Single particle characterization of automobile and diesel truck emissions in the Caldecott Tunnel

Individual aerosol particles emitted from light-duty vehicles (LDV) and heavy-duty vehicles (HDV) were sampled in the Caldecott Tunnel (Berkeley, CA) using an aerosol time-of-flight mass spectrometer (ATOFMS). This instrument determines both size and composition information of individual particles in real time. From the composition of individual particles, in conjunction with knowledge of the traffic patterns in the Caldecott Tunnel, information about the source of the particles can be determined. Based upon chemical composition, three main types of particles were detected: particles with significant mass spectral signal due to polycyclic aromatic hydrocarbons (PAH), elemental carbon (soot) particles, and inorganic particles containing substantial signal due to ions including Al+, Ca+, Fe+, Ba+ and BaO+. Preliminary analysis of these classes shows that they encompass 61.4%, 10.3%, and 11.0%, respectively, of the total number of particles sampled with the ATOFMS instrument in 3 h, heavy traffic sampling periods, in an LDV-only bore of the tunnel. They represent 57.4%, 11.8%, and 18.0%, respectively, of the total number of particles sampled with the ATOFMS instrument in a 3 h sampling period in a mixed traffic (HDV and LDV) bore of the tunnel.