4.1 Sources of PAHs and NPAHs 4.2 Chemical Characteristics of Vegetation Fires 4. Emission Sources 4.3 Vegetation Fires Globally There are many kinds of emission sources for PAHs and their derivatives: vehicles, ships, aircraft, coke production, industries such as iron-steel, aluminum and others, and agricultural machines that use fossil fuels. Petroleum cracking plants, gas stations, forest fires (wildfires) and open burning of crop residues constitute major outdoor sources. On the other hand, the combustion of coal, oil and gas, and the use of firewood and other vegetation fires in heating and cooking constitute indoor sources. Smoking is also a source, especially indoors. Of these sources, the contributions of residential/commercial biomass burning and open-field vegetation fires (agricultural waste burning, deforestation and wildfires) accounted for 60.5% and 13.6%, respectively, of the 16 global atmospheric PAHs in 2007, which were much larger than that of vehicles (12.8%) (Shen et. al., 2013). However, a survey of rural areas in China reported that the contribution of vegetation fires (15.9%) was smaller than the contribution of vehicles (32.7%) in 2020 (Li et. al., 2023). Thus, there have been large differences between reports in the contribution of vegetation fires to atmospheric PAHs. Several review reports have been published for PAHs emitted from biomass burning (Vicente and Alves, 2018; Zhang et al., 2022). The compositions of the PAHs and their derivatives were not very strongly affected by fuel type (Zhang et al., 2022), but with increasing combustion temperature, the fraction of higher molecular PAHs became larger than that of lower molecular PAHs (McGrath et al., 2003; Iinuma et al., 2007). On the other hand, the amounts of NPAHs emitted differed greatly depending on combustion temperature. Combustion temperatures in vehicle engines, coal stoves and wood Polycyclic Aromatic Hydrocarbons from Vegetation Burning and Health Effects stoves were 2,700 − 3,000°C, 1,100 − 1,200°C and 500 − 600°C, respectively (Hayakawa, 2016). Fig. 4 compares the concentrations of PAHs and NPAHs in PM emitted by diesel vehicles (DEP), coal burning (CEP) and wood burning (WEP). WEP showed the highest concentration of PAHs, followed by CEP. DEP showed the lowest concentration. On the other hand, DEP showed the highest concentration of NPAHs, followed by CEP. WEP showed the lowest concentration. The above result is explained as follows: The formation of NOx depends on combustion temperature and the formation of NPAHs from corresponding PAHs in the presence of NOx also depends on combustion temperature. Increased combustion temperature results in increased yield of NPAHs. The concentration ratio of NPAHs to their parent PAHs (= [NPAH]/[PAH]) increases temperature, depending on elevation of combustion suggesting an effective the combustion source. Based on this principle, a new method using 1-NP and Pyr as monitoring markers has been developed for analyzing source contributions (Hayakawa et al., 2020 and 2021). The [1-NP]/[Pyr] ratio of PM from vegetation fires is more than two orders of magnitude smaller than that of PM from vehicles. PAHs and their derivatives attract great attention their adverse health effects—not only because of endocrine carcinogenicity but disruption activity and reactive oxygen production activity. There have been many reports on the effects of combustion sources on organic and inorganic pollutants formed through biomass combustion. Among them, this report focuses on the combustion of biomass. Globally, the post-harvest burning of crops and forest fires results in widespread air pollution (Chuesaard et al., 2014; Pham et al., 2019; Tomaz et al., 2017; de Oliveira Galvao et al., 2018), and domestic heating and cooking using biomass index also mutagenicity, identifying for 17

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