Particle number size distributions and formation and growth rates of different new particle formation types of a megacity in China

To understand the contribution of new particle formation (NPF) events to ambient fine par ticle pollution,measurements of particle size distributions,trace gases and meteorologica conditions,were conducted at a suburban site (NJU) from October to December 2016 and a an industrial site (NUIST) from September to November 2015 in Nanjing.According to the temporal evolution of the particle size distributions,three types NPF events were observed typical NPF (Type A),moderate NPF events (Type B) and strong NPF (Type C) events.The fa vorable conditions for Type A events included low relative humidity,low concentration o pre-existing particles,and high solar radiation.The favorable conditions of Type B events were similar to Type A,except for a higher concentration of pre-existing particles.Type C events were more likely to happen with the higher relative humidity,lower solar radiation and continuous growth of pre-existing particle concentration.The formation rate of 3 nm(J3) was the lowest for Type A events and highest for Type C events.In contrast,the growth rates of 10 nm and 40 nm particles were the highest for Type A,and lowest for Type C.Re sults show that NPF events with only higher J3would lead to the accumulation of nucleation mode particles.Sulfuric acid was important for the formation of particles but had little effec on the growth of particle size.