This is a new series in which we hear from CARTEEH-affiliated researchers on current topics of interest related to our research program.
Air pollution in the United States (U.S.) was increasing at alarming rates in cities after the Great Depression and World War II, which negatively impacted public health and the environment. One significant attributable factor is more reliance on personal vehicles for transportation, leading to an increase in number of cars and trucks, as the economy recovered, population experienced growth, and rapid urbanization in cities1. On a positive note, there has been successful national efforts to regulate air pollution from vehicles since the passage of the Clean Air Act in 19701. The image below shows a comparison of smog levels in New York City from the 1970s and 2010s. As evident, there has been noticeable improvements in air quality and these changes were also observed in other major cities1.
Unfortunately, new images captured last week in New York City (as shown below)2 illustrate a return to significant, visible, air pollution of the past. The recent ravaging wildfires in eastern Canada clogged the air across northeastern U.S. with unhealthy levels of smog. The skies turned orange from the dangerous levels of pollution which are subsequently linked to adverse health impacts including respiratory issues, organ impairment and premature death3, 4.
What is causing an increase in the frequency of wildfires? Warmer and dry weather conditions are catalysts for wildfires3, 4, 5. Human activity is another common factor3. Wildfire season typically occurs between late May and early June however, changing climate conditions and extreme weather events has caused a shift in the start of the season. Wildfires in recent years have been starting earlier in the year5. They are also becoming more frequent and more destructive. Acres of land burned this year have already surpassed the area of land that burned from 2021’s extreme wildfire season3, 5. Climate change is driven by greenhouse gas (GHG) emissions from human activities. The transportation sector is a major contributor to GHG emissions as it accounted for 28% of total GHG emissions in 20216.Therefore, there is a strong correlation between traffic-related air pollution, climate change and the occurrence of wildfires.
Is pollution from wildfires and vehicle emissions similar or different? Smog blanketing inhabited areas can be caused by various polluting sources, predominantly from internal combustion engines in vehicles and wildfires. Studies have showed that there are some similarities in the pollutants released from wildfires and on-road cars and trucks6. Both sources release harmful microscopic particles known as fine particulate matter or PM2.5 (particles with aerodynamic diameter of 2.5 µm)7, 8. These particles are smaller than the diameter of a strand of human hair which allows them to penetrate the respiratory tract and enter bloodstream hence imposing health risk to humans8. Other pollutants released also include carbon monoxide, nitrogen oxides and volatile organic compounds. However, the composition of emissions from wildfires and vehicles might differ. According to researchers at Scripps Institution of Oceanography at UC San Diego, current toxicological studies demonstrated that PM2.5 released from wildfires are up to 10 times more toxic than PM2.5 released from other sources8. Moreover, the table below compares the characteristics of pollution from wildfires and vehicles.
|Characteristics||On-Road Transportation Sourcesfire||Wildfires|
|Pollutants released||Particulate matter (PM), carbon monoxide (CO), nitrogen oxide (NOx), volatile organic compounds (VOCs)7.||Particulate matter (PM), carbon monoxide (CO), nitrogen oxide (NOx), volatile organic compounds (VOCs)7.|
|Scale and intensity||Relatively small-scale impact from an individual vehicle but can be significant with larger volumes of cars and trucks7.||Large-scale but for shorter period (during wildfire events)7.|
|Spatial distribution||Higher concentration in urban areas, densely populated areas and near major roads7.||Pollutants disperse over larger geographic areas (depends on location and extend of wildfire)7.|
|Duration||On-going and persistent issue7.||Temporary (depends on intensity of wildfire and occur mostly during wildfire season)7.|
|Composition of harmful pollutants||PM from combustion by-product, brake and tire wear, and dust suspension7.||PM from combustion of vegetation which consist of complex carbon, organic and inorganic compounds7.|
|Health impact||PM related respiratory hospitalizations can range between 1.3% to 10PM related respiratory hospitalizations can range between 0.67% to 1.3%8.||PM related respiratory hospitalizations can range between 1.3% to 10%8.|
In conclusion, research findings indicate that climate change is increasing the chance of wildfires occurring more frequently in North America. Climate change is also intensifying the magnitude of wildfires. It is well established that there are interdependencies between warmer climate conditions and transportation emissions. The transportation sector emits a major proportion of greenhouse gases in the U.S. and these emissions are drivers for climate change. Harmful pollutants released from wildfires can have severe impacts on public health. A new study showed that approximately 25 million people in the U.S. were potentially breathing toxic air during the wildfire season9 with vulnerable populations experiencing higher risk for adverse health effects10.
Both wildfires and on-road transportation sources contribute to air pollution. Pollution from these sources can have certain similarities and at the same time, they can have different characteristics and impacts. As a result, it is important for air quality regulations to acknowledge the variability in the composition of harmful pollutants emitted from wildfires and vehicles as their impact on human health varies. Mitigating the exposure to unhealthy levels of air pollution heavily relies on community engagement. In other words, state and local agencies should provide households and communities with real-time air quality data and alert them on when to avoid smoke exposure. This can be achieved by improving air quality monitoring systems and public health programs with equity considered in the planning process.
- United States Environmental Protection Agency (2023). History of Reducing Air Pollution from Transportation in the United States. https://www.epa.gov/transportation-air-pollution-and-climate-change/history-reducing-air-pollution-transportation
- Jenny Gross (2023). What Happens When the Air Quality Index Surpasses 500? The New York Times. https://www.nytimes.com/2023/06/09/climate/air-quality-index-500.html
- Brian Owens (2023). Why are the Canadian wildfires so bad this year? Nature News Article. https://www.nature.com/articles/d41586-023-01902-4
- Cara Korte (2023). How did the Canadian wildfires start? A look at what’s causing the fires that covered the East Coast in smoke. CBS News. https://www.cbsnews.com/news/how-did-the-wildfires-in-canada-start-cause-nova-scotia-quebec/
- Rachel Ramirez (2023). Canada’s wildfire season is off to an ‘unprecedented’ start. Here’s what it could mean for the US. CNN. https://www.cnn.com/2023/06/10/us/canada-wildfire-season-us-impact-climate/index.html
- United States Environmental Protection Agency (2022). Climate Change Indicators: Greenhouse Gases. https://www.epa.gov/climate-indicators/greenhouse-gases
- United States Environmental Protection Agency (2023). Research on Near Roadway and Other Near Source Air Pollution. https://www.epa.gov/air-research/research-near-roadway-and-other-near-source-air-pollution
- R. Aguilera et al. (2021). Wildfire smoke impacts respiratory health more than fine particles from other sources: observational evidence from Southern California. Nature Communications. https://www.nature.com/articles/s41467-021-21708-0#Sec5
- Oliver Milman (2022). Number of Americans Exposed to Harmful Wildfire Smoke Has Increased 27-Fold. Yale E360 Digest and The Guardian. https://e360.yale.edu/digest/americans-pollution-unhealthy-wildfire-smoke#:~:text=The%20number%20of%20people%20in,potentially%20toxic%20air%20from%20fires.
- United States Environmental Protection Agency (2022). Which Populations Experience Greater Risks of Adverse Health Effects Resulting from Wildfire Smoke Exposure? https://www.epa.gov/wildfire-smoke-course/which-populations-experience-greater-risks-adverse-health-effects-resulting