Variation of size-segregated particle number concentrations in winter Beijing

Abstract. Aerosol number concentration varying spatially and temporally is a good indicator of the dynamic behavior of Beijing's atmospheric cocktail. This variation represents the strength of different contributing primary and secondary sources such as traffic and new particle formation, respectively. In this paper we report size-segregated particle number concentrations observed at newly developed Beijing station during winter 2018. Our measurements cover number size distributions of particles in a diameter range between 1.5 nm and 1 μm (cluster mode, nucleation mode, Aitken mode and accumulation mode), thus being descriptive of a major fraction of the processes happening in the atmosphere of Beijing. Here we aim to explain the concentration variation in the observed modes by relating them to potential aerosol sources as well as to understand the connection between the modes. We focused on two types of days (haze and new particle formation) and divided the data accordingly. Our results show that during new particle formation (NPF) days, an increase in the cluster mode particles was observed. In contrast, during haze days we observed a high concentration of accumulation mode particles. There was a clear correlation between the cluster and nucleation modes during NPF days, while it was absent during haze days. In addition, we correlated the different modes with concentrations of trace gases and other parameters measured at our station. Our results show that all modes in the sub-micron size range correlated with NO x which clearly reflects the contribution of traffic to all particle sizes.