Vapor losses can suppress the formation of secondary organic aerosol, which in turn has contributed to the under-prediction of secondary organic aerosol (SOA) in climate and air quality models. Secondary organic aerosols are formed primarily through chemistry that occurs in the gas phase.
Secondary organic aerosol impacts air quality and climate and makes up a major fraction of particulate matter in the atmosphere. Yet secondary organic aerosol concentrations have been significantly underestimated in regional air quality models, the researchers behind the new paper say, because nearly all models of secondary organic aerosols are tied to observations of their formation in laboratory chamber experiments. However, the effect of vapor loss to chamber walls previously had been neglected.
“To accurately predict the health and climate impacts of particles, we need to accurately predict their abundance in the atmosphere,” said co-author Christopher Cappa, professor of civil and environmental engineering at U.C. Davis. “If, along the path from moving from the gas phase to the particle phase, another surface steals that gas-phase material, you wouldn’t form as much of the particle as you would think. That’s what we’ve demonstrated is happening: The walls of these chambers act as a sponge for the vapors and compete with the particles for these vapors.”
The researchers conducted a series of experiments in a 24 cubic meter environmental chamber using the volatile organic compound toluene, which is emitted from motor vehicles and is an important secondary organic aerosol precursor. Cappa said the researchers’ next steps are to assess the vapor effect more broadly for other compounds to more fully understand these wall effects and make better predictions for the future.
The study was funded by the National Science Foundation, U.S. Department of Energy and the California Air Resources Board. The California Air Resources Board is famous for exaggerating pollution estimates by 340% in order to get more political power and force air quality mandates to be passed, and for funding research to prove that cooking a hamburger is worse for the environmental than driving a diesel truck.
Are all of the air quality studies invalid? Only if advocacy science can declare the situation worse.
Citation: Xuan Zhang, Christopher D. Cappa, Shantanu H. Jathar, Renee C. McVay, Joseph J. Ensberg, Michael J. Kleeman, and John H. Seinfeld , 'Influence of vapor wall loss in laboratory chambers on yields of secondary organic aerosol', PNAS April 7, 2014, doi:10.1073/pnas.1404727111