AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Investigating Submicron Inorganic Salts Biases Collected on Filters Collected in Airborne Campaigns
BENJAMIN A. NAULT, Pedro Campuzano-Jost, Douglas Day, Jack Dibb, Karl D. Froyd, Eric Scheuer, Jose-Luis Jimenez, CIRES, University of Colorado, Boulder
Abstract Number: 560 Working Group: Instrumentation and Methods
Abstract The mass concentration and speciation of accumulation and coarse mode aerosol is important to investigate the chemical and physical processes controlling aerosol from emission sources to the most remote regions of the atmosphere. Collection of aerosol onto filters to be analyzed off-line by chromatography is one technique widely used, especially for analysis of refractory salts (e.g., NaCl, NaNO3, MgSO4, etc.), as well as for NH4NO3, (NH4)2SO4, and HNH4SO4. Here, we use observations collected onboard the NASA DC-8 during recent NASA campaigns. Two substantial differences appear when comparing the submicron inorganic salts measured from filters versus real-time techniques.
First, we find that for an urban study (KORUS-AQ), where NH4NO3 is elevated due to anthropogenic emissions of NOx, nitrate measured from the filters can be lower than the nitrate measured by both AMS and on-line ion chromatography. Data from an airborne thermal denuder suggests that the higher temperatures in the cabin (vs. ambient) may lead to volatilization of nitrate off the filters during handling. A thermodynamic model simulation of this situation confirms that NH4NO3 on the filters will quickly volatilize as NH3 and HNO3. These results are important for interpreting aircraft results and comparisons when volatile nitrate dominates over non-volatile nitrate, such as East Asia and Europe.
Second, for recent remote studies (NASA ATom), the filters consistently show ammonium-to-sulfate molar ratios of 0.5 (equivalent to NH4HSO4) or higher. However, the AMS and a single particle mass spectrometer (PALMS) indicate a larger range of values. With literature values, we show that the substantial uptake of NH3 onto H2SO4 particles on the filters to form NH4HSO4 can occur in 20 s or less. Further experiments are being conducted with conditions representative onboard the DC-8 to validate the calculations. These results will allow improved interpretation of ammonium balances from filter and real-time measurements, especially in remote regions.