Ultrafine particles and pm _2.5 at three urban air monitoring stations in northern taiwan from 2011 to 2013

In this study, long term measurements of PM _2.5 and ultrafine particles (UFPs) for daily average mass concentration at Zhongshan (ZS), Sinjhuang (SJ), and Jhudong (JD) urban air monitoring stations were conducted from 2011 spring to 2013 autumn. The results showed that daily average UFPs mass concentrations in spring (average at 3 stations: 1.58 ± 0.74 μg m ^–3 ) and summer (average at 3 stations: 1.59 ± 0.53 μg m ^–3 ) were higher than those in autumn (average at 3 stations: 1.02 ± 0.28 μg m ^–3 ) and winter (average at 3 stations: 1.04 ± 0.48 μg m ^–3 ) due to the impacts by heavy traffic emission and new particle formation event. The effective density (ρeff) and dynamic shape factor (χ) for ultrafine particles (UFPs) were found to be 0.68 ± 0.16 g cm ^–3 and 2.06 ± 0.19, respectively, suggesting that the particle morphology was irregular shape. Based on the calculated ρeff and χ, the average number and surface area concentration ratio of UFPs to those of PM2.5 at these monitoring stations was determined to be 89.0 ± 5.5% and 42.1 ± 12.8%, respectively, suggesting that UFPs contribute significantly to the health-relevant PM _2.5 aerosol fraction in these stations.