Growth of sulphuric acid nanoparticles under wet and dry conditions

Abstract

Abstract. New particle formation, which greatly influences the number concentrations and size distributions of an atmospheric aerosol, is often followed by a rapid growth of freshly formed particles. The initial growth of newly formed aerosol is the crucial process determining the fraction of nucleated particles growing to cloud condensation nuclei sizes, which have a significant influence on climate. In this study, we report the laboratory observations of the growth of nanoparticles produced by nucleation of H 2 SO 4 and water in a laminar flow tube at temperatures of 283, 293 and 303 K, under dry (a relative humidity of 1 %) and wet conditions (relative humidity of 30 %) and residence times of 30, 45, 60 and 90 s. The initial H 2 SO 4 concentration spans the range from 2 × 10 8 to 1.4 × 10 10 molecule cm −3 and the calculated wall losses of H 2 SO 4 were assumed to be diffusion limited. The detected particle number concentrations, measured by the Ultrafine Condensation Particle Counter (UCPC) and Differential Mobility Particle Sizer (DMPS), were found to depend strongly on the residence time. Hygroscopic particle growth, presented by growth factors, was found to be in good agreement with the previously reported studies. The experimental growth rates ranged from 20 nm h −1 to 890 nm h −1 at relative humidity (RH) 1 % and from 7 nm h −1 to 980 nm h −1 at RH 30 % and were found to increase significantly with the increasing concentration of H 2 SO 4 . Increases in the nucleation temperature had a slight enhancing effect on the growth rates under dry conditions. The influence of relative humidity on growth was not consistent -at lower H 2 SO 4 concentrations, the growth rates were higher under dry conditions while at H 2 SO 4 concentrations greater than 1 × 10 9 molecule cm −3 , the growth rates were higher under wet conditions. The growth rates show only a weak dependence on the residence time. The experimental observations were compared with predictions made using a numerical model, which investigates the growth of particles with three different extents of neutralization by ammonia, NH 3 : (1) pure H 2 SO 4 -H 2 O particles; (2) particles formed by ammonium bisulphate, (NH 4 )HSO 4 ; (3) particles formed by ammonium sulphate, (NH 4 ) 2 SO 4 . The highest growth rates were found for ammonium sulphate particles. Since the model accounting for the initial H 2 SO 4 concentration predicted the experimental growth rates correctly, our results suggest that the commonly presumed diffusional wall losses of H 2 SO 4 in case of long-lasting experiments are not so significant. We therefore assume that there are not only losses of H 2 SO 4 on the wall, but also a flux of H 2 SO 4 molecules from the wall into the flow tube, the effect being more profound under dry conditions and at higher temperatures of the tube wall. Based on a comparison with the atmospheric observations, our results indicate that sulphuric acid alone cannot explain the growth rates of particles formed in the atmosphere.

Temperature effects on sulfuric acid aerosol nucleation and growth: initial results from the TANGENT study

“…Our results also show that the further growth is strongly dependent on the ozone level, implying that some unknown heterogeneous reaction processes involving SO 2 and ozone on sulfuric clusters may play important roles in NPF. These results can open a new research avenue for future studies to create a better understanding of the roles of heterogeneous reactions involving nanoparticles and the effects of SO 2 on the nanoparticle growth (Stangl et al, 2019). At present, it is not known why NPF takes place with high frequency and strong magnitude in extremely polluted megacities in China under the conditions with exceedingly high loadings of preexisting aerosol particles (Guo et al, 2014;Yao et al, 2018;Yu et al, 2017b;Lee et al, 2019).…”

“…FT-1 and FT-2 were coupled with an 0.2 m stainless steel tube with additional inlet ports for injection of ozone, zero air and SO 2 . The growth tube was described by Krasnomowitz et al (2019) and Stangl et al (2019). The growth tube consists of a 1.52 m long and 0.2 m inner diameter fused quartz tube fitted with stainless steel funnels on each end that reduce the inner diameter down to 0.051 m. The total volume of the tube and entrance and exit funnels is 52.4 L, giving a surface-to-volume ratio of 0.24 cm −1 .…”

“…Laboratory experiments of growth rates (GRs) of newly nucleated particles are even more sparse. Skrabalova et al (2014) studied GRs of newly formed particles in a flow tube at temperatures between 283 to 303 K and RH of 1 % and 30 %, designated as "dry" and "wet" conditions, respectively. [H 2 SO 4 ] was varied between 2 × 10 8 and 1.4 × 10 10 cm −3 .…”

Laboratory observations of temperature and humidity dependencies of nucleation and growth rates of sub‐3 nm particles

“…If considering the diffusional loss of H 2 SO 4 to the wall was 55-80% for the given residence time, H 2 SO 4 loss onto particles was neglected in further analysis of this study. The same treatment was made in recent nucleation flow tube studies like Young et al [2008], Skrabalova et al [2014], Neitola et al [2015], and Brus et al [2016].…”

Temperature-Dependent Diffusion of H2SO4 in Air at Atmospherically Relevant Conditions: Laboratory Measurements Using Laminar Flow Technique

“…The experimental setup used in this study was described in detail in our previous work [23,24] and therefore only a brief description is given here. All experiments were conducted at Finnish Meteorological Institute in Helsinki, and thus all above mentioned major sources of atmospheric amines are in the vicinity of the laboratory.…”