Differences of chemical species and their ratios between fine and ultrafine particles in the roadside environment

Chemical components of fine particles (FPs; aerodynamic diameter, Dp < 2.5 μm) and ultrafine particles (UFPs; Dp < 0.1 μm) at Japanese and German roadsides were investigated during summer. The UFPs/FPs ratio for organic carbon (OC) concentrations on weekdays was 34.5% and 25.0% at Japanese and German roadsides, respectively, whereas 3.3% and 6.4% for elemental carbon (EC) concentrations, respectively. These results thus indicate a higher OC and a lower EC contribution from UFPs at the Japanese roadside than at the German roadside. In particle samples, OC2 and OC3 constituted a high proportion of UFPs, and pyrolyzed OC and EC1 were predominant among FPs of 0.1 μm < Dp < 2.5 μm. Our results showed roadside environment exist not only primary FPs and UFPs but also secondary FPs and UFPs from photochemical reactions or long-range transport.

► OC2 and OC3 constitute a high proportion of UFPs.
► POC and EC1 were dominant among of FPs 0.1 < Dp < 2.5 μm.
► EC2 contributed to the total EC of UFPs in roadside environment.
► Higher minimum OC/EC ratio of UFP is affected by secondary or background particles.