High Concentration of Atmospheric Sub‐3 nm Particles in Polluted Environment of Eastern China: New Particle Formation and Traffic Emission

Abstract Observations of atmospheric sub‐3 nm particles are essential for understanding the initial stages of new particle formation (NPF) and the origin of aerosol particles. In this study, 3 years (2018–2020) of measurements of sub‐3 nm particles were conducted in the Yangtze River Delta (YRD) of eastern China. High concentrations of sub‐3 nm particles were observed, with number concentration in the range from 10 3 to 10 6 cm −3 . During the daytime, the sub‐3 nm particle concentration was found to peak at around the noon, indicating strong photochemical nucleation processes. The formation rates of sub‐3 nm particles were high during the NPF event days, with an average value of 86 cm −3 s −1 , and this rate was related to the sulfuric acid (SA) concentration. The particle growth rates below 3 nm were about 1–2 nm h −1 , much lower than the growth rates of larger particles. At nighttime, sub‐3 nm particle concentrations remained relatively high (3 × 10 3 to 1.2 × 10 4 cm −3 ) and were related to the NO x concentration, suggesting traffic emission to be a significant source. The sub‐3 nm proxy was developed to estimate the contributions of NPF and traffic emission. During the daytime, 74.8% and 12.4% of the sub‐3 nm particles were estimated to originate from SA‐driven NPF and traffic emissions, respectively. However, other sources were estimated to contribute 61.8% of sub‐3 nm particles at nighttime, suggesting the formation mechanisms of sub‐3 nm particles are still unclear in this environment. Our study sheds more light on the characteristics and sources of sub‐3 nm particles in polluted environments.