The third toxic gas I will be discussing is sulfur dioxide (SO2), a colourless but odorous gas that is highly toxic (United States Environmental Protection Agency, 2023). It is most commonly produced from the burning of fossil fuels and by the smelting of sulfur-containing mineral ores (Queensland Government, 2017). Naturally, erupting volcanoes are a significant source of SO2 emissions (Queensland Government, 2017). Similar to HF discussed in blog 11, SO2 is much more toxic compared to other gases released during the burning of lithium-ion batteries (LIBs) (Peng et al., 2020).
Within batteries, SO2 is produced from burning sulfur-based compounds which are commonly used as reduction-type additives (Peng et al., 2020; Zhang, 2006). Similar to other toxic gases released during the burning of LIBs, the concentration of SO2 released depends on the state of charge (SOC) of the battery (Peng et al., 2020). The higher the SOC, the higher the concentration of SO2 released (Peng et al., 2020) (Figure 1). Despite, a lower concentration at lower SOCs, SO2 continues to make up a large part of all the toxic gases released regardless of SOC (Peng et al., 2020). While the maximum concentration of SO2 released, 115 mg/m3 (around 43.89 ppm), does not pose an immediate threat to the survival of a person, this concentration is more than enough to cause, mucositis, irritation to mucous membranes (Peng et al., 2020; Cleveland Clinic, 2022 ).
According to Queensland Government (2017), the recommended air quality standards for sulfur dioxide are:
- 0.20 ppm for a 1-hour exposure period
- 0.08ppm for a 24-hour exposure period
- 0.02ppm for an annual exposure period.
Health impacts of high concentrations of SO2:
- Respiratory problems
- Difficulty to breath, people with existing respiratory problems such as asthma, and young children are particularly sensitive to the impacts of inhaling SO2.
- People with existing heart problems and diseases are also much more sensitive to the effects of SO2.
2. Painful sores in the mouth/ gastrointestinal symptoms
- High concentrations of SO2 will result in soreness in the mouth due to mucositis. Coughing and throat irritation are common symptoms related to high exposure to SO2 as well.
(United States Environmental Protection Agency, 2023; Queensland Government, 2017)
Besides the direct impacts of SO2, SO2 can react with other chemicals in the atmosphere to form small particles that can easily enter the lungs of a person causing adverse health impacts (Queensland Government, 2017). For instance, reactions between SO2 and NOx form sulfates, which form fine particles (He et al., 2015). These fine particles are often the main culprit behind haze in parts of the world (He et al., 2015). They were also the main cause of the major haze events in Beijing-Tianjin-Hebei regions in China in 2013 (He et al., 2015).
Figure 1: Haze event in Beijing in 2013 (Branigan, 2013)
Reference List
Branigan, T. (2013, January 14). Beijing smog continues as Chinese state media urge more action. The Guardian. https://www.theguardian.com/world/2013/jan/14/beijing-smog-continues-media-action
Cleveland Clinic. (2022). Mucositis: Types, Symptoms & Treatment. https://my.clevelandclinic.org/health/diseases/24181-mucositis#:~:text=Mucositis%20is%20inflammation%20of%20the,painful%20and%20carries%20certain%20risks
He, H., Wang, X., Ma, Q., Ma, J., Chu, B., Ji, D., Tang, G., Liu, C., Zhang, H., & Hao, J. (2015). Mineral dust and NOx promote the conversion of SO2 to sulfate in heavy pollution days. Scientific Reports, 4(1). https://doi.org/10.1038/srep04172
Peng, Y., Yang, L., Ju, X., Liao, B., Ye, K., Li, L., Cao, B., & Ni, Y. (2020). A comprehensive investigation on the thermal and toxic hazards of large format lithium-ion batteries with LiFePO4 cathode. Journal of Hazardous Materials, 381, 120916. https://doi.org/10.1016/j.jhazmat.2019.120916
Queensland Government. (2017, March 27). Sulfur dioxide. Environment, Land and Water | Queensland Government. https://www.qld.gov.au/environment/management/monitoring/air/air-pollution/pollutants/sulfur-dioxide#:~:text=Sulfur%20dioxide%20affects%20the%20respiratory,as%20asthma%20and%20chronic%20bronchitis
United States Environmental Protection Agency. (2023, February 16). Sulfur Dioxide Basics | US EPA. US EPA. https://www.epa.gov/so2-pollution/sulfur-dioxide-basics
Zhang, S. (2006). A review on electrolyte additives for lithium-ion batteries. Journal of Power Sources, 162(2), 1379–1394. https://doi.org/10.1016/j.jpowsour.2006.07.074