New source and process apportionment method using a three-dimensional chemical transport model: Process, Age, and Source region Chasing ALgorithm (PASCAL)

Abstract

We have developed a new source and process apportionment method, the Process, Age, and Source region Chasing ALgorithm (PASCAL), and implemented it in a three-dimensional chemical transport model, the Community Multiscale Air Quality (CMAQ) model. By adding new variables (tagged species), PASCAL traces 1) the source region of emissions (source apportionment), 2) the age of individual species (elapsed time from emissions), 3) net and gross production and loss amounts from individual physical and chemical processes during transport (Lagrangian way), and 4) local production and loss rates at individual grid cells (Eulerian way) for primary and secondary aerosols and their precursor gases. The main advantage of PASCAL is the third one, which can trace accumulated production and loss amounts of individual processes during transport from source regions to each grid cell (Lagrangian type of integration) for both gross (production and loss) and net (gross production − loss) concentrations. Currently the method is applied for mixing ratios of CO and SO2 and mass concentrations of black carbon and sulfate aerosols. This algorithm is not impacted by the non-linearity of chemical reactions and is computationally efficient. CMAQ/PASCAL model calculations were conducted over the East Asian region to test its performance. The overall validity of PASCAL calculations is confirmed for all species, periods, altitudes, and regions. This algorithm will be a useful tool in evaluating source regions as well as formation and loss processes of aerosols in the atmosphere in order to make effective strategies for emissions reduction.