Effect of Ambient Humidity on Dichotomous Sampler Coarse/fine Ratios

Abeam-A~osphe~c aerosols were measured in August 1983 on Allegheny Mountain and Laurel Hill in southwestern Pennsyivania. Ambient humidity was observed to influence the coarse to fine particle ratios as determined by dichotomous samplers. This influence is evident in the particle mass and in its component chemical species. The sampling run with the most pronounced mass shift resulted in an apparent loss of 50 % of the fine mass and 66 % of the fine particle sulfur to the coarse fraction. The magnitude of the mass shift appears to be related to the length of time that the aerosol was in a saturated environment and also to the original dry particle size. These observations have serious implications for receptor modeling with dichotomous sampler data whenever only the fine particles are considered.