文摘
We compared the status of carbonaceous aerosols inTokyo before and after the implementation of a diesel vehicleregulation intended to reduce the quantity of particulatecarbon from diesel engines in one of the largest scale everattempts at vehicle exhaust control. Radiocarbon (14C) inelemental carbon (EC) and total carbon (TC) were analyzedto identify fossil fuel carbonaceous particles emittedfrom diesel-powered vehicles. One-sided paired-montht-tests showed no distinct difference in the absoluteconcentrations of particles in terms of total mass (19.5 to18.0 g m-3; p = 0.321), EC (3.6 to 3.3 g m-3; p =0.272), and TC (6.3 to 6.2 g m-3; p = 0.418) for the finestparticles (da < 1.1 m) after the implementation of theregulation. The ratios of the concentrations of the chemicalconstituents were, however, altered after the regulation. EC/TC was significantly decreased from 56.7% to 50.2% (p= 0.039). Although it was not statistically significant, thepercentage of fossil carbon in EC also decreased (67.8% to63.8%; p = 0.104). Since EC is predominantly of combustionorigin, the observed decrease was likely due to thedecrease in fossil EC emissions from diesel-poweredvehicles. The decrease in EC/TC after the implementationof the regulation was also likely to have resulted fromattachment to diesel vehicle exhaust systems of particulatefilters as required as part of the regulation by the TokyoMetropolitan Government. The EC/TC of fossil carbon of thefinest particles decreased from 66.2% to 55.2% (p =0.066), but EC/TC of biomass carbon did not decrease butrose slightly from 43.6% to 44.5% (p > 0.5). Thus, therelative ratios of components of carbonaceous aerosolparticles, such as 14C, could provide a better understandingof the atmospheric pollution status, despite short-termfluctuations, than do measurements of absolute concentrations.
