| Abstract: |
Research Objectives
1. Assemble analytical equipment to measure scattering, backscattering and absorption by laboratory aerosols at high sub-saturated relative humidities (80%-98%) and at multiple visible wavelengths
2. Measure these optical properties for specific organic aerosol fractions, namely oxygenated aromatic species and polymerized light-absorbing aerosol, both pure and mixed with inorganic aerosol.
3. Model the optical properties of the aerosol independent of the measurements and evaluate closure between measured and predicted optical properties. Revise parameterizations if necessary.
4. Identify distinctive chemical measurements that indicate the presence of certain fractions of organic carbon.
5. Provide emission- and process-linked parameterizations of optical properties in the form required for implementation in next-generation climate models.
Project Description and Methods
Laboratory measurements will include deployment of a water bath to maintain temperature and constant, very high relative humidity; measurement of size and optical properties of dry and hydrated aerosol using Scanning Mobility Particle Sizer, nephelometer for scattering, and extinction minus scattering difference for absorption. We will examine absorbing organic aerosols from an existing pyrolysis generator, particularly polymerized material with higher absorption than humic-like organic material. This aerosol will be examined both in a fresh state and after mixing with inorganic material. We will characterize organic carbon groupings before and after this mixing using standard organic/elemental carbon analysis, liquid chromatography with UV-Visible detection, emission/ fluorescence spectra, and thermal desorption.
We will assess and refine parameterizations for existing and next-generation aerosol models, particularly those in the Community Atmosphere Model at the National Center for Atmospheric Research. We will compare calculations and measurements for physical and optical properties of pure and mixed aerosols to determine when these properties are adequately parameterized. The models we will evaluate include the Zdanovski-Stokes-Robinson (ZSR) model to describe molality and density, Mie-Lorenz theory including coated-sphere and homogeneous-sphere models, effective-medium theories that describe bulk properties of mixed aerosol, and optical models such as the band-gap approximation for spectral absorption.
Potential Impact
Improvements in the representation of light-absorbing organic aerosol and its mixtures with inorganic species will occur through focused laboratory studies which provide key optical properties for use in global climate models. A unique aspect is our ability to link findings with particular emission sources on a global basis for the past, present and future, resulting in a global, time-dependent depiction of net anthropogenic aerosol impact. Outcomes will therefore include an improved understanding of climate forcing (and hence climate response) in the past and potential climate in the future. |
