Journal of Geophsyical Research: Atmospheres
Oxygenated volatile organic species (oxygenates), including HCOOH, H2CO, CH3OH, HOCH2CHO (hydroxyacetaldehyde), CH3COOH, and C6H5OH, have recently been identified by Fourier transform infrared measurements as a significant component of the direct emissions from biomass combustion. These oxygenates have not generally been included in the hydrocarbon-based initial emission profiles used in previous photochemical simulations of biomass combustion smoke plumes. We explore the effects of oxygenates on this photochemistry by using an established initial emission hydrocarbon profile and comparing simulation results obtained both with and without addition of the above six oxygenates. Simulations are started at noon and carried out for 30 hours in an expanding Lagrangian plume. After an initial transient period during which [NOx] falls rapidly, conditions within the oxygenated smoke plume are found to be strongly NOx-sensitive, and the simulated final species profile is thus strongly dependent upon the Δ[NO]/Δ[CO] initial emission profile. Oxygenate addition results in very significant and complex effects on net O3 production, as well as on the relative amounts of long-lived HOx and NOx reservoir species (H2O2, organic hydroperoxides, HNO3, and peroxyacetyl nitrate (PAN)) that are mixed into the surrounding atmosphere. Oxygenates may either increase or decrease net O3 production (depending upon the initial Δ[NO]/Δ[CO]). However, they always increase H2O2 and organic hydroperoxide production as a result of increased rates of radical + radical reactions. These effects spring largely from accelerated removal of NOx from the smoke plume due to increased radical concentrations resulting both from photolysis of oxygenates (mainly CH2O) and from their relatively high reactivity. Predicted concentrations of H2O2, Δ[O3]/Δ[CO], Δ[NH3]/Δ[CO], and Δ[HCOOH]/Δ[CO] are compared with some available measured values.
Copyright 2001 by the American Geophysical Union