║ Tools
The Ocean Research Platform
The ocean research platform supports research activities in SWP-A and SWP-B.
Satellite observations for real time mission planning and post-campaign data interpretation
Near real time maps of sea surface temperature (SST), ocean colour (including chlorophyll a) and particulate inorganic carbon (PIC) will be produced on a data portal by the NERC Earth Observation Data Acquisition and Analysis Service (NEODAAS).
The images will be used to guide the ship toward frontal regions and different water patches containing varying levels of phytoplankton biomass. PIC and chlorophyll retrievals will give an indication of waters with high levels of coccolithophores (prolific producers of DMSP and DMS).
During the CARES fieldwork, daily email bulletins with data and expert interpretation will be used to inform mission planning. Earth observation data will also be used to provide spatial and temporal context (i.e., bloom evolution, duration, extent) for the interpretation of CARES ship and aircraft observations.
Quantification of seawater/atmospheric sulfur gas concentrations
Our team has recently developed a method to continuously measure the seawater concentration (e.g., for 20 minutes every hour) and the atmospheric concentration (e.g. for 40 minutes every hour) of DMS in alternation using a segmented flow coil equilibrator (SFCE) coupled to a PTR-MS (Ionicon HR-PTR-quad-MS1) and to a microCIMS (API-CIMS; Bell et al., 2021). Recent laboratory tests (and Lawson et al.2) confirm that CH3SH is well detected by the PTR-MS.
To achieve D1.1 and D1.4 from SWP-A, we will use the SFCE-PTR-MS and microCIMS systems to measure concentrations of DMS and CH3SH in the ocean and atmosphere (as well as seawater DMSP), and then use these data to estimate DMS and CH3SH emissions with the bulk method (i.e. flux equal to the transfer velocity multiplied by the air/sea concentration difference).
The Gothenburg ToF-CIMS will be used to measure atmospheric HPMTF, N2O5 and BrO on the ship, and we will analyse the data for diel cycles as well as variability in HPMTF:DMS and HPMTF:SO2 ratio as a function of measurements of the physical conditions (cloud cover, wind speed, temperature, solar irradiance, etc.) and chemical conditions (NOx, VOCs, etc.).
To identify HPMTF at night from the proximal N2O5 peak under conditions when the latter may be non-negligible, D2O will be switched into the CIMS sample inlet since HPMTF undergoes deuterium exchange
Eddy covariance (EC) flux measurements and supporting data
Air-sea fluxes of DMS and SO2 will be measured directly from the ship using the eddy covariance method. This requires rapid (~10 Hz) sampling of:
a) 3-dimensional wind velocities from a sonic anemometer
b) 3-dimensional acceleration and rotation from a motion sensor
c) the atmospheric mixing ratio for the gas of interest
When the HR-PTR-quad-MS is sampling the atmosphere (for 40 minutes every hour), the atmospheric DMS mixing ratio will be used to compute the DMS emission flux directly using the EC method. The HR-PTR-quad-MS has been used previously to measure the air-sea fluxes of methanol and acetone with the EC method3,4. Comparison of the bulk flux with the EC flux enables us to constrain the impact of waves and biological surfactants on the DMS transfer velocity, which is also applicable to CH3SH (D1.3 of SWP-A). The spatial variability in surfactants across the phytoplankton blooms will be assessed using the recently developed gas transfer efficiency method (see Yang et al.5). Wave information (e.g., significant wave height, wave direction) will be retrieved from high resolution ECMWF reanalysis.
The SO2 mixing ratio and deposition flux (D1.2 of SWP-A) will be measured directly using the University of California Irvine CIMS with the EC method (see Porter et al.6). The SO2 deposition velocity, will be compared to EC measurements of H2O, heat and momentum transfer as well as modelled rate of transfer. Difference in SO2 deposition velocity inside/outside of phytoplankton blooms at similar wind/wave conditions may suggest the impact of biological surfactants on the surface reactivity for SO2 (H1.1; D1.3).
Shipboard aerosol measurements
Measurements of MSA and nss-SO42- will be made using an Aerodyne High Resolution Aerosol Mass Spectrometer (HR-AMS), using quantification methods presented by Hodshire et al.7, supported by other measurements of particle size and composition. These can be linked to similar AMS measurements being performed on the aircraft.
Balloon radiosonde releases
In order to help interpret the diel cycles in atmospheric observations and constrain the exchange between the MBL and the free troposphere, we will release radiosondes from the ship approximately twice a day (noon and midnight local time). Vertical profile data will be relayed to the aircraft team for flight planning.
The Aircraft Laboratory
The ocean research platform supports research activities in SWP-B.
FAAM Bae-146
Central to testing the hypotheses outlined in CARES are advances in high resolution mass spectrometry, which enable trace (single ppt) levels of a wide range of atmospheric trace gases to be measured at high time frequency.
The primary emitted sulfur species DMS and CH3SH will be measured on the aircraft using the new University of East Anglia HR-PTR-ToF-MS instrument. The key intermediate, HPMTF, and BrO will be measured using the University of Manchester HR-ToF-CIMS instrument. This instrument has already provided significant data on the distribution of HPMTF throughout the North Atlantic as part of the ACSIS flight programme, and has a detection limit for HPMTF of 1 pptv.
Hydrogen peroxide (H2O2) is an important in cloud oxidant of SO2, and thus measurement of its concentration is vital. As part of CARES, funds have been requested to modify an Aerolaser AL2021 H2O2 monitor for use aboard the BAe-146.
