Abstract View

Evaluation and Applications of Methods for Quantification of Bulk Particle-phase Organic Nitrates Using Real-time Aerosol Mass Spectrometry

DOUGLAS DAY, Pedro Campuzano-Jost, Benjamin A. Nault, Brett Palm, Weiwei Hu, Paul Wooldridge, Ronald Cohen, Kenneth S. Docherty, J. Alex Huffman, Suzane de Sá, Scot T. Martin, Jose-Luis Jimenez, CIRES, University of Colorado, Boulder

Abstract Number: 488
Working Group: Instrumentation and Methods

Abstract
Particle-phase organic nitrates (pRONO₂) in the atmosphere can contribute to secondary organic aerosol formation, represent a substantial loss of reactive nitrogen, and comprise substantial fractions of particle-phase nitrate (pNO₃). However, pRONO₂ is infrequently measured and thus poorly understood. There is increasing prevalence of aerosol mass spectrometers (AMS), which have shown promise for determining quantitative pRONO₂ contribution to aerosols. An approach that relies on relative intensities of NO⁺ and NO₂⁺ ions in the AMS spectrum, calibrated NO_x⁺ ratio for NH₄NO₃, and inferred ratio for pRONO₂ has been proposed as a way to apportion pNO₃ signal to NH₄NO₃ and pRONO₂. This method is increasingly being applied to field and laboratory data. However, methods applied have been largely inconsistent and poorly characterized. We compiled an extensive survey of NO_x⁺ ratios measured for various pRONO₂ compounds and mixtures from multiple AMS instruments, groups, and laboratory/field measurements. We show that the pRONO₂ NO_x⁺ ratio can be estimated using a ratio referenced to the calibrated NH₄NO₃ ratio, a so-called “Ratio-of-Ratios” method (RoR=2.75±0.41). We systematically explore the basis for and uncertainties associated with quantifying pRONO₂ (and NH₄NO₃) with the RoR method using ground and aircraft field measurements conducted over a large range of conditions. The method is compared to another AMS method (PMF) and other pRONO₂ and related measurements, showing good agreement/correlation. PMF of thermal denuder measurements (applying RoR method) was conducted to construct thermograms and volatility basis sets of pRONO₂ for several campaigns, which were similar to those for less-oxidized oxidized organic aerosol PMF factors. A broad survey of ground/aircraft AMS measurements shows pervasive trends of higher contribution of pRONO₂ to pNO₃ with lower pNO₃ concentrations, which generally corresponds to shifts from urban-influenced to rural/remote regions.