Abstract
Abstract. Iodine plays a vital role in oxidation chemistry over Antarctica, with past observations showing highly elevated levels of iodine oxide (IO) leading to severe depletion of boundary layer ozone in West Antarctica. Here, we present MAX-DOAS-based (multi-axis differential absorption spectroscopy) observations of IO over three summers (2015–2017) at the Indian Antarctic bases of Bharati and Maitri. IO was observed during all the campaigns with mixing ratios below 2 pptv (parts per trillion by volume) for the three summers, which are lower than the peak levels observed in West Antarctica. This suggests that sources in West Antarctica are different or stronger than sources of iodine compounds in East Antarctica, the nature of which is still uncertain. Vertical profiles estimated using a profile retrieval algorithm showed decreasing gradients with a peak in the lower boundary layer. The ground-based instrument retrieved vertical column densities (VCDs) were approximately a factor of 3 to 5 higher than the VCDs reported using satellite-based instruments, which is most likely related to the sensitivities of the measurement techniques. Air mass back-trajectory analysis failed to highlight a source region, with most of the air masses coming from coastal or continental regions. This study highlights the variation in iodine chemistry in different regions in Antarctica and the importance of a long-term dataset to validate models estimating the impacts of iodine chemistry.
Highlights
Reactive halogen species (RHS) have been shown to play a critical role in causing ozone depletion events in the polar boundary layer (BL) (Barrie et al, 1988; Bottenheim et al, 1986; Kreher et al, 1997; Oltmans and Komhyr, 1986) and could contribute to new particle formation in this remote environment (Allan et al, 2015; Atkinson et al, 2012; O’Dowd et al, 2004)
Observations focused on bromine oxide (BrO), the presence of which was observed in the Antarctic using ground-based instruments (Kreher et al, 1997) and via satellites (Hollwedel et al, 2004)
Year-long ground-based observations of RHS made at Halley Bay showed the critical role that bromine and iodine compounds play in regulating the oxidizing capacity, causing ozone depletion and new particle formation in the Antarctic BL (Saiz-Lopez et al, 2007a)
Summary
Reactive halogen species (RHS) have been shown to play a critical role in causing ozone depletion events in the polar boundary layer (BL) (Barrie et al, 1988; Bottenheim et al, 1986; Kreher et al, 1997; Oltmans and Komhyr, 1986) and could contribute to new particle formation in this remote environment (Allan et al, 2015; Atkinson et al, 2012; O’Dowd et al, 2004). Observations focused on bromine oxide (BrO), the presence of which was observed in the Antarctic using ground-based instruments (Kreher et al, 1997) and via satellites (Hollwedel et al, 2004). Year-long ground-based observations of RHS made at Halley Bay showed the critical role that bromine and iodine compounds play in regulating the oxidizing capacity, causing ozone depletion and new particle formation in the Antarctic BL (Saiz-Lopez et al, 2007a).
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