Aerosols are ubiquitous throughout the environment and find numerous technological applications yet a comprehensive understanding of their properties and processes remains elusive. Optical tweezing has emerged as a technology that opens a microscopic window through which we can study aerosols in exquisite detail. In this publication, we describe state of the art measurements of hygroscopicity, phase, supersaturation and mass accommodation. Further, we discuss how the precision and elegance of aerosol tweezer measurements can provide a platform for micro-scale chemical and biological assays as well as a unique perspective on more general problems in physical chemistry and chemical physics. (C) 2009 Elsevier B.V. All rights reserved.