Why Climate Models Underestimate Organic Aerosols


Airborne particles impact human health, cause haze, and influence climate. New findings from researchers at the University of California, Irvine; Pacific Northwest National Laboratory (PNNL); Imre Consulting; and Portland State University may explain why the abundance of secondary organic aerosols (SOA), which make up more than half of airborne particle mass, has been significantly underestimated by currently accepted air quality and climate models. SOAs are derived from the oxidation of volatile organics, such as pinene, a substance excreted from pine trees. Using the SPLAT II mass spectrometer at PNNL’s Environmental Molecular Sciences Laboratory (EMSL), a unique instrument that allows users to study fundamental processes governing the chemistry and physics of particles at the nano- and microscale, the team showed that a-pinene reacts with ozone and nitrate to form organic nitrates and ozonolysis products, and that the latter nucleates and forms seed particles on which other products condense to form SOAs. The findings are contrary to expectations, including the view that SOAs evolve in the atmosphere as equilibrated liquid droplets and evaporate with time. Instead, the data show that SOA particles are quasi-solids that stick around for a long time. If found to be a general phenomena in the atmosphere, aerosol models may need to be reformulated to better predict SOA evolution in both indoor and outdoor environments, including climate prediction models.


Perraud, V., E. A. Bruns, M. J. Ezell, S. N. Johnson, Y. Yu, M. L. Alexander, A. Zelenyuk, D. Imre, W. L. Chang, D. Dabdub, J. F. Pankow, and B. J. Finlayson-Pitts. 2012. “Non-Equilibrium Atmospheric Secondary Organic Aerosol Formation and Growth,” Proceedings of the National Academy of Sciences 109(8), 2836-41. DOI: 10.1073/pnas.1119909109.

For more information, see the recent UC Irvine press release, Gases Drawn into Smog Particles Stay There, UCI-Led Study Reveals.