EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Global Survey of Aerosol Acidity from Polluted to Remote Locations: Measurements and Comparisons with Global Models

Benjamin A Nault1, Pedro Campuzano-Jost1, Duseong Jo1, Doug Day1, Roya Bahreini2, Huisheng Bian3,4, Mian Chin4, Simon Clegg5, Peter Colarco4, Jack Kodros6, Felipe Lopez-Hilfiker7, Eloise Marais8, Ann Middlebrook9, Andrew Neuman10, John Nowak11, Jeffrey Pierce6, Joel Thornton7, Kostas Tsigaridis12, Jose Jimenez1, and the ATom Science Team*
Benjamin A Nault et al.
  • 1University of Colorado, Boulder, CIRES, Chemistry , Boulder, United States of America (
  • 2University of California, Riverside, Environmental Sciences, Riverside, United States of America
  • 3Joint Center for Environmental Technology, UMBC, Baltimore, United States of America
  • 4Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, United States of America
  • 5University of East Anglia, Environmental Sciences, Norwich, United Kingdon
  • 6Colorado State University, Fort Collins, United States of America
  • 7University of Washington, Seattle, United States of America
  • 8University of Leicester, Leicester, United Kingdom
  • 9Chemical Science Division, ESRL, NOAA, Boulder, United States of America
  • 10CIRES, NOAA, Boulder, United States of America
  • 11NASA Langley Research Center, Langley, United States of America
  • 12Columbia University, New York City, United States of America
  • *A full list of authors appears at the end of the abstract

The inorganic composition of aerosol impacts numerous chemical and physical processes and properties. However, many chemical transport models show large variability in both the concentration of the inorganic aerosols and their precursors (up to 3 orders of magnitude differences) and the inorganic aerosol composition. Different models predict very different properties (e.g., aerosol liquid water concentration and aerosol acidity) and outcomes (e.g., heterogeneous uptake of gases or aerosols’ direct and indirect impacts on climate). Here, we use airborne observations from campaigns conducted around the world to investigate how the inorganic fine aerosol (PM1) composition, and one of its key parameters, aerosol acidity, changes from polluted regions (Mexico City, Los Angeles, Northeastern US, and Seoul) to remote ocean basins (the Atmospheric Tomography campaigns 1 and 2) in order to provide constraints for the chemical transport models. I find that the empirical ammonium balance with major ions (ammonium balance = mol NH4 / (2×mol SO4 + mol NO3)) rapidly decreases from ~1 at the highest inorganic PM1 concentration to 0 at the lowest inorganic PM1. The data indicate a robust trend for ammonium balance vs inorganic PM1 at all altitude levels in the troposphere, suggesting that NH3 emissions and subsequent neutralization of H2SO4 becomes negligible in the most remote (lowest inorganic PM1) regions. Further, a robust trend for PM1 pH (calculated with E-AIM) vs inorganic PM1 is observed at all levels for these campaigns, as well, decreasing from a pH of ~3 to a pH of ~ –1 from the highest to lowest inorganic PM1. The data overall implies very low NH3 (and NH4+) throughout most of the atmosphere, contrary to predictions of some models, implying different physical properties than predicted in models. We compare these trends of ammonium balance and pH vs inorganic PM1 against 9 chemical transport models (CTMs), and we find that the CTMs show large variability for both the ammonium balance and pH vs inorganic PM­1, compared to observations. Generally, we find a high bias in the ammonium balance and pH, likely due to too much NH­3 in model (possibly too high NH3 emissions over oceans or too long lifetime) and inclusion of externally mixed seasalt into the submicron pH calculation. These results overall would imply different aerosol properties in the models than observed, impacting the chemistry, optical properties, and cloud properties.

ATom Science Team:

Jason Schroder, John Crounse, Jack Dibb, Michelle J. Kim, Eric Scheuer, Paul O. Wennberg

How to cite: Nault, B. A., Campuzano-Jost, P., Jo, D., Day, D., Bahreini, R., Bian, H., Chin, M., Clegg, S., Colarco, P., Kodros, J., Lopez-Hilfiker, F., Marais, E., Middlebrook, A., Neuman, A., Nowak, J., Pierce, J., Thornton, J., Tsigaridis, K., and Jimenez, J. and the ATom Science Team: Global Survey of Aerosol Acidity from Polluted to Remote Locations: Measurements and Comparisons with Global Models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11366,, 2020.


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