Masayoshi Karasawa

The main component concentrations of fine particulate were measured at 17 sites by 24-hr sampling for two weeks by JCAP (Japan Clean Air Program) in the winter of 1999. The following results were obtained by multivariate data analysis using the data sets.

(1) The ratio of fine particulate to SPM was about 2/3 and a large difference between the observation points was not observed although some low values were indicated in the clean region.

(2) The fluctuation factor and Max/Min of Cl- concentration for space variation were the highest and those of SO₄^2- were the lowest among the six components.

(3) The deviations of space variation for Cele (elemental carbon) and NO₃^- concentrations were larger than for SO₄^2- concentrations. The peak concentration of Cele and NO₃^- for a site sometimes appeared at different dates. The fluctuation factor of space variation for the SO₄^2- concentrations was smaller than that of time variation. SO₄^2- concentration is thought to change similarly in a wide mesoscale area.

(4) Three factors were extracted by factor analysis of all data. Factor 1 is representative of the ammonium salt that is the main component of the secondary formatted inorganic particulate. Factor 2 is representative of the combustion source including vehicle exhaust and the secondary formatted organic particulate. Factor 3 is representative of sea salt and fine soil particulate.

A temperature-controlled smog chamber was used to investigate the temperature dependence of secondary organic aerosol (SOA) formation from photochemical reaction of three aromatic hydrocarbons (toluene, m-xylene and 1,2,4-trimethylbenzene). The experiments were performed at 283 K and 303 K for each hydrocarbon. A higher SOA yield was obtained at lower temperature and at a higher concentration of SOA generated. The relationship of SOA yield to temperature and SOA concentration is expressed by a gas/particle partitioning absorption model considering temperature dependence. Under the condition of the same SOA concentration, the SOA yield at 283 K was approximately twice that at 303 K. It has been clarified experimentally that temperature is one of the most important factors in SOA formation. The SOA yields of the aromatic hydrocarbons were higher in the order of toluene, m-xylene and 1,2,4-trimethylbenzene. The order of the SOA yield was the reverse of the reaction rate constant with OH radicals, which indicated the probability of SOA being generated by the secondary reaction.