Design and application of a portable atmospheric cold plasma jet for food safety and air quality improvement

Non-thermal technologies that can inactivate microorganisms without producing harmful gases, heat damage or chemical residues can contribute largely to food safety and environmental applications. This study reports the design, preliminary characterization, and application of a portable atmospheric cold plasma (ACP) jet intended for local food surface decontamination and indoor air pollutant degradation. The device was constructed with a dielectric-barrier configuration (6.58 mm electrode gap) and operated using filtered ambient air at 1.1 L/min. Electrical behavior was assessed via oscilloscope measurements, while reactive gas species (RGS) were evaluated using optical emission spectroscopy (OES) and colorimetric quantification of ozone and NOx. Additionally, methylene blue (MB) discoloration was performed to confirm oxidative activity and functional validation of the reactor. The plasma jet demonstrated peak-to-peak voltage and current reaching up to 11.8 kV and 87 mA respectively. The produced mean ozone and NOx concentrations were up to 50 ppm and 41.5 ppm, respectively, depending on operating voltage. Plasma treatment at 4.5 kV for 5 min numerically delayed Aspergillus flavus (A. flavus) growth by up to 4 days under refrigerated storage and reduced colony counts relative to controls. For the volatile organic compounds (VOC) treatment, maximum reductions of 92.17% (formaldehyde (HCHO)) and 91.89% (Total VOC or TVOC) were achieved at 4.5 kV after 38 min. Overall, the proposed handheld ACP jet demonstrated the feasibility of localized fungal growth suppression and VOC reduction while highlighting areas requiring further optimization.

Food safety is a critical concern worldwide, as the consumption of contaminated food can lead to severe health risks, including foodborne illnesses. Due to the nature of altering the food’s sensory attributes and nutritional quality losses, there is a growing demand for alternative technologies that can effectively eliminate pathogens and enhance food safety without compromising the quality of the products. Atmospheric Cold Plasma (ACP) is a non-thermal plasma technology that can generate a highly reactive mixture of ions, electrons, and neutral species, capable of broad-spectrum antimicrobial effect including inactivation of a wide range of bacteria, viruses, yeasts, and molds [1, 2]. Moreover, ACP can reach areas that are difficult to access by other decontamination methods, such as crevices and irregular surfaces. Additionally, plasma can cause destruction of spores hidden in the inner surfaces of the foods [3]. Cold plasma achieved effective microbial inactivation, although longer exposure times may be required for microorganisms residing within surface irregularities and grooves [4, 5]. The effectiveness and versatility of ACP along with the new advancements to overcome the hurdles have been studied previously in many studies [6–8].

Atmospheric cold plasma jet is an emerging tool developed based on plasma technology for enhancing food safety. The challenge of overcoming ACP effectiveness to complex natured foods and on the food surfaces, can be countered using plasma jets. Several studies demonstrated the bactericidal and virucidal impact of ACP jets on foods and their structural function ([9–11]; Lee at al., 2011; [12, 13]). The fungal spores are even less resistant to plasma damage [7, 14]. Since the ACP treatment is still in the lab scale stage, the upscale can be a major challenge [7]. The added challenges for commercial application are appropriate plasma reactor design, process control, and most importantly the regulatory approval [15, 16]. Nevertheless, to move forward with the ACP technology for upscale application and commercial utilization, ACP jets can be pivotal. The necessity of handheld or portable cold plasma treatment device for industrial scale use to treat fresh produce and other foodstuffs is at the pinnacle now. The portable nature of ACP jets can further bring enhanced usability in various food processing settings. These compact devices can be lightweight and easy to transport, allowing for on-site decontamination in food production facilities, restaurants, and even at consumer households. The portability of ACP jets can also offer flexibility and convenience in implementing food safety measures throughout the entire food supply chain. Hence, the current study addresses these challenges by designing and evaluating a portable ACP jet reactor for localized food surface decontamination and practical food safety applications.

