Filterable water-soluble organic nitrogen in fine particles over the southeastern USA during summer

Time integrated high-volume PM2.5 samples were collected separately during day and night from 1 August to 10 September 2008 at a paired urban (Atlanta)-rural (Yorkville) sites as part of the August Mini-Intensive Gas and Aerosol Study (AMIGAS). Selected filters (n = 96, 48 for each site) were analyzed for a suite of water-soluble chemical species, including major inorganic ions, water-soluble organic carbon (WSOC), water-soluble total and inorganic nitrogen (WSTN and WSIN), and levoglucosan. Semi-continuous analyses of PM2.5 mass, soluble ions, WSOC, and gaseous O3, SO2, NO, NO2, NOy, CO, and meteorological parameters were also carried out in parallel. This study focuses on the characteristics of filterable water-soluble organic nitrogen (WSON), estimated by the difference in the measured concentrations of WSTN and WSIN, determined from aqueous filter extracts. At both sites, WSON varied from below the limit of detection (25 ng-N m−3) to ∼600 ng-N m−3 and on average contributed ∼10% to WSTN mass, with the majority of soluble nitrogen being ammonium (∼82%). WSON:WSOC (or N:C) mass ratios ranged between 0 and 27% at both the sites with a median value of ∼5%, similar to what has been reported in another study in the southeastern USA. At both the urban and rural sites median nighttime levels of WSON and N:C were observed to be consistently higher than daytime values. Based on correlation analyses, daytime WSON sources appeared different than nighttime sources, especially at the urban site. Overall, the data suggest the importance of coal-combustion (e.g., link to SO2), vehicle emissions, soil dust and biomass burning as WSON sources, and that nitrogenous organic compounds are likely a fairly small fraction of the secondary organic aerosol for this location during summer.