Research Article

Influence of vapor wall loss in laboratory chambers on yields of secondary organic aerosol

Xuan Zhang, Christopher D. Cappa, Shantanu H. Jathar, Renee C. McVay, Joseph J. Ensberg, Michael J. Kleeman, and John H. Seinfeld
PNAS April 22, 2014 111 (16) 5802-5807; first published April 7, 2014; https://doi.org/10.1073/pnas.1404727111

  1. Contributed by John H. Seinfeld, March 12, 2014 (sent for review January 6, 2014)

Article Figures & SI

Figures

  • Fig. 1.
    Fig. 1.

    Hourly averaged lower bound SOA yields over the course of a toluene photooxidation experiment as a function of initial ammonium sulfate seed surface area for (A) high-NOx and (B) low-NOx conditions. Symbol color indicates the SOA mass concentration and symbol size the time after lights were turned on. The filled circles are from the current experiments and the open diamonds from ref. 21. The dashed gray line and × are the end-of-experiment yields from the optimized best-fit SOM simulations.

  • Fig. 2.
    Fig. 2.

    Observed (points) and simulated (lines) SOA concentrations for each photochemical oxidation experiment performed for different initial inorganic seed surface area for (A) low-NOx and (B) high-NOx conditions. The dashed lines indicate the experiment to which the SOM was explicitly fit, and the solid lines indicate simulation results based on those fits. (C) The wall loss bias factor, Rwall, as a function of seed surface area. Filled symbols use the optimal kw/α pair and the corresponding best-fit SOM parameters determined from A and B. Open symbols assume α = 1 and each experiment was individually fit using the optimal kw. The error bars indicate the 1σ SD in Rwall for each experiment over the period when COA > 0.5 μg m−3.

  • Fig. 3.
    Fig. 3.

    Calculated SOA yield bias as a function of initial toluene concentration and OH concentration when kw = 2.5 × 10−4 s−1 and Cw = 10 mg m−3. The Rwall values for a given [toluene] and [OH] are indicated by colors and contours, and are averaged over the period when CSOA > 0.5 μg m−3 to the end of an experiment at 18 h. Results are based on the optimal fit of the SOM to the low-NOx experiments.

  • Fig. 4.
    Fig. 4.

    Calculated vapor wall loss bias, Rwall, as a function of the effective wall mass concentration, Cw, for the low-NOx toluene photooxidation experiments at varying initial seed surface area. For each Cw, the SOM was fit to the experiment with seed surface area = 5.5 × 103 μm2 cm−3 using kw = 2.5 × 10−4 s−1 and α = 2 × 10−3. The determined best-fit SOM parameters were then used to simulate SOA formation for the experiments performed at other seed concentrations but assuming the same Cw.

Tables

  • Table 1.

    Average biases in SOA yields due to vapor wall losses for various VOCs under low- and high-NOx conditions

    VOC*Low-NOxHigh-NOx
    Graphic
    †
    Graphic
    †
    Toluene‡ (this study)2.1–3.62.1–4.2
    n-dodecane (16)4.1 ± 0.81.16 ± 0.08
    2-methylundecane (16)3.7 ± 0.51.4 ± 0.2
    Cyclododecane (16)3.0 ± 0.31.10 ± 0.05
    Hexylcyclohexane (16)2.4 ± 0.31.16 ± 0.07
    Toluene (21)1.9 ± 0.41.13 ± 0.06
    Benzene (21)1.8 ± 0.41.25 ± 0.1
    M-xylene (21)1.8 ± 0.41.2 ± 0.1
    M-xylene (23)1.6 ± 0.3
    Naphthalene (24)1.2 ± 0.11.2 ± 0.1
    α-pinene + OH (20)1.6 ± 0.31.3 ± 0.1
    Isoprene + OH (20)3.1 ± 1.32.2 ± 0.5

    • ↵* For all VOC’s except toluene (this study), kw = 1 × 10−4 s−1 and α = 1. For toluene (this study), kw = 2.5 × 10−4 s−1 and α = 0.002 (low NOx) or 0.001 (high NOx).

    • ↵† Calculated for the period when CSOA > 0.5 μg m−3 through the end of a given experiment.

    • ↵‡ For toluene, the reported Rwall indicate the range of values determined at different initial seed SA.

    • ↵ Uncertainties are 1σ over the averaging period.

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Secondary organic aerosol formation in chambers
Xuan Zhang, Christopher D. Cappa, Shantanu H. Jathar, Renee C. McVay, Joseph J. Ensberg, Michael J. Kleeman, John H. Seinfeld
Proceedings of the National Academy of Sciences Apr 2014, 111 (16) 5802-5807; DOI: 10.1073/pnas.1404727111
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Proceedings of the National Academy of Sciences: 111 (16)
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