Fine particle mass is frequently dominated by organic compounds, a large fraction of which are secondary in origin. To date lack of understanding of intermediates in oxidation sequences and reaction pathways and products have represented major sources of uncertainty (and barriers to numerical mechanism development) but advances in both theory and experimental techniques have advanced the science considerably in the last few years. Hence the major challenge for organic chemistry modeling is to reconcile the large numbers of compounds and reaction pathways with limitations imposed by available computing resources. Oxidation of biogenic compounds is known to significantly contribute to the burden of organic aerosol mass but many current generation coupled gas-aerosol models treat all biogenic compounds within a single class (typically represented by alpha-pinene). This paper will assess the adequacy of this treatment using a set of explicit mechanisms for five monoterpenes (a-pinene, b-pinene, 3-carene, d-limonene and ocimene) which are assumed to represent monoterpene emissions and chemistry in the atmosphere. The paper will document differences in the mechanisms and the potential for errors introduced by assuming that monoterpenes can be represented individually or by a limited number of groups. The paper will also present methods for condensing the mechanisms for inclusion in operational fully 3-D atmospheric chemistry models and quantifying errors introduced by mechanism reduction.