Climate Implications of Coal Fly Ash Particles Due to Ice Cloud Formation

This study investigates the impact fly ash particles have on cloud formation and climate. It examines the chemical properties of several types of fly ash particles using single particle mass spectrometry (SPMS) to estimate fly ash burdens from past aircraft campaigns. It also measures the efficiency with which these particles form cloud droplets and ice crystals in the laboratory. Fly ash particles are found to be moderately hygroscopic and are found to form ice in the deposition mode at temperatures colder than ~ -30ºC and in the immersion mode at colder than ~ -20ºC. The laboratory results and SPMS-derived atmospheric fly ash burdens are used to investigate the impacts of fly ash emissions on the properties of cirrus clouds and climate in a global climate model. The aircraft data constrain the sensitivity of the cloud forcing response to fly ash emissions. Overall, current levels of fly ash emissions are estimated to contribute ~ 0.1-0.6 W/m^2 of extra warming through their role in cirrus cloud formation.