Influence of LED temperature shift on measurement of NO3 radical by incoherent broadband cavity enhanced absorption spectroscopy

Abstract

Incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) based on light emitting diode (LED) has been used for quantitative measurement of NO₃ radical due to its high sensitivity. However, the fluctuation in LED temperature changes the center wavelength and intensity of LED radiation spectrum, resulting in reduction of performance of IBBCEAS instrument. In this paper, an IBBCEAS-based NO₃ measurement setup using red LED as light source is developed for investigating the influence of LED temperature shift on measurement of NO₃ radical. The reference IBBCEAS spectra recorded at from 0 ℃ to 40 ℃ of LED temperature with an interval of 5 ℃ are used to construct absorption spectra of 100 pptv NO₃. Another recorded spectrum at 20 ℃ is used as the reference IBBCEAS spectrum, combining with the constructed IBBCEAS absorption spectra, subsequently the absorption coefficients under different LED temperature shifts are obtained, and then we fit the NO₃ absorption cross section to the absorption coefficients for retrieving the NO₃ concentration. The results show that the standard deviation of fitting residual will increase by ~1.65×10⁻¹⁰ cm⁻¹ if LED temperature is shifted by 1 ℃, which indicates that the limit of detection for NO₃ is increased by ~1 pptv.