This invention relates to methods and systems for detecting contaminants that can precipitate and deposit on a workpiece during a carbon dioxide application, especially contaminants that are already present and dissolved in the fresh carbon dioxide fed to the application. One aspect of this invention includes a method of detecting contaminants dissolved in a carbon dioxide stream, including the steps of sampling at least a portion of the carbon dioxide stream to form a carbon dioxide sample; modifying at least one physical condition of the carbon dioxide sample to form an aerosol that includes gaseous carbon dioxide and at least one suspended contaminant; and detecting the number of particles of suspended contaminant in at least a portion of the carbon dioxide sample with at least one particle counter. A system for continuously detecting contaminants dissolved in a carbon dioxide stream is also described.