Calibration of measurement equipment to PN10 measures more particles than calibration to PN23. It is therefore logical that compliance with a limit when measured according to PN10 demonstrates compliance with the same limit according to PN23 but this text should be added for legal certainty.
The Intergovernmental Panel on Climate Change (IPCC) is the United Nations body for assessing the science related to climate change.
You can find more information about IPCC at their website.