From combustion to consequence: respiratory health concerns from primary and aged smoke at the wildland-urban interface.

As climate conditions worsen, wildfires are occurring more often, scorching millions of acres of land and carrying both flames and smoke into urban environments. The resulting smoke emissions from fires in the wildlands, as well from fires crossing into urban spaces, are highly toxic with a chemical composition and concentration changing from fire to fire, depending on material burnt and oxygen availability. Furthermore, as smoke ages and travels, it undergoes a process of oxidation where it converts from primary to secondary organic aerosols. Unfortunately, due to the complex nature of wildfire smoke, studying the health effects from smoke exposure has proven difficult. Currently, literature highlights the developments of various cardiovascular, respiratory, neurological, and mental health conditions from chronic or acute exposure, but the disrupted biological pathways, biomarker expression, and resulting pathophysiology of smoke toxin exposure related disease development remain unknown. In this review, we discuss commonly reported adverse health outcomes from wildland and wildland urban interface smoke exposures with a primary focus on respiratory conditions. Furthermore, we address the changing composition of primary versus secondary, or aged, smoke and how it relates to the wildfire public health concern. Lastly, we aim to delineate the actions needed to correlate chronic disease development to smoke toxin exposure and highlight the need for a reliable experimental system to study these unanswered questions.