Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 47, Issue 12, Pages 6349-6357Publisher
AMER CHEMICAL SOC
DOI: 10.1021/es401043j
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Funding
- Office of Science (BER), Department of Energy (Atmospheric Science Program) [DE-SC0006980, DE-FG02-05ER63995]
- Environmental Protection Agency through MIT [RD-83503301]
- Atmospheric Chemistry Program of the National Science Foundation [ATM-0854916, AGS-0904292]
- Aerodyne Research, Inc. [ATM-0837913, AGS-0855135]
- U.S. Department of Energy (DOE) [DE-SC0006980] Funding Source: U.S. Department of Energy (DOE)
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [0855135] Funding Source: National Science Foundation
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [0837913] Funding Source: National Science Foundation
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Brown carbon (BrC), which may include secondary organic aerosol (SOA), can be a significant climate-forcing agent via its optical absorption properties. However, the overall contribution of SOA to BrC remains poorly understood. Here, correlations between oxidation level and optical properties of SOA are examined. SOA was generated in a flow reactor in the absence of NOx by OH oxidation of gas-phase precursors used as surrogates for anthropogenic (naphthalene, tricyclo-[5.2.1.0(2,6)]decane), biomass burning (guaiacol), and biogenic (alpha-pinene) emissions. SOA chemical composition was characterized with a time-of-flight aerosol mass spectrometer. SOA mass-specific absorption cross sections (MAC) and refractive indices were calculated from real-time cavity ring-down photoacoustic spectrometry measurements at 405 and 532 nm and from UV-vis spectrometry measurements of methanol extracts of filter-collected particles (300 to 600 nm). At 405 nm, SOA MAC values and imaginary refractive indices increased with increasing oxidation level and decreased with increasing wavelength, leading to negligible absorption at 532 nm. Real refractive indices of SOA decreased with increasing oxidation level. Comparison with literature studies suggests that under typical polluted conditions the effect of NOx on SOA absorption is small. SOA may contribute significantly to atmospheric BrC, with the magnitude dependent on both precursor type and oxidation level.
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