Because of recent concerns about the health effects of ultrafine particles, we have been examining techniques for measuring particles in the 0.003 to 0.01 μm size range. In an earlier study, we found that the charge accepted by particles, as measured by the Electrical Aerosol Detector (BAD), is related to the 1.16 power of the mobility diameter. An inspection of the pattern of particle deposition in the lung, as a function of particle size, suggests that the EAD measurement might be a useful indicator of the surface area of particles deposited in the lung. In this study, we calculate the amount of particle surface area deposited in the lung, as a function of particle size, using atmospheric particle size distributions measured over a nine-month period at the St. Louis Supersite. The correlation between the amount of surface area deposited in the lung and powers of the mobility diameter, D X, for X = 0 to X = 3 was found to be high for X = 1.1 to 1.6. In addition, the correlation coefficients of the EAD signal and the amount of particle surface area deposited in the TB and A regions are in the range of 0.91-0.97 and 0.87-0.97, respectively. These high correlation coefficients suggest that EAD could serve as an indicator of particle surface area deposited in the lungs for use in exposure and epidemiological studies of human health effects of atmospheric particles.