Effects Of African BaP Emission From Wildfire Biomass Burning On Regional And Global Environment And Human Health

The vegetation burning caused by wildfires can release significant quantities of aerosols and toxic chemicals into the atmosphere and result in environmental pollution and health risk.Among these emitted pollutants,Benzo（a）pyrene（BaP）,the most toxic congener of 16 parent PAHs（polycyclic aromatic hydrocarbons）,has been classified into the Group 1 carcinogen by the International Agency for Research on Cancer（IARC）.As a result,BaP has received widespread concerns because of its carcinogenicity to human health.In the past decades,African wildfire contributed about 70%of burned area to the global total.Sub-Saharan Africa,in particular,has been experiencing the most severe wildfires in the world for the past decades.In these countries and regions,wildfires are the most significant source of PAHs,accounting for 70%to 80%of the total PAH emissions.Although wildfires in Africa caused severe air pollution and health consequences on local and global environment that inspired the efforts in the investigation of the environmental and health consequences of wildfire-induced PAH contaminations in Africa,there is still a lack of the continental-scale assessment of African wildfire-induced PAH contamination and health impact due to the knowledge and data gaps in wildfire biomass burning and PAH emissions,leading to considerable uncertainty in the assessment of PAH pollutions and health consequences in the continent.Based on the newly-developed global wildfire BaP emission inventory,this study quantitatively assesses PAHs pollution and corresponding health consequences in Africa,as well as the BaP environmental cycling and its effects on adjacent continents from 2001 to 2014 using the modified global atmospheric transport model Can METOP.Compared to the widely-used PKU-FUEL emission inventory（all sectors）,the new inventory from wildfire biomass burning was improved by the use of recently released forest carbon stocks and MODIS burned area.The new BaP emission inventory reveals that BaP emissions from African wildfires accounts for 48%of the global total emissions from all sectors from 2001 to 2014,and this share has been increasing over the last decade.Given continuously decreasing BaP emissions from anthropogenic sources due to worldwide emission control,it is likely that African emissions from wildfire biomass burning could dominate global PAHs emission and contamination in future.We identified significantly higher BaP emissions and concentrations across sub-Saharan Africa,where the annually averaged BaP concentrations were as high as 5-8 ng/m~3.Compared to BaP concentrations simulated using PKU-FUEL emission inventory,modeled BaP concentrations from African wildfires in the present study are factors of 2 higher.This could be attributed to significant underestimation of BaP emissions from the wildfire biomass burning in the old version of MODIS burning area employed in PKU-FUEL emission inventory due to neglecting small burned areas.This study also quantitatively assesses the impact of BaP pollution caused by wildfire burning in Africa on other continents.It is found that the African BaP emission from wildfires contributed,to some extent,BaP contamination to BaP contamination in Europe,South America,and other regions outside Africa,depending on the source-receptor proximity and atmospheric pathways under favorable atmospheric circulation patterns.By implementing modelled BaP concentrations from wildfire biomass burning in the Africa averaged from 2001 to 2014 into a cancer risk model,this study also assesses the lifetime cancer risk（LCR）due to inhalation exposure to BaP.The results reveal that the LCR values in many African countries exceeded the acceptable risk level at 1×10^-6,some of which suffer from very high exposure risk with the LCR greater than 1×10^-4.