Sensitivity of tropospheric oxidants to biomass burning emissions: implications for radiative forcing

Biomass burning is one of the largest sources of trace gases and aerosols to the atmosphere and has profound influence on tropospheric oxidants and radiative forcing. Using a fully coupled chemistry-climate model (GFDL AM3), we find that co-emission of trace gases and aerosol from present-day biomass burning increases the global tropospheric ozone burden by 5.1% and decreases global mean OH by 6.3%. Gas and aerosol emissions combine to increase CH4 lifetime nonlinearly. Heterogeneous processes are shown to contribute partly to the observed lower Delta O-3/Delta CO ratios in northern high latitudes versus tropical regions. The radiative forcing from biomass burning is shown to vary nonlinearly with biomass burning strength. At present-day emission levels, biomass burning produces a net radiative forcing of 0.19 W/m(2) ( 0.29 from short-lived species, mostly aerosol direct and indirect effects, +0.10 from CH4- and CH4-induced changes in O-3 and stratospheric H2O) but increases emissions to over 5 times present levels would result in a positive net forcing.