Monitoring Technology
| Air Pollutant/Parameter Category | Principle of Operation |
|---|---|
| Total VOC | Photoionization Detector |
| SO2 | Electrochemical Sensor |
| CO | Electrochemical Sensor |
| NO2 | Electrochemical Sensor |
| H2S | Electrochemical Sensor |
| PM2.5 | Laser Scattering |
| Wind Speed, Wind Direction, Temperature, Relative Humidity, Barometric Pressure | Sonic Anemometer and Various |
In the devices sampling occurs by allowing the ambient air to passively enter the devices exterior housing via small holes and pass over the surface of the sensor. Each device used in this project is solar powered and transmits data via cellular.
A Photoionization Detector (PID) sensor contains a lamp that produces photons that carry enough energy to break molecules into ions. The PID will only respond to molecules that have an ionization energy at or below the energy of the lamp; the PID used on this project employs a 10.6 electron-volt lamp.The produced ions then generate an electrical current that is measured as the output of the detector.
Electrochemical sensors measure the concentration of a specific gas within an external circuit via oxidation or reduction reactions. These reactions generate the positive or negative current flow through the external circuit. An electrochemical sensor is made up of a working, counter, and reference electrode. All of these components sit inside of a sensor housing along with a liquid electrolyte that is specific to the compound of interest.
The Federal Equivalent Method (FEM) NO2 analyzer provides direct measurements of the air pollutant by measuring the absorbance of light at a wavelength of 405 nm.
The H2S/SO2 uses UV fluorescence principle to measure SO2. The device is also equipped with an internally mounted catalytic converter that is set at 315°C and converts H2S to SO2. The analyzer operates in a switch measurement mode between H2S and SO2 every 10 minutes.
The GC- PID device measures benzene, toluene, ethyl benzene and xylenes (BTEX). A pre-concentrator is used to collect the sample and gas chromatography (GC) column is used to separate the BTEX compounds. The BTEX compounds are identified and measured using a PID detector, similar to the one described earlier.
The sampled particles are measured by the physical principle of light scattering. Each single particle is illuminated by a defined laser light and each scattering signal is detected at an angle of 90° by a photo diode. In accordance with the Mie theory, each measured pulse height is directly proportional to the particle size whereas each pulse is classified in an electronic register of 32 different size channels.