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

Individual aerosol particles emitted from light-duty vehicles (LDV) and hea vy-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 i n real time. From the composition of individual particles, in conjunction w ith knowledge of the traffic patterns in the Caldecott Tunnel, information about the source of the particles can be determined. Based upon chemical co mposition, three main types of particles were detected: particles with sign ificant mass spectral signal due to polycyclic aromatic hydrocarbons (PAH), elemental carbon (soot) particles, and inorganic particles containing subs tantial signal due to ions including Al+, Ca+, Fe+, Ba+ and BaO+. Prelimina ry 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 to tal number of particles sampled with the ATOFMS instrument in a 3 h samplin g period in a mixed traffic (HDV and LDV) bore of the tunnel.