Atmospheric Evolution of Brown Carbon from Wildfires in North America

作者：Jhao-Hong Chen, Uma Puttu, Han N. Huynh, Adam T. Ahern, Katherine Ball, Kelvin H. Bates, C. A. Brock, T. Campos, Matthew M. Coggon, John D. Crounse, J. A. de Gouw, Joshua P. DiGangi, Glenn S. Diskin, Georgios I. Gkatzelis, Hannah S. Halliday, Lu Hu, Abigail R. Koss, Yanshun Li, Ming Lyu, Georgia Michailoudi, S. M. Murphy, J. B. Nowak, Brett B. Palm, Jeff Peischl, Wade Permar, A. E. Perring, Rudra P. Pokhrel, Nell B. Schafer, Joshua P. Schwarz, Kanako Sekimoto, Vanessa Selimovic, Chelsea E. Stockwell, Amy P. Sullivan, Joel A. Thornton, N. L. Wagner, Siyuan Wang, C. Warneke, P. O. Wennberg, Linghan Zeng, R. J. Yokelson, Rodney J. Weber, Lu Xu · 发表于：Environmental Science & Technology · 年份：2025 · DOI：10.1021/acs.est.5c09020 · 被引用次数：6 · 研究领域：Atmospheric chemistry and aerosols、Atmospheric and Environmental Gas Dynamics、Atmospheric aerosols and clouds

Atmospheric brown carbon (BrC) from wildfires is a key component of light-absorbing carbon that significantly contributes to global radiative forcing, but its atmospheric evolution and lifetime remain poorly understood. In this study, we investigate BrC evolution by synthesizing data from one laboratory campaign and four aircraft campaigns spanning diverse spatial scales across North America. To estimate initial conditions for evaluating plume evolution, we develop a method to parametrize the emission ratios of BrC and other species using commonly measured inert tracers, acetonitrile and hydrogen cyanide. The evolution of BrC absorption in the free troposphere is characterized as a function of hydroxyl radical (OH) exposure, yielding an effective photochemical rate constant of 9.7 –1.6 +4.8 × 10 –12 cm 3 molecule –1 s –1 . The relatively slow reaction rate results in small BrC decay within the first few hours after emission, making it difficult to distinguish from source variability. This helps explain the absence of clear evolutionary trends in near-field studies. Assuming an OH concentration of 1.26 × 10 6 molecules cm –3, this rate constant corresponds to an e-folding lifetime of approximately 23 h. After extensive photooxidation (OH exposure ∼10 12 molecules cm –3 s), 4 ± 2% of the emitted BrC persists, representing a recalcitrant fraction with potential long-term climate impacts. These results improve our understanding of BrC variability and photochemical processing and ...