Relating particle hygroscopicity and CCN activity to chemical composition during the HCCT-2010 field campaign

Z J Wu,L Poulain,D Van Pinxteren,G Spindler,K Dieckmann,A Wiedensohler,W Birmili,H Herrmann,S Henning,K Müller,M Merkel,F Stratmann

doi:10.5194/acp-13-7983-2013

Abstract

Abstract. Particle hygroscopic growth at 90% RH (relative humidity), cloud condensation nuclei (CCN) activity, and size-resolved chemical composition were concurrently measured in the Thüringer Wald mid-level mountain range in central Germany in the fall of 2010. The median hygroscopicity parameter values, κ, of 50, 75, 100, 150, 200, and 250 nm particles derived from hygroscopicity measurements are respectively 0.14, 0.14, 0.17, 0.21, 0.24, and 0.28 during the sampling period. The closure between HTDMA (Hygroscopicity Tandem Differential Mobility Analyzers)-measured (κHTDMA) and chemical composition-derived (κchem) hygroscopicity parameters was performed based on the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. Using size-averaged chemical composition, the κ values are substantially overpredicted (30 and 40% for 150 and 100 nm particles). Introducing size-resolved chemical composition substantially improved closure. We found that the evaporation of NH4NO3, which may happen in a HTDMA system, could lead to a discrepancy in predicted and measured particle hygroscopic growth. The hygroscopic parameter of the organic fraction, κorg, is positively correlated with the O : C ratio (κorg = 0.19 × (O : C) − 0.03). Such correlation is helpful to define the κorg value in the closure study. κ derived from CCN measurement was around 30% (varied with particle diameters) higher than that determined from particle hygroscopic growth measurements (here, hydrophilic mode is considered only). This difference might be explained by the surface tension effects, solution non-ideality, gas-particle partitioning of semivolatile compounds, and the partial solubility of constituents or non-dissolved particle matter. Therefore, extrapolating from HTDMA data to properties at the point of activation should be done with great care. Finally, closure study between CCNc (cloud condensation nucleus counter)-measured (κCCN) and chemical composition (κCCN, chem) was performed using CCNc-derived κ values for individual components. The results show that the κCCN can be well predicted using particle size-resolved chemical composition and the ZSR mixing rule.

Highlights

Data Systems tial Mobility Analyzers)-measured and chemical composition-derived hygroscopicity parameters was performed based on the Zdanovskii–Stokes–Robinson (ZSR) mixing rule
We found tion of atmospheric particles and cloud droplets with incomthat the evaporation of NH4NO3, which may happen in a ing shortwave radiationH, thyedpraortlioclge yhygarnosdcopic growth is Hygroscopicity Tandem Differential Mobility Analyzers (HTDMA) system, could lead to a discrepancy in predicted and measured particle hygroscopic growth
The hygroscopicity parameter (κ) will be used to examine the relationship between the measured subsaturated water uptake, the CCN activity and the water uptake predicted from the aerosol composition

Summary

Introduction

Data Systems tial Mobility Analyzers)-measured (κHTDMA) and chemical composition-derived (κchem) hygroscopicity parameters was performed based on the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. Using size-averaged chemical composition, the κ values are substantially overpredicted The hygroscopic growth and the mixing state of aerosol particles play an important roGle efoor ssecvieeranl atitfmicospheric effects such as dation, the and cdlioreuMcdt foaoedrrmoesaoltiloDenffe(ePcvatenodlnioscpelitmmaal.et,e1,n9vt9is5i;biSliltoyandeegarnad- M. Introducing size-resolved chem- Wolff, 1985; McFiggans et al, 2006). Through the interacical composition substantially improved closure. We found tion of atmospheric particles and cloud droplets with incomthat the evaporation of NH4NO3, which may happen in a ing shortwave radiationH, thyedpraortlioclge yhygarnosdcopic growth is HTDMA system, could lead to a discrepancy in predicted and measured particle hygroscopic growth. The hygroscopic parameter of the organic fraction, κorg, is positively correone tion of the budget kaenyd,pthaurasm, celtiemrEsataienr(flItuPheCnCSci,ny2g0s0tth7ee).mtSeorrmeseturinaclerratdaiina--

Methods

Results

Conclusion