Seasonal variation of carbonaceous and ionic components in ultrafine and fine particles in an urban area of Japan

The carbonaceous and ionic components of atmospheric ultrafine particles (UFPs; Dp < 0.1 μm) and fine particles (FPs; Dp < 2.5 μm) were measured four times during one year in Saitama City, Japan, in order to observe the seasonal variation of chemical components, to characterize the chemical components for the two particle sizes, and to estimate the possible emission sources qualitatively. Generally, the carbonaceous and ionic components in UFPs and FPs tended to increase from summer to winter. Over the year, approximately 63∼67% of the total carbon (TC) consisted of organic carbon (OC) in FPs, whereas 80∼88% of TC consisted of OC in UFPs. Char-elemental carbon (EC) and soot-EC constituted equal proportions of the total EC in UFPs, while soot-EC accounted for only a small amount of the total EC in FPs, indicating that char-EC and soot-EC were mainly present in relatively larger particles and much smaller particles, respectively. The water-soluble OC concentration tended to decrease from summer to winter, indicating that secondary organic aerosol formation dominated the OC fractions during the summer sampling period. The transport of atmospheric particulate matter from cities to the north of the sampling site is one reason for the high levels of carbonaceous components in FPs for the fall and winter samples. On the other hand, Tokyo and other industrial cities near the ocean are responsible for the highest soot-EC concentrations found in the summer FP samples.