A method for stable carbon isotope ratio and concentration measurements of ambient aromatic hydrocarbons

A Kornilova,M Saccon,J Rudolph,W Zhang,L Huang,S Moukhtar

doi:10.5194/amt-8-2301-2015

Abstract

Abstract. A technique for compound-specific analysis of stable carbon isotope ratios and concentration of ambient volatile organic compounds (VOCs) is presented. It is based on selective VOC sampling onto adsorbent-filled cartridges by passing large volumes of air (up to 80 L) through the cartridge. The hydrocarbons are recovered by thermal desorption followed by two-step cryogenic trapping and then are separated by gas chromatography in the laboratory. Once separated, individual VOCs are subjected to online oxidation in a combustion interface and isotope ratio analysis by isotope ratio mass spectrometry. The method allows measurements of stable carbon isotope ratios of ambient aromatic VOCs present in low pptV to ppbV levels with an accuracy of typically better than 0.5 ‰. The precision of concentration measurements is better than 10%. Examples of measurements conducted as part of a joint Environment Canada–York University (EC-YU) measurement campaign at a semi-rural location demonstrate that the ability to make accurate measurements in air with low VOC mixing ratios is important to avoid bias from an overrepresentation of samples that are strongly impacted by recent emissions.

Highlights

Volatile organic compounds (VOCs) comprise an important class of atmospheric pollutants emitted in large quantities from anthropogenic and biogenic sources (Atkinson, 2000; Guenther et al, 2000; Niedojadlo et al, 2008; Piccot et al, 1992; Rudolph, 2002; Sawyer et al, 2000)
The atmospheric oxidation of these aromatics by reaction with OH and NO3 can result in formation of ozone as well as oxygenated and nitrated products that can contribute to the formation of secondary organic aerosol (Forstener and Flagan, 1997; Jang and Kamens, 2001)
Ambient VOCs were analyzed for concentration and isotope ratios (δ13C) using the following steps: (1) collection onto adsorbent packed cartridges, (2) thermal desorption of VOCs in a furnace at 553 K in a flow of high purity helium, (3) a two-stage preconcentration, (4) chromatographic separation, (5) combustion to CO2 and H2O in a furnace at 1173 K and (6) analysis of the CO2 isotopologues by isotope ratio mass spectrometry (IRMS)

Summary

Introduction

Volatile organic compounds (VOCs) comprise an important class of atmospheric pollutants emitted in large quantities from anthropogenic and biogenic sources (Atkinson, 2000; Guenther et al, 2000; Niedojadlo et al, 2008; Piccot et al, 1992; Rudolph, 2002; Sawyer et al, 2000). While their atmospheric mixing ratios are mostly in the ranges of pptV to ppbV, these compounds play an important role in tropospheric chemical processes (Atkinson, 2000; Jordan, 2009; Kleinman et al, 2003). The atmospheric oxidation of these aromatics by reaction with OH and NO3 can result in formation of ozone as well as oxygenated and nitrated products that can contribute to the formation of secondary organic aerosol (Forstener and Flagan, 1997; Jang and Kamens, 2001)

Methods

Results

Conclusion