Abstract View
New Inlet for Increasing Concentrations of Reactive Organic Gases in SCCM-Level Sample Flows
NAMRATA SHANMUKH PANJI, Gabriel Isaacman-VanWertz, Virginia Tech
Abstract Number: 286
Working Group: Instrumentation and Methods
Abstract
Organic aerosol (OA) in the atmosphere is of serious consequence to air quality, radiative climate forcing, and human health. A dominant fraction of this OA is formed through oxidation of reactive organic compounds, primarily emitted in the gas phase. These compounds, especially terpenes, contribute significantly to OA, O3 production, and oxidant removal, but are typically present in sub-ppt to sub-ppb concentrations. Additionally, some highly reactive volatile organic carbons (VOCs) with lower volatilities, such as sesquiterpenes, present analytical problems in the form of losses to instrument lines and surfaces. Consequently, measurements of many reactive gases suffer high 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. We present here a novel “enriching inlet” capable of increasing the concentration of organic gases in small sample flows (up to 5 sccm), thereby providing improved sensitivity and limits of detection. Inert gases are removed from the sample stream by selective permeation through Teflon™ AF-2400 tubing driven by a pressure gradient, concentrating remaining organic gases into a smaller flow for subsequent sampling. Significant enrichment (a factor of several) is demonstrated for several major classes of OA precursors; isoprene (C5H8), monoterpenes (C10H16, specifically α-pinene), and sesquiterpenes (C15H24, specifically β-caryophyllene). We present the relationships between pressure differential, inlet length, and sampling flow rate, to establish a model to predict enrichment of a given gas at a given sample flow.