Key Features of New Particle Formation Events at Background Sites in China

Long-term continuous measurements of particle number size distributions with mobility diameter sizes ranging from 3 to 800 nm were performed to study new particle formation (NPF) events at Shangdianzi (SDZ), Mt. Tai (TS), and Lin'an (LAN) stations representing the background atmospheric conditions in the North China Plain (NCP), Central East China (CEC), and Yangtze River Delta (YRD) regions, respectively. The mean formation rate of 3-nm particles was 6.3, 3.7, and 5.8 cm-3 s-1, and the mean particle growth rate was 3.6, 6.0, and 6.2 nm h-1at SDZ, TS, and LAN, respectively. The NPF event characteristics at the three sites indicate that there may be a stronger source of low volatile vapors and higher condensational sink of pre-existing particles in the YRD region. The formation rate of NPF events at these sites, as well as the condensation sink, is approximately 10 times higher than some results reported at rural/urban sites in western countries. However, the growth rates appear to be 1-2 times higher. Approximately 12%-17% of all NPF events with nucleated particles grow to a climate relevant size (>50 nm). These kinds of NPF events were normally observed with higher growth rate than the other NPF cases. Generally, the cloud condensation nuclei (CCN) number concentration can be enhanced by approximately a factor of 2-6 on these event days. The mean value of the enhancement factor is lowest at LAN (2-3) and highest at SDZ ( 4). NPF events have also been found to have greater impact on CCN production in China at the regional scale than in the other background sites worldwide. Based on the long-term measurement of NPF event at SDZ station (8-year dataset), it was found the first factor in determining the NPF occurrence was the condensation sink, and the second factor could be the concentration level of precursor vapors participating in the NPF event (e.g., sulfuric acid). Some emission control strategies applied in China will reduce the condensation sink, which is favorable for NPF event.