The Sift-MS Mobile Laboratory Part1: Spatial Mapping of Volatile Pollutants

Volatile organic compounds (VOCs) from anthropogenic sources are of significant concern due to their impact on human health and quality of life, as well as the environment. In the Republic of Korea (South Korea), selected ion flow tube mass spectrometry (SIFT-MS) has been adopted to monitor source emissions and their dispersion in real time at the fenceline – and beyond – using mobile laboratories, enabling more rapid response to pollution incidents.
This application note focuses on the South Korean application of SIFT-MS to mapping of VOC pollutants in industrial complexes using on-the-move spatial data acquisition.

INTRODUCTION

Effective management of VOC pollution is important because many VOCs are implicated in formation of ozone and secondary organic aerosols (SOAs), some are toxic, and some cause odor nuisance. Industry is a significant source of VOC pollution, including through use of solvents and processing of various natural products, but it can be very difficult to trace the source from which they are emitted in industrial complexes. Conventional analytical approaches, such as time-averaged thermal desorption-gas chromatography-flame ionization detection (TD-GC-FID) and grab sampling (using bags or canisters) followed by lab-based gas chromatography-mass spectrometry (GC-MS analysis), are impractical for characterizing the baseline pollution levels and do not provide the necessary time response to transient pollution events (Langford et al. (2023a)).
In contrast, the direct-analysis SIFT-MS technique provides the capabilities necessary for both characterizing baseline pollutant distribution at an industrial complex and effectively responding to pollution incidents. SIFT-MS uniquely combines the required analytical performance (broad-spectrum, high-sensitivity, and high-specificity analysis in real-time) with robustness that enables the instrumentation to be rapidly deployed in mobile laboratories. In fact, VOC data can even be acquired spatially with the instrument operating in a moving mobile laboratory.
This application note is the first in a two-part series focused on SIFT-MS VOC pollution monitoring in industrial complexes. Here, a case study from an industrial complex in South Korea illustrates applications of mobile SIFT-MS laboratories that support characterization of baseline pollutant distributions. Part 2 considers identification of pollution sources, which facilitates incident response. Mobile SIFT-MS laboratories excel in both applications.

METHODS

1. The SIFT-MS Technique
This work utilized Syft Technologies Voice200ultra SIFT-MS instruments operating on nitrogen carrier gas. SIFT-MS (Figure 1) uses soft chemical ionization (CI) to generate mass-selected reagent ions (Smith et al. (2023)) that can rapidly react with and quantify VOCs down to part-per-trillion concentrations (by volume, pptV). Up to eight reagent ions (H3O+, NO+, O2+, O−, OH−, O2−, NO2− and NO3− ) obtained from a microwave discharge in air are applied in commercial SIFT-MS instruments (Smith et al. (2023)).
These reagent ions react with VOCs and other trace analytes in well-controlled ion molecule reactions, but they do not react with the major components of air (N2, O2 and Ar). This enables direct, real-time analysis of air samples to be achieved at trace and ultra-trace levels without pre-concentration. Rapid switching between reagent ions provides high specificity because the multiple reaction mechanisms give independent measurements of each analyte. The multiple reagent ions frequently remove uncertainty from isobaric overlaps in mixtures containing multiple analytes (Langford (2023)).

2. Mobile SIFT-MS Laboratory

In general, mobile SIFT-MS laboratories comprise:
• Suitable van with modified electrical system to power the instrumentation and air conditioning.
• SIFT-MS instrument (e.g., Voice200ultra model operating on nitrogen carrier gas).
• Supply of carrier gas and Syft calibrant standard (Langford et al. (2023b)).
• Sample inlet system configured for flow-past sampling at the SIFT-MS instrument (which samples at 25 standard cubic centimeters per minute (sccm)).
• Weather measurement system (HD52.3D ultrasonic anemometer; GHM Group, Remscheid, Germany).
• Global positioning system (GPS; UBX-G7020 chipset; u-blox AG, Zurich, Switzerland).
• Cellular internet connection for continuous streaming of data to a central facility.
• Mapping software (Syft Technologies Korea, Seongnam, South Korea).

RESULTS AND DISCUSSION

The standard hazardous air pollutant (HAP) analysis in South Korea uses TD-GC-FID, which has a high cost per sample, poor trapping of important low molecular mass VOCs, complicated analysis, and time-averaged results (Kim (2022)). Hence the TD- GC-FID method is impractical for investigating dispersion of pollutants. Instead, enhanced spatial monitoring has been achieved by deploying robust SIFT-MS instruments in mobile laboratories, enabling real-time collection at both fixed locations and while moving.
In this article, the work of Youn et al. (2020) of the Korea Environment Corporation (KECO) at a petrochemical complex in Ulsan, South Korea, is summarized. Figure 2 shows a satellite image of the complex annotated with the fixed sampling locations and routes for on-the-move monitoring.
First, Youn et al. (2020) utilized a mobile SIFT-MS instrument to continuously monitor 25 HAPs at three fixed locations (Figure 2) over a 24-hour period. From this suite, a subset of characteristic compounds for the complex was identified and utilized in subsequent monitoring on the mobile monitoring routes. Figure 3 shows the temporal behaviors of selected compounds at each of the fixed monitoring locations.
Spatial distribution of characteristic pollutants at the petrochemical complex was investigated using real-time measurement while driving the mobile laboratory on the industrial facility’s roads (Figure 2). From these data, pollution maps were generated that show the spatial distribution of pollutants (Figure 4). Such data can aid the location of pollution sources. They also illustrate the difficulty involved in selecting fixed monitoring points in industrial facilities with many potential emission sources. A mobile SIFT-MS laboratory enables both fixed and on-the-move strategies to be used effectively.

CONCLUSIONS

•  High-sensitivity, broad-spectrum analysis of volatile compounds.
•  Robust SIFT-MS technology with field-proven deployment in mobile laboratories, even enables data collection while moving.
•  Mobile SIFT-MS laboratories are ideal for characterization of volatile pollutants in industrial complexes with diverse emission sources.
•  Real-time mapping of spatial pollution enables rapid response and decision-making during incidents.
•  Mobile SIFT-MS laboratories can also be used for fixed-location fenceline and ambient monitoring.