Effects of combustion emissions from the Eurasian continent in winter on seasonal δ13C of elemental carbon in aerosols in Japan

Abstract

Abstract We investigated suspended particulate matter (SPM, particles with a 100% cut-off aerodynamic diameter of 10 μm) and PM2.5 (particles with a 50% cut-off aerodynamic diameter of 2.5 μm) concentrations in aerosols sampled in Akita Prefecture, Japan, from April 2008 to January 2010, and the carbon isotope ratios (δ 13 C) of elemental carbon (EC) in both SPM and PM2.5 and in samples from possible sources. We also determined the ion contents of SPM and estimated the back trajectories of air masses arriving at Akita Prefecture during the study period. The SPM concentration was very low (annual average, 15.2 μg m −3 ), and it tended to be higher in spring and lower in winter. We attributed the higher SPM in spring to dust storms brought from the Asian continent. The average annual PM2.5 concentration was 8.6 μg m −3 . δ 13 C 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‰. δ 13 C 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 diesel vehicles (−24.3 ± 0.3‰). δ 13 C was enriched in SPM in winter compared with summer values, moreover, only a slight seasonal trend was detected in δ 13 C in PM2.5. From these data and the source results, we hypothesized that the enrichment of δ 13 C of SPM and PM2.5 in winter was a long-range effect of overseas combustion processes such as coal combustion. In addition, δ 13 C of SPM was correlated with Cl − and Mg 2+ contents 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.