Quantifying the emission of light-absorbing particles: Measurements tailored to climate studies

The emission rate of light-absorbing aerosols, which contribute to climate forcing, has previously been calculated using mass emission factors combined with fuel-use inventories. Several assumptions made in this calculation lead to overestimates that are significant, but as yet unevaluated. We propose a new measurement approach that augments, and may be preferable to, the mass-based method for modeling radiative forcing by aerosols: direct measurement of the source strength of absorption. This quantity, in units of absorption cross-section per unit time, may be used directly in models of atmospheric dispersion and transport to predict the three-dimensional, time-dependent distribution of the absorption of visible light by aerosols. In demonstration measurements made at a coal-burning plant, the emitted absorption is an order of magnitude lower than would be inferred from the previous method of calculation.