Aerosol analysis using a Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS): a new approach to study processing of organic aerosols

R Holzinger,T Röckmann,N M Donahue,J Lelieveld,F Herrmann,J Williams

doi:10.5194/acp-10-2257-2010

Abstract

Abstract. We present a novel analytical approach to measure the chemical composition of organic aerosol. The new instrument combines proton-transfer-reaction mass-spectrometry (PTR-MS) with a collection-thermal-desorption aerosol sampling technique. For secondary organic aerosol produced from the reaction of ozone with isoprenoids in a laboratory reactor, the TD-PTR-MS instrument detected typically 80% of the mass that was measured with a scanning mobility particle sizer (SMPS). The first field deployment of the instrument was the EUCAARI-IOP campaign at the CESAR tall tower site in the Netherlands. For masses with low background values (~30% of all masses) the detection limit of aerosol compounds was below 0.2 ng/m3 which corresponds to a sampled compound mass of 35 pg. Comparison of thermograms from ambient samples and from chamber-derived secondary organic aerosol shows that, in general, organic compounds from ambient aerosol samples desorb at much higher temperatures than chamber samples. This suggests that chamber aerosol is not a good surrogate for ambient aerosol and therefore caution is advised when extrapolating results from chamber experiments to ambient conditions.

Highlights

Organic aerosol (OA) sources in the global atmosphere are enormously uncertain
A compilation of aerosol mass spectrometer (AMS) field observations in the northern hemisphere shows that approximately 95% of the OA mass in the remote continental boundary layer has a characteristic electron-impact ionization mass spectrum dubbed “oxidized organic aerosol” (OOA), with urban environments containing about 67% OOA (Zhang et al, 2007)
We report first results obtained from chamber produced secondary organic aerosol (SOA) from ozonolysis of isoprenoids and from ambient aerosol as measured during the EUCAARI-IOP campaign in Cabauw, Netherlands, in May 2008

Summary

Introduction

Organic aerosol (OA) sources in the global atmosphere are enormously uncertain. While state-of-the-art models predict total organic aerosol formation rates of 12–70 Tg yr−1 (Hallquist et al, 2009; Kanakidou et al, 2005), alternative budgeting approaches indicate significantly higher OA production. Field observations consistently reveal 3–10 times more organic aerosol than predicted by models (Heald et al, 2005; Volkamer et al, 2006), while top-down estimates suggest between 60 and 330 TgC yr−1 (120–660 Tg OA yr−1) (Goldstein and Galbally, 2007), again several times higher than global model predictions The search for this “missing” source of OA has become a key research topic, with hypotheses including higher secondary organic aerosol (SOA) yields from volatile organic precursors such as isoprene (Kroll et al, 2006; Paulot et al, 2009) or toluene (Hildebrandt et al, 2009; Ng et al, 2007), heterogeneous uptake of glyoxal (Kroll et al, 2005; Volkamer et al, 2007), aqueous photochemistry (Ervens et al, 2008), or oxidation of low vaporpressure “intermediate volatility organics” (IVOC) (Donahue et al, 2006; Grieshop et al, 2008; Robinson et al, 2007). We report first results obtained from chamber produced secondary organic aerosol (SOA) from ozonolysis of isoprenoids and from ambient aerosol as measured during the EUCAARI-IOP campaign in Cabauw, Netherlands, in May 2008

The TD-PTR-MS instrument

Smog chamber measurements

Information obtained from the thermograms

Conclusions