Changing Climate and the Toxicity of Wildfire-derived Brown Carbon Particles: A Literature Synthesis and Science Assessment for Evaluating Potential Human Health Impacts
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The changing intensity, and scale of wildfire is a symptom of climate change with significant smoke-related impacts on public health and downwind ecosystems. On-going climate change will continue altering these patterns while at the same time affecting the variables that determine smoke toxicity and its impacts. Among the climate-sensitive variables impacting smoke chemistry and toxicity are those affecting the primary carbon content (both mass and chemical form) of smoke particles, the nature and rates of in-plume photochemical oxidation processes, and the altitudes and transit periods of smoke plumes. Climate impacts the carbonaceous content of primary smoke emissions by altering biomass species distributions and the form in which fuels are present in fire-prone ecosystems, as well altering meteorological patterns that control fuel moisture and burning conditions (i.e., drought versus extreme precipitation cycles, the occurrence of fire weather conditions influencing hot versus smoldering combustion conditions). Climate also influences the entrainment of soil and dust that can change mix of reactive species in a smoke plume.
The formation and photochemistry of atmospheric brown carbon (BrC) is a major subject of interest given its effect on radiative forcing of the climate system. The photochemical reactions studied and proposed as mechanisms for combustion-produced and photochemically formed brown carbon lead to particle-bound species that have clear implications for exposed human populations. This presentation will provide an overview of the theoretical climate à wildfire BrC àhuman health process based on a synthesis of available scientific literature and suggestions for additional research that can inform our understanding of the process. This work is a component of an EPA assessment intended to improve understanding of the potential influence of future climate change on wildfire smoke toxicity for humans and downwind ecosystems, in support of the development effective strategies for climate-adaptive public health and ecosystems protection strategies.