Atmospheric Chlorine and Ozone in the Quasi-Geostrophic Continuum
I frequently try to understand more about polar ozone hole assertions, simply because ozone theories are so wound up into hydrological circulation theory. I have read conventional resources to learn more about ozone and temperature inflections with elevation, for any atmosphere height profile. The featured image  is adapted from a 2017 post describing a notion that simple condensation of moisture might account for the lion’s share of the temperature trend reversal found at the tropopause. I also described some ozone – elevation profile references.
The scientific literature is convoluted and dense, but I recently found this more straightforward post by Dr. Parson:
The Parson resource has much which might interest any who try to chase ozone questions around. I’ve already learned a few things. I like the benefit of a resource that makes great points and thereby challenges my own notions. I hope in turn, if he ever becomes aware of this post, that he appreciates my challenges to his notions. So I took one of his tables and used that to sketch within the above featured image, the dotted green Hydrochloric Acid (HCL) relative concentration profile line above the tropopause.
As with Temperature and Ozone, an HCL concentration trend inflection at the tropopause (~ elevation 12 km) has been identified. The featured image shows that HCL concentrations rise starting at the inflection elevation. Dr. Parson uses this trend to assert that CFCs are photolytically destroyed near the tropopause. In his view, all of the natural HCL was rained out in the troposphere, below the tropopause. I’m maybe overboard in paraphrasing this way but colorful metaphors sometimes add value so worth a try to say: This Montreal Protocol type of assertion means that only the heavy man-made CFC molecules can float high into the sky, like Disney Fantasia Hippos. When the CFCs are sufficiently photolyzed by the Sun, the resulting hydrogen chloride (HCL) fragments float ever higher, destroying zone molecules as they hover or otherwise circulate over the Antarctic. Later in the Antarctic autumn, the special chlorine molecules may return to noctilucent clouds to await the next Spring. This leads me to also wonder where all of the CFCs and/or chlorines circulate to, or what other fate is in store for them when their cloud refuges frequently disappear?
My guess now is that as soon as a CFC molecule is released to the atmosphere, it begins to sink. And as soon as it is exposed to sunlight, it begins to dissociate. How those CFCs manage to reach the upper troposphere given their weight and without solar exposure are questions that no competent ozone scientist should fail to explore. I also must ask if CFCs have been sufficiently observed and quantified anywhere in our atmosphere
None of this chlorine talk impacts my own notions of moisture and ozone, but it’s important for me to understand. Conveniently Parson has included a breakdown of chlorine in the stratosphere, and claims that 80% of it comes from manmade sources such as CFCs. But he did not include any direct measurements of CFCs in the stratosphere or upper troposphere to support. Perhaps it is in his reference list, but nominally rummaging around there and across the Internet, I can only so far find carefully parsed narratives which don’t take me to any direct observations.
Parson’s document also never discusses ozone in the context of water. But he does indicate that as moisture condenses, HCL is freed from solution within the moisture solvent. Perhaps that is correct. Accordingly I wonder if that is the cause of the increasing HCL concentration with elevation above the tropopause, as the lime green curve suggests.
In my current view based on literature, regardless of any ozone connection, marine aerosols can account for the lion’s share of HCL in the upper or the lower atmosphere. They can be organic and/or inorganic depending upon the aerosol. Their semigeostrophic travels can easily get them into and out of the stratosphere. Upon breaching the tropopause, as its water solvent is stripped by condensation, the HCL would seem to become further concentrated higher within the stratosphere. In this post I looked at the same chlorine atmospheric profile inflection as tabulated by Parson, and speculated from basic geostrophic moisture circulation perspectives that the upper chlorine comes mostly from the lower chlorine. Parson also related that this chlorine largely and most naturally comes from our oceans. I added a corollary notion that CFCs are heavy, sluggish, rare, and photochemically fragile species which cannot even reach the stratosphere on their own horsepower.
If I’m not mistaken, there is no actual way to examine an HCL molecule and identify if its origins are organic or inorganic. On the other hand, I know that stable isotope investigations can add value to related questions of HCL patterns across the geostrophic continuum, so I’ll be alert to any related papers. Stable isotopes already challenge Parson’s claim and a related one in an old Scientific American article, that heavier molecules such as CFCs transport just as fast and far as lighter molecules such as oxygen, water vapor, or HCL. If he and the magazine were correct, then stable isotope atmospheric moisture tracking and dating, a useful practice which has benefited generations of scientists, would not be possible.
