Optical Properties of Particulate Matter
In 2011, the United States Environmental Protection Agency (US EPA) released the national standard for regulation of mercury from power plants. In the US, coal fire power plants account for the majority of mercury emissions, accounting for approximately 50% of emissions. Mercury, a toxic metal, can cause neurological disorders as well as hinder the development of fetuses in pregnant women. Trace concentrations of mercury, found in the form of both Hg2+and Hg0, can be found in the flue gases resulting from combustion processes in coal fire power plants. While Hg2+ is water soluble, and is easily removed via condensation onto fly ash, the elemental form, Hg0, is much more difficult to capture.
Over the past 20 years, in anticipation of the new EPA mercury standards, researchers in the US have been developing mercury capture technologies to incorporate into power plants across the country. Presently, a widely used technology for mercury capture is the injection of dry powdered sorbents, such as powder activated carbon (PAC), into flue streams for mercury absorption. The absorption process, which takes place inside an electrostatic precipitator (ESP), occurs simultaneously with the collection of the PAC along with fly ash and other power plant by products.
Clack and his group are generating fly ash-PAC admixture aerosols in the lab using a partially fluidized bed (a video of it is shown below) and measuring the aerosols’ optical properties to determine its potential climate forcing. It is hypothesized that escaped PAC may not only pose a threat to the environment as it contains absorbed mercury, but additionally, may function in as much the same manner as carbon and soot due to its light absorbing properties. With this research Clack hopes to determine the trade-offs of using PAC as an effective mercury absorption technology and its potential climate forcing properties.