Fig. 1. Physicochemical and cell viability characterization of the air pollution mixture derived from low-level VOCs + O₃ mixture.

Concentrations of the initial precursors are shown in Table 1. a Schematic of the exposure experiment. Cells are exposed for 1.5 h to the low-level or high-level air pollution mixtures. Cell viability from two cell inserts in a six-well plate is analyzed after exposure, and the remaining inserts are exchanged with fresh media and incubated at 37 °C. After 20 h from starting the exposure, two inserts are analyzed for cell viability. b Representative gas-phase composition during one of the low-level exposures (0–1.5 h), measured using the (H₂O)_nH₃O⁺ chemical ionization mass spectrometer (CIMS). Average integrated unit-mass ion intensities are shown. Labels indicate select dominant ions observed at the corresponding m/z. Ions ranging between m/z 2–79 and 201–400 were monitored, but not shown. The integrated ion intensities shown are not adjusted for sensitivities due to lack of authentic standards for oxidation products. c Size distribution of secondary organic aerosol as observed by the scanning electrical mobility system (SEMS), averaged over the period between 0 and 1.5 h from the start of the low-level exposure. Lognormal distributions are shown. d Typical f₄₄ vs f₄₃ profile, an estimator for aerosol oxidation state, observed by the aerosol chemical speciation monitor (ACSM) during the low-level exposure, period (0–1.5 h). Ambient data typically lies within the triangular region. e Cell viability at low-level exposures. Percentage of viable cells (at t = 1.5 h) after trypsinization of the adhered cells in the inserts, and after cell recovery (t = 20 h) determined by trypan blue dye exclusion method in an automatic viability analyzer (Vi-CELL) (n = 3 independent experiments). Statistical difference was computed using t test analysis (one-tailed homoscedastic). Error bars are expressed as one standard deviation (s.d.).