Origin, Size Segregation, and Fate of Nitrate Aerosols Aloft During the BRACE 2002 Field Intensive

As part of the May 2002 field intensive of the Bay Regional Atmospheric Chemistry Experiment (BRACE), the NOAA Twin Otter aircraft flew 21 missions in the greater Tampa region over urban, suburban, and rural areas, Tampa Bay, and the Gulf of Mexico. Among these flights were several vertical profiles extending from 60 to 3000 m above mean sea level over the Gulf, the Bay, and the ground sites. Aerosol samples on the Twin Otter were made with high flow rate filter packs followed by off-line ion chromatography for major anions and cations. Additional gas-phase species including ozone, oxides of nitrogen and total oxidized nitrogen, nitric acid, speciated volatile organic compounds, formaldehyde, and peroxides were measured on the aircraft with frequencies ranging from 1 Hz to 90 s. The degree of nitrate partitioning observed in the Twin Otter samples onto fine (°Ü2.5 µ) and coarse (2.5 to ~4 µ) aerosols is examined here separately for the three flow regimes that predominated during the intensive: strong synoptic, when local effects were overwhelmed; synoptic shift, with wind shifts due to changing synoptic features; and the sea and/or bay breezes, when local effects of the Gulf and Bay forced wind shifts. In addition, the role of nitric acid in the total nitrogen budget and in its interaction with sea salt aerosols and gas-phase ammonia is considered. Finally, the degree of chloride replacement on sea salt aerosols is tracked and contrasted for on-shore and off-shore prevailing winds, and for conditions of strong nitrogen oxide limitation encountered in long plume travel times out from the Tampa urban core.