Peroxymethacrylic nitric anhydride (MPAN), a potential atmospheric photoproduct, was synthesized and characterized in the laboratory for the first time. The compound was identified by FT-IR, GC-MS, GC/ECD, and decomposition studies. Purification of synthetic mixtures provided a sample suitable for calibration of instruments for ambient atmospheric sampling. Possible field identification of MPAN is reported, and the role of MPAN in the chemistry of the rural troposphere is discussed.