Humberto Collazo

Inertial Impactors to Measure Aerodynamic Diameters of Man-Made Organic Fibers

It is widely accepted that the aerodynamic diameter of a particle is one of the main factors that determines particle deposition into the human respiratory system. The determination of aerodynamic diameter of spheres or near spherical objects is routinely accomplished using impactors. The aerodynamic diameter of man made organic fibers (MMOF), on the other hand, has not traditionally been measured using impactors, because fibers of the same cross section may have different lengths and a variety of shapes (straight, curved, etc.) for each length. The aerodynamic size of the fibers is thus a function of fiber orientation. Single and multiple stage impactors have been developed, calibrated, and validated specifically for the determination of the aerodynamic diameter of large fibers with circumscribed diameters between 20 and 35 w m and an aspect ratio ranging from subfiber lengths (aspect ratio < 3) up to 40. The impactor allows measurements of the aerodynamic diameter of cellulose acetate fibers released during mechanical smoking of cigarettes. The performance characteristics were evaluated by spherical particles of known diameters, fibers of known length and diameter, and computational fluid dynamic calculations. Our methodology has shown that inertial impactors can be used to determine the aerodynamic diameter of large cellulose acetate fibers.

AERODYNAMIC DIAMETER MEASUREMENT OF CELLULOSE ACETATE FIBERS FROM CIGARETTE FILTERS: WHAT IS THE POTENTIAL FOR HUMAN EXPOSURE?

Aerodynamic diameter is a major determinant of particle and fiber deposition and toxicity in the respiratory tract. To characterize cellulose acetate fibers released from the filter end of cigarettes puffed under conditions approximating smoking, we designed multistage impactors to determine the aerodynamic diameters of large fibers with circumscribed diameters between 20 and 35 µm and aspect ratios ranging from subfiber ratios up to 40. This range of diameters encompasses all of the cellulose acetate fiber sizes that are commercially manufactured. When commercially available cigarettes with filters made from acetate fibers in this circumscribed diameter range were puffed directly into the impactor, on average 10 fibers/cigarette were released and their aerodynamic diameters were determined. In our studies, we found that the aerodynamic diameters of the cellulose acetate fibers were always greater than 23 µm. Using standard lung deposition models, we concluded that the fibers are nonrespirable with a very low probability of penetration to the distal lung. Our findings, which demonstrate release of only a small number of these large fibers with an extremely low likelihood of reaching the distal lung, indicate that these fibers are not a risk for human lung disease.