New data may explain why models underestimate organic aerosols
Airborne particles impact human health, cause haze, and influence climate. New findings reported by an EMSL user team in the Proceedings of the National Academy of Sciences may explain why the abundance of secondary organic aerosols (SOA), which make up more than half of the mass of airborne particles, has been significantly underestimated by currently accepted air quality and climate models. SOA result from the oxidation of volatile organics, such as pinene, which is excreted from pine trees into the air. In their PNAS article, the research team from the University of California, Irvine; Pacific Northwest National Laboratory; Imre Consulting; and Portland State University discuss their important and first-time observations of the non-equilibrium particle formation and growth of SOA. Using EMSL’s SPLAT II mass spectrometer, α-pinene was shown to react with ozone and NO3 to form organic nitrates and ozonolysis products; the latter were found to nucleate and form seed particles, on which organic nitrates and ozonolysis products condense, leading to SOA formation. This process was thought to represent a path along equilibrium partitioning between liquid particles and gas phase, but the team’s new data point to irreversable and kinetically determined uptake of nitrates onto existing, non-liquid SOA particles. Furthermore, SOA particles were thought to evolve in the atmosphere as equilibrated liquid droplets and evaporate with time. Instead, as the data show, SOA particles are quasi-solids that stick around for a long time. These results will be an important factor in rethinking the effect of airborne particles on human health and accounting for airborne particles in climate prediction models.
Learn more about this work in the UC Irvine press release, Gases Drawn into Smog Particles Stay There, UCI-Led Study Reveals, and related New York Times article.
Reference: Perraud V, EA Bruns, MJ Ezell, SN Johnson, Y Yu, ML Alexander, A Zelenyuk, D Imre, WL Chang, D Dabdub, JF Pankow, and BJ Finlayson-Pitts. 2012. “Non-equilibrium atmospheric secondary organic aerosol formation and growth.” Proceedings of the National Academy of Sciences 109(8):2836-2841.
Acknowledgement: This work was funded by the US Department of Energy and the National Science Foundation. Portions of the work were performed in collaboration with EMSL, a national scientific user facility located at PNNL.
Released: March 01, 2012