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

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 x 10(3) to 1.2 x 10(4) cm(-3)) and were related to the NOx 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.