UC San Diego

With 4.9% of total anthropogenic radiative forcing attributed to aircraft emissions, jet engines combust copious amounts of fuel producing gases including : NOx (NO + NO₂), SOx, VOC's and fine particles [IPCC (1999), IPCC (2007), Lee et al., 2009]. The tropospheric non- linear relationships between NOx, OH and O₃ contribute uncertainties in the ozone budget amplified by poor understanding of the NOx cycle. In a polluted urban environment, interaction of gases and particles produce various new compounds that are difficult to measure with analytical tools available today [Thiemens, 2006]. Using oxygen triple isotopic measurement of NO₃ to investigate gas to particle formation and chemical transformation in the ambient atmosphere, this study presents data obtained from aerosols sampled at NASA's Dryden Aircraft Operations Facility (DAOF) in Palmdale, CA during January and February, 2009 and Los Angeles International Airport (LAX) during Fall 2009, Winter 2010, and Spring 2010. The aerosols collected from jet aircraft exhaust in Palmdale exhibit an oxygen isotope anomaly ([Delta]10;17O =[delta]¹⁷O -0.52 [delta]¹⁸18O) increase with photochemical age of particles (-0.22 to 26.41%₀) while NO₃ concentration decreases from 53.76 - 5.35ppm with a radial distance from the jet dependency. Bulk aerosol samples from LAX exhibit seasonal variation with =[delta]¹⁷O and NO₃ concentration peaking in winter suggesting multiple sources and increased fossil fuel burning. Using oxygen triple isotopes of NO₃, we are able to distinguish primary and secondary nitrate by aircraft emissions allowing new insight into a portion of the global nitrogen cycle. This represents a new and potentially important means to uniquely identify aircraft emissions on the basis of the unique isotopic composition of jet aircraft emissions