For example, new regulations for continuous emissions monitoring of powerplants in China require measurement of lower levels of NOx. In NDIR, the cross interference with water vapor absorption in the IR wavelengths makes lower detection limits challenging. Since there is no absorption of water vapor in the 235 nm wavelength, the lower detection limits are easily reached with UV spectroscopy at this wavelength.
Another NOx monitoring application where LEDs are replacing traditional electrodeless discharge lamps (EDL) is in portable emission measurement systems (PEMS) for the automotive industry. New regulations require measurement of real driving emissions (RDE). The smaller footprint of LEDs enables combining multiple wavelength LEDs in one measurement module and thus, reduction in total cost.
In ozone monitoring for ambient air quality, LEDs offer advantage of lifetime and lower power consumption over mercury lamps. Over a 10-20 year life of the ozone analyzer, using LEDs instead of Hg eliminates the need to dispose of mercury 20 times. The LED also enables new portable monitor designs in ozone as well as in benzene exposure monitoring.
In biogas production, H2S in the gas is monitored and scrubbed to prevent corrosion of gas engines or pipelines if exported to the grid. Optical sensors with 235 nm LEDs offer the benefit of much longer lifetime than electrochemical sensors.
UVC LEDs also work well in measuring SOx emissions in marine, automotive or powerplant applications. New IMO regulations require the use of either low sulfur fuel or alternatively, the use of scrubbers to remove the SOx prior to exhausting into the atmosphere. In this case, compliance is demonstrated and reported from the actual ratio of SO2/CO2 ratio values in the exhaust. The relatively long lifetime and robust nature of LEDs enables long, uninterrupted, maintenance-free operation of SOx sensors on the high seas.
