Developing Non-Targeted Data Analysis Methods for Diffusive Samplers: Lessons from Past DatasetsAir Monitoring, Methods, and Technology
Poster Presentation
Prepared by J. Machesky1, C. Witherspoon2, T. Cousett1, K. Oliver1
1 - US EPA Office of Research & Development, 109 TW Alexander Dr, RTP, NC, 27711, United States
2 - Amentum, , Tullahoma, TN, United States
Contact Information: [email protected]; 919-541-3533
ABSTRACT
Diffusive samplers are a low-cost sampling technique for measuring select volatile organic compounds (VOCs). After collection, samples are analyzed using thermal desorption/gas chromatography-mass spectrometry (TD/GC-MS), allowing for the average concentration of select compounds to be determined during the sampling period. These samplers rely on diffusive uptake rates (DURs) to quantify concentrations of target compounds, which are time-intensive to determine and dependent on multiple factors, including but not limited to temperature, humidity, and sampling duration. US EPA Method 325A/B provides guidance on measuring fugitive emissions at and around fencelines using diffusive samplers and provides uptake rates for a limited number of VOCs for select diffusive samplers. Researchers at US EPA have deployed these samplers in multiple urban field campaigns over the past decade and quantified concentrations of target compounds, such as benzene, toluene, ethylbenzene, and xylenes. In addition to these compounds, non-targeted analysis can be employed on TD/GC-MS data collected in Scan or SIM/Scan mode to provide tentative identification for additional compounds. These additional compounds could be targeted for future DURs determination and provide insights into relative differences in these compounds between samples. While the quantification of compounds is limited, data analysis workflows for non-targeted analysis can be developed to explore differences in the relative abundance of non-targeted compounds between samples. Best practices for non-targeted analysis of diffusive samplers analyzed using GC-MS will be discussed, including but not limited to preliminary identification criteria and blank subtraction. These methods will enable additional analysis of diffusive sampler datasets from past field studies and provide additional compounds to target in future field studies.
