Abstract
The majority of atmospheric measurements of volatile organic compounds (VOCs) are usually limited to a small range, either in volatility or time resolution. A combined heart-cut gas chromatography (GC) with comprehensive two-dimensional GC (GC×GC) instrument was developed, specifically to increase the number of VOCs analysed using a single instrument. The system uses valve based modulation and was fully automated, making it suitable for use in the field. A laboratory comparison to an existing dual-channel GC (DC-GC) instrument demonstrated that this new GC-GC×GC can accurately measure atmospheric mixing ratios of C 5 -C 13 VOC species with a wide range of functionalities. Approximately hourly field measurements were conducted at a remote marine atmospheric research station in Bachok, Malaysia. This region was shown to be influenced by clean marine air masses, local anthropogenic and biogenic emission sources and aged emissions transported from highly polluted South East Asian regions. A dramatic shift in air mass direction was observed each day associated with the development of a sea breeze, which influenced the diurnal profiles of species measured at the Bachok site. A proton-transfer-reaction mass spectrometer (PTR-MS) was also deployed at Bachok and compared to the new GC-GC×GC instrument. Overall, the GC-GC×GC instrument has been shown to perform well in lab comparisons and during field observations. This represents a good compromise between volatility and high complexity o n l i n e measurements of VOCs.
Highlights
Volatile organic compounds (VOCs) play a central role in the atmosphere through reactions which can produce secondary pollutants such as secondary organic aerosol (SOA) and ozone (O3 ), both of which are detrimental to health
The heart-cut stage essentially acts to inject the most volatile volatile organic compounds (VOCs) (C4 -C7 ), which are unretained by the primary BPX-5 column, onto the secondary PLOT column
The gas chromatography (GC)×GC instrument detailed in Dunmore et al (2015) [3] performed well for the majority of compounds, it was unable to accurately quantify isoprene due to the incomplete separation and resolution of the species from surrounding compounds
Summary
Volatile organic compounds (VOCs) play a central role in the atmosphere through reactions which can produce secondary pollutants such as secondary organic aerosol (SOA) and ozone (O3 ), both of which are detrimental to health. Atmospheric VOC measurements generally fall into one of two categories; offline, where the sample is collected and analysed back at the laboratory, or online, where the instrument is deployed to the field. The majority of online, longer term atmospheric VOC measurements span a range of C2 -C8 hydrocarbons; including alkanes, alkenes and simple aromatic compounds such as benzene, toluene and xylenes. This select group of VOCs are routinely measured in many countries for compliance with air quality policy, there are potentially many thousands of VOC compounds that are not routinely measured and as a result their influence on local processes and secondary pollution generation is not well established. The complexity is further complicated by the exponential increase in structural isomers with increasing carbon number [2]
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