Question to the Department for Environment, Food and Rural Affairs:
To ask the Secretary of State for Environment, Food and Rural Affairs, for what reasons why Form PI-1 - Pollution Inventory Reporting sets the reporting threshold for PM2.5 at 1000kg per annum and the reporting threshold for PM10 at 1000 kg per annum when the reporting threshold for total particulate matter is 10,000 kg per annum.
The Environment Agency does not hold records on how the original PI thresholds were derived. However, since total particulate matter (TPM) will contain both PM10 and PM2.5, plus particles of other sizes, it is logical that the thresholds for PM10 and PM2.5 can be lower than TPM.