Emission of organic carbon, elemental carbon and water-soluble ions from crop straw burning under flaming and smoldering conditions

Abstract Emissions from major agricultural residues were measured using a self-designed combustion system. Emission factors (EFs) of organic carbon (OC), elemental carbon (EC), and water-soluble ions (WSIs) (K + , NH 4 + , Na + , Mg 2+ , Ca 2+ , Cl − , NO 3 − , SO 4 2– ) in smoke from wheat and rice straw were measured under flaming and smoldering conditions. The OC 1 /TC (total carbon) was highest (45.8% flaming, 57.7% smoldering) among carbon fractions. The mean EFs for OC ( EF OC ) and EC ( EF EC ) were 9.2 ± 3.9 and 2.2 ± 0.7 g/kg for wheat straw and 6.4 ± 1.9 and 1.1 ± 0.3 g/kg for rice straw under flaming conditions, while they were 40.8 ± 5.6 and 5.8 ± 1.0 g/kg and 37.6 ± 6.3 and 5.0 ± 1.4 g/kg under smoldering conditions, respectively. Higher EC ratios were observed in particulate matter (PM) mass under flaming conditions. The OC and EC for the two combustion patterns were significantly correlated ( p R  = 0.95 for wheat straw; p R  = 0.97 for rice straw), and a higher positive correlation between OC 3 and EC was observed under both combustion conditions. WSIs emitted from flaming smoke were dominated by Cl − and K + , which contributed 3.4% and 2.4% of the PM mass for rice straw and 2.2% and 1.0% for wheat straw, respectively. The EFs of Cl − and K + were 0.73 ± 0.16 and 0.51 ± 0.14 g/kg for wheat straw and 0.25 ± 0.15 and 0.12 ± 0.05 g/kg for rice straw under flaming conditions, while they were 0.42 ± 0.28 and 0.12 ± 0.06 g/kg and 0.30 ± 0.27 and 0.05 ± 0.03 g/kg under smoldering conditions, respectively. Na + , Mg 2+ , and NH 4 + were vital components in PM, comprising from 0.8% (smoldering) to 3.1% (flaming) of the mass. Strong correlations of Cl − with K + , NH 4 + , and Na + ions were observed in rice straw and the calculated diagnostic ratios of OC/EC, K + /Na + and Cl − /Na + could be useful to distinguishing crop straw burning from other sources of atmospheric pollution.