SIMULTANEOUS PARTICLE AND MOLECULE MODELING (SPAMM) - AN APPROACH FORCOMBINING SECTIONAL AEROSOL EQUATIONS AND ELEMENTARY GAS-PHASE REACTIONS

A method for writing the sectional aerosol equations in a form suitabl e for combination with a detailed kinetic model for gas-phase reaction s has been developed. The sectional equations are given for arbitrary values of d, the ratio of molecular weights of adjacent bin boundaries , and are solved for d greater than or equal to 2 for three different cases of the intra-bin distribution: (1) constant mass density w.r.t. ln(nu), where nu=molecular weight; (2) constant number density w.r.t. ln(nu), or alternately, constant mass density w.r.t. nu; (3) constant number density w.r.t. nu. All the solutions given conserve mass; the e xtent of deviation from conservation of particle number is evaluated. An example of the approach is given for soot formation in combustion. The aerosol sections describe mass above 400 amu, with d=2. Aerosol re actions are: bin-bin coagulation; addition of C2H2; addition of polycy clic aromatic hydrocarbons (PAH) with 2 to 10 benzenoid rings; oxidati on via OH attack. The set of aerosol reactions is appended to a detail ed elementary-step kinetic mechanism describing the gas-phase chemistr y, including growth of PAH up to C32H14 (398 amu). The method also dir ectly calculates the effect of the soot aerosol upon concentrations of gas-phase species such as PAH-a new capability for soot formation mod els. Predictions for a given set of conditions for the three cases of the intra-bin distribution show striking changes not only in the parti cle size distribution but also in predictions of total aerosol mass an d number concentrations. The extent of deviation from conservation of particle number for the three cases is shown to have a direct effect u pon the predicted aerosol dynamics. (C) 1997 American Association for Aerosol Research.