During the four seasons from May 2015 to February 2017, seasonal intensive sampling was conducted for two weeks at the Niigata-Maki National Acid Deposition Monitoring Station.
Daily mean concentrations of PM2.5 ranged from 4.2 µg m-3 to 33.4 µg m-3 during the observation period, which was lower than Japanese Air Quality Standard for PM2.5 (35 µg m-3). The higher concentrations of SO42-, NH4 + and organic carbon (OC) were observed in spring and summer, which may result from the photochemical activity and secondary OC production.
The major chemical components of PM2.5 were SO42-, NO3-, NH4 +, OC, elemental carbon (EC) and crustal elements. Compared with data at other urban sites, a lower concentration of EC and NO3- and higher OC/EC ratio were observed at the Niigata-Maki site, which may result from the lower anthropogenic origin such as stationary source or vehicular traffic and showed a character of the rural site.
PM2.5 source apportionment was characterized by positive matrix factorization (PMF) analysis, and the results inferred four major sources: sea salt (10.2%), biomass combustion (18.9%), soil dust (13.2%) and secondary aerosol (44.4%). The potential source contribution function (PSCF) analysis suggested that the major sources of secondary aerosol and sea salts were domestic in southwest Japan and the Sea of Japan, whereas the sources of biomass combustion and soil dust in specific seasons were transported long distance from the Northeast Asian continent (NEA).
Comparing with previous studies in western Japan, this study showed a large domestic contribution of southwest Japan for secondary aerosol, while a larger contribution of the NEA was observed in the previous studies. The significant contribution of biomass combustion from northeast China in autumn, and local area in Niigata and southwest Japan in the other seasons were uniquely observed in this study.
This work was partly supported by JSPS KAKENHI Grant Number 25502005 and Environment Research and Technology Development Fund (5-1306) of the Ministry of the Environment, Japan.
The paper on this study is as follows: