Abstract
An air quality standard for airborne particulate matter with diameter less than 2.5 μm (PM2.5) has been newly constituted in September 2009 in Japan. Although concentration of PM2.5 has been decreasing as well as suspended particulate matter (SPM, particles < 10 μm) in recent years, achievement of the PM2.5 air quality standard is not easy especially in urban areas, and effective countermeasures based on the actual situation of PM2.5 is needed. PM2.5 consists mainly of combustion generated particles and secondary particles formed from gaseous precursors in the atmosphere. Combustion sources vary widely and their exhaust particles are highly complex mixture. Secondary particle is also complex, especially for organics, and is not fully understood. Recent increase of the transboundary pollution from the Asian Continent makes their understanding more difficult. This review describes the current state of knowledge on the PM2.5 situation in urban areas in Japan and other countries from two viewpoints of measurement and model. Our recent study including comprehensive filed measurement, receptor analysis, and model simulation in Kanto area is also presented. Studies on transboundary pollution were outlined describing our field and modeling study in Western Japan. Finally, their major tasks ahead are discussed and future research directions toward a solution of PM2.5 situation are proposed.
