Critical Load Function Tool


Deposition of sulphur and nitrogen compounds can cause acidification, and both must be taken into account when assessing potential acidification impacts.

Over the last few years critical loads data in APIS has been updated to provide critical load functions for acidity, where available, rather than simply the empirical critical load. The function is defined by three quantities CLmaxS, CLmaxN and CLminN.

Calculating exceedance of an acidity critical load function, or the significance of a contribution from a source, is complex. Therefore, this tool calculates the exceedance for you. It enables you to compare acid deposition to the critical load function to help make a decision on the significance of a process contribution. Follow the instructions below. A detailed explanation of the approach is provided.

User data input

Critical Load Function

Deposition data

Sulphur DepositionNitrogen DepositionTotal Acid Deposition (S+N)
Process Contribution (PC)
Predicted Environmental Concentration (PEC)

Results - exceedance and deposition as a proportion of the CL function