Additionally, the diversity that can be brought by cold plasma is widespread and still under further investigation. The application of ACP to improve air quality has been studied a few times [17–20]. Since Volatile Organic Compounds (VOC) are crucial ambient air pollutants, it can be beneficial exploring the ACP impact on VOC abatement from the atmosphere. The probable mechanism of VOC reduction is the interaction of ionized and energetic electrons with VOC molecules through inelastic collisions [21]. The current study hence additionally focuses on treating VOCs for breakdown and conversion into non-harmful environmental gases. Although there has been some modest use of ACP technology in the medicine industry or skin treatment, the use of portable plasma jets in food industry is unknown to us. This work hence brings newness and innovation of using a single reactor platform for air quality and food safety applications. In addition, the study aimed to determine the preliminary applicability of the newly designed ACP jet in food safety and environmental quality.

Experimental set up and design of the reactor

A power supply equipped with a transformer (Model: PVM500-4000, Information Unlimited, Amherst, NH-03031, United States of America) was used for plasma generation. The transformer was connected to the power electrode (Figure 1) via a properly insulated flex wire and with grounded electrodes. A PVC tube was used as an outside barrier for the electrodes holding station, while a transparent vinyl tube of 1.1 mm thickness, 55 mm height, and 6.5 mm of Outer diameter (OD) was used as the dielectric barrier. A tungsten rod of 115 mm length and 3.25 mm diameter was used as the main electrode. For the grounding electrode, a copper tube of 12.7 mm OD, 1.77 thickness, and 10 mm height was used. The air gap between the electrodes was maintained at 6.58 mm. A tetra whisper air pump connected with an oxygen generator filter (Whatman filter, 0.5 micron, 6mm/5 mm interface size, 99.99% filtration accuracy) was used to draw filtered atmospheric air at 1.1 lpm flow rate into the reactor. The gap between the sample surface and the plasma source were maintained ranging from 10 to 15 mm. The reaction time of the air molecules inside the reactor is estimated to be 47.9 milliseconds. The reaction time was estimated using the ratio of the effective discharge volume to the volumetric airflow rate passing through the reactor, assuming steady-state flow.

Oscilloscope analysis

The voltage waveform and the current intensity for the measuring circuits from the discharge were obtained using a digital oscilloscope (4 channel, 100 MHz, 1 G/s sample Rate) (Model: RIGOL DS1104 Z plus, RIGOL technologies Inc, Portland, OR-97223, United States of America). A current transformer probe was connected to the main electrode current line from the oscilloscope. The discharge voltage and current were monitored using a Northstar PVM-4 high-voltage probe (1000:1, 40 kV, 110 MHz) and a Bergoz current transformer (1 V/A, 0.7 ns rise time), respectively [22]. The voltage decreases and the current spikes each time there is an electrical discharge event. Therefore, the peak to peak and rms voltage changes during the treatment were monitored and recorded.

OES measurement

A concave grating BLACK-Comet Spectrometer (StellarNet Inc., Tampa, FL, United States of America) paired with an F600-UV-SR fiber optic cable connected to SpectraWiz software (version 5.33; StellarNet) on a computer was used to determine a few of the created plasma gas species in the reactor. The fiber optic cable had a 0.25 mm aperture length and was directed to the reactor output with a 7 mm gap between it and the electrodes, as well as a 19 mm thick transparent plastic barrier to prevent electrical interference. The Spectrometer wavelength ranged from 220 nm to 850 nm, with a detection integration limit of 1 millisecond–8 min. The detection was done at a 5000 m integration time for the analysis, and the peaks were captured at different wavelengths and averaged over three samples. To reduce background noise, a pre-treatment background spectrum was determined and standardized. The spectra were evaluated and compared using the National Institute of Standards and Technology’s (NIST) atomic spectra database and published research papers [23, 24].

Ozone and NOx species quantification and methylene blue (MB) verification

To measure the ozone and NOx concentration produced in the reactor, a toxic gas detector pump (Model: 8014-400B, Matheson Tri-Gas Inc., PA, United States of America) was used along with gas measuring tubes (Range: 0–1000 ppm and 0–50 ppm; with relative standard deviation of 5%–10%). For methylene blue verification test, 10 mL of 0.001% MB liquid solution was taken on a weight boat and treated with plasma from the newly designed plasma jet reactor. The treated MB solution was stored in the refrigerator, and the absorbance was tested before and after using a UV-vis spectrophotometer (V-1200, Wavelength accuracy ±2 nm, Missouri, TX-77489, United States of America) at 610 nm wavelength to measure the discoloration from the reactive gas species.

