Abstract
Purpose In recent years, attention has been paid to the influence of the particle fraction≦2.5 μm in diameter (PM2.5) among suspended particulate matter (SPM) on health. However, the present status of particle contamination in Japan has hitherto not been adequately clarified.
To determine particle contamination in the outdoor air around Kagawa Medical School located on a hill in the suburb of Takamatsu City, we measured SPM according to diameter between February 1999 and January 2000.
Methods Mass concentrations of SPM were determined using an Andersen air sampler and light scattering counts were measured using a particle counter at the same site.
Results Of the entire year, the total SPM concentration (PM11) was 20-30 mg/m3, and the particle fraction≦2.1 μm in diameter (PM2.1) accounted for 25-60%. Both the PM11 and PM2.1 concentrations were the lowest in August when the wind blew mainly from rural areas, but high in January and February when the wind blew mainly from urban areas and April when yellow sand was wind borne from China.
The SPM particle count in April was markedly high when a misty aerosol containing yellow sand was extent. The SPM count for each diameter class rapidly decreased after rainfall during passage of storm fronts, but this was especially marked for smaller diameters. During the measurement period in August, air from rural areas often passed the measurement point, and the particle concentration ≦1 μm in diameter was markedly lower than that in April.
Conclusion The results suggest that the SPM levels around Kagawa Medical School located in the suburb of Takamatsu City are associated with seasonal climate and the wind direction from which the prevailing blew.
