Tracking the Brownian motion of aerosol particles as they settle in air allows a mass measurement. The particle typically falls downward at its terminal settling velocity; however, the particle occasionally will be displaced upwards due to Brownian fluctuations. The number of occurrences of upward and downward fluctuations is compared, using the formula for the work fluctuation theorem, to yield the mass. This method can be applied to either a single particle or a collection of particles. The advantages of this method include no required information about the size, shape, or density of the particle. Details of the analysis method are presented and illustrated with experimental data.