Breaking Calibration Barriers: Quantifying Oxidation Products in Chamber and Field Measurements via Voltage Scanning

Quantification of intermediate oxidation products is critical for understanding urban emissions and secondary pollution. Ammonium chemical ionization mass spectrometry is established as a detection method for a wide range of functionalized gas-phase compounds. However, conventional calibration methods are reaching their limits.

In this work, we use Voltage Scanning as a novel approach to estimate the detection sensitivity for uncalibrated compounds by comparing their dissociation patterns to patterns of well-calibrated gas standards. We performed extensive characterization and optimization of the method in laboratory experiments to determine optimal conditions at a high time resolution. We implement the method in experiments in the SAPHIR simulation chamber and onboard the NASA DC8 research aircraft. This enables the quantification of a substantial number of the oxygenated organic compounds that have not been previously quantified. We highlight the potential of Voltage Scanning as a powerful tool to further advance our understanding of urban air pollution for field studies, but also in simulation chamber experiments, moving a step closer to achieving carbon closure.