Hongbin Liu and ChangKyoo Yoo^*, A Robust Localized Soft Sensor for Particulate Matter Modeling in Seoul Metro Systems, Journal of Hazardous Materials(ISSN: 0304-3894, SCI, Top 5% journal), Elsevier, 305(3), pp.209-218 (2016.03) (Ack: Foundation of Nanjing Forestry University (No. 163105996) and NRF grant- MSIP- 2015R1A2A2A11001120)