Black carbon ageing in the Canadian Centre for Climate modelling and analysis atmospheric general circulation model

Four separate parameterizations of the ageing process are compared to a control simulationthat assumes no ageing occurs. These simulations use 1) an exponential decaywith a fixed 24h half-life, 2) a condensation and coagulationscheme, 3) an oxidative scheme, and 4) a linearcombination of the latter two ageing treatments. Global BC burdensare 2.15, 0.15, 0.11, 0.21, and 0.11TgC for the control run, and fourageing schemes, respectively. The BC lifetimes are 98.1, 6.6,5.0, 9.5, and 4.9 days, respectively. The sensitivity of modelled BCburdens, and concentrations to the factor of two uncertainty in theemissions inventory is shown to be greater than the sensitivity to theparameterization used to represent the BC ageing, except for theoxidation based parameterization. A computationally efficient parameterization that represents theprocesses of condensation, coagulation, and oxidation is shown tosimulate BC ageing well in the CCCma AGCM. As opposed to the globallyfixed ageing time scale, this treatment of BC ageing is responsive tovarying atmospheric composition. 展开▼