Abstract
A nitrogen dioxide (NO2) photoacoustic sensor for environmental monitoring was developed using a low-cost high-power laser diode emitting at 450 nm. A compact low-noise photoacoustic detection module was designed to reduce the sensor size and to suppress noise. A LabVIEW-based control system was employed for the sensor. The parameters of the sensor were studied in detail in terms of laser power and operating pressure. The linearity of the sensor response with laser power and NO2 concentration confirms that saturation does not occur. At atmospheric pressure, a 3σ detection limit of 250 ppt (part per trillion by volume) was achieved with a 1-s averaging time, which corresponds to the specific detectivity of 3.173 × 10−9 W cm−1 Hz−1/2. A 72 h outdoor continuous on-line monitoring of environmental NO2 was implemented to demonstrate the reliability and validity of the developed NO2 sensor.
Highlights
Nitrogen dioxide (NO2 ) is one of the primary atmospheric pollutants which mainly originates from natural lightning, vehicle exhaust emissions, and industrial combustion processes
NO2 concentrations in environmental monitoring is the chemiluminescence technique. This method involves the reduction of NO2 to NO using heated (300–350 ◦ C) molybdenum (Mo) surfaces or photolytic conversion followed by the gas-phase reaction between NO and O3 forming an electronically excited NO∗2 molecule that emits light, which is proportional to the NO concentration, and the NO2 concentration can be obtained from the NO concentration
The results results showed showed that that the the remained basically unchanged in this range, so the influence of water vapor was not considered when signal amplitude remained basically unchanged in this range, so the influence of water vapor was signal amplitude remained basically unchanged in this range, so the influence of water vapor was the reported NO2when sensor was applied to environmental monitoring
Summary
Nitrogen dioxide (NO2 ) is one of the primary atmospheric pollutants which mainly originates from natural lightning, vehicle exhaust emissions, and industrial combustion processes. The most widely used technique for the measurement of NO2 concentrations in environmental monitoring is the chemiluminescence technique This method involves the reduction of NO2 to NO using heated (300–350 ◦ C) molybdenum (Mo) surfaces or photolytic conversion followed by the gas-phase reaction between NO and O3 forming an electronically excited NO∗2 molecule that emits light, which is proportional to the NO concentration, and the NO2 concentration can be obtained from the NO concentration. In order to measure environmental NO2 concentrations accurately, it is of great significance to develop highly sensitive, interference-free, compact, and low-cost NO2 sensors. NO2 exhibits a strong absorption cross section with a broadband absorption feature in the green–blue–violet region, and a low-cost miniaturized blue laser diode (LD) is commercially available This provides the opportunity to develop the compact photoacoustic sensor for NO2 detection in environmental monitoring. After parameters optimization and performance evaluation, a three-day outdoor continuous on-line monitoring of environmental NO2 concentrations was carried out using the reported NO2 sensor
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