Decreasing trend of elemental carbon concentration with changes in major sources at Mega city Nagoya, Central Japan

The atmospheric concentration of elemental carbon (EC) in aerosol particles is a key parameter related to global warming and health effects. Emission regulations for diesel exhaust intended to reduce EC concentrations have been strengthened in recent years. To investigate regulation effects in Japan, daily EC concentrations in the megacity of Nagoya, central Japan, were measured during April 2003-March 2016. The EC concentrations showed a decreasing trend with changing seasonal variation: high concentrations were found in autumn and winter before 2011, but no seasonal variation was discernible after 2012. Strong correlation was found for annual vehicular EC emissions and annual mean EC concentrations during 2003-2009. However, the relation after 2010 was weaker in spring and summer. Based on the relation of EC with trace element (Pb, V, Sb, etc.) concentrations and the backward air trajectories on high concentration days, EC sources other than vehicles were found to be related to long-range transport of air pollution from China in spring and combustion of heavy oil, including ship engine exhaust, in summer.