Abstract
Iodine compounds destroy ozone (O3) in the global troposphere and form new aerosols, thereby affecting the global radiative balance. However, few reports have described the latitudinal distribution of atmospheric iodine compounds. This work reports iodine monoxide (IO) measurements over unprecedented sampling areas from Arctic to the Southern Hemisphere and spanning sea surface temperatures (SSTs) of approximately 0 °C to 31.5 °C. The highest IO concentrations were observed over the Western Pacific warm pool (WPWP), where O3 minima were also measured. There, negative correlation was found between O3 and IO mixing ratios at extremely low O3 concentrations. This correlation is not explained readily by the “O3-dependent” oceanic fluxes of photolabile inorganic iodine compounds, the dominant source in recent global-scale chemistry-transport models representing iodine chemistry, and rather implies that “O3-independent” pathways can be similarly important in the WPWP. The O3-independent fluxes result in a 15 % greater O3 loss than that estimated for O3-dependent processes alone. The daily O3 loss rate related to iodine over the WPWP is as high as approximately 2 ppbv despite low O3 concentrations of ~10 ppbv, with the loss being up to 100 % greater than that without iodine. This finding suggests that warming SST driven by climate change may affect the marine atmospheric chemical balance through iodine–ozone chemistry.
Highlights
Halogens play an important role in tropospheric and stratospheric chemistry through the catalytic destruction of ozone (O3), which affects the atmosphere’s oxidizing capacity and the radiative balance of the Earth (Alicke et al, 1999; Koenig et al, 2020; Read et al, 2008; Saiz-Lopez et al, 2012; Saiz-Lopez et al, 2014; Simpson et al, 2015)
Observations were limited to some seasons and years (e.g., Arctic measurements were limited to the Northern Hemisphere summer), whole latitudinal bands were covered from 74°N to 67°S, and strong latitudinal variations of iodine monoxide (IO) concentrations were observed, with a maximum detected clearly in the tropics (10°S – 10°N), but not at higher latitudes in either hemisphere
We report negative correlation between IO and O3 concentrations over the IO maximum, even under extremely low O3 conditions, which few earlier studies have demonstrated
Summary
Halogens play an important role in tropospheric and stratospheric chemistry through the catalytic destruction of ozone (O3), which affects the atmosphere’s oxidizing capacity and the radiative balance of the Earth (Alicke et al, 1999; Koenig et al, 2020; Read et al, 2008; Saiz-Lopez et al, 2012; Saiz-Lopez et al, 2014; Simpson et al, 2015). Iodine forms aerosol particles; it can thereby affect the global radiative balance (O'Dowd et al, 2002; Sipila et al, 2016; Gómez-Martín et al, 2020; Baccarini et al, 2020; Gómez-Martín et al, 2021). Because of their low concentrations in the atmosphere, iodine compounds are difficult to quantify. The primary source of iodine in the troposphere has long been regarded as organic compounds in coastal areas (Davis et al, 1996; Carpenter et al., 2012; Prados-Roman et al, 2015a). Results of recent studies suggest that iodine compounds over the open ocean are emitted from inorganic sources following O3 deposition over the ocean surface (Carpenter et al, 2013; Macdonald et al, 2014; Prados-Roman et al, 2015a). The inorganic sources are regarded as the dominant emission term over the oligotrophic
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