Ppb-level QEPAS NO2 sensor by use of electrical modulation cancellation method with a high power blue LED

Abstract

A novel electrical modulation cancellation method (E-MOCAM) is proposed to suppress the background noise in the case of the excitation light source with a poor beam quality. For its practical implementation, an E-MOCAM based on-beam QEPAS NO2 sensor by use of a commercial high-power wide-stripe LED is developed. The E-MOCAM ultimately suppressed the background noise caused by the stray light by three orders of magnitude. A 1σ detection limit of 1.3ppb (part per billion by volume) was achieved at 1s integration time in this experiment, which corresponds to a normalized noise equivalent absorption coefficient (NNEA) 4.2×10−9Wcm−1Hz−1/2. A 9h continuous on-line monitoring of ambient atmospheric NO2 was carried out on the campus of Shanxi University.