Fungi inoculation

One of the most dominant fungi for fruit and vegetables, Aspergillus flavus, was purchased from Carolina Biological (Carolina Biological Supply Company, Charlotte, NC 28260, United States of America). About 23 g agar was taken and mixed with 1L dH2O in a screw top bottle with a stirring bar. The bottle was then sterilized in an autoclave at 121 °C and plated in the Petri dish. After plating, a wait period of 30 min was maintained to cool and solidify, then it was put in an incubator at 37 °C for 24 h (keeping plates upside down).

For inoculant preparation, 6–8 mL distilled water was poured on the sporulating plate purchased from Carolina Biological. The mycelium growth was then scraped with a sterile loop or spoon and all liquid was transferred into a conical tube. The solution was mixed on a vortex for 60 s, filtered to remove mycelial fragments, and centrifuged at 1800 rpm for 10 min to produce supernatants. The supernatants were removed, and 1 mL distilled water added to the remaining solution in the tube, and vortexed again. The remaining amount was then added with glycerol solution to make 20% final glycerol solution. The mixture was serially diluted two time and used for inoculation or stored at −20 °C for future use. About 10 µL of inoculants were plated on the 90 mm * 15 mm PDA prepared Petri dishes in the center maintaining 1 cm 2 spread area and were treated with the designed plasma jet.

Plasma treatment and Morphological analysis

The reactor with the handheld capacity was used manually to treat directly on the surface of the sample, in this case on the Petri dish (Supplementary Figure S1). Fungi inoculated Petri dishes were treated for 3 min and 5 min exposure length with newly designed plasma jet (Supplementary Table S1). All control/treatment types were in triplicate form. The untreated (0 min) control samples served as a common baseline for all treatment groups under identical storage conditions. After the treatment, controls and treated samples were kept in room temperature (22 o C) and freezing temperature at 4 o C to mimic the storage conditions of fruits and vegetables. The growth was monitored every 12 h for 3–10 days for colony counts and compared using a computer aided microscope (Olympus SZ61, Olympus Latin America Inc., Miami, FL-33126, United States of America).

Formaldehyde production and treatment

Formaldehyde gas (HCHO) was produced from 10% neutral buffered formalin, (9.5%–10.5% v/v solution; VWR International LLC, Radnor, PA-19087) through heating at 82–90 o C and using metal oxides (Coarse SiO 2; Wards Science, Rochester, NY-14692) as catalyst [25, 26]. The produced gases were diluted with filtered ambient air flow using a small air flow pump. Two portable multifunctional air quality monitors (Manufactured by NALACAL; Model: ED-8I-J) were placed in the produced gas line before and after the plasma treatment. These AQ monitors can measure HCHO (0–1 mg/m 3 range), Total Volatile Organic Compounds (TVOC) (0–2 mg/m 3 range), CO 2 (350–2000 ppm range), Temperature (0–90 o C), and Relative Humidity (0%–99%) of the gas. The gas analyzers were calibrated before sampling. The expected output gases from the breakdown of the HCHO gas were obtained and recorded using the gas analyzing air quality monitor. The schematic design of the overall set up and gas flow is presented in Supplementary Figure S2. A tube heater was added to the exhaust line to break down the ozone generated during the plasma treatment. The IBM SPSS statistical program (version 21), Python, and Microsoft Excel were used to analyze the data. All the samples were tested for significance at the 0.05 level using one-way ANOVA analysis.

Oscilloscope analysis

Current intensity is instrumental in understanding the plasma discharge nodes [27, 28]. Discharge phenomena and power requirement can be achieved from the voltage signal (V) and current waveforms (I) passing the rod electrode. Both V and I were determined at different VI control input of the plasma power supply. Oscilloscope analysis commonly uses voltage amplitude, period, frequency, and phase shift to interpret signal behavior. An example of voltage waveform generated at 19.2 KHz frequency is demonstrated in Supplementary Figure S3. The period of waveform of the mentioned is 52.4 µs showing the discharge rate in microseconds with a rise and fall time of 13.7 µs and 15.8 µs respectively, consistent with the 20 µs/div horizontal scale.

