The summer 2010 fires in European Russian documented the degree to which smoke from open agricultural burning significantly and negatively impacts human health, with Russian authorities estimating that 25,000 additional deaths occurred that summer in Moscow alone. Recent studies show that 5-10 percent of global air pollution deaths (approximately 250,000 deaths annually) are due to open biomass burning. Lelieveld et al. (2015) note that PM2.5 from agricultural sources is the main contributor to premature mortality from air pollution for East and Southeast Asia, the eastern U.S., Europe and Russia/Ukraine. In Delhi during the November 2017 fire emergency, PM2.5 levels sometimes peaked over 1000ppm, well above rates with documented severe health effects.
More recently, authorities have focused on the longer-term impacts of smoke exposure, even to a single exposure over a longer fire period. Much of this research interest has come recently due to frequent wildfires in a drier and warmer climate, especially in the western U.S. When a wildfire raised PM levels in a small town in Utah during the month of July 2017, visits to the local emergency room increased for respiratory diseases, something also seen during other fires. However, local health authorities continued to monitor the situation, and discovered that rates for such visits remained higher than prior to the wildfire, for at least a year after the actual fire event. They are now following the trend for a second year, but it indicates how the effects of a single exposure incident may be long-term, with the young (<age 6) as well as the elderly and those with existing respiratory conditions most seriously affected.
 Lelieveld et al. (2015), The contribution of outdoor air pollution sources to premature mortality on a global scale, Nature, 525, 367-371, doi:10.1038/nature15371.