Fig. 3. Analysis of atmospheric layer development, phase-partitioning, and chemical reactions on the enhancement of nocturnal OOA.

A The ion mass spectrum of NO-OOA(Bio) for summer and an averaged spectrum of NO-OOA(bb) for the other seasons (detailed spectra in the Supplementary Fig. 7) obtained by the PMF analysis of measurements of aerosol nitrate and organics. B Competition between NO₃ and O₃ oxidation of VOCs (label as relative importance (green)) and the comparison of secondary organic aerosol (SOA) yield of biogenic VOCs (BVOCs) (isoprene, α-pinene, β-pinene, and limonene) and biomass-burning volatile organic compounds (bbVOCs) (furan, naphthalene) by different oxidants (NO₃ and O₃) (red), with the median values represented by the bars and the range of variability indicated by the error bars. (Supplementary Table 2). C Correlation of NO-OOA(Bio) and NO-OOA (bb) with the SO⁺ fragment originating from HMS and aerosol liquid water content (ALWC). D Averaged diurnal variations of the sulfate (SO₄) aerosol mass concentrations and observed NO-OOA obtained by the PMF analysis, as well as the PBL height obtained from the EURAD-IM in summer and autumn during the JULIAC campaign. Plots showing results for the other seasons can be found in the Supplementary Fig. 18. E The variation of mass ratio of NO-OOA (Bio) to total OA in summer, and NO-OOA (bb) to total OA in the other seasons as a function of the minimum nocturnal temperature and corresponding relative humidity during these periods. Data is restricted to the period ±2 hours of the minimum temperature. The averaged diurnal variations of temperature, RH, and the ratio of NO-OOA/OA are also displayed in the plot by yellow, blue, and green bars, respectively.