range where the xad 2 u00ae resin is very efficient in collecting the exhaust gas components of interest exiting the water trap 9 the exhaust gas passes through an open shut valve 29 which is used to close off the sample train from the rest of the system for purposes of calibrating the blower 43 with the lfe 24 downstream of valve 29 makeup air is added to the exhaust gas at a junction 30 and the combined exhaust gas and makeup air is then passed through a heat exchanger 35 and valve 41 used for leak checks and finally to exhaust through a roots u00ae trademark of dresser inc blower 43 the roots u00ae blower 43 serves to draw the exhaust gas sample and the makeup air through the system and operates at an approximately constant volumetric flow rate the volumetric flow rate through the blower 43 is determined by calculation based on the rotational speed of the blower 43 pressure measurements upstream and downstream of the blower 43 by pressure sensors 37 and 45 and the temperature of the exhaust gas entering the blower 43 as measured by thermocouple 39 compressed air is introduced through a container of desiccant 13 exiting the desiccant container 13 the makeup air passes through a regulator valve 15 which serves to set the desired pressure of air at the inlet of the laminar flow element 24 after exiting the regulator valve 15 the air passes through solenoid valve 17 which is used to close off the compressed air for performing a leak check on the system exiting the solenoid valve 15 the humidity of the makeup air is determined by use of humidity.