Fine Aerosol Acidity and Water during Summer in the Eastern North Atlantic

• Published in: Atmosphere
• Main Authors: Theodora Nah, Junwei Yang, Jian Wang, Amy P. Sullivan, Rodney J. Weber
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2021
• Subjects: aerosol water; aerosol pH; aqueous phase; remote marine boundary layer; non-volatile cations; Meteorology. Climatology; QC851-999; North Atlantic
• Online Access: https://doi.org/10.3390/atmos12081040; https://doaj.org/article/7521401c1b0c49e3bf49c9bebe70a005

Aerosol pH governs many important atmospheric processes that occur in the marine boundary layer, including regulating halogen and sulfur chemistries, and nutrient fertilization of surface ocean waters. In this study, we investigated the acidity of PM 1 over the eastern North Atlantic during the Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA) aircraft campaign. The ISORROPIA-II thermodynamic model was used to predict PM 1 pH and water. We first investigated the sensitivities of PM 1 pH and water predictions to gas-phase NH 3 and HNO 3 concentrations. Our sensitivity analysis indicated that even though NH 3 and HNO 3 were present at very low concentrations in the eastern North Atlantic during the campaign, PM 1 pH calculations can still be sensitive to NH 3 concentrations. Specifically, NH 3 was needed to constrain the pH of populations of PM 1 that had low mass concentrations of NH 4 + and non-volatile cations (NVCs). We next assumed that gas-phase NH 3 and HNO 3 concentrations during the campaign were 0.15 and 0.09 µg m −3 , respectively, based on previous measurements conducted in the eastern North Atlantic. Using the assumption that PM 1 were internally mixed (i.e., bulk PM 1 ), we determined that PM 1 pH ranged from 0.3–8.6, with a mean pH of 5.0 ± 2.3. The pH depended on both <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>H</mi><mrow><mi>a</mi><mi>i</mi><mi>r</mi></mrow><mo>+</mo></msubsup></mrow></semantics></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>W</mi><mi>i</mi></msub></mrow></semantics></math> . <math xmlns="http://www.w3.org/1998/Math/MathML" ...