The horizontal displacement between the two traces (Yellow and Cyan color in Supplementary Figure S3) indicates a phase difference; this can be estimated using ϕ=(Δt/T)×360 ∘, a standard oscilloscope-based phase calculation method. The smoother cyan signal may represent an attenuated response or secondary coupled signal, while the yellow trace represents the main excitation signal. The electrical impedance is sometimes noticeable during plasma discharge, often caused from the movement of the reactor, time, and the complexity of resistor configuration [29]. Overall, the waveform stability suggests consistent plasma jet operation with repeatable electrical behavior.

The current design was operated at 90% frequency and 90% of duty cycle of the generator keeping a safety bar for short circuit free continuous plasma generation. Additionally, the proposed reactor was able to sustain at the maximum 90% of the VI control input above which short circuit occurrence observed. Even at 75% VI controls, there was still some occurrence of short circuits causing the breakdown of plasma discharge. The plasma gas characterization was limited at that level and thus excluded in validation and characterization steps. This can also be considered as the limitation of the proposed plasma jet design. However, the presented reactor design could generate maximum peak to peak (pp) voltage of 11.8 kV and a current of 87 mA (Figure 2). Both the maximum and minimum voltage generation showed linearity with the increasing control input. Additionally, the consistency of the power measurement is not guaranteed due to the deviated characteristics of the waveform during each individual plasma generation event. The optimized treatment condition considering the scenarios discussed lies in the range of 15%–60% VI control. Although voltage and current characteristics were monitored to evaluate reactor operation, deposited discharge power, specific input energy, and energy yield were not determined in the present study and should be investigated in future work for performance benchmarking. Discharge power can be estimated using established Lissajous or instantaneous power integration methods and Q-V plots, as demonstrated in previous and most recent atmospheric cold plasma studies [30, 31].

Ozone (O 3) and NOx analysis

The level of O 3 and NOx species generated in the plasma at different voltages is graphed in Figure 3. Previously, many studies reported that the concentration of Ozone increases with the increasing voltages [32, 33]. Hence, the present study plotted the rise of O 3, NO, and NO 2 concentration with the function of voltages which was determined using the oscilloscope results in the previous section. Maximum mean O 3 of 50 ppm and NOx (NO and NO 2 combined) of 41.5 ppm was generated at 10.34 kV peak-to-peak voltages (Figure 3). Higher energy as in higher voltage can facilitate faster dissociation of air molecules and gases provided to convert to high energy species like O 3, NO, and NO 2.

Additionally, the reaction pathway for O 3 generation shown in Equations 1–3 below adopted from Huang et al. [34]. Due to the presence of Nitrogen (N 2) gas in the air, the super excited nitrogen oxide species are also generated in the plasma gas following Equations 4–7 [35]. Moreover, penning ionization can initiate the formation of metastable nitrogen molecules which ultimately transform into NOx species. Increasing power resulted in higher NOx species in the present study agreeing with previous study on DBD discharge plasma from He-N 2 gas mixtures [36].

It is noteworthy that the feeding air for plasma generation was not dry, and the humidity of the air during the treatment conditions ranged from 52% to 69%. The plasma discharges from the reactor may contain more than the mentioned reactive species and were characterized by OES in the next section. The electric field requirements for air in atmospheric pressure to cause Townsend breakdown of 1 cm size gap is about 32 kV/cm [37]. However, chemical changes in the humid air are more complex than the dry air.

Thermal images were collected using an FLIR thermal infra-red camera (Supplementary Figure S4) which showed to have maximum 2 o C difference in the plasma zone compared to the reactor surface environment. This complies with the ionization characteristics from temperature differences of the non-equilibrium cold atmospheric pressure plasmas.

OES spectrum for RGS characterization and methylene blue validation

The elevated emission intensity observed in the present study at higher applied voltage, which enhances electron-impact excitation, dissociation, and ionization reactions inside the plasma plume (Figure 4). The voltage and current individually or in combination (power) regulates the concentration or the intensity of RGS. Added to this, it is well known that feeding gas flow rate, electrode geometry, pulse frequency, and humidity strongly influence the characteristics, lifetime, and or types of RGS produced in a plasma system. However, moderate humidity increases OH density [37], while high humidity can reduce residence time and conversion efficiency. Furthermore, stronger electric fields accelerate electrons, increasing collisions with N 2, O 2, and H 2 O (from sample surface or humidity) molecules, thereby promoting the formation of excited N 2 states, atomic oxygen, OH radicals, ozone precursors, and NOx intermediates [39]. The majority of the short-lived (ns-µs) excited N 2 states generated in the plasma plume [40] has cell rupture and electron dissociation potential.

