The goal of the project is to determine the identities, amounts, and key properties of Particular Organic Nitrogen (PON) in organic aerosol, over a wide geographical and temporal range. Coverage of such a range will be achieved by analyzing previously collected, archived filter samples from a number of locations worldwide, including those associated with NOAA campaigns. Sites vary greatly in terms of anthropogenic influence, ranging from an urban/polluted area (CalNex 2010, Pasadena CA), to suburban/rural areas influenced by urban outflow or biomass burning (NEAQS 2004; Chapel Hill, NC; BEACHON-RoMBAS 2011, Manitou Forest, CO; SOAS 2013, Look Rock, TN), to a very remote site (Cape Grim, Australia). At this last site, high-volume aerosol filter samples have been continually collected since 1988, enabling studies of changes to background aerosol over the course of the last quarter-century. Filter samples will be extracted and subsequently analyzed by three state-of-the-art analytical techniques, liquid chromatography/electrospray ionization mass spectrometry (for the measurement of individual PON species), liquid chromatography/diode array detection (for the measurement of their light-absorbing properties), and high-resolution aerosol mass spectrometry (for the measurement of total amount and ensemble properties of the PON). Such measurements will help address a number of key scientific questions, including the sources and transformations of PON compounds, their role in light absorption, and changes to background PON over the last two decades.