The whole of the northern hemisphere suffered deterioration of air quality as a result of 2023's record-setting Canadian wildfires, not just Canada and the northern United States. 

Numerical air quality models have described the extent of severe negative impacts on air quality resulting from the record 2023 Canadian wildfires, according to a study published in Advances in Atmospheric Sciences on Nov. 17. 

"What we know about long-range transport of particulate matter means that the fires likely impacted Europe and Asia as well. We just didn't know to what extent," said Dr. WANG Zhe from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences, lead author of the study. 

The researchers used air quality model, called the Aerosol and Atmospheric Chemistry Model of the Institute of Atmospheric Physics (IAP-AACM), a module within the broader Chinese Academy of Sciences Earth System Model (CAS-ESM). Similar to climate models, air quality models use mathematical techniques to simulate how weather and chemical reactions impact the dispersal of air pollutants. 

They found that while Canada was most severely affected, almost the whole of the northern hemisphere was subject to marked significant declines in air quality due to long-range wind transport of pollutants. 

There were six main widespread air pollution episodes over the course of Canada's wildfire "season": May 15-22, June 5-9, June 24-July 1, July 12-19, August 17-15, and August 17-22. 

In addition to Canada itself, the first such episode affected air quality in the central northern parts of the US. The second episode impacted the northeastern US, and particularly badly. 

The model results here match real-world observations. The concentration of fine particles with diameters of 2.5 microns or less (termed "PM_2.5") on June 7 was found by 11 monitoring sites in New York City to have reached the worst air quality level for more than 50 years. 

During the third main episode of severe air pollution, the model suggested that PM_2.5 pollutants were transported to Europe, while the fourth such episode concentrated its severest presence in western Canada and the central northern US once again. The fifth episode mainly affected northern Canada, while the sixth episode affected both western and eastern coast regions of the USA. Due to the northward movement of the wildfires, high concentrations of PM_2.5 were transported to the Arctic region over the course of the mid and late summer. 

PM_2.5 concentrations higher than the World Health Organization air-quality guidelines of 15 micrograms per cubic meter mainly occurred over North America, with an excess of 40 pollution days exceeding this limit over western and eastern Canada, as well as more than 10 such days over the northeastern USA. 

But due to the wildfire plumes being transported by prevailing westerly winds across the Atlantic Ocean, vast swathes of Europe and western, central and east Asia suffered from increases in such concentrations. This meant that maximum PM_2.5 concentrations exceeded one microgram per cubic meter over most areas of the Northern Hemisphere—lower than the WHO guideline but not without impact. PM_2.5 concentration in the northwest region of China increased to roughly two micrograms per cubic meter. 

Western and eastern Canada were most severely impacted, suffering PM_2.5 concentration over 150 PM_2.5, some ten times the WHO maximum. 

While focusing on air quality, the researchers also used computer modeling to investigate the global distribution of greenhouse gases (GHGs) produced by the Canadian fires. They found that the conflagration had resulted in an increase in carbon dioxide levels mainly over North America in May, and also over Europe and northwestern Asia in June. The wildfire-related CO₂ concentrations exceeded 0.1 part per million (ppm) over most Northern Hemisphere areas 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 the fires enhanced warming in these regions atop existing global warming intensifies the likelihood of the sort of conditions that exacerbated wildfires.