Mechanism reduction for the formation of secondary organic aerosol for integration into a 3-dimensional regional air quality model: α-pinene oxidation system A. G. Xia1,*, D. V. Michelangeli1, and P. A. Makar2 1Department of Earth and Space Science and Engineering, York University, Toronto, Ontario, Canada 2Air Quality Research Division, Environment Canada, Toronto, Ontario, Canada *now at: Air Quality Research Division, Environment Canada, Toronto, Ontario, Canada
Abstract. A detailed α-pinene oxidation mechanism was reduced systematically
through the successive application of five mechanism reduction techniques.
The resulting reduced mechanism preserves the ozone- and organic
aerosol-forming properties of the original mechanism, while using less
species. The methodologies employed included a directed relation graph
method with error propagation (DRGEP, which removed a large number of
redundant species and reactions), principal component analysis of the rate
sensitivity matrix (PCA, used to remove unnecessary reactions), the
quasi-steady-state approximation (QSSA, used to remove some QSS species), an
iterative screening method (ISSA, which removes redundant species and
reactions simultaneously), and a new lumping approach dependent on the
hydrocarbon to NOx ratio (which reduced the number of species in
mechanism subsets for specific hydrocarbon to NOx ranges).
This multistage methodology results in a reduction ratio of 2.5 for the
number of both species and reactions compared with the full mechanism. The
simplified mechanism reproduces the important gas and aerosol phase species
(the latter are examined in detail by individual condensing species as well
as in classes according to four functional groups: PANs, nitrates, organic
peroxides, and organic acids). The total SOA mass is also well represented
in the condensed mechanism, to within 16% of the detailed mechanism under
a wide range of conditions. The methodology described here is general, and
may be used in general mechanism reduction problems.
Citation: Xia, A. G., Michelangeli, D. V., and Makar, P. A.: Mechanism reduction for the formation of secondary organic aerosol for integration into a 3-dimensional regional air quality model: α-pinene oxidation system, Atmos. Chem. Phys., 9, 4341-4362, doi:10.5194/acp-9-4341-2009, 2009.