The critical relative humidity (CRH) of urea, the point at which it begins to absorb moisture from the atmosphere, is around 72.5% at 30°C.

 The critical relative humidity (CRH) of urea, the point at which it begins to absorb moisture from the atmosphere, is around 72.5% at 30°C. 

Here's a more detailed explanation:

What is CRH?

The critical relative humidity (CRH) is the relative humidity level at which a substance (like urea) starts to absorb moisture from the surrounding air. 

Why is it important?

Understanding the CRH of urea is crucial for proper storage and handling, as moisture absorption can lead to caking, reduced quality, and other problems. 

Urea's CRH:

The CRH for urea is approximately 72.5% at 30°C. 

Other fertilizers:

It's worth noting that other fertilizers, like ammonium nitrate, have different CRH values. 

Mixtures

The CRH of a mixture of urea and ammonium nitrate is lower than either of the individual materials 

Temperature effect

The CRH value can vary slightly depending on the temperature. 

Caking

Above the CRH, urea will absorb moisture, which can lead to particles becoming soft, sticky, and caking together. 

Solubility

Urea is highly soluble in water, which contributes to its tendency to absorb moisture.