In my previous entry, I discussed how green infrastructure could be employed to improve outdoor air quality. However, indoor air quality is another pertinent issue that should not be overlooked. While most people might associate good indoor air quality with the use of air purifiers, I want to introduce another form of technology less commonly heard of – the electrostatic precipitator (ESP).
According to Afshari et al. (2020), ESPs are famed for their ability to efficiently filter out air pollutants while causing pressure drops that are lower in magnitude as compared to high-efficiency particulate air (HEPA) filtration systems. The authors explain the mechanism underlying ESPs to be the “[using] the forces of an electric field on charged particles to separate gas particles from a gas stream”. Through this process, charged particles stick to an “oppositely charged electrode” serving as a collection surface, allowing clean air to flow out of the ESP.
Figure 1. Schematic of the basic processes of an electrostatic precipitator (Afshari et al., 2020)
The effects of using ESPs have been studied by Lusiandri et al. (2019), who highlight that ships running on high fuel oil (HFO)s generate and emit large volumes of pollutants that could be harmful to those aboard. Drawing inspiration from the idea of installing ESPs in chimneys to clean the air that will be passed into ship rooms, the authors found that ESPs were able to reduce the overall emission of pollutants from the main engine of a diesel machine within just 15 minutes. In particular, nitrogen dioxide and sulphur dioxide emissions were decreased by 50% and 45.2% respectively, indicating significantly cleaner air quality.
Figure 2. Set-up of data collection where an ESP was in the main engine of a diesel machine (Lusiandri et al., 2019)
Figure 3. Percentage of nitrogen dioxide and sulphur dioxide emitted by the diesel machine’s main engine before and after using the ESP (Lusiandri et al., 2019)
Pellegrin et al. (2022) also demonstrate the effectiveness of ESPs as a replacement for traditional HEPA filtration systems in aeroplane cabins. Aside from savings in power consumption associated with the low pressure drops, the authors noted another key benefit of electrical charging by ESPs over mechanical filtration in HEPA systems. Mechanical filtering by HEPA systems may end up providing a conducive environment for the development of bioaerosols released from passengers such as microorganisms and bacteria. On the other hand, electrical charging from ESPs can impede the survival of bioaerosols and restrict their growth. Overall, ESPs were found to have collection efficiencies of over 90% and 88% for particulate matter with diameters of 0.5µm or larger and ultrafine particles, respectively. However, this is least to say that ESPs should definitely be implemented in all aircraft cabins without further research.
A common concern arising from the use of ESPs raised in many publications pertains to the emission of ozone. According to Day et al., (2018) , the process of electrically charging the air causes ESPs to generate ozone as a byproduct. Their study found that the absence of ESPs were responsible for a 2.2 ppb decrease in 24-hour mean ozone exposure. Furthermore, the removal of ESPs was associated with a -16.1% change in plasma soluble P-selectin as well as a -3.0% change in systolic blood pressure indicative of lower cardiovascular risks. Hence, this study illustrates the double whammy of increased ozone exposure as a result of ESP usage and the adverse health consequences that follow.
Much like green infrastructure, the use of ESPs also has its own drawbacks and limitations that call for further research efforts. Could ESPs be developed to function with minimal ozone emission, or will technological advancements yield an innovative complement to ESPs such that we obtain the best of both worlds? In either case, it is becoming clearer and clearer that the management of air pollution is truly not as easy as it seems, spelling a whole list of problems that will emerge should nothing be done about the situation.
Until the next entry, breathe safe and be safe!
References
Afshari, A., Ekberg, L., Forejt, L., Mo, J., Rahimi, S., Siegel, J., Chen, W., Wargocki, P., Zurami, S., & Zhang, J. (2020). Electrostatic precipitators as an indoor air cleaner—a literature review. Sustainability, 12(21), 8774. https://doi.org/10.3390/su12218774
Day, D. B., Xiang, J., Mo, J., Clyde, M. A., Weschler, C. J., Li, F., Gong, J., Chung, M., Zhang, Y., & Zhang, J. (2018). Combined use of an electrostatic precipitator and a high-efficiency particulate air filter in building ventilation systems: Effects on cardiorespiratory health indicators in healthy adults. Indoor Air, 28(3), 360–372. https://doi.org/10.1111/ina.12447
Lusiandri, A. Y., Kristiyono, A. E., & Waskito, K. L. (2019). The application of electrostatic precipitator (ESP) as pollutant reduction in ship. Research, Society and Development, 8(12). https://doi.org/10.33448/rsd-v8i12.1650
Pellegrin, B., Berne, P., Giraud, H., & Roussey, A. (2022). Exploring the potential of electrostatic precipitation as an alternative particulate matter filtration system in Aircraft Cabins. Indoor Air, 32(2). https://doi.org/10.1111/ina.12990