Quantifying the Hygroscopicity of Black-Carbon-Containing Aerosol

Wednesday, 17 December 2014: 9:00 AM
Joshua Peter Schwarz1,2, Anne Elizabeth Perring2,3, Milos Z Markovic1,4, Ru-Shan Gao3, Sho Ohata5, Justin Langridge6 and David W Fahey1,4, (1)NOAA ESRL, Boulder, CO, United States, (2)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (3)NOAA Earth System Research Lab, Boulder, CO, United States, (4)CIRES / NOAA Earth System Research Laboratory, Boulder, CO, United States, (5)University of Tokyo, Tokyo, Japan, (6)Met Office, Exeter, United Kingdom
We have humidified a Single Particle Soot Photometer (SP2), an instrument that can measure the optical size and black carbon (BC) mass content of individual particles. Control of sample relative humidity (RH) permits exploration of water uptake by BC-containing particles, an important process that can affect BC-containing aerosol optical properties and lifetime. A Mie and k-Kohler theory framework was developed to relate humidity-dependent changes in BC aerosol optical size to the hygroscopicity parameter (k) of the non-BC content in the particles (which is responsible for any water uptake by these particles). Agreement between the theoretical results and laboratory measurements for the homogenous aerosols validates the experimental methodology, and constrains the range of reasonable use of Mie theory to these ends. We have configured two SP2s sampling in parallel, one dry and one humidified, to permit continuous monitoring of water uptake by materials internally mixed with BC in rapidly changing air masses. This system was flown on the NASA DC8 research aircraft during the 2012 DC3 and 2013 SEAC4RS campaigns, and we present engineering and early science results from these data sets.