ASSOCIATIONS |
INCORPORATING COLD CHAIN |
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exercise for artificial intelligence managing |
The focus has shifted several times over |
the air-conditioning market in the 1990s has |
the other hand , the environmentalists |
the plant operation , but there is a danger |
the years ; from ozone depletion to global |
now been transformed into its breakdown |
point out that there is no feasible |
that anything that is too complicated or not |
warming and then from global warming |
products and the HFO released just a few |
method of removing TFA from water at |
sufficiently transparent in control strategy |
to persistent organic pollutants . At each |
weeks ago has already gone . |
scale : once it is present in the ocean it |
will simply be disabled by the operator if |
stage the decisive action taken to address |
is hard to shift . It tends to accumulate |
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they don ’ t trust it . |
a specific issue has had some unintended |
Table 2 : Atmospheric Lifetime of |
to higher levels in playas ( inland salt |
In the fluorinated refrigerant sector , the |
and unwelcome consequences . For |
Various Refrigerants |
lakes ) and as it passes through surface |
process of change will continue , and it is possible that it will end with fluorinated substances being banned completely , or at best being reserved for essential |
example , the substitution of R-22 with R404A reduced the ozone depleting potential of a leaked refrigerant from 0.05 to 0 but increased the GWP on |
Refrigerant Type Lifetime * ODP GWP PFAS
R-12 CFC 140 years 1.0 10 900 No
R-22 HCFC 13.3 years 0.05 1 810 No
R-134a HFC 14.6 years 0 1 430 Yes
R-32 HFC 5 years 0 675 No
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freshwater to get from the point of formation to the ultimate sink ( the playa or the ocean ) the levels will be much higher than the background level found |
uses only . At present these fluorinated products have been lumped together into a category known as perfluorinated alkyl substances ( PFAS ) and there are several jurisdictions around the world developing legislation to restrict their use . Most of |
the 100-year time horizon from 1,810 to 3,922 – more than double . This accelerated the adoption of lower GWP alternatives like R-410A , but its GWP is still higher than R-22 , at 2,088 ( and it is still designated as ‘ high GWP ’ according |
R-1234yf HFO 11 days 0 4 Yes
The atmospheric lifetime of the refrigerant is defined ( AR6 , 2023 ) as the mass of substance in a reservoir ( the atmosphere ) divided by the rate of removal from the reservoir . For some substances this is a constant but for others the rate of removal is influenced by the quantity in the reservoir , so it varies as time goes by .
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in the ocean .
A couple of interesting points about TFA are that it forms an azeotrope with water ( which is why it is hard to remove from the environment ) and that one of the few mechanisms identified for its degradation
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the fluorinated refrigerants fall into the |
to Table 1 ). The fluorinated chemicals with |
is through biotransformation , producing |
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most common definition of PFAS , which is that the carbon chain contains at least one – CF2 – group in the middle or at least one – CF3 group on the end . However , many of the serious health concerns that are making headlines around the world relate to other forms of PFAS , such as perfluorooctanoic acid ( PFOA ), perfluorobutanesulfanoic acid ( PFBS ) and hexafluoropropylene oxide ( HFPO ).
Conflating these serious health concerns with the widespread use of fluorinated refrigerants is very misleading and doesn ’ t help to clarify the advantages and disadvantages of using HFCs and HFOs as refrigerants . One of the quirks of this definition of PFAS is that R-32 is not in this category . We may therefore find that ultra-low GWP substances like R-1234yf are regulated sooner than moderate GWP substances ( R32 is the only single-substance refrigerant in the moderate GWP band ).
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a low GWP designation are all olefins , with a carbon double bond in the main chain , which means they decompose relatively quickly in the atmosphere and therefore make little contribution to global warming , particularly when measured against the traditional 100-year time horizon . The unintended consequence of this approach is that the end products of the breakdown reaction may not be entirely environmentally friendly , and those substances are transferring into the biosphere much faster than the more stable compounds that they are replacing , as shown in Table 2 .
One of the remarkable things about the data in Table 2 is the implication that some of the R-12 manufactured by Thomas Midgley in the 1920s is still in the atmosphere and has not transitioned into any other substance yet , whereas most of the R-32 released since its introduction to
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One of the most common breakdown
products for most of the refrigerants is
trifluoroacetic acid , known as TFA . This
is similar in structure to acetic acid , the
main active ingredient in vinegar , but with
the methyl group ( -CH3 ) replaced with a
fluorinated group ( -CF3 ). It is the subject of
intense debate between environmentalists
and the chemical industry . The chemical
producers point out that there are
background levels of TFA in the environment
all over the world , even on remote islands
in the Pacific Ocean , and in deep water
samples that are thousands of years old .
These background levels are
several orders of magnitude lower than
levels that would harm aquatic life or
humans and in an assessment study
for UNEP it is estimated that all known
anthropogenic sources of TFA would
raise the background level by less than
10 % by 2050 ( Solomon et al , 2016 ). On
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carbon dioxide and R-23 , which has an atmospheric life of 270 years and a GWP100 of 14 800 . Obviously , this process is not common but all of these factors suggest that a precautionary approach to the widespread adoption of short-life fluorochemicals is warranted , at least until the environmental impact of the atmospheric chemistry is better understood . CLA
Continued in Part 3 …
The focus has shifted several times over the years ; from ozone depletion to global warming .
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