Laboratory chamber walls have been stealing vapors, causingresearchers to underestimate the formation of secondary organicaerosol in the atmosphere.
A study published April 7 in PNAS Online Early Edition describes howa team of scientists, including researchers from the University ofCalifornia, Davis, showed that vapor losses to the walls oflaboratory chambers can suppress the formation of secondary organicaerosol, which in turn has contributed to the underprediction of SOAin climate and air quality models.
SOA impacts air quality and climate and makes up a major fraction ofparticulate matter in the atmosphere. Yet SOA concentrations havebeen significantly underestimated in regional air quality models.
Nearly all models of secondary organic aerosols are tied toobservations of their formation in laboratory chamber experiments.However, the effect of vapor loss to chamber walls previously hadbeen 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 andenvironmental engineering at UC Davis.
Secondary organic aerosols are formed primarily through chemistrythat occurs in the gas phase.
"If, along the path from moving from the gas phase to the particlephase, another surface steals that gas-phase material, you wouldn'tform as much of the particle as you would think," Cappa said. "That'swhat we've demonstrated is happening: The walls of these chambers actas a sponge for the vapors and compete with the particles for thesevapors."
Researchers from UC Davis and the California Institute of Technologyconducted a series of experiments in a 24 cubic meter environmentalchamber using the volatile organic compound toluene, which is emittedfrom motor vehicles and is an important SOA precursor.
Cappa said the researchers' next steps are to assess the vapor effectmore broadly for other compounds to more fully understand these walleffects and make better predictions for the future.
Source: University of California - Davis