Melinda Beaver
B.S., Chemistry and Environmental Studies, 2003

Cirrus clouds over Boulder, Colorado. Photo by Mark A. Zondo.

Laboratory studies of the effect of relative humidity on light scattering by surrogates for atmospheric aerosols

Atmospheric particulate matter affects Earth’s climate and local visibility through the direct interaction of the particles with solar radiation. Extinction, the sum of scattering and absorption, is dependent on the particle size, composition, and shape. Ambient relative humidity affects extinction by causing changes in particle size, and possibly shape) due to hygroscopic growth. A schematic of the relationship between aerosol particle characteristics and light extinction is shown in Figure 1. Laboratory quantification of the optical growth of particles of varying composition is necessary for inclusion into climate models, and also useful for comparison to particle growth factors measured using other techniques.

Figure 1. Relationship between aerosol particle characteristics and extinction.

These studies are currently conducted with a cavity ring-down aerosol extinction spectrometer in the Tolbert laboratory. Generally, the extinction of laboratory generated particles is measured at λ=532nm. Extinction of particles at a desired relative humidity can be measured and referenced to extinction by the dry particles to provide insight on the optical growth factors. The experimental design is shown in Figure 2.

Figure 2. Experimental design for studying the effects of relative humidity on extinction by aerosol particles.

Current Tolbert Group

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