Abstract. A short, but severe, wildfire smoke episode in July 2015, with an aerosol
optical depth (AOD) approaching 9, is shown to strongly impact radiation
budgets across four distinct land-use types (forest, field, urban and
wetland). At three of the sites, impacts on the energy balance are also
apparent, while the event also appears to elicit an ecosystem response with
respect to carbon fluxes at the wetland and a forested site. Greatest impacts on
radiation and energy budgets were observed at the forested site where the
role of canopy architecture and the complex physiological responses to an
increase in diffuse radiation were most important. At the forest site, the
arrival of smoke reduced both sensible and latent heat flux substantially
but also lowered sensible heat flux more than the latent heat flux. With
widespread standing water, and little physiological control on
evapotranspiration, the impacts on the partitioning of turbulent
fluxes were modest at the wetland compared to the physiologically dominated
fluxes at the forested site. Despite the short duration and singular nature
of the event, there was some evidence of a diffuse radiation fertilization
effect when AOD was near or below 2. With lighter smoke, both the wetland
and forested site appeared to show enhanced photosynthetic activity (a
greater sink for carbon dioxide). However, with dense smoke, the forested site
was a strong carbon source. Given the extensive forest cover in the Pacific
Northwest and the growing importance of forest fires in the region, these
results suggest that wildfire aerosol during the growing season potentially
plays an important role in the regional ecosystem response to smoke and
ultimately the carbon budget of the region.