Study On New Particle Formation,growth And Precursors At Coastal Sites In Qingdao

As an important source of atmospheric aerosol and atmospheric cloud condensation nuclei(CCN)number concentration,the New Particle Formation(NPF)has potential effects on earth’s radiation balance.The NPF events is generally divided into two stages,firstly,the gaseous precursors condensate and form clusters of about 1 nm,and then grow to a larger size(>2～3 nm)through condensation and coagulation,etc.The NPF events depend on the competition between gaseous sources and condensing sinks.The frequent NPF events have been observed in diverse atmospheric environments,resulting in differences in their characteristics of nucleation,growth and physicochemical processes.As the junction of land and marine atmospheres,the interaction of abundant anthropogenic pollutants and precursors released by marine organisms jointly affects the formation and growth of new particles in coastal areas.In this study,two field observations were conducted based on different altitudes sites in the coastal area of Qingdao.The atmospheric particle number size distributions,which were measured by a Wide-range Particle Size Spectrometer(WPS),a Scanning Mobility Particle Size Spectrometer(SMPS)and Neutral cluster and Air Ion Spectrometer(NAIS),combined with meteorological parameters,backward trajectories,the inorganic and organic gaseous precursors and particulate chemical compositions,were used to analyze the NPF events in different seasons and explore the influences of gaseous precursors on NPF events and the potential climatic effects at different altitudes.The particle number size distributions and the characteristics of NPF events showed the seasonal differences in the coastal ground site of Qingdao.During the observation period,the mean values of the atmospheric total particle number concentrations in spring,summer(except July 20,2019),autumn and winter were(1.3±0.7)×104,(1.7±2.9)×104,(1.1±0.6)×104 and(1.2±3.5)×104 molecules cm-3,respectively.The particle number concentration in summer was 1.3～1.5 folds higher than other seasons.The annual averages frequency of NPF events was 25.3%,with the highest frequency occurred in spring(61%),followed by autumn(47%),winter(24%)and summer(12%).In addition,the NPF events can decreased the peak of the size spectrum from 55～100 nm to 34～66 nm,and increased the particle number concentration by 1.1～1.8 times.And the increase of the particle number concentration is most significant in summer.Furthermore,the studies have shown that the low relative humidity(RH),low condensation sink and the influence of continental air masses tend to favor the occurrence of NPF events.In summer,the lowest NPF events frequency was related to the humid marine air masses and lower concentrations of gaseous precursors(i.e.,SO2),while the strong atmospheric oxidization capacity was in favor of particle formation and growth,resulting the higher]apparent formation rate and growth rate than other seasons.In winter,high concentrations of SO2,usually accompanied by high condensation sinks,was unfavorable to NPF events.Seasonal differences of the effects of anthropogenic volatile organic compounds(AVOCs)such as benzene,toluene,acetylene and biogenic volatile organic compounds(BVOCs)such as isoprene on the NPF events were captured.In summer,the concentrations of AVOCs decreased with the increase of the apparent formation rate(FR),suggesting that AVOCs may inhibit the NPF events,while isoprene might promote the NPF events,which is related to the stronger biological activity.In winter,the correlation results suggest that AVOCs and BVOCs have a weaker effect on NPF events.In the coastal mountain areas of Qingdao(Mt.Lao),the frequency of NPF events was 21.2%,and the high RH caused by frequent fog and rainy inhibited NPF events.The concentration of gaseous sulfuric acid([H2SO4])was(0.9～3.8)×107 cm-3 during NPF events,which could contribute to the growth of particles((12.3～62.9)%).The concentrations of H2SO4 was consistent with the initial growth of particles of 3～6 nm,indicating that the[H2SO4]generated by SO2 oxidation could promote the NPF event at Mt.Lao.On the dust day,NPF events occurred associating with the higher formation rate,and the higher concentration of "source",i.e.,abundant SO2 gaseous precursors,was the key factor to promote the NPF events during the such high background aerosol loading condition.And the particles could grow to larger sizes in dust day,indicating that dust may increase the probability of new particles activated into CCN.In addition,the diverse growth stages of NPF events lead to different potential climate effects of new particles.For example,in the coastal areas of Qingdao,44%～62%of NPF events can directly grow to larger than 50 nm(CCN sizes).The net increase in the NPF-derived CCN number concentration is(3.4～7.4)×103 cm-3,and the survival probability of growing to the CCN size range(SP)is(25.8～49.1)%,and the seasonal difference of above paramcters were higher in summer and winter than in spring and autumn.The strong photochemical reactions at ground site in summer and the abundant gaseous sulfuric acid in spring at Mt.Lao can promote new particles continue grow to CCN sizes.In other seasons,some NPF events need to undergo two-stage growth to reach CCN size.The first-stage growth occurred in daytime and the second-stage observed at nighttime.At ground site in winter and mountain site in spring,the NH4NO3 was the key species in the growth of new particles to CCN sizes.This study conducted depth research on the characteristics of new particle formation and growth in the coastal area of Qingdao,and provided the data support for the impact of gaseous precursors on NPF events and the potential climate effects of new particles.To a certain extent,it makes up for the lack of long-term observation of NPF events in the eastern coastal areas,and has certain scientific significance.