Abstract
Adopting simple field theoretical techniques the author demonstrates how the Smoluchowski approach to reaction-diffusion models can be systematically corrected. Focusing on coagulation/fragmentation processes he identifies the upper critical dimension dc=2 below which finite mobility corrections are important and full universality (lattice independence, etc.) can be achieved. Trends seem by direct simulation of simple lattice models for d>2 are confirmed, whilst problems of interpretation exist for d<2.