- 1Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, United Kingdom (john.halfacre@york.ac.uk)
- 2Department of Earth and Environmental Science, Centre for Atmospheric Science, School of Natural Sciences, The University of Manchester, Manchester, United Kingdom
- 3Department of Environmental Sciences & Engineering, University of North Carolina, Chapel Hill, North Carolina, United States
- 4Aerodyne Research Inc., Billerica, Massachusetts, United States
- 5National Centre for Atmospheric Science, University of Manchester, Manchester, United Kingdom
- 6National Oceanic & Atmospheric Administration, Earth System Research Laboratories, Boulder, Colorado, United States
- 7Department of Chemistry, University of Colorado, Boulder, Colorado, United States
- 8National Centre for Atmospheric Science, University of York, York, United Kingdom
Reactive chlorine radicals are known to efficiently react with ambient hydrocarbons, thereby affecting boundary layer oxidation capacity and pollutant lifetimes. HCl is the most abundant and long-lived inorganic chlorine reservoir species in the troposphere, yet high frequency, in situ observations are limited due to sampling challenges. In this work, we report HCl field observations using a Tunable Infrared Laser Direct Absorption Spectrometer (TILDAS), deployed in Manchester, England, during the 2021-2022 Integrated Research Observation System for Clean Air campaign. Instrument precision was estimated as 1.1 pptv (Allan Werle minimum of 1.4 minute), with 3σ limits of detection of 3.3 pptv.
Observations obtained during June and July 2021 generally exhibited a diurnal profile on clear days, peaking at midafternoon (mean daily mixing ratios ranging between 15 – 89 pptv). Conversely, observations from February 2022 displayed no obvious profile with mixing ratios remaining muted throughout the observation period (mean daily mixing ratios ranging between 7-13 pptv), suggesting suppression of Cl-liberation mechanisms. Despite observations occurring in an inland polluted urban environment, particle dispersion analysis for both seasons shows air masses spend most of their time passing over the ocean in the 72-hours preceding arrival at the observation site. The thermodynamic equilibrium model ISORROPIA II will be used to explore the role of partitioning between particulate phase Cl- and gas phase HCl, with model inputs supplied from observed non-refactory, submicron particulate SO42-, NO3-, NH4+, and Cl- ions, as well as gas phase observations of HCl, HNO3 and NH3. Data will be further interpreted using gas phase box modelling, further incorporating co-located CIMS observations of other inorganic Cl-species, including ClNO2 andCl2, to gain a greater understanding of seasonal chlorine chemistry mechanisms at an inland, urban measurement site.
How to cite: Halfacre, J. W., Stewart, J., Rowlinson, M., Matthews, E., Bannan, T., Green, J. R., Vizuete, W., Evans, M. J., Herndon, S. C., Roscioli, J. R., Dyroff, C., Yacovitch, T. I., Allan, J., Coe, H., Andrews, S. J., Brown, S. S., and Edwards, P. M.: Comparison of seasonal differences in hydrogen chloride observations from an inland urban site, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17490, https://doi.org/10.5194/egusphere-egu25-17490, 2025.
