the equilibration timescale for semi-volatile compounds is on the order of seconds or minutes for most conditions in the planetary boundary layer, but it can be longer than one hour if particles adopt glassy or amorphous solid states with high glass transition temperature at low relative humidity. In the free troposphere with lower temperatures it can be longer than hours or days even at moderate or relatively high RH due to kinetic limitations of bulk diffusion in highly viscous particles. The timescale of partitioning of low-volatile compounds is shorter compared to semi-volatile compounds, as it is largely determined by condensation sink due to very slow re-evaporation. These results provide critical insights into thermodynamic or kinetic treatments of SOA partitioning for accurate predictions of gas- and particle-phase concentrations of semi-volatile compounds in regional and global chemical transport models. By implementing the estimation method of glass transition temperature of SOA, the CMAQ modeling is conducted to simulate spatial distribution and temporal evolution of SOA phase state in the U.S., especially focusing on DOE-ARM sites including HI-SCALE. We analyzed the available ASR field data on amine concentrations measured by the TDCIMS for HI-SCALE. Kinetic modeling was conducted to investigate kinetic limitations of diffusive transport from uptake of amines.
