Emission Factors of Polycyclic Aromatic Hydrocarbons and Oxidative Potential of Fine Particles Emitted from Crop Residues Burning

Abstract

Mexico displays significant agricultural activity that, in notorious instances unfolds closely associated with undesirable burning practices of crop residues, which could rise climate change and cause adverse effects to human health, due to emission of fine particles (PM2.5). PM2.5 contain organic compounds such as quinones, soluble organic carbon and polycyclic aromatic hydrocarbons (PAHs), which can be associated to carcinogenic and mutagenic diseases and in some cases to cellular oxidative stress. Presently, we carried out simulation burning of crop residues in an open burning to collect PM2.5 samples by an isokinetic methodology (Method 201a of Environmental Protection Agency). The NIOSH870 method was used to quantify organic carbon (OC) and elemental carbon (EC) fractions. PAHs from PM2.5 were extracted and analyzed by gas chromatography-mass spectrometry while the oxidative potential was measured through the dithiothreitol (DTT) consumption and PM2.5 concentration. The results showed that OC fractions concentration are associated with the modified combustion efficiency (MCE). The most abundant fractions were OC1 and OC2. Emission factors of the sum of 18 PAHs (ƩPAHs) showed a large variation between crops; from 0.49 mg kg−1-fuel (for barley) to 9.16 mg kg−1-fuel (for cotton), then, a single emission factor that includes the burning of all crop residues should not be considered, since the emission factor varies according with the type of biomass burned. Whereas PAHs of 4-6 rings (> 97%) were the most abundant, the concentrations of carcinogenic and mutagenic PAHs accounted for 60% of the sum of all PAHs concentrations. Some diagnostic ratios were identified, but these varied between crops. Burning of residues with low combustion efficiencies presented the highest oxidative potential, such as cotton and sorghum. Oxidative potential correlated with OC concentration, but not with PAHs, suggesting the presence of other compounds.