Articles | Volume 16, issue 22
Research article
23 Nov 2016
Research article |  | 23 Nov 2016

Morphology and mixing of black carbon particles collected in central California during the CARES field study

Ryan C. Moffet, Rachel E. O'Brien, Peter A. Alpert, Stephen T. Kelly, Don Q. Pham, Mary K. Gilles, Daniel A. Knopf, and Alexander Laskin

Abstract. Aerosol absorption is strongly dependent on the internal heterogeneity (mixing state) and morphology of individual particles containing black carbon (BC) and other non-absorbing species. Here, we examine an extensive microscopic data set collected in the California Central Valley during the CARES 2010 field campaign. During a period of high photochemical activity and pollution buildup, the particle mixing state and morphology were characterized using scanning transmission X-ray microscopy (STXM) at the carbon K-edge. Observations of compacted BC core morphologies and thick organic coatings at both urban and rural sites provide evidence of the aged nature of particles, highlighting the importance of highly aged particles at urban sites during periods of high photochemical activity. Based on the observation of thick coatings and more convex BC inclusion morphology, either the aging was rapid or the contribution of fresh BC emissions at the urban site was relatively small compared to background concentrations. Most particles were observed to have the BC inclusion close to the center of the host. However, host particles containing inorganic rich inclusions had the BC inclusion closer to the edge of the particle. These measurements of BC morphology and mixing state provide important constraints for the morphological effects on BC optical properties expected in aged urban plumes.

Short summary
Atmospheric black carbon (BC), commonly known as soot, is an important constituent of the earth that imparts a warming similar to that of carbon dioxide. However, BC is much shorter lived and has uncertain warming due to its mixture with other solid and liquid components. Here, advanced microscopic methods have provided a detailed look at thousands of BC particles sampled from central California; these measurements will lead towards a better understanding of the effects that BC has on climate.
Final-revised paper