Credit: CC0 Public domain
Credit: CC0 Public domain
Numerical air quality models have described the extent of severe negative air quality impacts from Canada’s record wildfires in 2023, demonstrating that almost the entire Northern Hemisphere, not just Canada and the northern United States, was affected.
An article describing the results has been published in the journal Advances in atmospheric science.
Canada’s record-breaking wildfires in 2023 have made headlines around the world not only for their scale (the largest area burned in the country’s history), but also for the severity of their impacts. air quality across this very large country, and even deep into the United States. Smoke from the fires has prompted repeated air quality alerts and even evacuations in many places.
But it was unclear how far such dangerous air pollution had reached beyond Canada and the northern United States, and even in North America, understanding of the dispersal of the most harmful pollutants was limited.
“There were photographs of New York in July in media around the world that showed the city trapped in an almost unbreathable orange haze, as if out of a dystopian film,” said Zhe Wang, lead author of the study and researcher at the State Key Laboratory of Atmospheric Boundary Layer Physics, Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences.
“But what we know about the long-range transport of particles means the fires probably affected Europe and Asia as well. We just didn’t know to what extent.”
So Dr. Wang and other IAP researchers set out to calculate the full global scope of this public health threat using numerical air quality models. Like climate models, air quality models use mathematical techniques to simulate the impact of weather and chemical reactions on the dispersion of air pollutants.
For this work, IAP scientists used the Institute of Atmospheric Physics Aerosol and Atmosphere Chemistry Model (IAP-AACM), a computer model developed in-house as a module within the model. Broader Earth System of the Chinese Academy of Sciences (CAS-ESM). .
The researchers found that although Canada was most severely affected, almost the entire northern hemisphere was subject to a significant decline in air quality due to the transport of pollutants by wind over long distances.
There were six major episodes of widespread air pollution during Canada’s wildfire “season”: May 15-22, June 5-9, June 24-July 1, July 12-19, from August 17 to 15 and from August 17 to 22. Besides Canada itself, the first such episode affected air quality in the north-central United States. The second episode hit the northeastern United States particularly hard.
The model results here match real-world observations. The concentration of fine particles with a diameter of 2.5 microns or less (called PM2.5— the most dangerous particles, compared to larger but less harmful particles with a diameter of 10 microns, or PMten) on June 7, 11 monitoring sites in New York City found that air quality had reached the worst level in more than 50 years.
During the third main episode of severe air pollution, the model suggested that PM2.5 pollutants were transported to Europe, while the fourth such episode concentrated its most severe presence in western Canada and in the north central United States, once again. The fifth episode mainly affected northern Canada, while the sixth episode affected the west and east coast regions of the United States. Due to the northward movement of wildfires, high concentrations of PM2.5 were transported to the Arctic region in mid-to-late summer.
PM2.5 concentrations above the World Health Organization air quality guidelines of 15 micrograms per cubic meter occurred primarily in North America, with more than 40 days of pollution exceeding this limit in Western and Eastern Canada, as well as more than 10 such days. over the northeastern United States.
But due to wildfire plumes carried by prevailing westerly winds across the Atlantic Ocean, large swaths of Europe and western, central and eastern Asia have suffered from an increase in these concentrations. This meant that maximum PM2.5 concentrations exceeded 1 microgram per cubic meter in most parts of the northern hemisphere, below WHO guidelines, but not without impact. The concentration of PM2.5 in China’s northwest region has increased to around two micrograms per cubic meter.
Western and eastern Canada were most severely affected, with PM2.5 concentrations above 150 PM2.5, about ten times the WHO maximum.
While focusing on air quality, researchers also used computer modeling to study the global distribution of greenhouse gases (GHGs) produced by fires in Canada. They found that the conflagration led to an increase in carbon dioxide levels, mainly in North America in May, as well as in Europe and northwest Asia in June. CO linked to forest fires2 concentrations exceeded 0.1 parts per million (ppm) in most parts of the Northern Hemisphere, except Southeast Asia, India and southern China, in July , and increased to more than 0.2 ppm in August.
This increase in GHGs due to fires has two major consequences. First, the fact that it causes increased warming in these regions, on top of existing global warming, increases the likelihood of conditions similar to those that exacerbated the wildfires. In other words, more wildfires means more wildfires.
Second, the level of greenhouse gas emissions from wildfires in Canada in 2023 was more than twice the country’s legislative plan for cumulative reductions in human-caused GHGs over the next ten years.
“Canada’s 2030 emissions reduction plan was wiped out by a single year of wildfires,” said Zifa Wang, corresponding author of the study.