The sentence in the OP is from a student’s composition. Here it is.
These years, great changes have taken place in my hometown. Almost everything has changed. A few years ago, people went out mainly by bike or by bus. And the roads were narrow. There were some chemical factories pouring dirty water into the stream and the air was also polluted. But now almost every family has its own car. And the roads have become wide. The stream has become clean and the air has been fresh. People have lived happily. I'm glad to see these changes. I believe we'll have a better life in the future.
I changed two sentences for her.
First, I changed “the air has been fresh” to “the air has turned fresh” or just “the air is fresh”.
Second, I changed “People have lived happily” to “People live happily”.
In order to explain to her why “the air has been fresh” is not right there correctly and clearly, I asked the question in the OP. Would you please enlighten me about the reason why the sentence is not suitable there and how to correct it?