Abstract
ABSTRACT Prior studies have shown that neglecting the vapor wall loss could lead to the underestimation of the secondary organic aerosol (SOA) yields in smog chamber experiments. The majority of the previous studies investigated vapor wall loss of a wide range of semi-volatile organic vapors at room temperatures using extensive chemical analysis. This study poses a question: Can vapor wall deposition in a smog chamber be observed only using physical measurements of aerosol properties? This study assesses the significance of vapor wall loss using only the size evolution of pure organic compound particles. To our knowledge, this technique is used for the first time in assessing the vapor wall loss of chemical species in chamber experiments. Dark experiments were conducted by injecting pure levoglucosan particles into an outdoor smog chamber at multiple ambient temperatures, ranging from –10°C to +15°C. Peak diameter analysis revealed levoglucosan particles shrunk by ~37% at 15°C and ~20% at 10°C experiments, whereas no shrinkage was observed at temperatures below 0°C suggesting significant vapor wall loss of levoglucosan at warmer temperatures (> 10°C). Two-Moment Aerosol Sectional (TOMAS) and additional simple kinetic model simulations suggest that the effects of temperature on vapor wall loss can primarily be explained by the change in saturation vapor pressure of the organic compound and that the lack of apparent vapor wall loss of levoglucosan below 0°C was due to kinetics, i.e., slow evaporation relative to the chamber experiment timescales. The same approach can be applied to other organic species to expand the range of volatility relevant to chamber experiments.
Highlights
Smog chambers are one of the widely-used experimental systems to study atmospheric chemistry (Akimoto et al, 1979; Finlayson-Pitts and Pitts, 1986)
This study developed a relatively simple approach to observe vapor wall loss in a smog chamber using only pure particles size distributions under different temperatures
The evolution of the levoglucosan particle size indicated that levoglucosan vapor wall loss was significant above around 10°C whereas negligible below around 0°C under the experimental conditions used in this study
Summary
Smog chambers are one of the widely-used experimental systems to study atmospheric chemistry (Akimoto et al, 1979; Finlayson-Pitts and Pitts, 1986). Smog chambers induce biases to measurements due to their walls (FinlaysonPitts and Pitts, 1986). Smog chamber studies on ozone formation observed various contamination effects due to sorption processes on the surfaces of chambers (Bufalini et al, 1977). Grosjean (1985) measured vapor wall-loss rates of several organic (toluene, pyruvic acid, ammonia, etc.) and inorganic (SO2, O3, NOx) gaseous species on the walls of an outdoor Teflon chamber in dark and sunlight conditions. McMurry and Grosjean (1985) systematically investigated wall losses of particles and gases on Teflon walls. The effects of wall losses of semi-volatile compounds on SOA formation yield estimations were not well understood
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