Formation and growth of sub-3-nm aerosol particles in experimental chambers

Abstract

Atmospheric new particle formation (NPF), which is observed in many environments globally, is an important source of boundary-layer aerosol particles and cloud condensation nuclei, which affect both the climate and human health. To better understand the mechanisms behind NPF, chamber experiments can be used to simulate this phenomenon under wellcontrolled conditions. Recent advancements in instrumentation have made it possible to directly detect the first steps of NPF of molecular clusters (~1-2 nm in diameter) and to calculate quantities such as the formation and growth rates of these clusters. Whereas previous studies reported particle formation rates as the flux of particles across a specified particle diameter or calculated them from measurements of larger particle sizes, this protocol outlines methods to directly quantify particle dynamics for cluster sizes. Here, we describe the instrumentation and analysis methods needed to quantify particle dynamics during NPF of sub-3-nm aerosol particles in chamber experiments. The methods described in this protocol can be used to make results from different chamber experiments comparable. The experimental setup, collection and post-processing of the data, and thus completion of this protocol, take from months up to years, depending on the chamber facility, experimental plan and level of expertise. Use of this protocol requires engineering capabilities and expertise in data analysis.

PyCHAM (v1.3.4): a Python box model for simulating aerosol chambers

“…This characteristic is consistent with observations of new particle formation (Riccobono et al, 2014;Dada et al, 2020;Wang et al, 2020).…”

“…The simulation of nucleation to produce newly-formed suspended particles is one of the most active areas of ongoing atmospheric research and many important advances in observing the nucleation process have been, and will continue to be, made through appropriate measurements in chamber experiments and their interpretation (Dada et al, 2020). PyCHAM is not intended to interpret and examine chamber experiments designed to resolve the mechanisms involved in molecular clustering,…”

Molecular understanding of new-particle formation from α-pinene between −50 and +25 °C

“…Due to very low particle concentrations in the chamber, the data are close to the lower detection limit of the measurable formation rates. Both factors lead to a higher uncertainty in the nucleation rate calculation (Dada et al, 2020).…”

Retrieval of process rate parameters in the general dynamic equation for aerosols using Bayesian state estimation

“…Most of the research dealing with NPF event analysis has used similar methodology as outlined in the 'protocol' described by Kulmala et al (2012); Dada et al (2020). Particle formation rates, at the detection limit of the instrument (typically in the range 2-3 nm), are usually estimated from the time evolution of either the total number concentration or the number concentration below a certain size (for example 20 nm), correcting for coagulation loss and condensation growth with very simple and approximate balance equations.…”

“…Methods 1 and 2 are applicable to cases, in which there is a clear nucleation mode growing, as is the case, for example, for the multitude of events analyzed from the Hyytiälä forest station in Finland Maso et al (2005). For chamber experiments, where the aerosol size distribution approaches steady state Dada et al (2020), these two approaches cannot be used. Method 3 can then be applied to the transition stage of the dynamics, before steady-state is reached.…”