PNNL

The Science

Aerosols play an important role within the Earth’s energy balance by scattering and absorbing radiation and modifying cloud properties and precipitation. However, their effect on Earth’s climate remains uncertain, partly because the number of particle property measurements, such as size, is far fewer than the extensive meteorological measurements collected worldwide. To address this issue, researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL) partnered in a study to test an alternative approach to determine the mean size of atmospheric particles from remote sensing instruments. Called spectral deconvolution, this method was used with data collected during the 2010 Carbonaceous Aerosols and Radiative Effects (CARES) field campaign in California and produced estimates of particle size that compared well to independent, direct measurements of particle size.

The Impact

Light scattering by atmospheric particles has a net cooling effect on climate that helps offset greenhouse-gas induced climate warming. Determining the size of these particles can improve understanding of their net cooling effect. Direct measurements of particle size are relatively scarce and not easily obtained. Finding ways to use the optical properties of aerosols to estimate the effective radius and fine mode fractions can increase the amount of information on particle size available to climate scientists.

Summary

The amount of radiation scattered by particles depends on the size of the particles as well as the wavelength of the radiation. While routine measurements of atmospheric radiation are available worldwide, routine direct measurements of aerosol size are relatively rare. The US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program’s CARES campaign was carried out in June 2010 in the central valley of California to collect a wide range of unique aerosol and radiation measurements and provide a better understanding of how atmospheric particles affect climate. An approach to estimate particle size and mass from the more routine radiation measurements was developed and shown to produce results that compared well with traditional methods that directly measure particle size and mass. Smaller particles, largely originating from manmade emissions, are called “fine mode aerosol,” while larger particles, largely originating from natural sources such as dust and sea-salt, are called “coarse mode aerosol.” This suggests that estimates of particle size and source attribution could be derived from operational radiation measurements worldwide, greatly increasing the amount of information on particle properties needed to better constrain parameterizations used in climate models.

PNNL Contact

Jerome Fast, Pacific Northwest National Laboratory, Jerome.Fast@pnnl.gov 

Funding

This work was supported by the Atmospheric System Research (ASR) program sponsored by the US Department of Energy (DOE), Office of Biological and Environmental Research (OBER), including grant no. DE-SC0008937.