High Number Concentration of Atmospheric Sub-3 nm Particles in Polluted Environment of East China: three-year Observation at SORPES Station

Atmospheric aerosols are of great concern due to their impacts on human health, visibility, and climate. Sub-3 nanometer particles are initially formed through gas-to-particle conversion with a typical size of 1-3 nm, which is crucial for understanding the steps of new particle formation and sources of aerosol particles in the atmosphere. In this study, sub-3 nm particle concentration was measured from 2018 to 2020 at SORPES station in the Yangtze River Delta, China by particle size magnifier (PSM). Based on three years’ measurement, a high number concentration of sub-3 nm particles was observed all year round. Sub-3 nm particle concentration in polluted urban environments is two orders of magnitude higher than that in clean environments, e.g., Hyytiälä. Moreover, formation rates and growth rates of sub-3 nm particles were calculated in these 3 years. The formation rate in anthropogenic pollution regions is much higher than that in the clean environment, while the growth rate is similar to other field observations. Besides the secondary formation of sub-3 nm particles via new particle formation, we found traffic primary emission is a neglectable source of sub-3 nm particles in the urban area. We estimated the contribution of traffic emission and new particle formation on sub-3 nm particle concentration using sulfuric acid and NO_x concentration as tracers. During the daytime, the contribution of traffic emissions can be over 50% on non-NPF-event days, and the contribution even comes to 13% on NPF-event days. During the nighttime, the contribution of traffic emissions can be up to 70%. Furthermore, in some conditions, synergistic effects of traffic emission and new particle formation can happen in the daytime, which causes an extremely high concentration of sub-3 nm particles. Our study also suggests that regional and global air quality models should consider traffic emissions as a primary source of sub-3 nm particles in anthropogenic pollution areas.