Aerosol spectra and new particle formation observed in various seasons in Nanjing

The aerosol number spectrum and gas pollutants were measured and the new particle formation (NPF) events were discussed in Nanjing. The results showed that the size distributions of aerosol number concentrations exhibited distinct seasonal variations, implying the relations of particle sizes and their sources and sinks. The number concentrations of particles in the nuclei mode (10-30 nm), Aitken mode (30-100 nm), accumulation mode (100-1000 nm) and coarse mode (1 m) varied in the order of summer spring autumn, summer autumn spring, autumn summer spring, and spring autumn summer, respectively. The diurnal variation of total aerosol number concentrations showed three peaks in all observed periods, which corresponded to two rush hours and the photochemistry period at noon. In general, the NPF in summer occurred under the conditions of east winds and dominant air masses originating from marine areas with high relative humidity (50%-70%) and strong solar radiations (400-700 W m-2). In spring, the NPF were generally accompanied by low relative humidity (14%-30%) and strong solar radiations (400-600 W m-2). The new particle growth rates (GR) were higher in the summertime in the range of 10-16 nm h-1. In spring, the GR were 6.8-8.3 nm h-1. Under polluted air conditions, NPF events were seldom captured in autumn in Nanjing. During NPF periods, positive correlations between 10-30 nm particles and O3 were detected, particularly in spring, indicating that NPF can be attributed to photochemical reactions.