Molecular-level characterization of urban aerosol analogues in controlled atmospheric simulations

Abstract

Urban air pollution consists of complex mixtures of gases and particulate matter. Understanding the molecular-level composition of these mixtures is essential for interpreting biological responses, but such characterization is difficult under ambient conditions. This study presents the chemical characterization of two controlled atmospheric scenarios generated in the CESAM smog chamber and transferred to the PolluRisk exposure isolator. The standard urban scenario consisted of selected anthropogenic and biogenic volatile organic compounds (VOCs) with primary ammonium sulphate seed particles. The biomass burning enhanced scenario included the same precursors and seed particles, with additional wood-pellet combustion emissions. Solar simulator was continuously turned on throughout the experimental periods and no day/night or dark-aging cycle was applied. Mean PM 1 concentrations in the exposed isolator were 15 ± 7 µg m −3 for the standard urban scenario and 63 ± 24 µg m −3 for the biomass burning scenario. Organic aerosol represented approximately 17 % and 40 % of PM 1 , respectively. Proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) identified 23 VOCs, with oxygenated compounds accounting for 74 %–77 %. Ultrahigh-performance liquid chromatography electrospray ionization ion mobility quadrupole time-of-flight mass spectrometry (UPLC/ESI-IMS-QTOFMS) revealed 32 distinct particle-phase compounds. The biomass burning scenario showed features compatible with combustion-related and oxidation-related products, including source-specific tracers such as a levoglucosan isomer, nitrophenolic compounds (e.g., 3-methyl-4-nitrocatechol, nitroguaiacol), and oxidized aromatics. Estimated volatility classes covered the semi-volatile, low-volatility, and extremely low-volatility organic compound ranges ( C ∗  < 300 µg m −3 ), indicating substantial functionalization and partitioning. The two simulated scenarios showed distinct compositions under the controlled operating conditions. These measurements provide a chemical framework for separate biological exposure experiments. This framework is intended to support mechanistic exposure-health studies, to be reported in a companion manuscript. However, the experiments were not designed to reproduce the full chemical composition of ambient urban air, determine an equivalent atmospheric age, or quantify the relative contributions of primary and secondary organic aerosol.