Search
Close this search box.

Drive & Detect: Integration of the Vocus B for Mobile Air Quality Monitoring in Conventional Cars

Priyanka Bansal, Katie Schmidt, Felipe Lopez-Hilfiker
TOFWERK, Switzerland

Current rapid environmental and urban developments have led to an increasing demand for comprehensive air quality and climate data. Mobile air measurements offer a critical solution to this challenge, providing a level of spatial and temporal resolution that stationary methods cannot achieve. These mobile platforms collect essential data for regulatory and research agencies to help identify point sources of pollution, understand the chemical reactions within the troposphere, and quantify risks to human health.

In this example, TOFWERK deployed its newly developed Vocus B chemical ionization time-of- flight mass spectrometer (CI-TOF) into a standard personal vehicle to both demonstrate the feasibility of such installation, and to show that comprehensive mobile data acquisition does not require a sophisticated mobile laboratory. The compact Vocus B offers fast switching reagent ion capabilities and ultra-soft chemical ionization. This combination allows the user to measure an unprecedented range of compounds in real time using just one instrument.

Installation of the Instrument in a Conventional Car

The Vocus B was installed in a conventional hybrid-electric vehicle as shown in the schematic in Figure 1 and was powered by the car battery. The power consumption required by the instrument was about 700 W and that of the nitrogen generator 350 W, excluding the periodic cycling of the compressor. The instrument was mounted on shock mounts to minimize the impacts and vibrations during the drive. The gas inlet was mounted on the vehicle’s roof, facing the front of the vehicle. Instrument exhaust was routed outside the car via the passenger window.

The car was driven from TOFWERK headquarters in Thun, Switzerland for about 25 kilometers through small towns and agricultural fields to the city of Bern, Switzerland.

Vocus B and compact nitrogen generator installed in a conventional electric vehicle for mobile air measurements. Both the instrument and the generator were powered by the car battery for a drive time of about three hours in the Bernese Oberland in Switzerland.
Figure 1. Vocus B and compact nitrogen generator installed in a conventional electric vehicle for mobile air measurements. Both the instrument and the generator were powered by the car battery for a drive time of about three hours in the Bernese Oberland in Switzerland.

Vocus B Compound Coverage

The Vocus B was able to simultaneously measure compounds that would typically require multiple mass spectrometers. Due to its multiple ultra-soft ion chemistries made possible by fast reagent and polarity switching, the Vocus B measured inorganic acids, hydroperoxides, hydrocarbons, and ammonia – all at the same time.  

Figure 2 shows a timeseries of ammonia, nitric acid and monoterpenes measured during the drive. This data demonstrates the instrument’s capability to simultaneously detect multiple distinct chemical species. Such measurements would typically require several side-by-side instruments, requiring significantly more energy and space. At the bottom, a magnified view on the mass spectrum per reagent ion chemistry with detected parent ion molecules of species is depicted in the time series. The combination of soft ionization and reagent ion selectivity allows more compact, lower resolution instruments to still achieve robust, sensitive detection of even trace, sticky and reactive compounds which are challenging for other online measurement techniques.

Figure 2. Ammonia, nitric acid, monoterpenes and isoprene hydroxy hydroperoxides (ISOPOOH) timeseries, which is straightforward to generate thanks to simple mass spectra with negligible fragmentation. Vocus B is able to measure compounds that are typically difficult to measure with a single ion mode thanks to its ultra-soft ionization technology and fast reagent ion switching.

Beyond its broad-spectrum detection abilities, the Vocus B also exhibits a high sensitivity for identifying hydrocarbons at trace levels, an analytical task typically ascribed to Proton Transfer Reaction Mass Spectrometry (PTR-MS). The Vocus B can detect these substances with detection limits in the single-digit ppt range with high temporal resolution. Figure 3 below shows timeseries obtained during the drive of toluene, xylenes, formic acid, propylene glycol monomethyl ether (PGME), and trimethylbenzene (TMB) at low ppb concentrations.

Figure 3. Toluene, xylene, TMB, formic acid and PGME timeseries. Formic acid was well distributed in the drive area because it is an oxidation product, while there were more localized sources of toluene, xylene, and TMB.

Mapping and Real-Time Data

Figure 4 shows concentration data for three representative compounds geographically mapped using simultaneously recorded GPS data. The left panel shows the spatial distribution of ammonia levels measured in the valley between Bern and Thun. The hotspots can be attributed to agricultural activity in the area. The top right panel (panel A) shows a zoomed-in section of the drive path, illustrating the concentration of PGME in an urban area of Thun. The elevated concentration of PGME possibly arises from the printing facility located in the vicinity of the drive path. The bottom right panel (panel B) shows monoterpene measurements in the forested region in the hills between Thun and Goldiwil, Switzerland.

Maps showing the concentrations of ammonia, PGME and monoterpenes measured on the drive between Bern and Thun. The route taken by the mobile air monitoring car is marked with a color coding corresponding to a legend on the right-hand side. The color gradient ranges from low (blue) to high (red) concentrations. Points A and B marked on the map are shown in more detail in the right panels.
Figure 4. Maps showing the concentrations of ammonia, PGME and monoterpenes measured on the drive between Bern and Thun. The route taken by the mobile air monitoring car is marked with a color coding corresponding to a legend on the right-hand side. The color gradient ranges from low (blue) to high (red) concentrations. Points A and B marked on the map are shown in more detail in the right panels.

The fast switching ability of the Vocus B not only enables better compound coverage but also allows real-time monitoring of concentration changes without missing transient signals. Figure 5 shows the timeseries of methyl ethyl ketone (MEK) detected using acetone reagent ions, and a sudden increase in concentration near a car wash facility can be seen. Analyzing the mass spectra of the event highlighted in blue shows presence of other solvents like PGME and n-butyl acetate (nBA). Meanwhile, analyzing the mass spectrum for the event highlighted in red discloses the detection of other compounds, including xylene, TMB, toluene and other hydrocarbons. These changes are presumably associated with emissions from nearby vehicles and a gas station. This example highlights how the Vocus B enables real-time, comprehensive analysis, allowing us to pinpoint specific events and correlate them with their contributing factors.

Figure 5. Multiple point events during the mobile air monitoring campaign involving increase in MEK concentration near a car wash facility (left). Integrated mass spectra of corresponding highlighted events for acetone and benzene segments shown in blue and red, respectively.

Conclusion

The measurements presented here demonstrate that the Vocus B can be integrated into a conventional car for mobile air monitoring without any permanent alterations while being powered entirely from the car’s existing battery system.

Moreover, we show that the Vocus B stands out in its ability to simultaneously detect a diverse array of chemical compounds, traditionally assessed with several different technologies. This is possible because of the Vocus B series’ unique combination of the soft-ionization Vocus Aim reactor with fast polarity-switching technology. This ensures accurate, real-time measurement of compounds with negligible fragmentation.  Thanks to these unprecedented capabilities, the Vocus B is uniquely well suited to mobile air monitoring. Not only is this instrument portable and compact, it also offers powerful detection abilities and produces easy-to-interpret results. What might previously have required a broad suite of instruments and large-scale consumption of both space and electricity is now possible with just one: the TOFWERK Vocus B.