Integrated Absorption Spectroscopic Measurement of 2-Nitrophenol and Naphthalene

Area of Science:

• Atmospheric Chemistry
• Spectroscopy
• Chemical Physics

Background:

• Accurate gas-phase absorption cross sections are vital for atmospheric and high-temperature process modeling.
• Existing data for low-volatility organic compounds (LVOCs) often show discrepancies, especially at elevated temperatures.

Purpose of the Study:

• To develop and validate a high-precision measurement system for gas-phase absorption cross sections of LVOCs, particularly semi-volatile organic compounds (SVOCs).
• To determine the temperature dependence of these cross sections under atmospherically relevant conditions.

Main Methods:

• Utilized Integrated Absorption Spectroscopy (IAS) coupled with a temperature-controlled inlet and cell (473 K) and nitrogen carrier gas.
• Measured absorption cross sections for 2-nitrophenol (2-NP) and naphthalene in the UV-Vis range (250-400 nm).

Main Results:

• Determined peak cross sections for 2-NP at 473 K: 2.31 × 10⁻¹⁷ cm²/molecule (260 nm) and 1.16 × 10⁻¹⁷ cm²/molecule (335 nm).
• Measured naphthalene cross sections decreasing from 1.62 × 10⁻¹⁷ to 1.28 × 10⁻¹⁷ cm²/molecule (258-280 nm) at 473 K.
• Observed spectral broadening and reduced peak cross sections at high temperatures, consistent with thermodynamic theory and resolving low-temperature data discrepancies.

Conclusions:

• The developed IAS system provides a robust method for quantifying absorption cross sections of SVOCs at high temperatures.
• High-temperature data generated by this system enhance the reliability of atmospheric models by resolving existing data conflicts.