Characterization and applicability of online and offline monitoring systems for reactive trace gases using TD-GC-FID/MS analysis

Continuous long-term in-situ measurements of reactive trace gases in observational and environmental chamber platforms is essential to identify their impact on future air quality under climate change and the switch to renewable energy. Despite new and more advanced technologies for online and/or offline monitoring using pre-concentration and thermal desorption (TD), followed by gas chromatography (GC) coupled to mass spectrometry (MS) and/or flame ionization detection (FID), the complexity of such measurements is still challenging.

Within the framework of the ACTRIS Centre for Reactive Trace Gases in Situ Measurements CiGAS, this work presents the characterization and orthogonal comparison of two modern systems for online and offline sampling, respectively, coupled to GC dual-columns (Deans Switch heart cut approach) and FID/MS detection. We evaluate the advantages and limitations of these systems regarding the versatility of the sample inlets during collection (e.g., direct line, canisters, and multi-bed TD tubes) as well as automated calibration strategies (e.g., variable sample volume through MFC and loop mode), providing differences in compound coverage, signal responses and sorbent background. We evaluate their performance in terms of sensitivity, reproducibility, linearity, and relative recovery by performing, (1) laboratory calibrations using high purity certified mixtures of non-methane hydrocarbons and monoterpenes and, (2) ambient measurements using the characterized and calibrated analytical methods with particular emphasis on urban emissions from cooking, cleaning, and traffic. In addition, we compare results from the TD-GC-FID/MS to a high time resolution chemical ionization mass spectrometer, called VOCUS, and present the resulting volatile profiles, their variability, and interferences among the different measurements methods.