Measurement of gas phase naphthalene with deep-UV broadband cavity-enhanced and integrated absorption spectroscopy

Naphthalene, a representative semi-volatile organic compound (SVOC), poses significant challenges for optical quantification due to surface adsorption and the difficulty of generating stable standards. To address these issues, a deep-ultraviolet Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy (IBBCEAS) system (mirror reflectivity >99.25%, 245-275 nm) was developed. The system achieved a detection limit of 1.3 × 10^-7 cm^-1 A dual-mode sampling strategy was employed to validate quantitative performance. First, steady-state saturation transpiration measurements yielded naphthalene absorption cross sections that agreed excellently with high-resolution literature data which validated the system. Second, an Integrated Absorption Spectroscopy (IAS) strategy was implemented to quantify transient pulse injections. The method demonstrated a strict linearity (R² ≈ 0.99) between the flow integrated optical signal and injected mass. Crucially, the physical validity of the IAS framework was rigorously supported by varying the carrier gas flow rate: a slope ratio of ≈2.0 was observed when the flow rate was halved, consistent with the principle of mass conservation. This work demonstrates that the IBBCEAS-IAS framework effectively mitigates quantification errors caused by adsorption desorption hysteresis. Furthermore, the proven capability for measuring transient pulses highlights the method's potential for coupling with preconcentration desorption techniques (e.g., adsorbent tubes or cold traps) to accurately quantify the total concentration of sticky SVOCs.