Polar Tropospheric Ozone Depletion Events

TY - CHAP

T1 - Polar Tropospheric Ozone Depletion Events

AU - Halfacre, J. W.

AU - Simpson, W. R.

PY - 2022

Y1 - 2022

N2 - Polar sunrise in both the Arctic and Antarctic coincides with sharp, episodic decreases of tropospheric ozone mixing ratios. These “ozone depletion events” (ODEs) are caused by reactive, gas-phase halogen species, which originate largely from halide-containing aerosol particles and frozen surfaces. In this review, we discuss recent advances in the scientific community’s understanding of ODEs. While reactive bromine species dominate the ozone-depleting chemistry, other halogens such as chlorine and iodine also can profoundly affect ODEs. For example, reactive chlorine species play an important ancillary role in promoting reactive bromine recycling. Reactive iodine has large potential in enhancing ODEs because of its direct reaction with ozone and lack of other sinks, though the extent of its role is still being assessed as in situ observations increase. The effects of non-halogen species involved in ODE chemistry, such as nitrogen oxides and formaldehyde, are also discussed. The inclusion of recently observed mole fractions of the molecular halogens into models suggests in situ ODE chemistry can be faster (e.g., occur on a timescale of hours) than previously thought (i.e., days), consistent with in situ investigations of ozone depletion timescales. Additionally, the physical structures of single events have been found to extend laterally to distances greater than 1000 km and vertically as high as a few kilometers, though most often they are confined to the boundary layer (within several hundred meters of the surface). While literature has hypothesized roles for many frozen saline surfaces in halogen activation, growing evidence suggests snow may be the most important. Further, recent evidence suggests appropriate chemistry may occur under a variety of meteorological conditions, including warmer temperatures approaching 0°C, both high and low atmospheric pressures, and a range of wind speeds. Finally, outstanding questions for the field are discussed, such as the relative roles of the snowpack and windblown snow in halogen activation, the effects of pollution and climate change on ODEs, and how the underlying chemistry in ODEs may translate to lower latitudes and to the free troposphere.

AB - Polar sunrise in both the Arctic and Antarctic coincides with sharp, episodic decreases of tropospheric ozone mixing ratios. These “ozone depletion events” (ODEs) are caused by reactive, gas-phase halogen species, which originate largely from halide-containing aerosol particles and frozen surfaces. In this review, we discuss recent advances in the scientific community’s understanding of ODEs. While reactive bromine species dominate the ozone-depleting chemistry, other halogens such as chlorine and iodine also can profoundly affect ODEs. For example, reactive chlorine species play an important ancillary role in promoting reactive bromine recycling. Reactive iodine has large potential in enhancing ODEs because of its direct reaction with ozone and lack of other sinks, though the extent of its role is still being assessed as in situ observations increase. The effects of non-halogen species involved in ODE chemistry, such as nitrogen oxides and formaldehyde, are also discussed. The inclusion of recently observed mole fractions of the molecular halogens into models suggests in situ ODE chemistry can be faster (e.g., occur on a timescale of hours) than previously thought (i.e., days), consistent with in situ investigations of ozone depletion timescales. Additionally, the physical structures of single events have been found to extend laterally to distances greater than 1000 km and vertically as high as a few kilometers, though most often they are confined to the boundary layer (within several hundred meters of the surface). While literature has hypothesized roles for many frozen saline surfaces in halogen activation, growing evidence suggests snow may be the most important. Further, recent evidence suggests appropriate chemistry may occur under a variety of meteorological conditions, including warmer temperatures approaching 0°C, both high and low atmospheric pressures, and a range of wind speeds. Finally, outstanding questions for the field are discussed, such as the relative roles of the snowpack and windblown snow in halogen activation, the effects of pollution and climate change on ODEs, and how the underlying chemistry in ODEs may translate to lower latitudes and to the free troposphere.

U2 - 10.1142/9789811230134_0008

DO - 10.1142/9789811230134_0008

M3 - Chapter

SN - 978-981-12-3012-7

SP - 411

EP - 452

BT - Chemistry in the Cryosphere

PB - World Scientific

ER -