Characterization of PM_2.5 source profiles from typical biomass burning of maize straw, wheat straw, wood branch, and their processed products (briquette and charcoal) in China

Chemical profiles from burning of raw biomass materials (i.e., maize straw, wheat straw and wood branch) and their processed products (i.e., briquette and charcoal) were determined with a customized cleaning stove in a combustion chamber. Inorganic species such as water-soluble ions and elements, and carbonaceous fractions including saccharide and polycyclic aromatic hydrocarbons (PAHs) in fine particulate matter (PM_2.5) were quantified. Organic carbon (OC) was the highest fraction with a mass contribution to PM_2.5 ranging from 17.65 ± 0.15% to 40.17 ± 3.83%. Potassium (K⁺) and chloride (Cl⁻) were the two most abundant water-soluble ions (4.31 ± 1.57% and 3.05 ± 1.29%, respectively). Most elements (e.g., heavy metals) had relatively low fractions (<0.01%) or below detection limit. For organics, levoglucosan averagely accounted for over 60% in total quantified saccharides, while 4-ring PAHs was the most dominant fraction. The proportions of OC, sum of quantified PAHs (∑PAHs) and levoglucosan, as well as diagnostic ratios such as OC/element carbon (EC), K⁺/EC, and sum of quantified saccharides (∑saccharides)/PM_2.5 showed a characteristic descending order of raw fuels > briquette > charcoal. In comparison, charcoal burning had lower fractions of the organics since most volatile matters and moisture had been removed during carbonization. In addition, the similarities of chemical profiles from different bio-fuels burning were assessed by calculating the coefficient of divergence (CD) and their correlations. Relatively low CD (0.21–0.36) and high correlation (R > 0.97) suggest that the chemical profiles from straw and their briquettes were similar. However, the profiles from charcoal burning showed significant differences between their corresponding raw fuels (CDs = 0.26–0.47, R = 0.69–0.99) and also large variations from each other (CDs = 0.40–0.49, R < 0.90). The results of this study summarize that the processed fuels especially charcoals are unique in source apportionment and inventory studies.