Comment on acp-2022-797

Abstract

Aerosol particles play important roles in air quality and global climate change. In this study, we analyzed the measurements of particle size distribution from March 12th to April 6th, 2016 in Beijing to characterize new particle formation (NPF) by using the observational data of sulfuric acid, meteorological parameters, solar radiation, and PM2.5 mass concentration. During this 26-day campaign, 11 new particle formation events were identified with obvious bursts of sub-3 nm particle number concentrations and subsequent growth of these nucleated particles. It is found that sulfuric acid concentration in Beijing did not have a significant difference between NPF and non-event days. Although the temperature during NPF days in Beijing was slightly higher than that on non-event days, temperature was not necessarily the key factor to determine NPF because higher solar radiation intensity usually increases the temperature. Low relative humidity (RH) and high daily total solar radiation appeared to be favorable to the occurrence of NPF events, which was more obvious in this campaign. A quantitative analysis indicated that more than 90 % of NPF events occur when the daily total solar radiation was greater than 19 MJ/m2/day and RH was less than 26.5 %. The PM2.5 mass concentration can also be used as a rough and simple criterion to predict the occurrence of NPF events. In addition, 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, were conducted to study the particle number concentrations and new particle formation process. Our comparisons between measurements and simulations indicate that BHN scheme and BIMN scheme significantly underestimated the observed particle number concentrations, and the THN scheme captured well the total particle number concentration on most NPF event days but failed to capture the noticeable increase in particle number concentrations on March 18th and April 1st. TIMN scheme had obvious improvement in terms of total and sub-3 nm particle number concentrations and nucleation rates. This study provides a basis for further understanding of new particle nucleation mechanism in Beijing.