Modeling ambient Data with EPA-CMB 8.2

Modeling ambient Data with EPA-CMB 8.2 The chemical mass balance (CMB) model is one of several existing receptor models used for an estimation of source contributions to ambient air concentrations of PM10, PM2.5 (particles with an aerodynamic diameter smaller than 10 and 2.5µm respectively) and VOC (volatile organic compounds). Receptor models use chemical as well as physical properties of gases and particles measured at the source and at the receptor to identify the presence and to quantify the source contribution to receptor concentrations. Receptor models differ from other models like dispersion models that use pollutant emission rate estimates, meteorological transport and chemical transformation mechanisms. The CMB model results consist of a solution of linear equations, which describe the concentration found at the receptor as the sum of products of source profile abundances and contributions. The source profile abundances (e.g. it can be the mass fraction of a chemical component in the emissions from each source type) and the receptor concentrations (with uncertainty estimates) serve as input data for the CMB. The model output consists of the amount contributed by each source type represented by a profile to the total mass as well as to each chemical species. CMB calculates values for the contributions from each source and the uncertainties of those values.

The model requires: • Identification of the contributing source types • selection of chemical species or other properties to be included in the calculation • knowledge of the fraction of each of the chemical species which is contained in each source type (=source profile) • estimation of the uncertainty in both ambient concentrations and source profiles • solution of the chemical mass balance equations

CMB model structure