Evaluation of a Passive Sampling Method for Long-Term Continuous

Aug 17, 2018 - Environmental Protection Agency Method 325 was developed for continuous passive monitoring of volatile organic compounds (VOCs), ...
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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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. A

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approaches in the range 0.1-28 ppbv, although some low concentration tube samples (