Gas-to-Particle Partitioning of Products from Ozonolysis of Δ3-Carene and the Effect of Temperature and Relative Humidity

Formation of oxidized products from Δ3-carene (C10H16) ozonolysis and their gas-to-particle partitioning at three temperatures (0, 10, and 20 °C) under dry conditions (<2% RH) and also at 10 °C under humid (78% RH) conditions were studied using a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) combined with a filter inlet for gases and aerosols (FIGAERO). The Δ3-carene ozonolysis products detected by the FIGAERO-ToF-CIMS were dominated by semivolatile organic compounds (SVOCs). The main effect of increasing temperature or RH on the product distribution was an increase in fragmentation of monomer compounds (from C10 to C7 compounds), potentially via alkoxy scission losing a C3 group. The equilibrium partitioning coefficient estimated according to equilibrium partitioning theory shows that the measured SVOC products distribute more into the SOA phase as the temperature decreases from 20 to 10 and 0 °C and for most products as the RH increases from <2 to 78%. The temperature dependency of the saturation vapor pressure (above an assumed liquid state), derived from the partitioning method, also allows for a direct way to obtain enthalpy of vaporization for the detected species without accessibility of authentic standards of the pure substances. This method can provide physical properties, beneficial for, e.g., atmospheric modeling, of complex multifunctional oxidation products.


Content of this file
Table S1: Selected monomer compounds from Δ 3 -carene + O3 experiments at around 2 hours experiment time.

Table S2:
The equilibrium saturation vapor pressure pi 0 (Pa) of compound i derived from the corresponding partitioning coefficient Kp,i.

Ion signals to mass concentration of FIGAERO-ToF-CIMS
2][3][4] The sensitivity factor differs based on the setup of the instrument and the chemical species being analyzed.For the particle phase, the integrated signal during the desoption was used to calculate the concentration of respective species.Here the sampling volume (duration and flow) was taken into account to properly compare to the gas phase measurement done during the same time interval.Our primary focus in this study was on partitioning; therefore, here we discuss the variations in sensitivity between gas-phase and particle-phase measurements.
First, the setup of the instrument parameters was the same in both gas phase and particle phase measurements.The iodide flow (Fiodide) is always 2 liters per minute (LMP) for both phases.The sample (gas-phase) flow (Fgas) is 2 LMP.When the FIGAERO inlet changes to the particle phase (desorption mode), the sample (particle phase) flow (Fparticle) was set to 2 LPM, however, due to the resistance induced by the filter, the real flow going to the IMR was 1.6 LPM.The IMR pressure was compensated by the pressure controller by adjusting the IMR pumping outflow during the campaign.The difference in the flows into the IMR changes the residence time (t) of the analyte molecules in the IMR and the dilution of sampling flow (Fsampling) due to the iodide flow.At a certain IMR pressure, the residence time can be represented by the physical volume of the IMR (VIMR) and the total volumetric flow (VIMR /(Fiodide + Fsampling)).The reduced flow gave 1.11 longer residence time for the particle phase measurement.The dilution factor can be represented by (Fsampling /(Fiodide + Fsampling)).Here the reduced flow gave a reduction in dilution by a factor of 0.89 for the particle phase.Thus, the overall correction factor on the ratio between particle and gas phase measurement considering both residence time and dilution will then be 0.99 (1.11 × 0.89).Thus, ion signals of the gas phase and particle phase after this correction can be directly compared and the ratio could be calculated.

Method comparison for Deriving Partitioning Coefficients (Kp,i)
The Kp,i values of the 13 compounds derived from the point method and the slope method are illustrated in Figure S5.Note that there are four values for each compound from the point measurements while the slope method provides one value.To elucidate the effect on the temperature dependency (ΔHvap) point data at around 2 hours in each experiment were used (Figure S7).Here no obvious bias or deviating trend could be observed and one may conclude that the two methods are providing consistent values.However, in the main manuscript, the slope method was preferred since it provides information using data from measurement points.2. Kp,i values are derived from Ci,particle/Ci,gas ratios versus organic aerosol mass during experiment time (56-66 min, 112-122 min, 168-178 min, 224-234 min).The error bar is given at the 95% confidence level of the linear regression fitting.  2 derived from Kp,i extracted from experiment time at around (112-122 min) versus ΔHvap dervied from Kp,i derived from the slope of particle to gas ratios versus Morg during experiment time (56-66 min, 112-122 min, 168-178 min).The error bar is given at the 95% confidence level of the linear regression fitting.Table S1.Selected monomer compounds from Δ 3 -carene + O3 experiments at around 2 hours experiment time, i.e. the marked formulas in Figure 1.Total ion signals are the sum of gas phase and particle phase signals.Ion signals are the extracted ion counts per second (cps) normalized by reagent ion I − , multiplied by 10 6 .Fp,i is the particle fraction.

Supplementary Tables
Compounds MW (g mol

Figure S2 :
Figure S2: Monomer region mass spectra of gas and particle phases from humid, 10 °C-2 experiment.

Figure S4 :
Figure S4: The SOA mass concentration measured by SMPS over experiment time during the dry, 20°C experiment.

Figure S5 :
Figure S5: Kp,i derived from each Ci,particle to Ci,gas ratio against Morg point versus Kp,i derived from the slope of Ci,particle to Ci,gas ratio versus Morg.

Figure S7 :
Figure S7: ΔHvap derived from the point method versus ΔHvap derived from the slope method.

Figure
Figure S4.The SOA mass concentration measured by SMPS over experiment time during the dry, 20°C experiment.The time slots in the red frame correspond to the FIGAERO-CIMS sampling time 0-10 min, 56-66 min, 112-122 min, 168-178 min and 224-234 min.

Figure S6 .
Figure S6.Kp,i of the 13 compounds in Table2.Kp,i values are derived from Ci,particle/Ci,gas ratios versus organic aerosol mass during experiment time (56-66 min, 112-122 min, 168-178 min, 224-234 min).The error bar is given at the 95% confidence level of the linear regression fitting.

Figure S7 :
Figure S7: ΔHvap of the 13 compounds in Table2derived from Kp,i extracted from experiment time at around (112-122 min) versus ΔHvap dervied from Kp,i derived from the slope of particle to gas ratios versus Morg during experiment time (56-66 min, 112-122 min, 168-178 min).The error bar is given at the 95% confidence level of the linear regression fitting.

Table S2
The equilibrium saturation vapor pressure pi 0 (Pa) of compound i derived from the corresponding partitioning coefficient Kp,i, applying Equation 3 and assuming an activity coefficient of 1.