Novel Low-Cost Concentrating Inlet for Enhancing Instrument Sensitivity and Level of Detection for Reactive Organic Gases in Small Sample Flows

There are thousands of different organic compounds in the atmosphere, carrying a wide range of impacts on air quality, radiative forcing, and human health. However, despite their significant impacts, they are usually present in ppt to ppb concentrations. Moreover, many of the most reactive compounds also have low volatilities and may get lost to instrument lines and surfaces. As a result, measuring reactive gases requires very low levels of detection. This has been particularly limiting for low-cost instrumentation (e.g., photoionization detectors), which frequently have levels of detection too high to be useful under typical ambient conditions. Here, we introduce a novel inlet with the ability to concentrate organic gases in small sample flows (up to 5 sccm), and consequently provide improved sensitivity and limits of detection. Inert gases are selectively removed from the sample stream, leaving organic gases concentrated into a smaller flow to the detector. We demonstrate enrichment up to a factor of several at ~1 sccm for major reactive atmospheric gases: monoterpenes (C₁₀H₁₆, specifically α-pinene), sesquiterpenes (C₁₅H₂₄, specifically β-caryophyllene), and n-alcohols (specifically methanol and butanol). We model the relationship between inlet design parameters, operating conditions, and inlet efficiency, estimating that enrichment by an order of magnitude or more is possible at sccm-level flows for a moderate cost.