a sample inlet coupled to a plurality of laminar flow, condensational growth tubes, the plurality comprising a number of growth tubes, each of the plurality of growth tubes having interior walls that are wet such that a sample flow entering the inlet is split between the plurality of growth tubes, each condensational growth tube configured to operate at a first temperature along a first length of the tube which is adjacent to the inlet and a second temperature along a second length positioned between the first length and a growth tube outlet, the tube in the second length comprising a supersaturation region within the condensation growth tube;

a nozzle plate having a plurality of nozzles, the plurality of nozzles comprising a number of nozzles, each of the nozzles having an input configured to receive the output of one of the plurality of growth tubes and an output in an exposure chamber, the input having a greater area than the output such that the output focuses enlarged particles to hold in vitro cell culture systems positioned at a distance from the output, each nozzle having a nozzle diameter; and

a temperature regulator adapted to control a temperature of the nozzle plate and exposure chamber; and

a controller including instructions operable to cause the controller to maintain a relative humidity within the exposure chamber by controlling at least the second temperature of the growth tube and the temperature of the exposure chamber, and controlling a flow rate of CO2 introduced into the apparatus;

wherein the first length, the second length, the tube diameter, the number of the plurality of growth tubes, the number of nozzles, and the nozzle diameter of each of the plurality nozzles are configured to produce an output velocity of a flow at the output of less than 22 m/s for a sampling flow rate of 6.0 L/m and a deposition efficiency at inertial impaction velocities having a Stokes number above 0.2.