Integrated Absorption Spectroscopic Measurement of 2-Nitrophenol and Naphthalene

This study presents a generalized, high-precision measurement system based on Integrated Absorption Spectroscopy (IAS) for determining gas-phase absorption cross sections of low-volatility organic compounds (LVOCs), particularly semi-volatile organic compounds (SVOCs) in the atmosphere. Accurate cross sections and their temperature dependence are essential for modeling atmospheric and high-temperature processes. We coupled a temperature-controlled inlet and cell (473 K) with a nitrogen carrier gas to measure the cross sections of 2-nitrophenol (2-NP) and naphthalene from 250 to 400 nm. At 473 K, peak cross sections for 2-NP were 2.31 × 10^-17 cm²/molecule at 260 nm and 1.16 × 10^-17 cm²/molecule at 335 nm. For naphthalene, values between 258 and 280 nm decreased from 1.62 × 10^-17 to 1.28 × 10^-17 cm²/molecule. Thermally induced spectral broadening and reduced peak cross sections align with thermodynamic theory. These high-temperature data resolve discrepancies among low-temperature datasets. For example, our maximum cross section for 2-NP (300-400 nm) is 29% lower than that reported by Chen et al. (293 K), whereas the value from Sangwan and Zhu (295 K) is 86.8% lower than Chen's, supporting the higher reliability of Chen's data. The IAS method thus offers a robust approach for quantifying absorption cross sections under atmospherically relevant conditions.