From the current study, nitrogen (N 2) species band at 337.20 nm wavelength was the highest intensity discovered in the plasma jet stream [36, 41]. The dominating nitrogen concentration in the air also caused the generation of more transitional nitrogen species at 295.96 nm and 612.79 nm wavelengths. In food safety, OH radicals, ozone, singlet oxygen, and nitrogen oxides can damage microbial cell walls, proteins, and nucleic acids, leading to rapid decontamination of fresh produce, packaging surfaces, and processing equipment without significant thermal damage [1]. Some examples of the metastable species from electron collision excitation are presented in Figure 4 (inset). The current study RGS is also compared with previously studied air plasma and found similar trend in peaks but with higher intensity [42]. However, lower energy input/power reduced the intensity level of the generated gas species and diminished some completely. Reactive oxygen species (ROS) were predominant at 357.50 nm and 375.24 nm wavelengths. These ROS can drive VOC removal by attacking aromatic rings and C–H bonds, leading to fragmentation and oxidation of pollutants such as toluene into smaller oxygenated intermediates [43].

From the above plasma gas species quantification and spectral characterization, it is eminent that VI control 45 and 60 provides higher emission intensity of reactive species considering the reactors consistency for long term operation and sustainability. For that reason, the microbial growth study and VOC treatment only accounted for these two plasma generation controls. VI control 45 generates a voltage of 3.6 kV, while VI control 60 generates 4.5 kV maximum.

Additionally, the methylene blue degradation capacity of each two voltages of VI 45 and VI 60 at both 3 min and 5 min treatment times are presented in Figure 5. One-way ANOVA revealed a significant effect of treatment on methylene blue degradation (p < 0.001). Tukey’s HSD post-hoc test showed that all treatment groups differed significantly from one another (p < 0.05), with the highest degradation mean of 52.48% achieved at 4.5 kV for 5 min. These results indicate that increasing both the applied voltage and treatment duration significantly enhanced the oxidative degradation efficiency of the plasma jet.

Evaluation of fungal growth analysis

Fungal growth on the plate was observed every 12 h and recorded in days. In the control groups, fungi growth occurred earliest in the room temperature. The plasma jet treatment delayed the fungal growth compared to control groups in the plates (p < 0.05) except the plate treated at 4.5 kV for 3 min and stored at 4 °C. For the plates stored in room temperature, the fungal growth delayed 2 days maximum when treated with 4.5 kV plasma jet stream for 5 min (Figure 6). Moreover, plates stored at 4 °C showed maximum 4 days fungal growth delay compared to controls when treated with 4.5 kV plasma for 5 min. The overall trend of fungal growth delays as function of time and voltage combination was increasing which eventually suggests that treatment duration influences fungal growth delay and merit further investigation on real food matrices. This trend is consistent with previous studies reporting that plasma-generated reactive oxygen and nitrogen species (RONS), UV photons, charged particles, and localized electric fields damage fungal spores through membrane oxidation, leakage of intracellular materials, and disruption of DNA and enzymatic systems [14].

The earliest spoilage in untreated room-temperature controls was expected because A. flavus grows rapidly under warm conditions with favorable metabolic activity. In contrast, refrigerated storage alone slowed fungal growth, while combining refrigeration with plasma treatment produced higher preservation effect. Greater fungal growth delay was observed when plasma-treated samples were stored under refrigeration. This observation may be attributed to reduced fungal growth kinetics at low temperature together with the reduced viable spore population following plasma treatment. However, the present experimental design was not intended to isolate the interaction between plasma treatment and storage temperature. Similar benefits of plasma combined with cold storage have been reported for fresh produce and bakery systems [4, 44].

