Diurnal Profile of Particle-bound Polycyclic Aromatic Hydrocarbon (pPAH) Concentration in Urban Environment in Tokyo Metropolitan Area

Traffic emits particles under 1 m. The particles arethe most responsible to particle-bound polycyclic aromatichydrocarbon (pPAH) which can impact human health. To assessthem as health hazards, we monitored diurnal changes in theconcentration and distribution of pPAH near roads in Tokyo.The total pPAH concentration was determined using aphotoelectric aerosol sensor (PAS) which ionized PAH-adsorbingparticles. The total pPAH concentration was compared withchemical analyses by gas chromatography/mass spectrometry(GC/MS). Two sampling sessions, one in August and one inSeptember 2000, were done at three sampling sites at the Hongo Campus of the University of Tokyo. Monitoring was every two minutes for six consecutive days for the first session and for seven consecutive days for the second session.Correlation of the pPAH concentration with traffic flow andwith meteorological conditions were also assessed. The pPAHconcentration varied in the same manner on all days: it sharplyincreased in the early morning by a sudden burden of traffic, and it rapidly decreased during the daytime, probably owing tophotodegradation and/or dilution by rising in the mixingzone. The local wind field, and consequently thetransportation of pPAH from the road, were stronglyinfluenced by the configuration and location of thesurrounding buildings. The pPAH clearly changed in 1- and0.5 day cycles, particularly at the roadside.