Source Sensitivity of Fine Particlse at Kumamoto Central Area during Winter 2014

Abstract

Source apportionments of PM_2.5 in central Kumamoto during the winter of 2014 were evaluated based on the air quality model (CMAQ) by applying the zero-out approach. The largest source sensitivity was estimated to abroad emissions with 70% relative percentage due to the trans-boundary air pollution from East Asia during the study period, and the second largest source was the Kumamoto emissions of 20%. For nitrate and ammonium, Kumamoto dominated with 80% and 40%, respectively. From the detailed analysis of the Kumamoto emissions involving combustion, automobile, agriculture and livestock sources, the nitrate and ammonium were associated with agriculture and livestock in Kumamoto (Agri.[Ku]). A nonlinear response of nitrate was found in the emission reduction range between of 20–50%. A sensitivity analysis suggested that reduction of the Agri.[Ku] emission caused a decrease in the particulate and gaseous ammonium, and caused a decrease in the particulate nitrate and increase in nitric acid (HNO₃). These results and backward trajectory suggested that the long-range transported HNO₃ from East Asia reacted with locally emitted ammonia in central Kumamoto, and formed particulate ammonium nitrate. The results indicated that observation of HNO₃ is important for promoting our understanding of the PM_2.5 sources during the winter in Kumamoto.