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

• An innovative electrical modulation cancelation method (E-MOCAM) is proposed.
• A high-power broadband LED was used as the light source of on-beam QEPAS sensor.
• The use of E-MOCAM suppresses the background noise by three orders of magnitude.
• A detection limit of 1.3 ppb is achieved by the novel E-MOCAM-based QEPAS sensor.
• A continuous on-line monitoring of ambient atmospheric NO2 was carried out.

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 1.3 ppb (part per billion by volume) was achieved at 1 s integration time in this experiment, which corresponds to a normalized noise equivalent absorption coefficient (NNEA) 4.2 × 10−9 W cm−1 Hz−1/2. A 9 h continuous on-line monitoring of ambient atmospheric NO2 was carried out on the campus of Shanxi University.