Cloud condensation nuclei activity, droplet growth kinetics, and hygroscopicity of biogenic and anthropogenic secondary organic aerosol (SOA)

D F Zhao,Th F Mentel,J M Flores,R Tillmann,A Kiendler-Scharr,F Rubach,Å K Watne,I Kourtchev,M Hallquist,H Fuchs,Y Rudich,P Schlag,K Kristensen,M Kalberer,A M K Hansen,M Glasius,B Kortner,A Buchholz,A Wahner

doi:10.5194/acp-16-1105-2016

Abstract

Abstract. Interaction of biogenic volatile organic compounds (VOCs) with Anthropogenic VOC (AVOC) affects the physicochemical properties of secondary organic aerosol (SOA). We investigated cloud droplet activation (CCN activity), droplet growth kinetics, and hygroscopicity of mixed anthropogenic and biogenic SOA (ABSOA) compared to pure biogenic SOA (BSOA) and pure anthropogenic SOA (ASOA). Selected monoterpenes and aromatics were used as representative precursors of BSOA and ASOA, respectively.We found that BSOA, ASOA, and ABSOA had similar CCN activity despite the higher oxygen to carbon ratio (O/C) of ASOA compared to BSOA and ABSOA. For individual reaction systems, CCN activity increased with the degree of oxidation. Yet, when considering all different types of SOA together, the hygroscopicity parameter, κCCN, did not correlate with O/C. Droplet growth kinetics of BSOA, ASOA, and ABSOA were comparable to that of (NH4)2SO4, which indicates that there was no delay in the water uptake for these SOA in supersaturated conditions.In contrast to CCN activity, the hygroscopicity parameter from a hygroscopic tandem differential mobility analyzer (HTDMA) measurement, κHTDMA, of ASOA was distinctively higher (0.09–0.10) than that of BSOA (0.03–0.06), which was attributed to the higher degree of oxidation of ASOA. The ASOA components in mixed ABSOA enhanced aerosol hygroscopicity. Changing the ASOA fraction by adding biogenic VOC (BVOC) to ASOA or vice versa (AVOC to BSOA) changed the hygroscopicity of aerosol, in line with the change in the degree of oxidation of aerosol. However, the hygroscopicity of ABSOA cannot be described by a simple linear combination of pure BSOA and ASOA systems. This indicates that additional processes, possibly oligomerization, affected the hygroscopicity.Closure analysis of CCN and HTDMA data showed κHTDMA was lower than κCCN by 30–70 %. Better closure was achieved for ASOA compared to BSOA. This discrepancy can be attributed to several reasons. ASOA seemed to have higher solubility in subsaturated conditions and/or higher surface tension at the activation point than that of BSOA.

Highlights

Secondary organic aerosol (SOA) is an important class of atmospheric aerosol with impacts on air quality, human health, and climate change
Recent studies suggested that interactions between biogenic volatile organic compounds (VOCs) and anthropogenic emissions can enhance secondary organic aerosol (SOA) formation and often, ambient OA concentrations correlate with anthropogenic tracers such as CO or isopropyl nitrate
We investigated the effect of the interaction of anthropogenic SOA (ASOA) and biogenic SOA (BSOA) on CCN activity and hygroscopicity of aerosol

Summary

Introduction

Secondary organic aerosol (SOA) is an important class of atmospheric aerosol with impacts on air quality, human health, and climate change 14C carbon isotopic analysis showed that the SOA material itself is composed mostly of modern carbon, i.e., arises from biogenic sources, including biomass burning (Weber et al, 2007; Zotter et al, 2014). These observations suggest that a consideration of an anthropogenic enhancement can reduce the discrepancies between models and observations (de Gouw et al, 2005; Goldstein et al, 2009; Hoyle et al, 2011; Worton et al, 2011; Glasius et al, 2011)

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Conclusion