Hygroscopic Properties of Aerosol Organics
EMSL Project ID
25635
Abstract
While organics constitute a large fraction of ambient aerosol mass, their role and effect on particle hygroscopic growth and cloud nucleation remains unclear. Organics are most often present in particles together with sulfates and/or nitrates and their presence is clearly expected to impact the behavior of the particles as a function of the atmospheric relative humidity. Most of the compounds comprising the organic fraction have not been specifically identified. We propose a comprehensive study to characterize the effect of organics on the water activity of atmospheric particles under sub- and supersaturated conditions at the Desert Research Institutes Storm Peak Laboratory (SPL) in northwestern CO (3250 AMSL). SPL frequently resides in the free troposphere and experiences transport from a variety of surface sources including urban areas, power plants, and natural fires. We are requesting that EMSL provide their two aerosol mass spectrometer; the AMS and SPLAT II to enable us to relate the measured hygroscopic properties to the size-resolved chemical composition of the dry ambient aerosol. We will evaluate the impact of the relative abundance of organics and especially the oxygenated component to the measured hygroscopic growth curves and supersaturation spectra. Using Köhler theory and thermodynamic equilibrium models such as the ZSR relationship (Pilinis et al., 1987) and the AIM model (Clegg et al., 1998), we will calculate the growth factors and critical supersaturation for each dry particle size. With this information we will attempt to demonstrate closure or lack thereof between the inorganic composition (only) of the size selected particles and their growth curves and CCN activity. This will provide a first-order evaluation of whether organics are contributing to water activity, testing the common assumption that organics do not contribute solute or act as surfactant (i.e. Medina et al., 2006). We request the deployment of the SPLAT II and high-resolution AMS at SPL for February and August 2008. We plan to deploy both instruments during the summer to sample photochemically processed aerosols and biomass burning events. The winter month will allow more extensive opportunities for free-tropospheric air and cloud-processed aerosols. One month of data is required for each field campaign to ensure both data quantity and the likelihood of intercepting events such as nucleation and biomass burning.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-06-05
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members