Complex effects arising in smoke plume simulations due to inclusion of direct emissions of oxygenated organic species from biomass combustion

Oxygenated volatile organic species (oxygenates), including HCOOH, H,CO, CH 3OH, HOCH2CHO (hydroxyacetaldehyde), CH3COOH, and C6H5OH, have recently bee n identified by Fourier transform infrared measurements as a significant co mponent of the direct emissions from biomass combustion. These oxygenates h ave not generally been included in the hydrocarbon-based initial emission p rofiles used in previous photochemical simulations of biomass combustion sm oke plumes. We explore the effects of oxygenates on this photochemistry by using an established initial emission hydrocarbon profile and comparing sim ulation results obtained both with and without addition of the above six ox ygenates. Simulations are started at noon and carried out for 30 hours in a n expanding Lagrangian plume. After an initial transient period during whic h [NOx] falls rapidly, conditions within the oxygenated smoke plume are fou nd to be strongly NOx-sensitive, and the simulated final species profile is thus strongly dependent upon the Delta [NO]/Delta [CO] initial emission pr ofile. Oxygenate addition results in very significant and complex effects o n net O-3 production, as well as on the relative amounts of long-lived HOx and NOx reservoir species (H2O2, organic hydroperoxides, HNO3, and peroxyac etyl nitrate (PAN)) that are mixed into the surrounding atmosphere. Oxygena tes may either increase or decrease net O-3 production (depending upon the initial Delta [NO]/Delta [CO]). However, they always increase H2O2 and orga nic hydroperoxide production as a result of increased rates of radical + ra dical reactions. These effects spring largely from accelerated removal of N Ox from the smoke plume due to increased radical concentrations resulting b oth from photolysis of oxygenates (mainly CH2O) and from their relatively h igh reactivity. Predicted concentrations of H2O2, Delta [O-3]/Delta [CO], D elta [NH3]/Delta [CO], and Delta [HCOOH]/Delta [CO] are compared with some available measured values.