Significance and Use
5.1 Vapor intrusion testing has been performed traditionally using multiple canister samples or thermal desorption tube samples. These discontinuous measurements have been shown to be snapshots and provide averages of exposure. In many cases a higher temporal resolution is desirable to identify peaks of emissions due to specific occupancy or environmental changes. For these cases, a continuous real-time monitoring solution is desirable. These continuous monitoring setups can be either short-term or be part of a long-term monitoring plan as described in ASTM guide “Standard Guide for the development of LongTerm Monitoring Plans for Vapor Mitigation Systems” (E2600).
5.2 The PTR-MS provides real-time measurement of multiple VOCs at ultra-trace levels, that is, in the µL/L (ppm) to less than pL/L (ppt) range. Its strengths lie with the ability to measure VOCs in real-time and continuously (that is, ~1 Hz or faster, using time-of-flight analyzers), and with limited sample pre-treatment, compared to a gas chromatograph (GC) system, which is commonly the method of choice to measure VOCs using a variety of detectors. In case of PTR-MS with quadrupole analyzers, the terms would be nearreal-time and semi-continuous. The high temporal resolution of the PTR-MS measurement in the range of second(s) is often desired when studying the atmospheric chemistry or source emissions that result in unpredictable, sudden, and short-term fluctuations. For a detailed description on the design and theory and practical aspects of operation for the different types of PTR-MS, please refer to Yuan et al. (2017)(1).
5.3 For ambient air measurements, such as vapor intrusion (VI) related emission testing, the PTR-MS can be used in three different modes of operation: (1) in scanning mode to identify sources and VI entry points within buildings; (2) in variation identification mode, as a continuous monitoring instrument with seconds to minutes of temporal resolution covering a large number of VOCs; (3) in source tracking mode, as a scanner of indoor and outdoor sources and as a rapid tracking device for external emissions; this requires the instrument to be mounted on a moveable platform, such as on an (autonomous) vehicle or trolley. The same operation can be used to identify various other constituents in air, depending on the application—be it fugitive emissions from toxic materials or illicit materials, or metabolic reactions to infections expressed in different breath emissions.
5.4 Spatial and temporal variability are two common challenges with ambient air measurements and source assessments. Within a given building, the sources for vapors can be few or many and are generally irregularly spaced; they may be obscured from view by floor coverings, furniture or walls, which in itself can be a large source of VOC. The current methods of choice require the use of time-discreet monitoring or time-averaged monitoring of a specific sampling spot. Real-time monitoring provides a method to assess the spatial distribution of vapor concentrations, which may help to rapidly and efficiently identify the location of vapor entry points.
5.5 Real time assessment is valuable as a component of a program of assessment with two or more supporting lines of evidence and can be used to:
5.5.1 Provide support for real-time decisions such as where and when to collect long-term samples for fixed laboratory analysis using canisters or sorbent tubes;
5.5.2 Verify data quality (for example, monitoring the efficacy of soil gas probe purging prior to sampling, providing leak checks; and
5.5.3 Measure changes in VOC vapor concentrations in response to changes in building pressure, temperature, solar irradiation, or other weather conditions and factors affecting vapor fate and transport, including secondary chemistry occurring within the building.
5.5.4 Identify alternative pathways based on prior identified intrusion compounds or based on emissions within such pathways, such as stormwater drains.
5.6 Screening of a property prior to a real estate transaction based on site specific potential sources of concern. The option for voluntary investigative assessments of potential VI in the real estate business is described in ASTM method E2600-15.
Note 1: The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
Scope
1.1 This test method describes a technique of quantifying the results from measuring various volatile organic compound contents using a chemical ionization mass spectrometer resulting in the production of positively charged target compound ions. Depending on the nature of production of so-called primary ions, the associated instruments having the capability to perform such analyses are either named Proton Transfer Reaction Mass Spectrometers (PTR-MS), Selected Ion Flow Tube Mass Spectrometers (SIFT-MS) or, in the most generic term, Mid-pressure chemical ionization mass spectrometers (MPCI-MS). Within this standard, the term PTR-MS is used to represent any of these instrumentations.
1.2 Either of the instrument types can be used with the two main mass analyzers on the market, that is, with either quadrupole (QMS) or time-of-flight (TOFMS) mass analyzer. This method relates only to the quantification portion of the analysis. Due to large differences in user interfaces and operating procedures for the instruments of the main instrument providers, the specifics on instrument operation are not described in this method.
1.3 Details on the theoretical aspects concerning ion production and chemical reactions are included in this standard as far as required to understand the quantification aspects and practical operation of the instrument in the field of vapor intrusion analyses. Specifics on the operation and/or calibration of the instrument need to be identified by using the user’s manual of the individual instrument vendor. A comprehensive discussion on the technique including individual mass-line interferences and in-depth comparison with alternate methods are given in multiple publications, such as Yuan et al. (2017) (1) and Dunne et al. (2018) (2)2.
1.4 Units—Values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
1.5.1 The procedures used to specify how data are collected/recorded or calculated in the standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering data.
1.6 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
