Real-Time, Single-Particle Volatility, Size, and Chemical Composition Measurements of Aged Urban Aerosols

Aerosol particles undergo significant amounts of atmospheric processing within the Los Angeles basin. To assess the major sources and degree of aging, ambient particle volatility, size, and chemical composition were measured concurrently in real-time during the Study of Organic Aerosols conducted in Riverside, CA in November 2005. A thermodenuder (TD) was coupled to an aerosol time-of-flight mass spectrometer (ATOFMS) to characterize the chemistry of the individual submicrometer particles remaining after heating. Aged organic carbon (OC) particles contained >50% by volume secondary species, primarily ammonium nitrate, ammonium sulfate, and amines. At 230 degrees C, the chemistry of the 100-150 nm residues were elemental carbon (29% by number), OC (27%), and biomass burning (15%). Sea salt(47%) and dust (15%) were the major contributors at the larger sizes (750-800 nm). Many particles at 230 degrees C possessed signatures similar to those of fresh vehicle emissions, biomass burning, sea salt and dust particles, showing that the TD-ATOFMS method can be used to apportion particles in highly aged environments to their original sources, while providing insight into the relative contributions of primary and secondary species.