ANSWER: Only 2
Explanation:
- HFCs came in to replace the CFCs, or chlorofluorocarbons, gases that were being used extensively in the air conditioning, refrigerant industries, etc.
- CFCs were found to be primarily responsible for a hole in the ozone layer of the atmosphere, which could have dangerous health impacts.
- The HFCs, which were just as effective for industrial applications, replaced the CFCs all but seamlessly.
- It was realised only later that while HFCs did not deplete the ozone layer these were very powerful greenhouse gases, much more dangerous than carbon dioxide, which is mainly blamed for global warming.
- A set of 19 HFCs are used in different applications and many of them are several hundreds or thousands of times more potent than CO2.
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