Rethinking Organic Aerosols: Semivolatile Emissions and Photochemical Aging

TLDR

Primary organic particles are largely semivolatile, evaporating during dilution and generating substantial low‑volatility gas‑phase material. The study argues that controlling organic particulate concentrations requires major revisions to current measurement and regulation methods. Laboratory experiments show that diesel photo‑oxidation produces abundant organic aerosol from low‑volatility gases, and incorporating partitioning and photochemical processing of primary emissions yields a more widespread aerosol distribution and better agreement with observations.

Abstract

Most primary organic-particulate emissions are semivolatile; thus, they partially evaporate with atmospheric dilution, creating substantial amounts of low-volatility gas-phase material. Laboratory experiments show that photo-oxidation of diesel emissions rapidly generates organic aerosol, greatly exceeding the contribution from known secondary organic-aerosol precursors. We attribute this unexplained secondary organic-aerosol production to the oxidation of low-volatility gas-phase species. Accounting for partitioning and photochemical processing of primary emissions creates a more regionally distributed aerosol and brings model predictions into better agreement with observations. Controlling organic particulate-matter concentrations will require substantial changes in the approaches that are currently used to measure and regulate emissions.