title: Comparison of carbonaceous aerosols in Tokyo before and after implementation of diesel exhaust restrictions.
abstract: We compared the status of carbonaceous aerosols in Tokyo before and after the implementation of a diesel vehicle regulation intended to reduce the quantity of particulate carbon from diesel engines in one of the largest scale ever attempts at vehicle exhaust control. Radiocarbon (14C) in elemental carbon (EC) and total carbon (TC) were analyzed to identify fossil fuel carbonaceous particles emitted from diesel-powered vehicles. One-sided paired-month t-tests showed no distinct difference in the absolute concentrations of particles in terms of total mass (19.5 to 18.0 microg m(-3); p = 0.321), EC (3.6 to 3.3 microg m(-3); p = 0.272), and TC (6.3 to 6.2 microg m(-3); p = 0.418) for the finest particles (d(a) < 1.1 microm) after the implementation of the regulation. The ratios of the concentrations of the chemical constituents 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, the percentage of fossil carbon in EC also decreased (67.8% to 63.8%; p = 0.104). Since EC is predominantly of combustion origin, the observed decrease was likely due to the decrease in fossil EC emissions from diesel-powered vehicles. The decrease in EC/TC after the implementation of the regulation was also likely to have resulted from attachment to diesel vehicle exhaust systems of particulate filters as required as part of the regulation by the Tokyo Metropolitan Government. The EC/TC of fossil carbon of the finest particles decreased from 66.2% to 55.2% (p = 0.066), but EC/TC of biomass carbon did not decrease but rose slightly from 43.6% to 44.5% (p > 0.5). Thus, the relative ratios of components of carbonaceous aerosol particles, such as 14C, could provide a better understanding of the atmospheric pollution status, despite short-term fluctuations, than do measurements of absolute concentrations.
authors.affiliation: Institute of Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa-shi, Chiba 277-8561, Japan. yamanao@is.icc.u-tokai.ac.jp
authors.forename: Naomichi
authors.initials: N
authors.lastname: Yamamoto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Muramoto
authors.forename: Jun
authors.initials: J
authors.lastname: Yoshinaga
authors.forename: Ken
authors.initials: K
authors.lastname: Shibata
authors.forename: Michio
authors.initials: M
authors.lastname: Endo
authors.forename: Osamu
authors.initials: O
authors.lastname: Endo
authors.forename: Motohiro
authors.initials: M
authors.lastname: Hirabayashi
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Tanabe
authors.forename: Sumio
authors.initials: S
authors.lastname: Goto
authors.forename: Minoru
authors.initials: M
authors.lastname: Yoneda
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Shibata
mesh_terms: D000336:Aerosols / Q000032:analysis* / Q000737:chemistry; D000393:Air Pollutants / Q000032:analysis / Q000737:chemistry; D002244:Carbon / Q000032:analysis* / Q000737:chemistry; D002250:Carbon Radioisotopes; D004784:Environmental Monitoring / Q000379:methods; D010316:Particle Size; D013997:Time Factors; D014041:Tokyo; D001335:Vehicle Emissions / Q000032:analysis* / Q000331:legislation & jurisprudence
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D002250:Carbon Radioisotopes; D001335:Vehicle Emissions; D002244:Carbon