High Time-Resolution Optical Sensor for Monitoring Atmospheric Nitrogen Dioxide

High time-resolution monitoring of nitrogen dioxide (NO<sub>2</sub>) is of great importance for studying the formation mechanism of aerosols and improving air quality. Based on the Griess–Saltzman (GS) reaction, a portable NO<sub>2</sub> optical sensor was developed by employing a porous polypropylene membrane tube (PPMT) integrated gas permeation collector and detector. The PPMT was filled with GS reagents and covered with a coaxial jacket tube for gas collection. Its two ends were respectively fixed with a yellowish-green light-emitting diode and a photodiode for optic signal reception. NO<sub>2</sub> was automatically introduced through the collector by two air pumps cooperating with a homemade gas injector. Under the optimized conditions, the device presented good performance for monitoring NO<sub>2</sub>, such as a limit of detection of 5.1 ppbv (parts per billion by volume), an intraday precision of 4.1% (RSD, relative standard deviation, <i>n</i> = 11, <i>c</i> = 100 ppbv), an interday precision of 5.7% (RSD, <i>n</i> = 2–3 per day for 5 days, <i>c</i> = 100 ppbv), an analysis time of 4.0 min, and a linearity range extended to 700 ppbv. The developed device was successfully applied to analyzing outdoor air with a comparable precision to that of the standard method of China. The high time-resolution characteristic that includes sampling 15 times per hour and a good stability for 10 days of urban air analysis had also been evaluated.