Manvendra K. Dubey — Los Alamos National Laboratory
Tyler Capek — Michigan Technological University
Jared Lam — Los Alamos National Laboratory
Dian Romonosky — Los Alamos National Laboratory
Christian Carrico — Colorado State University
James Edward Lee — Los Alamos National Laboratory
Allison C Aiken — Los Alamos National Laboratory
Timothy B Onasch — Aerodyne Research, Inc.
Andrew Freedman — Aerodyne Research, Inc.
Claudio Mazzoleni — Michigan Technological University
Michael Jensen — Brookhaven National Laboratory
Category
Absorbing aerosol
Description
a) ĸext vs. inorganic fuel fraction or fuel ion content, b) AAE versus SSA for ambient fires and laboratory biomass burns, c) SSA and d) Absorption of size selected nigrosine vs. RH
We advance predictive treatments of relative humidity (RH) effects of carbonaceous aerosols by: (1) laboratory and field studies of RH effects on biomass burning aerosols and (2) developing a new dedicated instrument to measure light absorption as a function of RH without any filter bias.
Laboratory burns of specific semi-arid fuels were used to elucidate the role of fuel type, chemical composition, and ignition on the hygroscopicity of smoke. A custom controlled RH nephelometry system that measures aerosol light scattering with two nephelometers—one at dry conditions and one at a controlled at RH ~ 85% was used. Aerosol hygroscopicity was highly variable with the enhancement in light scattering in the range of 1.02 < f(RH = 85%) < 2.1 and corresponding to the kappa parameter (κneph) ranging from 0 to 0.18. Hygroscopicity is determined primarily by the fuel's inorganic ion content. We construct an empirical relationship between κneph and the inorganic content of the fuel or smoke to predict water uptake. We test it using mixing rules on ambient wildfire data. We perform optical property comparisons that show that in the Single Scatter Albedo and Absorption Angstrom Exponent space data on ambient fires are more clustered and less variable than fresh laboratory burns due to mixing and aging. Ambient fires aerosols are shifted towards the brown and organic carbon mixing regime relative to the laboratory fires.
In order to probe RH-dependent effects on mixed carbonaceous aerosols, we have modified a Cavity Attenuated Phase Shift-Single Scatter Albedo (CAPS PMssaRH) instrument to simultaneously measure light scattering and extinction in the same sample volume under humidified (RH>80%) and dried conditions (RH<20%) at 450nm. Change in scattering and extinction as a f(RH) is measured directly and derived for absorption from the difference. We have calibrated our system using experiments on size selected ammonium sulfate, polystyrene, nigrosin, aquadag and fullerene soot and Mie theory. We will present new measurements of fresh and aged size selected soot from an inverted burner and biomass burning. We plan to gain mechanistic insight into the drivers of RH uptake by the aforementioned carbonaceous aerosols by simultaneous chemical analysis with our SP-AMS. We propose to deploy some of our f(RH) aerosol instruments for ARM’s TRACER in Houston to help understand carbonaceous aerosol impacts on deep convection.
