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.
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.