Figure 7 demonstrates the Aspergillus flavus CFU/plate counts after day 5 and day 10 of storage of the plates. Maximum 3.86 logCFU/plate A. flavus was observed in control room temperature plates after 10 days of storage. One-way ANOVA revealed significant differences among treatment groups on both Day 5 (p < 0.001) and Day 10 (p < 0.001). Tukey’s HSD post-hoc analysis showed that refrigerated treatments exhibited significantly lower fungal counts than the corresponding room-temperature treatments (p < 0.05), whereas differences among plasma treatment durations (3 and 5 min) and voltages (3.6 and 4.5 kV) within the same storage condition were not statistically significant. However, the lowest fungal population after 10 days was recorded for samples treated at 4.5 kV for 5 min, although this was not statistically different from the other plasma treatment conditions within the same storage condition. This also denotes the reduced susceptibility of sample surfaces to A. flavus after the proposed plasma jet treatment. Although, the complexity of food surfaces may bring additional entanglement in extending the shelf-life using plasma treatment. Since A. flavus is also a known aflatoxin-producing fungus, reducing its surface growth has added food safety importance beyond shelf-life extension, as inhibition may lower risks of toxin formation during storage [45]. Unlike bulk thermal treatments, plasma jets can be directed to localized food surfaces and irregular geometries, allowing targeted delivery of reactive species with minimal heat damage while preserving product quality. Recent review studies further highlight plasma jet as promising non-chemical tools for fungal control, aflatoxin reduction, and shelf-life extension in foods [46, 47].

VOC abatement analysis

The VOC abatement profiles further support that atmospheric plasma jet treatment was moderately effective for degrading indoor gaseous pollutants, with removal efficiency strongly dependent on applied voltage and exposure time. The data from the monitor were recorded every 120 s for the 3.6 kV while every 30 s for the 4.5 kV. These sampling intervals were selected according to the observed degradation rate at each operating voltage to adequately capture the concentration changes throughout the treatment period. In Figures 8, 9, HCHO and TVOC reductions increased rapidly during the initial treatment period, followed by a slower approach toward saturation, indicating that readily available pollutant molecules were first oxidized, while remaining compounds required longer residence time and repeated interactions with reactive species. This non-linear behavior is commonly observed in plasma oxidation systems where pollutant concentration declines progressively as treatment proceeds. Maximum 48.64% of formaldehyde reduction was observed after a 90 min continuous plasma treatment at 3.6 kV. The plasma jet treatment continued until good quality air was observed considering the HCHO level of less than 0.040 mg/m 3. The maximum TVOC reduction recorded was 47.23% at 90 min.

The substantially faster removal at 4.5 kV compared with 3.6 kV demonstrates the importance of discharge energy in VOC degradation which agrees with a previous study of achieving higher removal efficiency with more discharge power or voltage [21]. Higher applied voltage is expected to increase electron energy and excitation processes [39, 40]. This can stimulate the generation of reactive oxygen and nitrogen species such as O, OH, O 3, and NO radicals, which actively attack VOC molecules through bond cleavage, oxidation, and mineralization pathways. Compared with the 92.17% reduction observed for HCHO at 4.5 kV, the lower MB removal mentioned in segment 3.3 above can be attributed to the plasma-liquid interaction, where reactive species must diffuse across the gas-liquid interface and are partially consumed by recombination and scavenging reactions before reacting with dye molecules. In contrast, gaseous VOCs are directly exposed to energetic electrons and reactive species over a longer treatment duration (38 min), enabling more efficient oxidation and degradation. Formaldehyde is typically converted through intermediate formate species into CO 2 and H 2 O, while mixed VOCs undergo fragmentation into smaller oxygenated compounds before final oxidation [39, 48]. Additionally, plasma induced chemical changes include bond scission, oxidation, and partial conversion to low molecular weight oxygenates [49], while strong ionization heavily influences VOC degradation [50].

Additionally, the relationship between initial and post-treatment concentrations was evaluated using scatterplots with 95% confidence bands (Figure 10) in python. A strong positive linear association was observed for both HCHO and TVOC, with R 2 values of 0.81 and 0.85, respectively, indicating that the initial concentration explained most of the variability in the remaining concentration after plasma treatment. Most data points were distributed within the confidence band, supporting the consistency of the fitted regression models and association between initial and residual concentrations under the tested operating conditions. The upward trend suggests that samples with higher initial HCHO and TVOC concentrations generally retained higher residual concentrations after treatment, even though substantial reduction occurred. This indicates that plasma jet treatment was effective, but degradation efficiency may become limited at higher pollutant loading due to increased competition for reactive gas species, shorter effective reaction availability, and incomplete oxidation of volatile compounds within the treatment period.

