Peroxyacetyl nitrate (PAN) concentration was automatically controlled in a PAN expoeure system for plant to enable accurate PAN exposure experiments to be carried out effectively.
Gaseous PAN generated by bubbling nitrogen into a dilute PAN solution was introduced to air stream which blowed into an exposure box. The PAN concentration in the exposure box was measured with a chemiluminescent NO_x analyzer continuosly and with an electron capture detection gas chromatograph (ECD-GC) at 7-min intervals. The PAN concentration was controlled with a computer as follows: (1) the flow rate of nitrogen introduced into the PAN solution was PID-controlled continuously to maintain a constant NO_x analyzer response between ECD-GC outputs; (2) the NO_x analyzer was recalibrated for PAN concentration at 7-min intervals by ECD-GC.
Using this system, PAN concentration in exposure air was kept within a range of ±5% deviation from a desired set point in the major time course of an experiment.