Aerosol Size Distribution And New Particle Formation In Yangtze River Delta Of East China:Measurements And Simulations

Atmospheric aerosols receive lots of attentions because of their climate and environmental(health)effects.New particle formation(NPF),as one of important initial processes of secondary aerosols,occurs under various environmental conditions.The particle's nucleation and their subsequent growth can affect the climate by contributing almost 50%of global cloud condensation nuclei.Based on the measurements at SORPES(The Station for Observing Regional Processes of the Earth System)station,together with MALTE-BOX(The model to predict new aerosol formation in the lower troposphere-box model)model,the aerosol size distribution and new particle formation in western part of Yangtze River Delta(YRD)were studied.The averaged(± standard deviation)number concentration of 6-800 nm particles was 19200 ± 9200 cm-3,with 5300 ± 5500 cm-3 in the nucleation mode(6-30 nm),8000 ± 4400 cm-3 in the Aitken mode(30-100 nm)and 5800 ± 3200 cm-3 in the accumulation mode(100-800 nm).In winter the averaged diurnal pattern of the aerosol size distributions was affected by direct emissions while in spring,summer and autumn it was dominated by new particle formation.At SORPES station,the new particle formation events were observed on 44%of the analyzed days with the highest frequency in spring,followed by summer and autumn but only 11%in winter.A higher temperature,radiation intensity and O3 concentration together with a lower relatively humidity(RH),PM2.5 and condensation sink(CS)tended to favor the occurrence of new particle formation events.The averaged(± standard deviation)formation rates of 6 nm particles were 3.6 ± 2.4,2.1 ±1.4,2.1 ± 1.9 and 1.8 ±1.6 cm-3s-1 in spring,summer,autumn and winter,respectively,and the corresponding particle growth rates were 10.0 ± 3.4,12.8 ± 4.4,8.9 ± 2.9,9.5± 3.3 nm/h,respectively.The particle formation rate was negatively correlated with RH and positively correlated with radiation and O3 while particle growth rate was positively correlated with temperature,RH,radiation,O3 and CS.As the ion formation rate at 6 nm is only 7%of total particle formation rate,the ion induced nucleation played weak roles in new particle formation in YRD.The origins of air mass were found not only influence the aerosol size distribution,but also the new particle formation.The coastal air masses had the lowest concentrations of accumulation mode particles but relatively high concentrations of nucleation mode particles,continental air masses had the highest concentrations of nucleation mode particles with frequent NPF,and YRD air masses had the highest concentrations of accumulation mode particles but lowest concentration of nucleation mode particle and lowest frequency of NPF because of the elevated coagulation/condensation sinks.Comparing the footprint of air masses during NPF days with high and low formation rate or growth rate,we found that YRD air masses can suppress the particle formation but promote the growth of newly formed particles.When the air masses were from southern China with abundance of monoterpene emissions,a class of NPF,which occurred within one hour after sunrise(defined as Early-morning NPF),was observed at SORPES.The oxidation of monoterpene was demonstrated to play an important role in inducing this kind of Early-morning NPF and high pre-existing particles,in contrast,would postpone the start-time of NPF.The sensitive tests by MALTE-BOX model showed that the start-time of NPF was more sensitive to monoterpene concentration than SO2 concentration.Higher particle formation rates prefer occurring with high monoterpene concentrations but low PM2.5 concentrations.In case of the increase of biogenic volatile organic compounds emission under the context of global warming and the reduction of PM2.5 due to the control of government,a more important contribution of monoterpene oxidation to NPF is expected in the future in the urban regions around the world.The new particle formation in boreal forest of Finland(SMEAR ? station)and YRD aera(SORPES station)was simulated by MALTE-BOX model sperately.Compared with measurements,MALTE-BOX can simulate the sulfuric acid,highly oxidized multi-functional compounds(HOMs)and also the aerosol size distributions(Note:the comparisons of sulfuric acid and HOMs were conducted at SMEAR ?station and the aerosol size distributions were done at both stations.).Comparing the simulation results at two stations,the concentrations of sulfuric acid,HOMs monomers and HOMs nitrates at SORPES were obviously higher than at SMEAR ?while the HOMs dimers concentrations were lower than at SMEAR ?.In YRD area,the kinetic coefficients of nucleation showed more discrepancies than in boreal forest in Finland,which means the more complicated and various nucleation mechanism in urban aera like YRD.Comparing the relative contributions of sulfuric acid and HOMs to the growth of 1-100 nm particle at two stations,in YRD area sulfuric acid and HOMs nitrates contributed more to the growth while HOMs dimers played a weak role in growth.