Continuous generation of realistic atmospheric pollution for medical studies and other applications
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Date
2025-10-08
Authors
Βασιλείου, Αθηνά
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Abstract
The problem of atmospheric pollution has been escalating rapidly in the present century, affecting air quality, human health, and ecosystems worldwide. It consists of both primary pollutants, which are directly emitted from sources such as vehicles, industry, and biomass burning, and secondary pollutants, which are formed in the atmosphere through chemical reactions of primary compounds, including ozone, secondary organic aerosols, and oxidized volatile organic compounds. While primary pollutants can often be controlled at their sources, secondary pollutants are more challenging to manage due to their formation through complex atmospheric chemistry. Knowledge and technology are rapidly advancing to help mitigate atmospheric pollution. Atmospheric simulation chambers provide controlled environments to study pollutant formation and evolution, allowing precise investigation of chemical processes. This work focuses on developing a portable chamber that continuously generates mixtures of primary and secondary gas and particulate pollutants at atmospheric concentrations, enabling both chemical studies and medical experiments on pollution related health effects.
The developed system simulates the operation of a continuous stirred-tank reactor (CSTR) with complete mixing, with walls constructed from Teflon. Three series of experiments were conducted. The first series aimed at the continuous generation of ammonium sulfate particles ((NH4)2SO4) under stable conditions, which constitute a secondary particulate pollutant. The second series focused on the continuous generation of diesel particles, which are considered primary particulate pollutants. Finally, in the third series of experiments, a more complex system was developed, consisting of an intermediate-volatility organic compound (IVOC), β-caryophyllene, and two oxidants: ozone (O₃) and hydroxyl radicals (OH). The hydroxyl radicals were generated in the system through ozone photolysis under ultraviolet (UV) irradiation, while in some cases their concentration was further enhanced by the addition of hydrogen peroxide (H₂O₂). In this way, the production of both oxidation products in the particulate phase (secondary organic aerosol, SOA) and products in the gas phase was investigated, with and without the influence of ultraviolet (UV) irradiation.
Regarding the ammonium sulfate ((NH₄)₂SO₄) particle generation experiments, three runs were conducted in order to cover a wide range of mass concentrations (10-222 μg m⁻³). In all three cases, the system reached steady state approximately 2–3 hours after injection and remained at a satisfactorily stable level (maximum deviation of the mean mass concentration among the three experiments: 11.6 %) for up to 69 hours. The produced particles, in all three cases, were within the size range of 14–250 nm. Overall, in these experiments, the system successfully simulated the behavior of a continuous stirred-tank reactor (CSTR).
For the experiments using the diesel particle generator, the system faced several challenges affecting its stability. The most stable period achieved lasted 7.7 hours, with an average mass concentration of 16.2 μg m⁻³ (8.8% deviation) and a mean particle mass diameter of 175 nm. Although the system was able to operate almost autonomously and safely for several days, the overall conclusion was that the diesel particle generator did not meet the requirements for stable production in terms of either concentration or particle size.
Finally, particularly interesting results were obtained from the third series of experiments. In this more complex system, fluctuations were observed, which are natural due to the coexistence of gas and particulate phases. During the dark ozonolysis experiments, the second run was the most stable, with a secondary organic mass concentration of 10.6 μg m⁻³ (12% deviation) lasting almost 41 hours, reaching steady state about 8.5 hours after ozone injection. In these dark ozonolysis experiments, the mean mass particle diameter was 320 nm. Ozone concentration was also very stable at 457 ppb (0.6 % deviation). In this experiment, the mean SOA yield was 6 %, with an O:C ratio of 0.41 ± 0.07. Exposure of the system to UV irradiation led to a decrease in the produced organic mass and an increase in the concentration of gas-phase oxidation products, while the O:C ratio decreased. Τhe addition of an external hydroxyl radical source (H₂O₂) enhanced both the production of secondary organic aerosol and gasphase oxidation products. Finally, the offline analysis revealed the remarkable chemical diversity of β-caryophyllene oxidation, with 374 distinct products identified.
The mobile simulation chamber that was designed can be conceptually approximated to the behavior of an ideal CSTR, while enabling the collection of sufficient sample volumes for subsequent offline chemical analyses. Moreover, its flexibility and portability make it a valuable tool for health-related exposure studies. However, the stability of this system could be improved through an optimized design of selected parts of the experimental setup.
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Keywords
Atmospheric pollution, Medical studies, Atmospheric simulation chambers, Continuous generation of ammonium sulfate particles, Continuous generation of diesel particles, Continuous generation of seconadry organic aerosol (SOA)