Development of a reduced chemical scheme for use in mesoscale meteorological models

A new Regional Lumped Atmospheric Chemical Scheme (ReLACS) is introduced. This mechanism is intended to be valid for clean to polluted conditions. ReLACS is derived from a new reactivity weighting approach which may be applied to any atmospheric chemical scheme. In this work, ReLACS is based upon the reduction of the regional atmospheric chemistry mechanism (RACM) (Stockwell et al., 1997. Journal of Geophysical Research D22, 25847–25849) on a given moderately polluted emission scenario. However, sensitivity tests around this scenario show that ReLACS compares favorably with RACM, not only for ozone but also for other important atmospheric oxidants. The gain obtained from this lumping in the number of species allows ReLACS to be suitable to perform, otherwise costly, three dimensional pollution studies when coupled with mesoscale meteorological models.