Odor-Cued Grab Air Sampling for Improved Assessment of Transient Downwind Environmental Odor Events

Abstract

Downwind odor characteristics can vary, depending upon the size of the upwind source, interim topography, and wind conditions. At one extreme, the downwind odor plume from a relatively large source located on a flat open plain and under stable, near-straight-line wind conditions, can be rather broad, sustained, and predictable. In contrast, the plume from a small point-source (e.g., a roof vent stack) located on irregular topography and under rapidly shifting wind conditions can be intermittent and fleeting (‘spikes’ or ‘bursts’). These transient odor events can be surprisingly intense and offensive despite their fleeting occurrence and perception. This work reports on improving and optimizing an environmental sampling strategy for such transient downwind odor conditions. The optimization, addresses the challenges of (1) sampling of transient odor 'spikes' and (2) prioritizing odors/odorants from multiple, closely co-located point sources under transient event conditions. Prioritizing is defined as identifying the key impactful odorants downwind. Grab air sampling protocol refinement has emerged from community environmental odor assessment projects. The challenge of assessing transient odor events has been mitigated utilizing: (a) rapid, odor-cued whole-air grab sampling (i.e., activated by and synchronous with the perceived sensory spikes) into metalized polymeric gas sampling bags; (b) immediate transfer onto solid-phase microextraction (SPME) fibers or sorbent tubes; (c) refrigerated storage and shipment conditions and (d) in-laboratory analysis. Results demonstrated approximately 11 fold increases in target odorant yields for 900 mL sorbent tube transfers from 2-3 s 'burst' odor event bag-captures compared to equivalent direct collections at the same downwind receptor location but during perceived (stable) odor 'lull' periods. An application targeting general odor sampling and point-source differentiation utilizing tracer gases is also presented.