We detected a peroxyacyl nitrate (PAN)-type compound, peroxyacryloyl nitrate (CH2&dblbnd;CHC(O)OONO2, APAN) which has not previously been reported in the atmosphere. Identification of APAN was made from negative ion chemical ionization (NICI) mass spectra of a cryogenically concentrated ambient air sample by comparison with a synthesized standard. The thermally fragile nature of the compound, and the retention time of the synthesized standard provide additional evidence for the existence of APAN in ambient air. Observations made at a suburban site in Tokyo, and at Rishiri Island, a remote site in northern Japan, suggest the ubiquitous presence of APAN in the global atmosphere. While its mixing ratio was usually low (<1% of PAN), high-APAN episodes (~4% of PAN) were observed at Rishiri Island. APAN can be formed from acrolein, which is directly emitted from vehicle exhaust, and may be produced by oxidation of 1,3-butadiene and aromatics. Further measurements of APAN along with acrolein and other NMHCs are required to understand its distribution, behavior, and sources in the atmosphere. ¿ 2001 American Geophysical Union