A research team led by Prof. XIE Pinhua from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has developed a highly sensitive multi-pass thermal dissociation cavity ring-down spectrometer (PNs/ANs-TDCRDS) that can accurately quantify organic nitrates in the gas and particle phases in real time.

The research results were published in Sensors and Actuators B: Chemical.

Gas-phase organic nitrates (peroxy nitrates [PNs] and alkyl nitrates [ANs]) can easily convert to particle-phase organic nitrates via gas-particle partitioning or additional oxidation. Accurate, simultaneous measurement of organic nitrates in both phases is essential to understanding key tropospheric processes, such as atmospheric oxidation, ozone (O₃) and nitrogen oxides (NO_x) cycling, and secondary organic aerosol formation. However, such measurements remain limited.

In this study, the researchers developed a sensitive, portable, and fully automated PNs/ANs-TDCRDS system integrating custom thermal dissociation inlets, an automated valve control unit, and a three-channel NO₂-CRDS detector. This new instrument effectively overcomes key technical challenges, including particle-phase adsorption interference, high-sensitivity detection, and measurement accuracy during phase switching, enabling reliable simultaneous detection of organic nitrates in both gas and particle phases.

By continuously monitoring NO₂, the system captures rapid concentration changes, significantly reducing their impact on the quantification of low-abundance PNs and ANs and minimizing switching-related measurement biases. The accuracy and stability of the switching measurement mode were further validated through consistent NO₂ measurements in both gas- and particle-phase configurations.

Laboratory evaluations and field observations conducted on Hefei Science Island demonstrated the instrument's strong performance. Results showed that particle-phase PNs and ANs accounted for substantial fractions at night, reaching 41% and 54%, respectively.

"Our findings provide valuable technical support and analytical tools for further research and development of PNs and ANs in gas and particle phases," said Prof. XIE.