Does Haze over Cities Contribute to Air Pollution and Climate Forcing?


Hanging over many major cities for days on end, and especially during summer, is a brownish haze that some scientists think contributes to air quality issues and climate forcing because of its potential for absorbing sunlight and trapping surface heat. A team of scientists from Pacific Northwest National Laboratory and the Department of Energy’s Environmental Molecular Sciences Laboratory (EMSL) has started to examine the chemistry of brown carbon, a type of particle found in that haze. The team used analytical capabilities at EMSL, including high-resolution mass spectrometry, to study the particles that form around the chemical toluene, a common pollutant emitted to the atmosphere and found in the haze. They discovered that the addition of nitrogen oxide, which is found in the exhaust from combustion engines, produced heat-trapping particles, and that at high levels, the particles not only held significantly more heat but also turned yellowish brown. The research, highlighted on the cover of a recent issue of Physical Chemistry Chemical Physics, provides new insights that could improve atmospheric and climate models.

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Lin, P., J. Liu, J. E. Shilling, S. M. Kathmann, J. Laskin, and A. Laskin. 2015. “Molecular Characterization of Brown Carbon (BrC) Chromophores in Secondary Organic Aerosol Generated from Photo-Oxidation of Toluene,” Physical Chemistry Chemical Physics 17, 23312–25. DOI: 10.1039/c5cp02563j.