Scope and challenges of cold plasma jet

The versatility of cold plasma technology makes it easy-to-adopt process for utilization in food and agriculture, environmental treatment, and medicine. The newly designed plasma jet has the potential to mitigate air pollutants and surface disinfection. However, there are some challenges associated with using cold plasma technology, including questions about the treatment period or reaction time required for effective control and the environmental impact of the wide range of reactive gas species it produces. The proposed design also exerts a notable amount of ozone and other reactive gas species. Direct release of ozone produced through the plasma system into the atmosphere can cause environmental pollution. Hence, the recommendation to counter this problem is to use a smart heater to break down the Ozone faster (needs to be lowered below 0.3 ppm) to be released into atmosphere. The present study did not measure Ozone at the tube heater outlet and consider this as a limitation. Additionally, while there is experimental data that verifies the effects of cold plasma on different fields including food safety and air improvement, more evidence through substantial research considering scalability, cost effectiveness, and system appropriateness is needed to show that it can be used effectively in agricultural fields and commercial or indoor facilities. Table 1 represents the current study reactor performance comparative to previous studies using atmospheric pressure cold plasma jets. The scope of plasma jet application in commercial scale is still in rigorous development stage with a few industrial applications already initiated. A study on the efficacy of aluminum alloy surface treatment using an industrial atmospheric pressure plasma jet system was able to successfully improve paint adhesion properties [51]. However, another study on particulate food using a pilot scale atmospheric plasma jet treatment system could not significantly decontaminate bacteria populations (maximum log reduction was about 1.1 CFU/g) from rice germ when the treatment time was 3–10 min [52]. Although increasing treatment time could improve microbial inactivation demonstrating longer treatment time requirement for efficient reduction. Biodiesel production waste cooking oil can also be facilitated using the plasma jet through treatment at 20 °C and plasma catalysis at 65 °C contributing to energy conversion from waste [53]. It is also expected that cold plasma treatment can potentially hydrogenate the unsaturated double bonds of oil compounds and convert straight chain saturated alkanes due to the production of hydroxyl radicals and other RGS and interacting through energetic inelastic collisions. The utilization of non-thermal DBD plasma for CO 2 conversion and VOC abatement from waste air has been reviewed in other study which thoroughly explored the pathways for CO 2 conversion and pollution control [54, 55].

To summarize, although the present study demonstrates proof-of-concept applications, future work should include deposited discharge power measurements, energy-yield analysis, reactor optimization, validation on complex food surfaces, and assessment under realistic indoor air environments before practical implementation. Atmospheric cold plasma technology is regularly providing new approaches for solving environmental and health problems. This new paradigm shifting technology can bring sustainability in agriculture and the environment and bears tremendous potential to improve human health by delivering breathable air and safe food.

The motivation for this work stems from the significant economic and health burden associated with postharvest losses and indoor air pollution. Existing microbial spoilage decontamination and VOC abatement approaches such as thermal processing, chemical fumigation, and conventional air filtration systems often compromise product quality, require chemical inputs, or lack effectiveness for low-concentration pollutants.

This preliminary study demonstrates the feasibility of a portable atmospheric cold plasma jet as a non-thermal alternative with measurable performance benefits and potential for future development. The reactor generated maximum 50 ppm O 3 and 41.5 ppm NOx combined, confirming effective reactive species production. Microbial analysis showed up to 4-day delay numerically in Aspergillus flavus growth under refrigerated conditions indicating the potential for delayed fungal growth under refrigerated laboratory conditions. In parallel, the system achieved up to 92.17% HCHO and 91.89% TVOC reduction at 4.5 kV within 38 min, outperforming lower voltage operation and demonstrating the importance of discharge energy in pollutant degradation kinetics.

Statistical analysis (R 2 = 0.92 - 0.78) for HCHO confirmed strong correlations between initial and residual pollutant concentrations at slow and fixed air flow rate, highlighting system consistency while also indicating reduced efficiency at higher pollutant loading due to reactive species limitations. Compared to conventional treatments, the plasma jet offers zero thermal damage and high operational flexibility, making it suitable for decentralized or on-site applications.

Despite these promising results, practical implementation requires further investigation, including airflow dynamics, energy efficiency, ozone mitigation, and validation on real food matrices and complex air streams. Overall, this study provides a foundation for future optimization and integral step toward scalable, portable plasma technologies with the potential to reduce food losses and improve indoor air quality, thereby contributing to both economic savings and public health protection.