Repetitive-scanning derivative spectrometer as a monitor of environmental air pollution

The derivative spectrometer, developed for monitoring environmental air pollutants, employs signal processing to subtract the mean value of the minima of second derivative from the maximum, and to average the subtracted values. The signal processing leads to compensation of the long-term drift and hence to improvement of the sensitivity, i.e., the detection limit is 2-3 ppb or less for such gases as SO2, NO, and NO2, under circumstances where the ambient temperature fluctuates between 0 and 40 degrees C.