Suddenly I feel my tears just about to pour out.

suddenly i want to cry.

It means " I want to cry" Because when you are cry, you will feel a little strange in your nose. And this feeling is expressed as "酸“ in Chinese. However, "酸” is only used is this place with this meaning.

It is on behalf of a state that I'm touched and I want to cry,but won't cry. You know,nose is connect with tear gland.So this sentence uses euphemistic expression to shows I'm touched. “酸”in this sentence shows a state before people are crying.but usually means a feeling of taste.

Sudden burst of sadness hit me in the nose, if translated literally