Emission characteristics and optical properties of brown carbon during combustion of pine at different ignition temperatures under high-time resolution

Abstract

Biomass burning is a major contributor to atmospheric brown carbon (BrC). However, the properties of BrC from biomass burning can vary significantly based on combustion conditions and stages. To investigate these variations, we simulated the combustion cycle of pine at three different ignition temperatures (400, 600 and 800 °C) in a quartz tube furnace. Highly time-resolved samples were collected to analyze the emission and light-absorption properties of BrC during different combustion processes. Our findings revealed that the absorption emission factor at 370 nm was highest at 800 °C (14.96 ± 6.15 g·m−3) and lowest at 600 °C (3.48 ± 1.05 g·m−3). At lower combustion temperatures, we observed a higher content of low molecular weight organic compounds in BrC (OC1, OC2). Furthermore, the emission and light-absorption properties of BrC varied significantly throughout the combustion cycle, with clear bimodal distributions observed for OC, EC, and mass absorption efficiency at 365 nm at all three temperatures. The unimodal distribution of the absorption Ångström exponent indicated that highly aromatic BrC molecules were mainly produced at the beginning and end of the combustion events. We also found that low volatile OC components (OC3 + OC4) had a dominant effect on the variation in MAE365 at 400 and 600 °C, while high volatile OC components (OC1 + OC2) were more significant at 800 °C. These results suggest that the optical properties of BrC components can vary significantly depending on ignition temperature.