Abstract
The chemical components of daily sampled PM2.5 were monitored in Nagano city in the summers of 2012 and 2013. We conducted multiple linear regression analyses with sulfate as the dependent variable and with an oil combustion tracer element (V or Ni) and coal combustion tracer element (As, Pb, or Cd) as explanatory variables taking into account the existence of an outlier. As a result of the regression analyses using V as the oil combustion tracer element, the regression equations explained 90% of the sulfate variation. However, the sulfate concentrations from 26 to 29 July, 2012 were unusually high, and were excluded as outliers. The intercept of the equations were nearly equal to zero, and most of the observed sulfates was considered to have originated from the oil and coal combustion. The average ratio of sulfate from the oil combustion to that from the coal combustion was estimated to be 54:46. For the backward trajectories from the area around Mainland China, the East China Sea, and Japan, the sulfate concentrations from oil combustion were estimated to be 2.7, 2.5, and 2.3 μg/m3, respectively, and those from coal combustion were estimated to be 3.8, 2.1, and 1.3 μg/m3, respectively. Therefore, as for the sulfate concentrations from coal combustion, they were higher for the trajectories nearer to Mainland China, and the contributions from the area around Mainland China were suggested to be high. The influence of volcanoes in Kyushu, such as Sakurajima, was considered the cause of the high sulfate concentrations from 26 to 29 July, 2012. The volcanic sulfates were estimated to be 5 to 6 tenths of the observed sulfates during the period.
