https://doi.org/10.1351/goldbook.S05906
Pressure defined as \(101\ 325\ \text{Pa}\) and used as unit of pressure with the symbol \(\text{atm}\).
Sources:
CODATA Bull. 1986, 63, 1 [Terms] [Book]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 993 [Terms] [Paper]