Effects of combustion emissions from the Eurasian continent in winteron seasonal d13C of elemental carbon in aerosols in Japan
We investigated suspended particulate matter (SPM, particles with a 100% cut-off aerodynamic diameter of10 mm) and PM2.5 (particles with a 50% cut-off aerodynamic diameter of 2.5 mm) concentrations in aerosolssampled in Akita Prefecture, Japan, from April 2008 to January 2010, and the carbon isotope ratios (d13C) ofelemental carbon (EC) in both SPM and PM2.5 and in samples from possible sources. We also determinedthe ion contents of SPM and estimated the back trajectories of air masses arriving at Akita Prefecture duringthe study period. The SPM concentration was very low (annual average, 15.2 mg m3), and it tended to behigher in spring and lower in winter. We attributed the higher SPM in spring to dust storms brought fromthe Asian continent. The average annual PM2.5 concentration was 8.6 mg m3. d13C of source samples(gasoline and diesel vehicle exhaust, fireplace soot, open biomass burning emissions, street dust, soil,charcoal, and coal) ranged from 34.7& to 1.8&. d13C values of soot from gasoline light-duty(24.4 0.7&) and passenger vehicles (24.1 0.6&) were very similar to that of soot from all dieselvehicles (24.3 0.3&). d13C was enriched in SPM in winter compared with summer values, moreover,only a slight seasonal trend was detected in d13C in PM2.5. From these data and the source results, wehypothesized that the enrichment of d13C of SPM and PM2.5 in winter was a long-range effect of overseascombustion processes such as coal combustion. In addition, d13C of SPM was correlated with Cl and Mg2þcontents in SPM, suggesting the influence of sea salt. We verified this hypothesis by back trajectory analyses. The results indicated a continental influence effects on EC of SPM and PM2.5 in winter.