How to write 零下零下

zero; nought; zero sign; fractional; fragmentary; odd (of numbers); (placed between two numbers to indicate a smaller quantity followed by a larger one); fraction; (in mathematics) remainder (after division); extra; to wither and fall; to wither

down; downwards; below; lower; later; next (week etc); second (of two parts); to decline; to go down; to arrive at (a decision, conclusion etc); measure word to show the frequency of an action