Effect of back-pressure on absorption efficiency of impingers used for air sampling

The gas-liquid absorption method, using an impinger as an extracting device, is the most common method for quantifying most gaseous pollutants. The performance of conventional impingers was studied, and several modified impingers were tested. It was found that the sampling efficiency varied from impinger to impinger, which resulted from back-pressure differences between impingers. The back-pressure of ten tested impingers ranged between 160 mm to 520 mm water gage when a 50 mL absorbing solution was used, which caused the ammonia concentration coefficients of variations to be up to 15%. It was also verified that an open bubble distribution tube could be used to eliminate back-pressure variations between impingers. Nearly identical back-pressure (44 4 mm water gage) could be obtained. This modification can improve measurement repeatability significantly and reduce the coefficient of variation of measurements to 1.2%. With this modification to the impingers, greater accuracy, repeatability and comparison of results can be achieved in the measurement of gaseous pollutants in air.