Investigation Of The Features Of Atmospheric New Particle Formation Events In Nanjing

New particle formation(NPF)is an important source of secondary aerosols in the atmosphere.We carried out field studies(at Nanjing University of Information Science&Technology in spring and winter during 2014 to 2015,and at Gucheng Lake ecological observation station of Gaochun from September to November of the field observation experiment for a period of 3 months in Nanjing),and analyzed and discussed the nucleation and growth the event into the atmosphere below 3 um particles,and calculated the nucleation rate and growth rate,got the intensity of new particle formation events.The seasonal and diurnal variations of the polluted urban atmosphere and the clean atmosphere environment are analyzed,and the promoting factors and limiting factors of the new particle formation events are studied.The conclusions are as follows:Field study at representation Nanjing northern suburban site(Nanjing University of Information Science&Technology):(1)Sub-3 nm nucleation event,occurred on 25 out of total 59 observation days,but only 9 times new particles can grow to cloud condensation nuclei(CCN)-active sizes.In winter and spring with relatively heavy pollution,the gaseous precursor concentration is high enough,there is no limit to below 3 nm particle nucleation.As long as the weather conditions are met,such as the lower condensation sink,temperature and relative humidity,the higher solar radiation intensity,the nucleation event occurs immediately.However the concentration of gaseous precursor may once again become a limiting factor of particles of sub-3 run growing to CCN-active sizes.(2)Initial J1.4 at the onset and peak J1.4 at the noontime could be up to 2.1×102 cm-3s-1 and 2.5×103 cm-3s-1,respectively,during the seven nucleation events selected from different seasons.Time-dependent J1.4 usually showed good linear correlations with a sulfuric acid proxy for every single event.However,due to changes in temperature or seasons,the total correlation between J1.4 and H2SO4 concentrations decreased in all event days.New particle growth rate(GR)did not increase monotonically with particle size,but had a local maximum up to 25 nm h-1 between 1 and 3 um.Field study at representation Nanjing clean city.atmospheric conditions(Gucheng Lake Ecological Observation Station of Gaochun in Nanjing):(1)During September,October and November a total of 28 times new particles formation events have been observed.The average condensation sink of events in these three months were 0.019 S-1,0.022 S-1 and 0.022 S-1.All of the new particle formation events,it seems to maintained high UV*SO2 value and relatively low CS value,which indicates that higher concentrations of gaseous sulfuric acid and low condensation sink help new particle formation events.(2)The average value of J3 in Septemberthe was higher than in October,the highest J3 was 84.22 cm-3s-1.In October the maximum of J1.38 can reach 98.21 cm-3s-1,with the increase of particle size,the value of J decreased rapidly,the J3 is about 28%of J1.38;the formation rate of new particles at 10 nm particle size is about only 8%of J1.38,indicating that there is a strong competition between the new particle growth process and collision.By comparison,the nucleation rate of particle of sub-3 nm in the polluted atmosphere environment is much larger than that of the clean atmosphere environment.In the clean atmosphere of Nanjing,there is no subsequent growth of high intensity after nucleation particles,probably due to the concentration of gaseous substances contribute to the subsequent growth of new particles is too low.