Influence of Aerosol Chemical Composition on Condensation Sink Efficiency and New Particle Formation in Beijing

Abstract

Relatively high concentrations of preexisting particles, acting as a condensation sink (CS) of gaseous precursors, have been thought to suppress the occurrence of new particle formation (NPF) in urban environments, yet NPF still occurs frequently. Here, we aim to understand the factors promoting and inhibiting NPF events in urban Beijing by combining one-year-long measurements of particle number size distributions and PM 2.5 chemical composition. Our results show that indeed the CS is an important factor controlling the occurrence of NPF events, with its chemical composition affecting the efficiency of the background particles in removing gaseous H 2 SO 4 (effectiveness of the CS) driving NPF. During our observation period, the CS was found to be more effective for ammonium nitrate-rich (NH 4 NO 3 -rich) fine particles. On non-NPF event days, particles acting as CS contained a larger fraction of NH 4 NO 3 compared to NPF event days under comparable CS levels. In particular, in the CS range from 0.02 to 0.03 s –1 , the nitrate fraction was 17% on NPF event days and 26% on non-NPF event days. Overall, our results highlight the importance of considering the chemical composition of preexisting particles when estimating the CS and their role in inhibiting NPF events, especially in urban environments.

Survival probabilities of atmospheric particles: comparison based on theory, cluster population simulations, and observations in Beijing

“…Lehtipalo et al (2016) have previously shown that if the concentrations of stabilizing vapors such as dimethylamine are high, resulting in low or negligible evaporation rates, cluster-cluster collisions can have a major contribution to the growth of clusters and particles, especially if CS is low. The same has also been observed in studies utilizing cluster population simulations (Kontkanen et al, 2022).…”

“…However, it is possible that only a fraction of all the collisions lead to coagulation due to, e.g., chemical properties of the particles. This is analogous to the effectiveness of CS in removing condensable vapors such as sulfuric acid (Tuovinen et al, 2021(Tuovinen et al, , 2020, which has been shown to be higher for ammonium-nitrate-rich background particles (Du et al, 2022). If the effectiveness of CoagS for particles between 1.5 and 3 nm varies between 0.25 and 1.0, almost all of the observed J 3 /J 1.5 that are larger than predicted based on the simulations or L-2007 can be explained.…”

“…The survival probability is governed by the growth rate (GR) and loss rate of small particles and clusters (Kerminen and Kulmala, 2002;Kulmala et al, 2017). GR depends on the concentrations of condensable precursor vapors (Kulmala et al, 2005;Sihto et al, 2006;Wang et al, 2015;Stolzenburg et al, 2020) and population dynamics such as cluster-cluster collisions (Kontkanen et al, 2022). In addition, chemical reactions in the particle may affect GR (Apsokardu and Johnston, 2018;.…”

“…The formation rates will then be used to determine survival probabilities. Cluster population simulations make it possible to consider the effects of particle population dynamics on survival probabilities (Kontkanen et al, 2022). Two different sets of simulations will be conducted: first, assuming that there are no collisions between newly formed particles (i.e., particles grow only by collisions of vapor molecules) and then allowing collisions between new particles to occur.…”

Survival probabilities of atmospheric particles: comparison based on theory, cluster population simulations, and observations in Beijing

“…However, it is possible that only a fraction of all the collisions lead to coagulation due to e.g., chemical properties of the particles. This is analogous to effectiveness of CS in removing condensable vapors such as sulfuric acid (Tuovinen et al, 2021(Tuovinen et al, , 2020, which has been shown to be higher for ammonium-nitrate rich background particles (Du et al, 2022). If the effectiveness of CoagS for particles between 1.5 nm and 3 nm varies between 0.25 and 1.0, almost all the observed J3/J1.5 that are larger than predicted based on the simulations or L-2007 can be explained.…”