40 Air Monitoring
REAL-TIME MEASUREMENT OF EPA REGULATED HON COMPOUNDS AND ENVIRONMENTAL POLLUTANTS USING SIFT-MS
SUMMARY
Method detection limits (MDLs) have been determined for the newly regulated HON (Hazardous Organic NESHAP (National Emission Standards for Hazardous Air Pollutants)) compounds, which validate selected ion fl ow tube mass spectrometry (SIFT-MS) as an eff ective solution for measuring these toxic volatile organic compounds (VOCs) and other environmental pollutants in ambient air, whether at the fenceline or in a mobile setting. SIFT-MS off ers unparalleled speed, sensitivity and ease of use for environmental monitoring applications.
Introduction
There are over 200 chemical plants in the United States producing chemicals that pose a signifi cant cancer risk to nearby communities. These are known as HON facilities. In January 2024, the US Environmental Protection Agency (EPA) enacted a rule mandating fenceline monitoring of six toxic VOCs produced by these facilities: ethylene oxide (EtO), chloroprene, benzene, 1,3-butadiene, ethylene dichloride, and vinyl chloride. Action levels for these compounds, established by the new regulations, are thresholds for annual average air concentrations (see Table 1); if these levels are exceeded at the fenceline, facilities must identify and address the pollution source to effectively manage hazardous emissions.
SIFT-MS offers real-time, direct monitoring of VOCs and inorganic compounds in air. SIFT-MS has been adopted by governmental agencies and industry worldwide for environmental monitoring. For example, the South Korean government agencies have relied on SIFT-MS for years to monitor toxic VOCs at both federal and state levels (Langford et al. (2023a)). Recently, the US EPA has
Table 1. Action levels for HON compounds.
also adopted SIFT-MS for use in mobile laboratories across real- time mobile monitoring applications.
In response to the new HON Rule, Syft Technologies has developed robust methods for sampling these toxic VOCs. These methods have achieved MDLs in the low- to mid- part per trillion by volume (pptV) range, validating SIFT-MS as an excellent solution for monitoring these compounds as well as other compounds in ambient air.
With SIFT-MS, users get real-time monitoring that will connect emissions to specifi c events, giving a deeper understanding of plant operations while still meeting regulatory requirements.
Method
In SIFT-MS, real-time specifi city is achieved by the combination of rapidly switchable reagent ions and various reaction mechanisms to distinguish multiple compounds in a single analysis. Reliable quantifi cation of target compounds is provided by mass spectrometric detection combined with library records of ion molecule reaction rate constants.
This work uses a SIFT-MS instrument (Syft Tracer) operating with nitrogen carrier gas and equipped with a high- performance inlet (HPI). The HPI provides direct sample analysis, minimizing loss of volatiles. Samples were prepared by diluting reference standards in clean, humid air to produce a consistent fl ow at the concentration of interest with 40-50% relative humidity. Samples were delivered to the HPI with a fl ow past arrangement.
Library entries were used to create one-minute methods for each of the compounds. For compounds that were reactive with more than one reagent ion, all rapid reactions were included in the methods. For methods using both positive reagent ions (H3 NO⁺ and O2⁺) and negative reagent ions (O- NO3
O⁺, , OH- allocated to each phase.
MDLs were determined using US EPA procedure EPA 821-R-16- 006 (US EPA (2016)).
EtO quantitation with H3 O⁺ is known to be affected by the
presence of its isomer acetaldehyde (Swift et al. (2023)). The method tested here included a subtraction for acetaldehyde based on acetaldehyde’s reactivity with NO⁺. The EtO MDL was measured in the presence of 2.5 ppbV acetaldehyde, to ensure the MDL results were representative of analysis of a realistic environmental sample.
RESULTS *μgm3 to pptV conversion at 20 O C.
In addition to the HON compounds, MDLs were also determined for other environmentally important compounds. The MDLs in Table 2 and Table 3 represent what is achievable for each compound in one minute with the SIFT-MS system.
IET SEPTEMBER / OCTOBER 2024 , O2 -, NO2 - and -), the total measurement time was 2 minutes; with 1 minute †
EtO MDL over 30 minutes in presence of 2.5 ppbV acetaldehyde (see Discussion).
Table 2. Comparison of MDLs using SIFT-MS with HON compound action levels. Results are for one-minute methods using a single reagent ion, except for EtO.
Table 3. MDLs for environmentally important compounds using SIFT-MS. Results are for one-minute methods using a single reagent ion.
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