The following question came out in Paper 1 - Final Year Examination for English Form 1 last year:
"This park is the only green lung in the city." What is the meaning of green lung in this sentence?
"Green lung" is a new phrase in English. Try searching its meaning in the Oxford dictionary or www.merriam-webster.com or even google; and you'll find none!
Since I couldn't find its meaning neither in the dictionary nor on the internet, I consulted the experts in English. According to Dr. Maskanah Mohd Lutfie, a senior English lecturer in UIAM, green lung refers to a space in an urban area that has lots of plants, not about the colour of the foliage. As a result the area is healthier.
So, it is kind of inaccurate to say that "green lung" literally means the source of oxygen. If a park is the only green lung in a city, we can infer that the park is the source of oxygen due to fact that it has lots of plants no matter what the colour the plants have. As stated by Dr. Maskanah, green lung doesn't also mean green plants.

I did asked my lecturer from IPBA, Dr. Sharmini Ghanaguru regarding this matter. She has a slightly different view on the meaning of "green lung" by quoting, "The green lung here is an expression that states the place that contains green plants which in turn becomes a good source of oxygen."
Hi,
green lung:

Life Sciences & Allied Applications / Environmental Science: An area of parkland within a town or city, considered in terms of the healthier environment it provides.

Sri
I did asked my lecturer from IPBA, Dr. Sharmini Ghanaguru regarding this matter. She has a slightly different view on the meaning of "green lung" by quoting, "The green lung here is an expression that states the place that contains green plants which in turn becomes a good source of oxygen."

Sounds me to me like a pretty shallow explanation for what a "Green Lung" is. Obviously green lung does not refer to only to green plants but any area of a city that has been designated as a park with lots of foliage. These foliage thru the process of photosynthesis remove harmful carbon dioxide from the air and replace them with oxygen. It has nothing to do with being a "source of oxygen" but rather a filter that removes carbon dioxide from the air and and ogygen being the by product of the whole process. Green lungs within a city also aid in lowering temperatues of the surrounding area due to their ability to absorb heat from the sun during its photosynthesis proecess.
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In my country Indonesia, such place is called "paru-paru kota" (literally means "city lungs").

hi I am Dr Sharmini . Please do not quote my name as I had not mentioned any of the above matters pertaining to ‘green lung’ . Thank You

Meaning of green lung,,,,, An area of natural parkland within an urban region, supposed to replenish the air with oxygen.

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