A Comparison of Brown Carbon Aerosol Optical Properties from Recent Laboratory and Field Measurements
Abstract
In most climate models, organic carbon (OC) is typically considered to be externally mixed and purely scattering, contributing negligibly to atmospheric light absorption in the visible solar spectrum. However, purely-scattering OC not only contributes to absorption enhancement in internal mixtures with black carbon (BC), but a broad class of OC called Brown Carbon (BrC) absorbs light on its own in the near-UV wavelengths. Its wavelength dependence, parameterized by the Absorption Ångström Exponent (AÅE), is much stronger than that of BC (AÅE of ~1 in the UV-Vis), potentially as high as 12-14 for the near-UV and diminishing with increasing wavelength.
BrC has been extensively studied in laboratory settings over the last several years. Most laboratory studies focus on secondary BrC aerosol generated from the oxidation of gas-phase precursors in an oxidation flow reactor, while some have examined the heterogeneous oxidation of primary particles. The degree to which the analyte is oxidized is a proxy to how a real-world system would experience atmospheric aging, and different oxidizers can be chosen to simulate different processes, i.e., hydroxyl radical for daytime photooxidation, and nitrate radical for nighttime processes. Using data from a suite of instruments including a new optical instrument which measures aerosol absorption and scattering at four wavelengths (405, 488, 561, and 637 nm), this presentation builds on a series of successful laboratory experiments conducted at the Washington University Biomass Burning Chamber that investigated optical and physical properties of primary BrC aerosol from smoldering Alaskan and Indonesian peatlands. Those laboratory results will be compared with preliminary data from real-world North American wildfire measurements, including simultaneous chemical and physical characterization. This presentation will close with recommendations for future experimental designs to better represent ambient phenomena.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A23E..03S
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0368 Troposphere: constituent transport and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3359 Radiative processes;
- ATMOSPHERIC PROCESSES