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

Abstract. Atmospheric new particle formation (NPF) events are regularly observed in

urban Beijing, despite high concentrations of background particles which,

based on theory, should inhibit NPF due to high values of coagulation sink

(CoagS). The survival probability, which depends on both CoagS and particle

growth rate (GR), is a key parameter in determining the occurrence of NPF events

as it describes the fraction of newly formed particles that survive from a

smaller diameter to a larger diameter. In this study, we investigate and

compare survival probabilities from 1.5 to 3 nm (J3/J1.5), from 3 to

6 nm (J6/J3), and from 6 to 10 nm (J10/J6) based on analytical

formulae, cluster population simulations, and atmospheric observations from

Beijing. We find that survival probabilities based on the cluster population

simulations and one of the analytical formulae are in a good agreement.

However, at low ratios between the background condensation sink (CS) and GR,

and at high concentrations of sub-3 nm clusters, cluster–cluster collisions

efficiently lower survival probabilities in the cluster population

simulations. Due to the large concentrations of clusters and small particles

required to considerably affect the survival probabilities, we consider it

unlikely that cluster–cluster collisions significantly affect atmospheric

survival probabilities. The values of J10/J6 observed in Beijing show

high variability, most likely due to influences of primary particle

emissions, but are on average in relatively good agreement with the values

based on the simulations and the analytical formulae. The observed values of

J6/J3 are mostly lower than those predicted based on the simulations

and the analytical formulae, which could be explained by uncertainties in CS

and GR. The observed values of J3/J1.5 at high CS / GR are much higher

than predicted based on the simulations and the analytical formulae. We argue

that uncertainties in GR or CS are unlikely to solely explain the observed

values of J3/J1.5 under high CS conditions. Thus, further work is

needed to better understand the factors influencing survival probabilities

of sub-3 nm atmospheric particles in polluted environments.