Toward Recreating the Breath of Cities in the Atmospheric Simulation Chamber SAPHIR

Atmospheric simulation chambers are essential for studying oxidation processes, yet many experiments rely on single-precursor systems at concentrations that limit their representativeness for the chemical complexity of urban air. Here, we present a framework linking emission inventories, chamber experiments, and field observations by constructing emission fingerprints of major urban sources, including vegetation, volatile chemical products, cooking emissions, and gasoline and diesel exhaust. Applied during the CHANEL campaign in the SAPHIR outdoor chamber, these fingerprints advanced toward reproducing gas-phase mixtures representative of Los Angeles (gasoline-dominated traffic), a diesel-dominated city, and a future low-vehicle-emission scenario. The resulting mixtures generated peroxy-to-hydroperoxy radical ratios (RO2/HO2) close to unity, bimolecular RO2 lifetimes comparable with urban atmospheric observations, although lower NO levels favored RO2 + HO2 over RO2 + NO reactions. Comparison with aircraft measurements over Los Angeles using ammonium (NH4+) chemical ionization mass spectrometry showed reasonable agreement, with 465 organic product ions detected in both data sets, representing 78% of the product ions observed in the ambient air. Furthermore, 87% of common product ions agreed within a factor of 3 of the linear correlation, demonstrating that chamber experiments can capture key aspects of both atmospherically relevant radical chemistry and the oxidation product diversity of urban air.