Smoke plume impacts on photolysis frequencies during SEAC4RS
Friday, 19 December 2014
The Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign during the summer of 2013 was strongly impacted by smoke from fires in the western United States. Scattering and absorption by particles in the plume directly impact actinic flux spectra which drives the photochemistry. Near the fire, high absorption results in low photolysis rates. In combination with strong plume convection (including pyro-convection), this permits injection of volatile, normally short-lived species to the free troposphere and beyond. Measurements from the Charged-coupled device Actinic Flux Spectroradiometers (CAFS) onboard the NASA DC-8 aircraft show penetration of the California Rim fire reduced in situ ozone photolysis by as much as 95% and nitrogen dioxide photolysis by 80%. Downstream, the aged plume can contain high concentrations of strongly scattering particles attributed to hygroscopic growth. Evidence will be sought for enhancement of photolysis above such plumes by comparison with a radiative transfer model.