Understanding Indoor Ozone and Its Impact on Air Quality:
Welcome to another episode of Air Quality Matters. Today, I had the pleasure of talking with Charles Weschler, a distinguished expert in indoor air chemistry. Charles’s impressive career spans decades, starting with his PhD in chemistry from the University of Chicago, postdoctoral studies at Northwestern University, and a notable tenure at Bell Laboratories. He currently holds positions at Rutgers University and the Technical University of Denmark and has been a visiting professor at Tsinghua University in Beijing.
In this episode, we delve into the intricate and often misunderstood world of ozone, its formation, and its significant role in indoor environments. Charles provides a comprehensive understanding of ozone, explaining its composition and reactivity. Ozone, a molecule consisting of three oxygen atoms, is a more potent oxidant compared to the oxygen we breathe. While it’s less abundant than dioxygen, its reactivity with certain molecules, particularly those with carbon-carbon double bonds, is critical in indoor air chemistry.
The Formation and Behavior of Ozone
Outdoor ozone primarily forms through the action of sunlight on a mix of organic compounds and nitrogen oxides. This photochemical reaction peaks during the day, particularly in the summer, and diminishes at night. In urban areas with high motor vehicle emissions, ozone levels can drop to almost zero overnight due to reactions with nitric oxide from exhaust gases. In contrast, suburban and rural areas may experience elevated ozone levels at night, influenced by air masses transported from urban centres.
Understanding outdoor ozone is essential for comprehending indoor ozone dynamics since most indoor ozone originates from the outdoors. Charles explains that while indoor ozone levels are generally lower than outdoor levels, the transport of outdoor ozone into buildings plays a significant role in indoor air quality.
Health Implications of Ozone
One of the key points Charles emphasises is the health impact of ozone. Long-term exposure to elevated ozone levels is associated with various adverse health outcomes. A notable study by Turner et al. (2016) highlights that a 10 ppb increase in outdoor ozone correlates with a 12% increase in respiratory mortality, a 3% increase in cardiovascular mortality, and a 2% increase in overall mortality. These findings underscore the importance of understanding and mitigating ozone exposure.
Indoor ozone levels are typically lower due to reactions with indoor surfaces and chemicals in the air. For example, in a scenario where outdoor ozone is 35 ppb, indoor levels might be around 5 ppb. However, because we spend most of our time indoors, the cumulative exposure to ozone indoors can be comparable to outdoor exposure. This residual concentration of ozone indoors, after reacting with various indoor elements, is a critical factor in assessing indoor air quality.
Mitigating Indoor Ozone
Charles discusses several strategies for mitigating indoor ozone levels. One approach is using materials and surfaces that react with ozone without producing harmful byproducts. For instance, activated carbon and certain clay-based paints can effectively remove ozone..
In commercial buildings, activated carbon filters in HVAC systems can significantly reduce ozone levels before they enter indoor spaces. This proactive approach is more effective than relying solely on standalone air cleaners, which may only address ozone after it has already entered the indoor environment and initiated reactions.
The Role of Indoor Chemistry
Indoor chemistry, particularly reactions involving ozone, is a complex and evolving field. Charles highlights the importance of considering human activities and materials that can influence indoor ozone levels. For example, limonene, a common terpene found in scented products, reacts rapidly with ozone, producing formaldehyde and other potentially harmful compounds. Therefore, selecting products with lower reactivity to ozone can be a practical step in improving indoor air quality.
Cooking activities also contribute to indoor ozone chemistry. Unsaturated cooking oils, such as olive oil, react more readily with ozone, producing aldehydes and other byproducts. While these oils may be healthier for consumption, their reactivity with ozone poses a challenge for indoor air quality management.
The Future of Indoor Air Chemistry Research
Advancements in instrumentation and monitoring technology offer promising opportunities for furthering our understanding of indoor air chemistry. The development of sensitive, cost-effective instruments for measuring indoor ozone and its byproducts will enable more comprehensive studies and better-informed mitigation strategies. Additionally, the exploration of biomarkers to differentiate between ozone exposure and ozone product exposure could provide valuable insights into the health impacts of indoor air chemistry.
Charles underscores the need for continued research and funding in this area, emphasising the importance of understanding the intricate interactions between ozone and various indoor elements. As we navigate the complexities of indoor air quality, it becomes increasingly clear that proactive measures and informed choices can significantly impact our health and well-being.