AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Effect of Aging on Brown Carbon Optical Properties Emitted from Biomass Pyrolysis
MARIAM FAWAZ, Benjamin Brem, Tami Bond, University of Illinois at Urbana Champaign
Abstract Number: 85 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Brown carbon is the light absorbing organic aerosol component of organic carbon. To date, few studies have touched on the optical properties of freshly emitted brown carbon; even fewer have examined the effect of the particle aging in the atmosphere on the optical properties. Aging, occurring during the lifetime of particles in the atmosphere, ranges from hours to days, where particles undergo physical and chemical reactions that alter their physicochemical properties. In this work, we study the effect of atmospheric aging on brown carbon light absorption, and report, under laboratory settings, the optical properties of freshly emitted organic aerosols and aged organic aerosols from biomass pyrolysis. We measure the light extinction, light scattering, and light absorption coefficient of organic carbon at three wavelengths (460 nm, 520 nm, and 670 nm). We use a short pathlength extinction cell to measure light extinction, a nephelometer to measure light scattering and we calculate light absorption as the difference between extinction and scattering. Brown carbon was aged by exposing the particles to atmospherically relevant concentrations of ozone (O$_3) and ammonia (NH$_3). We show that the O$_3 and NH$_3 treatments increase the absorption coefficient of brown carbon by an average of 20% and 250% respectively. Aged brown carbon aerosols absorb more light than when freshly emitted; thus, the effect of the aging processes exacerbate the impact of brown carbon concentrations in the atmosphere on global radiative forcing.