Combustion of Volatiles Produced in Situ from the Fast Pyrolysis of Woody Biomass: Direct Evidence on Its Substantial Contribution to Submicrometer Particle (PM₁) Emission

Using a novel two-stage pyrolysis/combustion system, volatiles produced in situ from the fast pyrolysis of a woody biomass at 800–1000 °C were combusted in a drop-tube furnace (DTF) at 1300 °C to investigate its contribution to submicrometer particle (PM 1 ) emission. During pyrolysis, the majority of Na, K, and Cl (43.5–97.2%) was volatilized and the consequent combustion of Na-, K-, and Cl-containing volatiles contributed substantially to PM 1 emission (77.4–89.3% of total PM 1 collected from the combustion of volatiles and char). Oppositely, the majority (83.9–97.5%) of Mg and Ca was retained in chars, and as a result, 97.5–99.7% of the yield of total PM 1–10 is from char combustion. An increase in the pyrolysis temperature leads to an increase in the PM 0.1 yields and the mass of Na, K, and Cl in PM 0.1 from volatiles combustion, as a result of enhanced volatilization of Na, K, and Cl during pyrolysis. The mass-based particle size distributions (PSDs) of PM 10 and elemental-mass-based PSDs of Na, K, and Cl (which are dominantly contained in PM 1 ) from volatiles combustion generally show a unimodal distribution with a fine mode range from ∼0.022 to ∼0.043 μm. The mass-based PSDs of PM 10 and elemental-mass-based PSDs of Mg and Ca (which are dominantly contained in PM 1–10 ) from char combustion also generally show a unimodal distribution but with a coarse mode of ∼6.8 μm. The results clearly demonstrate that the combustion of volatiles (therefore Na, K, and Cl included) produced in situ from the fast pyrolysis of woody biomass is a key mechanism responsible for PM 1 emission. There are strong correlations between the PM 1 yields and the contents of (Na + K + Cl), (Na + K), and Cl in the volatiles during combustion.