Lung deposited surface area of atmospheric aerosol particles at three observatories in Japan

The lung deposited surface area (LDSA) measured by diffusion charging (DC) method has been recently receiving increased attention as it is believed to accurately represent the surface reactivity of the particles, including ultrafine particles. To characterize regional and seasonal behaviors of the LDSA in the atmosphere and the factors controlling them, we measured the LDSA concentrations, using the DC method, and other physicochemical properties at three sites in Japan, including urban and rural areas. Comparisons among the three sites in the same season showed the highest LDSA concentration at the urban site Fukuoka, due to high concentrations and low particle sizes. In addition, this urban site frequently recorded high LDSA concentrations with high specific LDSAs, which represents the high contribution of ultrafine particles to the LDSA concentration. This is because the site was dominated by ultrafine black carbon particles emitted from surrounding cities, along with low contribution of long-range transported particles from the continent. In contrast, the dominance of these transported particles, which is typically observed at the three sites during this season, caused the specific LDSA to fall within a low and narrow range. However, even at rural areas, the active formation of organic particles in the summer caused high specific LDSAs, although their concentrations were low. Thus, the particles in urban areas, where ultrafine particles are probably emitted with high concentration from surrounding cities, have the potential to cause a greater adverse effect on human health even for the identical LDSA concentration. In addition, our observations showed that the LDSA of atmospheric aerosol particles measured by the DC method can be roughly represented by the theoretical LDSA of particles assuming spherical shape. Our characterizations using the specific LDSAs provide useful information for applying the LDSAs as the toxicity indicator of atmospheric aerosol particles, including ultrafine particles.