INTRODUCTION New particle formation (NPF) can also proceed effectively in polluted urban environments, often mediated by oxygenated organics, especially in the phase of early growth (Stolzenburg et al., 2023). The volatility distribution of these organics, typically described using a volatility-basis-set (VBS), determines when they contribute to NPF (Stolzenburg et al., 2022). However, the urban organic mix is changing due to regulations and changing consumer habits (McDonald et al., 2018), with volatile chemical products (VCPs), now expected to surpass combustion as major volatile organic compounds (VOC) sources (Gkatzelis et al., 2021). Many VCPs are known secondary organic aerosol (SOA) precursors, but their role in oxidation and NPF remains poorly understood (Coggon et al.,2021, Shah et al., 2020). Recent work emphasizes the importance of knowing the full volatility range, including moderately oxygenated molecules (MOM), to assess their NPF potential (Stolzenburg et al., 2025). Understanding the full oxidation chain up to highly oxygenated molecules (HOMs) is also key to improving product design and minimizing their air quality impact. METHODS We employ multi-pressure chemical ionization to analyze the oxidation chain (VOCs to MOM and HOM) of specific VCP sources using an ultra-high resolution Orbitrap Exploris mass spectrometer (Shcherbinin et al., 2024). VOCs are measured using the internal fluoranthene (C16H10) ion sources at low pressure (<1 mbar), MOMs are quantified using at atmospheric pressure with protonated urea (CN2H5O+) and HOMs are ionized at atmospheric pressure using the negatively charged nitrate (NO3-). The volatiles from the precursor VCP are oxidized in a newly designed oxidation flow reactor with a high cross-section to volume ratio to minimize wall interactions. Results of a simple α-pinene ozonolysis experiment are shown in Figure 1, with three different concentrations of α-pinene introduced to the OFR. We present time series data for α-pinene and its primary oxidation products within the C10H16Ox series, alongside traces of reagent ions reflecting the transitions between ionization modes. RESULTS & DISCUSSION VCPs emitters (e.g., multi cleaner and floor cleaners) were oxidized, and oxidation products were assigned a volatility based on earlier approaches (Stolzenburg et al., 2022, 2025). Combination of the different high-pressure ionization modes is based on the molecular ions which are identified in both modes, assuming uniform charging efficiency, as done previously (Stolzenburg et al., 2018, 2025). To validate this, we compared VBS spectra to α-pinene ozonolysis, a known NPF reference, under the assumption that charging efficiencies might be well-related to compound volatility (Riva et al., 2019) This allowed us to estimate the relative NPF potential of VCPs. Low-pressure ionization enabled identification of VOC precursors that could be targeted in product reformulation. Figure 1. Demonstration of multi-pressure chemical ionization mass spectrometry coupled with an oxidation flow reactor and supporting measurements for three intensities of α-pinene ozonolysis. The upper panel illustrates the switching between different ionization modes once steady state conditions have been reached in the flow reactor. The second panel shows the evolution of the precursors (α-pinene and ozone) and the third panel shows the evolution of the major products of the C10H16Ox series. The lower panel shows the evolution of the particle size distribution at the OFR exit during the course of the experiments. CONCLUSIONS We show how multi-pressure chemical ionization can be used to map out the contribution of different VCP sources to future urban air pollution through NPF and simultaneously identify key precursor molecules which could be altered in product design. This illustrates the power of multi-pressure chemical ionization coupled with ultra-high resolution Orbitrap mass spectrometry and a state-of-the-art oxidation flow reactor as a tool to investigate NPF involving emerging urban organic sources, such as cleaning products, personal care products, architectural coatings and even asphalt.