Volatile chemical products as potential emerging drivers of urban new particle formation

New particle formation (NPF) proceeds efficiently in polluted urban areas, where oxygenated organic compounds are crucial for early particle growth. Their contribution to NPF depends on volatility distribution, described by the volatility basis set (VBS). Urban volatile organic compound (VOC) emissions have shifted significantly due to regulations and changing consumer habits. Volatile chemical products (VCPs) from cleaning agents, personal care products, and coatings, now rival or exceed combustion sources as primary urban VOC emitters. Though many VCP constituents are secondary organic aerosol (SOA) precursors, their oxidation pathways and NPF contributions remain poorly understood. Recent research highlights that assessing NPF potential requires knowing the full volatility range, including moderately oxygenated molecules (MOMs).

We investigate the full oxidation chain of selected VCP emissions, from VOC precursors to MOMs to highly oxygenated molecules (HOMs) and resulting particle yields. Oxidation occurs in a newly developed flow reactor designed to minimize wall losses and enable steady-state conditions. We employ multi-pressure chemical ionization mass spectrometry with an ultra-high-resolution Orbitrap mass spectrometer. By switching between low-pressure (<1 mbar) ionization for VOC detection using the internal fluoranthene (C₁₆H₁₀) ion source and two different atmospheric-pressure ionization schemes for MOMs (uronium, CH₅N₂O⁺) and HOMs (nitrate, NO₃^-), we capture the VBS across the full volatility range. New particle yields are quantified using a scanning mobility particle sizer (SMPS) and their chemical composition is evaluated using nanoelectromechanical sensors with Fourier transformation infrared spectroscopy (NEMS-FTIR).

We access household cleaning products as potential VCPs emitters. Method performance and consistency are evaluated using limonene oxidation as a reference system for NPF-relevant oxidation chemistry. The obtained VBS distributions can be compared to limonene ozonolysis, under the assumption that charging efficiencies might be well-related to compound volatility. This comparison enables an estimation of the relative NPF potential of different VCP emitters. We find significant variety in the NPF potential among cleaning products of different suppliers. While lemon-scented products resemble limonene (a major ingredient of these products) spectra, we can clearly demonstrate that the complex mixtures present in the cleaning products can enhance the NPF potential of certain products. Altogether, our results demonstrate that multi-pressure chemical ionization provides a powerful approach to link molecular composition, volatility, and NPF potential for emerging urban organic sources. Beyond advancing mechanistic understanding of urban aerosol formation, this framework enables identification of key VOC precursors in e.g. source apportionment approaches. In addition, our first results from different cleaning products show that through product reformulation new opportunities arise to mitigate air quality impacts associated with VCP emissions.