AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Role of MSA for New-particle Growth and the Cloud-albedo Aerosol Indirect Effect
ANNA HODSHIRE, Betty Croft, Jeffrey R. Pierce, Colorado State University
Abstract Number: 657 Working Group: Aerosol Chemistry
Abstract New-particle formation (NPF) is a significant source of aerosol particle number to the atmosphere. In order to impact climate, these ~1 nm in diameter particles must grow to ~30-100 nm. New-particle growth is facilitated primarily by net uptake of sufficiently low-enough volatility species emitted by both natural and anthropogenic sources. Dimethylsulfide (DMS), emitted by the oceans, can oxidize to methanesulfonic acid (MSA), a compound that may reach a low-enough volatility to have the potential to contribute to new-particle growth on regional scales. However, the volatility of MSA -- and therefore its ability to contribute to growth -- depends upon temperature, relative humidity, and concentration of gas-phase bases available for salt formation. Furthermore, presently there are knowledge gaps about whether MSA in its lowest volatility state can contribute to particle nucleation or if it only participates in growth. Currently, global aerosol microphysics models often do not include MSA in aerosol growth. Using a global chemical-transport model with aerosol microphysics (GEOS-Chem-TOMAS), we calculate the impacts of MSA on: aerosol growth, the aerosol size distribution, and the cloud-albedo aerosol indirect effect. We present results of limiting-case simulations, which treat MSA as 1) a sulfuric-acid-like compound that participates in nucleation, 2) a non-nucleating extremely low-volatility organic compound, and 3) a semi-volatile organic compound. Further, we present a simulation where the volatility of MSA is a function of relative humidity, temperature, and amount of gas-phase base available, based on offline thermodynamic calculations done in the Extended Aerosol Inorganic Model (E-AIM). We discuss the implications of omitting MSA from global aerosol models.