A11K-0218
Observations of Particle Organic Nitrate from Airborne and Ground Platforms in North America: Insights into Vertical and Geographical Distributions, Gas/Particle Partitioning, Losses, and Contributions to Total Particle Nitrate.
Monday, 14 December 2015
Poster Hall (Moscone South)
Douglas A Day1,2, Pedro Campuzano Jost1,2, Brett B Palm1,2, Weiwei Hu1,2, Benjamin Nault3, Paul J Wooldridge4, Ronald C Cohen3,4, Kenneth S Docherty5, Nicholas L Wagner6 and Jose L Jimenez1,2, (1)University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (2)University of Colorado, Dept. of Chemistry and Biochemistry, Boulder, CO, United States, (3)University of California, Dept. of Earth and Planetary Science, Berkeley, CA, United States, (4)University of California, Dept. of Chemistry, Berkeley, CA, United States, (5)Alion Science and Technology, Research Triangle Park, NC, United States, (6)NOAA, Earth System Research Laboratory, Boulder, CO, United States
Abstract:
Organic nitrate formation in the atmosphere represents a sink of NOx and a termination of the HOx/NOx O3-formation cycles, can act as a NOx reservoir transporting reactive nitrogen, and contributes to secondary organic aerosol (SOA) formation. However, particle organic nitrates (pRONO2) are rarely measured and thus poorly understood. We use measurements of pRONO2 and total (gas+particle) organic nitrate (totRONO2), OA, and ammonium nitrate from the DC3 and SEAC4RS aircraft and several ground campaigns to investigate vertical and geographical distributions, gas/particle partitioning, losses, and contributions to total particle nitrate (pTotNO3). Quantification with aerosol mass spectrometry is evaluated. The fraction of pTotNO3 that is pRONO2 shows a steep inverse relationship with pTotNO3, approaching 100% at low pTotNO3, primarily at rural and remote locations. pRONO2 was typically 10-30% of totRONO2 with little vertical gradient in gas/particle partitioning from the boundary layer (BL) to the upper troposphere (UT). However, pRONO2 and totRONO2 concentrations show strong vertical gradients, with a steep decrease from the top of the BL up through the residual layer. pRONO2 contribution to OA shows a moderate increase with lower OA loadings in the BL and free troposphere (~2-3% by mass of nitrate group) with higher contributions at the lowest OA (5-8%), mostly observed in the UT. In the BL, RONO2 gas/particle partitioning shows a trend with temperature, with higher particle fraction at lower temperatures, as expected from partitioning theory. However, the temperature trend is much weaker than for single compound partitioning, which may be due to a broad mixture of species. Little to no dependence of pRONO2/OA on RH or estimated particle water was observed in the BL, suggesting that losses of pRONO2 species due to hydrolysis are too rapid to observe in this dataset and there may be a substantial fraction of pRONO2 species that are not prone to rapid hydrolysis.
