At any
given electrical potential, particles of predictable size
pass through the collection slit and enter a separate air
stream (1.6 L/min) that carries them to a particle
counter. The particle counter first enlarges the particles
by condensing a vapor onto each particle and then detects
the droplets, now several microns in diameter, via
light scatter. Knowledge of the electrical potential applied
to the DMA, the dimensions of the DMA, and the
flow rate of air passing through the DMA permits accurate
calculation of particle diameter and the number
of particles in a discrete size range. Particle diameter is
determined from the following equation