In exploring this line, the stable isotopes of chlorine might not be helpful given that there is little variation to work with. Radioisotopes of chlorine might be helpful in some cases. On the other hand, the H in the HCL offers relatively straightforward opportunities to compare any sampled HCL volume from any location to the Meteoric Water Line (MWL). This would allow some interpretation. My guess is that regardless of the HCL upper atmosphere sample, the MWL would be honored and that would further support my notion that the upper atmosphere HCL simply comes from the lower atmosphere HCL and not from rare CFCs. But that is why such a sampling would add value. If the isotope ratios didn’t match the MWL, then one might need to look to other origins. A new post is in the works.
I should also become familiar with the state of CFC detection observations in the atmosphere. CFCs can be identified from spectral absorption plots, so I did search a paper  for the associated gas chromatography spectral measurements of the CFCs. Unfortunately I learned that the spectral data was to be found in an earlier reference . I visited that reference and could not find the gas chromatography measurements or associated spectra, but that reference did cite another reference  which might have the information. But that would be impossible because reference  is from 2008, and the gas chromatography measurements were supposed to have been taken in 2011. Sometimes I can’t find things right under my nose so I’ll continue to comb through. recent edit: There is this NOAA site  which appears provide ample evidence of direct measurements of halocarbons and CFCs.
On the other hand, I still can’t seem to find any spectral readings. Those would help to begin to confirm the apparent circulations of these heavy molecules.
Another part of that circulation must go through the ground. In fact, the only other wide-spread and conventional descriptions of CFC direct detection in the environment are for groundwater. Perhaps atmospheric sedimentation to the Earth’s surface, rather than photolysis, would be the ultimate destination of the heavy CFCs. Groundwaters happen to also be one of the few domains on Earth where the CFCs would not be exposed to the Sun. It might not surprise some to learn from this comprehensive USGS resource  that CFCs sink deeply into our Earth, through the unsaturated zone and down to any water table or impermeable surface. There are some additional points of comparison worthy of attention because the USGS resource attributes solubility to some important CFCs.
The utility of CFCs to date water tables within unconsolidated aquifers is yet another reason for me to also wonder about published photolysis rates for CFCs. Through ongoing combing of the literature, I will keep searching for basis data on photolysis of CFCs including rate constants and quantum yields. Also I am noting many new terms of art to me, about or associated with CFCs in the atmosphere, such as Ozone Depletion Potential (ODP), Fractional Release Factor (FRF), and even Global Warming Potential (GWP).
This is only a blog, taking some swings towards the consensus views of the Ozone Hole, but also agreeing with other interesting notions:
- All agree that chlorine readily dissolve in raindrops, and raindrops access the full atmosphere over short time spans. It happens that ozone also readily dissolves in raindrops. My next post will follow up, given the precipitation resources often featured at this website.
- Those CFCs are alleged to not be destroyed by sunlight until they travel, through sunlight, to the tropopause and persist there for years to decades.
- The CFCs are alleged to not largely sink upon release into the atmosphere, even as these molecules can be used to date groundwater.
- Those CFCs are attributed to be the source of 80% of the Chlorine in the upper atmosphere, even though direct evaluations of the organic or inorganic origin of any individual Chlorine atom cannot be made.
- Those CFCs and/or the essential chlorine member molecules are alleged to also reside much of each year in rarely investigated noctilucent clouds, only to engage in wholesale but never-directly-witnessed ozone destruction every Antarctic Spring.
 featured image adapted from Figure 1 of https://www.ucar.edu/communications/gcip/m1sod/m1pdfc1.pdf
 Laube, J.C., Keil, A., Bönisch, H., Engel, A., Röckmann, T., Volk, C.M., and Sturges, W.T. 2013. Observation-based assessment of stratospheric fractional release, lifetimes, and ozone depletion potentials of ten important source gases. Atmospheric Chemistry and Physics. 13, 2779-2791 doi:10.5194/acp-13-2779-2013
 Laube, J.C., Engel, A., Bönisch, H., Möbius, T., Sturges, Bras, M., and Röckmann, T. 2010. Fractional release factors of long-lived halogenated organic compounds in the tropical stratosphere. Atmospheric Chemistry and Physics. 10, 1093-1103
 Laube, J. C., Engel, A., Bönisch, H., Möbius, T., Worton, D. R., Sturges, W. T., Grunow, K., and Schmidt, U.: Contribution of very short-lived organic substances to stratospheric chlorine and bromine in the tropics – a case study, Atmos. Chem. Phys., 8, 7325–7334, 2008
*Ozone molecules can self-destruct (react) and/or simply rapidly dissolve in raindrops, without a catalyst like chlorine.
1367total visits,13visits today