Physical and chemical characterization of atmospheric aerosols by atomic force microscopy

A new approach to the measurement of the size distribution of atmospheric particles as a function of chemical reactivity is demonstrated. In this method, particles are collected on an atomically fiat mica substrate and imaged using atomic force microscopy. The particle size distribution is obtained from analysis of the image. The sample is then repeatedly exposed to a reactive gas such as ozone or oxygen atoms and reimaged. The dimensions of organic and graphitic (soot) particles are found to shrink at different rates due to formation of volatile products, while inorganic particles remain unchanged. Using this approach, it is possible to classify particles as organic, graphitic, or inorganic and to obtain the size distribution for each chemical class.