Errors in nanoparticle growth rates inferred from measurements in chemically reacting aerosol systems

Abstract

Abstract. In systems in which aerosols are being formed by chemical transformations, individual particles grow due to the addition of molecular species. Efforts to improve our understanding of particle growth often focus on attempts to reconcile observed growth rates with values calculated from models. However, because it is typically not possible to measure the growth rates of individual particles in chemically reacting systems, they must be inferred from measurements of aerosol properties such as size distributions, particle number concentrations, etc. This work discusses errors in growth rates obtained using methods that are commonly employed for analyzing atmospheric data. We analyze "data" obtained by simulating the formation of aerosols in a system in which a single chemical species is formed at a constant rate, R. We show that the maximum overestimation error in measured growth rates occurs for collision-controlled nucleation in a single-component system in the absence of a preexisting aerosol, wall losses, evaporation or dilution, as this leads to the highest concentrations of nucleated particles. Those high concentrations lead to high coagulation rates that cause the nucleation mode to grow faster than would be caused by vapor condensation alone. We also show that preexisting particles, when coupled with evaporation, can significantly decrease the concentration of nucleated particles. This can lead to decreased discrepancies between measured growth rate and true growth rate by reducing coagulation among nucleated particles. However, as particle sink processes become stronger, measured growth rates can potentially be lower than true particle growth rates. We briefly discuss nucleation scenarios in which the observed growth rate approaches zero while the true growth rate does not.

Enhanced growth rate of atmospheric particles from sulfuric acid

“…As all of our growth rate measurements, independent of the ammonia concentration and temperature, fall on the same line (see Fig. 1), this also points towards negligible evaporation effects at reduced ammonia levels (below 10 pptv) and up to 20 • C. don dispersion forces (London, 1937). The magnitude of the enhancement is described by the Hamaker constant A (Hamaker, 1937), which we use as the single free parameter to fit a collision-enhanced kinetic limit.…”

Enhanced growth rate of atmospheric particles from sulfuric acid

“…Moreover, the insignificant effect of ammonia on growth ( Fig. 1) and the same high ratio (>100) between sulfuric acid monomer and dimer concentrations for all experiments, point towards a negligible clustering effect, which could have influenced our measured growth rates (Li and McMurry, 2018). Additionally, in Fig.…”

“…evaporation rates from the monomer onwards are zero (Jen et al, 2014;Kürten et al, 2014;Olenius et al, 2013). In this case, cluster coagulation also plays an important role in the growth process due to the strong clustering behaviour of sulfuric acid and amines (Kontkanen et al, 2016;Lehtipalo et al, 2016;Li and https://doi.org/10.5194/acp-2019-755 Preprint. Discussion started: 15 November 2019 c Author(s) 2019.…”

Estimating the influence of transport on aerosol size distributions during new particle formation events

“…The aerosol size distributions on a total of 38 days were recorded during the campaign, while the rest of the data were missing because of the instability of the electricity supply or the malfunction of the local hydropower station. A particle size distribution (PSD) system including two scanning mobility particle spectrometers (SMPSs) covering different size range and one aerodynamic particle sizer (APS, TSI 3321) was used to measure particles ranging from 3 nm to 10 µm (Liu et al, 2016). The sub-3 nm aerosol size distributions were measured using a prototype diethylene glycol SMPS (DEG-SMPS, Jiang et al, 2011;Cai et al, 2017a) and a commercialized particle size magnifier (PSM, Airmodus A11).…”