Emissions of size-segregated aerosols from on-road vehicles in the Caldecott Tunnel

Particulate matter emissions from the California in-use vehicle fleet were measured as 37 500 vehicles traveled through two bores of the Calclecott Tu nnel located in the San Francisco Bay area. Microorifice cascade impactors and filter-based samplers were used to determine the particle chemical comp osition as a function of particle size. Ammonia emissions from the vehicle fleet were measured as well. Concentrations of aerosol mass, organic carbon , elemental carbon, sulfate ion, nitrate ion, and ammonium ion, as well as 13 elements are reported. The particle mass distribution peaks in the parti cle size range 0.1-0.18 mum aerodynamic diameter (D-a). Elemental carbon an d organic matter were the largest components of particle mass in all the si ze ranges studied. The Caldecott Tunnel bores studied include one which car ries light-duty vehicle traffic and one which carries a mixture of light- a nd heavy-duty vehicle traffic. From experiments conducted in both bores, es timates are made of the size distribution and chemical composition of parti culate matter emissions extrapolated to the 100% light-duty and 100% heavy- duty vehicle fleets. The heavy-duty vehicle fleet emitted 1285 +/- 237 mg o f fine particulate matter (D-a < 1.9 mum)/kg of C contained in the fuel bur ned (corresponding to approximately 430 +/- 79 mg/km driven). Light-duty ve hicles emitted less than 85 +/- 6 mg/ kg of C in the fuel burned (correspon ding to less than approximately 5.5 +/- 0.4 mg/km driven). Emissions of gas phase ammonia in the Caldecott Tunnel were measured to be 194 and 267 mg/L of gasoline-equivalent fuel burned in the tunnel. The ammonia emissions are attributed to automobiles that were equipped with 3-way catalysts and oper ating fuel rich.