Wildfire air pollution hazard during the 21st century

Abstract

Abstract. Wildfires pose a significant risk to human livelihoods and are a substantial health hazard due to emissions of toxic smoke. Previous studies have shown that climate change, increasing atmospheric CO 2 , and human demographic dynamics can lead to substantially altered wildfire risk in the future, with fire activity increasing in some regions and decreasing in others. The present study reexamines these results from the perspective of air pollution risk, focussing on emissions of airborne particulate matter (PM 2.5 ), combining an existing ensemble of simulations using a coupled fire-dynamic vegetation model with current observation-based estimates of wildfire emissions and simulations with a chemical transport model. Currently, wildfire PM 2.5 emissions exceed those from anthropogenic sources in large parts of the world. We further analyse two extreme sets of future wildfire emissions in a socio-economic, demographic climate change context and compare them to anthropogenic emission scenarios reflecting current and ambitious air pollution legislation. In most regions of the world, ambitious reductions of anthropogenic air pollutant emissions have the potential to limit mean annual pollutant PM 2.5 levels to comply with World Health Organization (WHO) air quality guidelines for PM 2.5 . Worst-case future wildfire emissions are not likely to interfere with these annual goals, largely due to fire seasonality, as well as a tendency of wildfire sources to be situated in areas of intermediate population density, as opposed to anthropogenic sources that tend to be highest at the highest population densities. However, during the high-fire season, we find many regions where future PM 2.5 pollution levels can reach dangerous levels even for a scenario of aggressive reduction of anthropogenic emissions.

Emission of trace gases and aerosols from biomass burning – an updated assessment

“…Recent estimates of global excess mortality from outdoor air pollution range from 4.2 to 8.9 million annually (Cohen et al, 2017;Lelieveld and Pöschl, 2017;Shiraiwa et al, 2017;Burnett et al, 2018;Lelieveld et al, 2019), with smoke from open vegetation burning accounting for up to 600 000 premature deaths per year globally (75th percentile of model estimates; Johnston et al, 2012). In addition to outdoor exposure, pollution from indoor solid fuel use, much of it biofuel burning, has been estimated to cause 2.8 million premature deaths annually (Kodros et al, 2018).…”

Emission of trace gases and aerosols from biomass burning – An updated assessment

“…The volatile organic compounds 5 (VOCs) and NOx in biomass smoke undergo smog photochemistry in the atmosphere, leading to the production of ozone and other pollutants, which impact plant productivity (Crutzen and Andreae, 1990;Andreae, 1991;Pacifico et al, 2015;Yue and Unger, 2018). These gaseous pollutants, and even more so the particulate matter emitted from biomass burning, pose grave risks to human health (Naeher et al, 2007;Dennekamp et al, 2015;Knorr et al, 2017;Apte et al, 2018). Recent estimates of global excess mortality from outdoor air pollution range from 4.2 to 8.9 million annually (Cohen et al, 2017;Lelieveld and 10 Pöschl, 2017;Shiraiwa et al, 2017;Burnett et al, 2018;Lelieveld et al, 2019), with smoke from open vegetation burning accounting for as much as 600,000 premature deaths per year globally (Johnston et al, 2012).…”

Historical (1700-2012) global multi-model estimates of the fire emissions from the Fire Modeling Intercomparison Project (FireMIP)

“…5). The 1997-1998 high emission values are caused by peat fires in equatorial Asia in 1997 and widespread drought-induced fires in 1998 associated with the most powerful El Niño event in 1997-1998 recorded in history Kondo et al, 2018). Most FireMIP models cannot reproduce the 1997-1998 peak, except for CLM4.5 as the only model that simulates the burning of plant tissue and litter from peat fires (although burning of soil organic matter is not included) and the drought-linked tropical deforestation and degradation fires Kondo et al, 2018).…”

“…The 1997-1998 high emission values are caused by peat fires in equatorial Asia in 1997 and widespread drought-induced fires in 1998 associated with the most powerful El Niño event in 1997-1998 recorded in history Kondo et al, 2018). Most FireMIP models cannot reproduce the 1997-1998 peak, except for CLM4.5 as the only model that simulates the burning of plant tissue and litter from peat fires (although burning of soil organic matter is not included) and the drought-linked tropical deforestation and degradation fires Kondo et al, 2018). CLM4.5, CTEM, and LPJ-GUESS-SIMFIRE-BLAZE present the highest temporal correlation between models and satellite-based products (0.55-0.79 for CLM4.5, 0.51-0.68 for CTEM, and 0.39- 0.72 for LPJ-GUESS-SIMFIRE-BLAZE), and thus are more skillful than other models at reproducing the interannual variability observed from satellite-based products (Table 7).…”