Observation of new particle formation and growth events in Asian continental outflow

Abstract

This study is based on 3-year continuous measurements (January 2008–December 2010) of aerosol number size distributions recorded with a Scanning Mobility Particle Sizer (SMPS) at two regional background stations, Gosan Climate Observatory (GCO) and Korea Global Atmosphere Watch Center (KGAWC), in Korea. We identified new particle formation and growth (NPF) events by applying the Cyclostationary Empirical Orthogonal Function (CSEOF) technique to aerosol number size distributions. Based on the first mode loading vectors and the corresponding principle components in the CSEOF analysis, we classified strong, weak, and non NPF days. A strong NPF event was observed on 7.5% of days (60 days out of a total 800 days) at GCO and on 14.6% of days (140 days out of a total 958 days) at KGAWC. The maximum occurrence of strong NPF events was reported in spring at GCO, but in winter at KGAWC. Only 16 of these days were considered as simultaneous NPF events, and 7 days were identical NPF events. The airmass history analysis on simultaneous NPF days indicated the NPF events to be associated with a fast-moving cold and dry airmass from the Asian continent after the passage of a frontal system. The particle formation rate (FR) and growth rate (GR) were estimated to be 1.44 (1.20) cm−3 s−1 and 4.4 (4.7) nm h−1, respectively, at GCO and KGAWC (in parentheses). Almost identical values for the condensation sink were estimated in strong NPF (8.3 × 10−3 s−1) and non NPF (8.2 × 10−3 s−1) events at GCO, whereas the condensation sink for strong NPF days (8.5 × 10−5 s−1) was lower than that of non NPF days (1.1 × 10−2 s−1) at KGAWC. The FR, GR, condensation sink, and vapor source rate at both GCO and KGAWC were lower than those reported in polluted urban areas, but higher than those at clean sites.