Analysis And Numerical Simulation Of New Particle Generation Conditions In Typical Cities In Eastern Chin

In recent years,with the development of urbanization,atmospheric aerosols have attracted people’s attention due to their climate and environmental effects.New particle formation（NPF）is one of the important physical and chemical processes of aerosol particles,which not only has a significant impact on air quality,but also plays a crucial role in weather and climate change.Therefore,studying the conditional characteristics of NPF and changes in aerosol particle size distribution and number concentrations is essential for further understanding the environmental and climatic effects of NPF events.In this study,we first analyzed the quantitative characteristics of meteorological and solar radiation conditions for NPF events in Beijing from March to April 2016,in Shanghai from November 2013 to January 2014,and in Guangzhou from December 2019 to March 2020.The study found that low relative humidity,low PM_2.5 mass concentration,and high solar radiation seem to favor the occurrence of NPF events and an increase in particle number concentration.During the period,the average condensation sink（CS）in Beijing is 0.04 s^-1.Besides,there are significant differences in meteorological and solar radiation conditions between NPF and non-event days in Beijing.When the daily total solar radiation is greater than 19 MJ/m²/day and RH is less than 26.5%,there are 11 days,including 10 out of 11 NPF days,and NPF events account for 91%.Based on observations at different times in Beijing,it is found that if the precursor gas concentration is enough for new particle formation,there is a high probability of NPF events occurring as long as the relative humidity and solar radiation reach a certain threshold.The suitable relative humidity and solar radiation for NPF events in Beijing also show seasonal characteristics.In Shanghai,there are 17 days when the daily total solar radiation is greater than or equal to 10.94 MJ/m²/day and the relative humidity is less than or equal to 46%,including10 NPF event days,accounting for 58.8%.In addition,the average CS on 7 non-event days(0.088 s^-1)is higher than that on NPF days(0.066 s^-1),and high CS may affect new particle formation in these non-event days.There are many non-event days in Shanghai and Guangzhou with similar background conditions to NPF event days.Even if these meteorological conditions reach a certain threshold in Shanghai and Guangzhou,there is still a high possibility that NPF would not occur.In the NPF events,the aerosol number concentration increases rapidly.The simulations using four nucleation schemes,i.e.,H₂SO₄-H₂O binary homogeneous nucleation（BHN）,H₂SO₄-H₂O-NH₃ ternary homogeneous nucleation（THN）,H₂SO₄-H₂O-ion binary ion-mediated nucleation（BIMN）,and H₂SO₄-H₂O-NH₃-ion ternary ion-mediated nucleation（TIMN）,based on a global chemistry transport model（GEOS-Chem）coupled with an advanced particle microphysics（APM）model,are conducted to study new particle formation process and evaluate the model.The BHN scheme and BIMN scheme significantly underestimate the observed particle number concentrations,and the THN scheme captures well the total particle number concentration on most NPF event days but fails to capture the noticeable increase in particle number concentrations on March 18th and April 1st in Beijing.TIMN scheme has obvious improvement in terms of total and sub-3 nm particle number concentrations and nucleation rates,but the predicted NPF event on March 28th is not found.Besides,the simulated particle number concentrations based on TIMN on March 27th and April 1st are also underestimated.Overall,TIMN agree better than other nucleation schemes used in this study.Nevertheless,in real atmosphere,there is probably more than one nucleation mechanisms occurring in some cases.We acknowledge that it is possible H₂SO₄-amine and H₂SO₄-organics nucleations may also simultaneously contribute to NPF in polluted urban areas,which needs further study in the future.In Shanghai and Guangzhou,the four nucleation mechanism schemes could not capture the increase of particle number concentrations on most NPF days.Because of the differences in geographical location and environment,the nucleation mechanisms in different cities might be different,so more nucleation mechanism schemes could be considered for further discussion to optimize simulated particle number concentration.