Increasing Availability of Continuous and Real-Time VOC Monitoring Technologies for VI Assessment

Transcription

1 Increasing Availability of Continuous and Real-Time VOC Monitoring Technologies for VI Assessment Chase Holton, CH2M Robert Truesdale, RTI International

2 Introduction Drivers for Continuous & Real-Time Temporal variability in indoor air VOC concentrations of 2-3 orders of magnitude observed at wellstudied sites Conventional grab sampling approaches may result in falsenegative decisions if uncertainty tolerance is low Observations possible through continuous and real-time monitoring Renewed focus on identification of short-term risks (e.g., TCE), and near worst case VI, reasonable maximum exposure (RME) Holton et al., 2013, ES&T 2

3 Tools for Managing Temporal Variability Building depressurization Allows for quick screening and notice of potential high-end risks May not be feasible in large or leaky buildings Passive sampling Provides time-weighted average concentration data Can be deployed over long time periods May not be appropriate for potential rapid response situations Continuous and real-time monitoring Provides temporal trends of concentration data Allows for implementation of real-time alarms Several challenges to consider. 3

4 Challenges of Continuous and Real-Time Monitoring QA/QC 4 Calibration frequency, blank frequency; calibration stability Remote operation challenges Moisture interference and temperature effects Data interpretation Selection of averaging times, risk communication approaches Statistical analysis for comparison to screening levels or exposure limits, vs conventional methods Regulatory and stakeholder acceptance Instrument considerations Sensitivity, selectivity, dynamic range, operator skill requirements Durability, response time, robustness to loss of power, and small size

5 Monitoring 101 Classes, Definitions Continuous Monitoring Devices Provide continuous * measurement (e.g., sensors, onsite/portable GCs) or sample collection (e.g., passive samplers). ug/m Office Area (P2) PCE Real-Time Monitoring Devices Provide data output for immediate review from frequent/continuous measurements Run # Courtesy of Dr. Blayne Hartman Common detectors used in VI instruments Photo Ionization Detector (PID) Flame Ionization Detector (FID) Electron Capture Detector (ECD) Mass Spectroscopy (MS) *Frequent measurement cycles (e.g., minutes) can be functionally continuous. 5

6 Monitoring 101 (cont d) - Continuous & Real Time Microelectromechanical systems (MEMS)- based technologies Microfabricated instrumentation and components (e.g., μgcs) developed to reduce cost, size, and complexity Sensor-based technologies Devices designed to produce measurable signal output when analyte(s) cause recognition event Most focused on portability, affordability, and ease of use Use a variety of operating principles (e.g., metal oxide semiconductors, chemiresistors) Kim et al., 2012, ES&T Courtesy of E. Forzani (ASU) 6

7 Technology Summary Brand/Product Operating Principle Stage Est. Cost Deployment Sensitivity Radiello Passive sorbent/ GC/MS Commercial $150 per sample Fixed lab sub ppbv TO 15 Summa Canister / GC/MS Commercial $150 per sample Fixed lab sub ppbv TO 17 Active Active sorbent / GC/MS Commercial $150-$175 per sample Fixed lab sub ppbv Defiant Technologies FROG GC/PID Commercial $25,000 CAP Portable sub ppbv Inficon HAPSITE ER GC/MS Commercial >$100,000 CAP Portable sub ppbv PerkinElmer Torion T-9 GC/MS Commercial >$100,000 CAP Portable sub ppbv TCE Vapor Analyzer Cavity ring-down spectroscopy (CRDS) and diffusion time-offlight (DiTOF) incorporating stationary phases Proof of Concept >$100,000 CAP Field Deployable 20 pptv RAE Systems MultiRAE 3000 PID Commercial $7,000 CAP Portable low ppbv Thermo Scientific TVA2020 Toxic Vapor Analyzer FID and PID Commercial $12,500 CAP Portable sub ppmv SRI 8610 GC with ECD GC/ECD Commercial $35,000 CAP Field Deployable sub ppbv SRI 8610 GC with FID GC/FID Commercial $30,000 CAP Field Deployable sub ppmv Capacitive micromachined ultrasonic transducer (CMUT) array Low power CMUT sensor; array for better VOC selectivity; polymer functionalized CMUT resonator in Colpitts oscillator feedback loop Proof of concept Unknown Portable 20 ppmv RTI International VOC Sensor Carbon nanotube resistance Lab Proof of Concept $2,000 CAP Portable sub ppbv 7 CAP = capital cost; blue shade are compound specific; gray are compound class; orange are not compound specific (total VOCs) Full summary table available upon request Please submit suggestions to help us build this resource

8 Example Data Set #1 EPA Research House, Indianapolis, IN VOCs monitored in indoor air, outdoor air, and soil gas using FROG (Defiant Technologies; run time of 8 minutes) and SRI GC/ECD Results compared to AlphaGUARD (radon), passive samplers, & TO-17 8

9 Example Data Set #2 Sun Devil Manor, Layton, UT VOCs monitored in indoor air (shown below), outdoor air, and soil gas using SRI GC/ECD with 10-port autosampler, run time of 40 minutes Data set used in long-term building depressurization study TCE Concentration [ppb v ] Indoor Air - Attic Indoor Air - Lower Level 0.0 9/8/12 11/7/12 1/6/13 3/7/13 5/6/13 7/5/13 9/3/13 Time

10 Conclusions We have several techniques for managing/assessing temporal variability, each with their own benefits and challenges There are numerous technologies available for continuous/realtime monitoring that are rapidly being developed Need to understand application, purpose, capabilities, and limitations No one technology yet combines everything you d want accuracy, sensitivity, selectivity, reliability, low cost, etc. (EPA/600/R-15/122 May 2015) Like everything else VI, continuous/real-time monitoring provides just one line of evidence that needs to be considered with all other evidence to best understand VI at a site 10

11 Thank You Contact for further information: Chase Holton, Ph.D. Robert Truesdale