4 ms·
Well spotted - It must be a typo because normally I hear parts per billion in reference to these figures, never ppm.
by nealdt 8y ago
Well spotted - It must be a typo because normally I hear parts per billion in reference to these figures, never ppm.
- detaro 8y agoregulations site also says ppm: https://www.ecfr.gov/cgi-bin/text-idx?SID=a3b649316ccb17c31211db2edd81f789&mc=true&node=pt40.24.180&rgn=div5#se40.26.180_1364 https://www.ecfr.gov/cgi-bin/text-idx?SID=a3b649316ccb17c312... (warning: massive HTML file)