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Environmental Measurements Methods
Evaluation of a passive sampling method for long-term continuous monitoring of volatile organic compounds in urban environments Robert Healy, Julie Bennett, Jonathan M Wang, Nicholas S Karellas, Colman Wong, Aaron Todd, Uwayemi Sofowote, Yushan Su, Linda Di Federico, Anthony Munoz, Jean-Pierre Charland, Dennis Herod, May Siu, and Luc White Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b02792 • Publication Date (Web): 17 Aug 2018 Downloaded from http://pubs.acs.org on August 18, 2018
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Environmental Science & Technology
Evaluation of a passive sampling method for long-term continuous monitoring of volatile organic compounds in urban environments Robert M. Healy*1, Julie Bennett1, Jonathan M. Wang1, Nicholas S. Karellas1, Colman Wong1, Aaron Todd1, Uwayemi Sofowote1, Yushan Su1, Linda Di Federico1, Anthony Munoz1, JeanPierre Charland2, Dennis Herod2, May Siu2, Luc White2 1
Environmental Monitoring and Reporting Branch, Ontario Ministry of the Environment,
Conservation and Parks, Toronto, Ontario M9P 3V6, Canada 2
Air Quality Research Division, Environment and Climate Change Canada, Ottawa, Ontario
K4M 1B4, Canada
Corresponding author contact details:
[email protected] Ontario Ministry of the Environment, Conservation and Parks 125 Resources Road, Etobicoke, ON M9P 3V6, Canada
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Abstract
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EPA Method 325 was developed for continuous passive monitoring of volatile organic
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compounds (VOCs), particularly benzene, at petroleum refinery fencelines. In this work, a
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modified version of the method was evaluated at an Ontario near-road research station in winter
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to assess its suitability for urban air quality monitoring. Samples were collected at 24 hour and
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14 day resolution to investigate accuracy for different exposure times. Tubes were analyzed by
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thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS), and eleven VOCs
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were quantified including aromatic air toxics. The same VOCs were simultaneously monitored
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using traditional canister sampling for comparison, and a subset of four were also monitored
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using a novel miniature gas chromatograph. Good agreement (within 10%) was observed
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between the 14 day passive tube samples and the canister samples for benzene. However, field-
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calibrated uptake rates were required to correct passive tube concentrations for lower volatility
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aromatics. Passive tube deployment and analysis is inexpensive, sampling does not require
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power and accurate measurements of benzene are demonstrated here for an urban environment.
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The method is expected to be advantageous for the generation of long term continuous benzene
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datasets suitable for epidemiological research with greater spatial coverage than is currently
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available using traditional monitoring techniques.
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Introduction
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The measurement of volatile organic compounds (VOCs) in ambient air through passive
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sampling is becoming more prevalent1-4, and applications include indoor air quality5-7, outdoor
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air quality8-12, and soil vapor intrusion assessments13. Passive sampling approaches include
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permeation devices14, 15, polyurethane foam disks16, 17, solid phase microextraction fibres18-20 and
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thermal desorption (TD) tubes packed with sorbent materials21-23. EPA Method 325, involving
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passive sampling of VOCs on low cost stainless steel TD tubes containing Carbopack X, is
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currently in use for assessing VOC concentrations at petroleum refineries in the United States
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under the Code of Federal Regulations (CFR), title 4024. The method has also recently been
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introduced by refineries in Ontario, Canada, to meet the province’s Petroleum Refining Industry
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Standard25. Method 325 was developed to enable continuous monitoring of VOCs associated
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with fugitive emissions from refineries with an emphasis on benzene, a known carcinogen26, 27.
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Fugitive VOC emissions are difficult to predict through modeling28, and thus continuous year-
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round VOC monitoring offers the advantage of capturing any unexpected or intermittent
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emission events, irrespective of their duration.
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In Method 325 applications, each TD tube is housed in a shelter, fitted with a diffusion endcap,
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and exposed to ambient air for a period of up to two weeks during which ambient VOCs diffuse
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to the sorbent and are retained24. While laboratory-based testing has demonstrated good
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agreement between Method 325 and traditional evacuated canister sampling for a range of VOCs
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under controlled conditions29, field studies assessing accuracy and potential biases of the method
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are few, and are focused on petrochemical facility fenceline sampling locations22,
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previous side-by-side comparison of 24 hour passive Carbopack X tube samples and evacuated
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canister samples in indoor environments demonstrated good agreement between the two
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approaches in the range 0.1-28 ppbv, although some low concentration tube samples (