Formaldehyde (HCHO) is key to estimating oxidation by the OH radical and this will be measured by the University of Leeds LIF instrument, which has been demonstrated on the BAe-146 previously8 with detection limits of < 50 pptv.
SO2 will be measured by the new University of York SO2-LIF instrument which uses recent advances in fibre laser technology to reach single pptv precision at high time resolution9.
The dependence of HPMTF formation on NOx levels is a key factor in determining its importance under present day, pre-industrial and future emission scenarios. Accurate measurements of low (< 10 pptv) NOx levels in remote marine environments is a known challenge for the current FAAM chemiluminescence instrument, with variable background signals equivalent to 10-100 pptv. A laser induced fluorescence system for the highly sensitive detection of NOx has recently been demonstrated for use from an aircraft platform10. In order to ensure the highest possible level of constraint on the system, funds have been requested to convert this prototype NO-LIF system for field measurements aboard the BAe-146.
A range of supporting gas phase measurements will also be made, including O3, CO, CH4, VOCs, and OCS. Eddy covariance fluxes of HPMTF and SO2 will be derived using the 4 Hz CIMS measurements and the 10 Hz SO2 data combined with the 10 Hz turbulence probe data following the approach developed by Novak et al.11.
The University of Manchester ToF-AMS will be used to measure detailed non-refractory aerosol composition and an SP-2 enables black carbon (BC) measurements, for characterisation of particulate pollution in the airmass. CCN activity spectra and total aerosol number (CN) together with aerosol number and size distribution (10nm – 20mm) will be measured from a Scanning Mobility Particle Sizer (SMPS) and awing-mounted on-board Optical Particle Counters (OPCs).
Cloud and drizzle drop size distributions will be obtained from the range of FAAM cloud probes from 2 to 640 mm. Cloud droplet residual number, size and composition will be measured using a CN counter, optical sizing probes, AMS and SP-2 sampling from a counterflow virtual impactor (CVI).
Numerical Models
The ocean research platform supports research activities in SWP-B and SWP-C.
Composition-Climate models
The United Kingdom Chemistry and Aerosol model (UKCA) forms the core chemistry and aerosol component of UKESM-112. We will run UKESM-1 in atmosphere only mode (UKESM-A13). The majority of runs are at N98L85; a horizontal resolution of 1.875˚×1.25˚ (longitude–latitude), with 85 terrain-following levels spanning the altitude range from the surface to 85 km (with 50 levels below 18 km), but we will also run simulations at much higher horizontal resolution (N216L85: 0.83˚×0.56˚ lon-lat).
Emissions will be based on the standard CMIP6 CEDS emissions datasets14. Simulations with UKESM-A will be run on the Archer2 HPC facility, with data transferred between the Met Office mass storage system (MASS) and JASMIN.
The box model version of the UKCA code encompasses the full functionality of the UKCA model for a single grid point, enabling rapid and efficient turnaround for development and testing. The box model will be run on an existing high-performance computer at the University of Cambridge for both the perturbed parameter ensembles (PPE) screening work and in the atmospheric process investigations in SWP-B.
A new DMS and CH3SH oxidation scheme based on best available knowledge has already been implemented into the UKCA codebase (Fig. 1) and will be used as the starting point of the PPE work. This mechanism includes all recent insight into the gas phase and aerosol/cloud removal of HPMTF and the rapid conversion of CH3SH into SO215. We will use this mechanism as the template for further mechanism development and reduction work. Our goal with mechanism reduction work is to develop a succinct representation of the chemistry outlined in Fig. 1 for the ESM MIP simulations we will perform in SWP-C (D3.4).
As proof of principle we conducted One At a Time (OAT) UKESM-A sensitivity simulations varying the rate constant for the MSP H-shift from that measured by Berndt et al.16 to that calculated by Veres et al.17.
We show in Fig. 2 that this test results in a spread in modelled HPMTF and SO2 that is wider than the range of observations from ATom17 and providing support that this parameter can be constrained.
Process-based models
Box models, based around the MCM, will focus on short and intermediate lifetime gas-phase species. We will use constrained MCM box modelling to focus on the role of NO3 and halogens (Cl, BrO) in forming HPMTF in the MBL (NO3 will be determined by constraining to O3, NOx, DMS, aerosol surface area and the concentration of N2O5 measured on board the ship with the University of Gothenburg ToF-CIMS).
The coupling of the MCM to Chemical Aqueous Phase RAdical Mechanism (MCM-CAPRAM), constrained to the gas species, aerosols and physical properties (temperature, humidity, cloud liquid water) determined in (D3.1 of SWP-C), will be used to constrain gas-aerosol-cloud coupling and determine in-aerosol/cloud processes
Constraining to the observations we make in SWP-A & SWP-B will extend previous work by CARES project partner Herrmann18, which used hypothetical conditions. This is especially important for the in-cloud oxidation via H2O2 where we will be able to constrain the rates of reaction through observed H2O2.
To further examine the interactions between gas-phase species, aerosols and clouds we will set-up a representative case study with the Met Office–NERC Community Model (MONC). The MONC is a Large-Eddy Simulation (LES) model with modules for clouds and radiative transfer. It is ideally suited to simulating clouds and turbulence in the cloud-topped MBL. The simulations will use a vertical domain extending from the surface to 3 km (into the free-troposphere), with a horizontal domain of 16 km × 16 km.
We will compute O(103) Lagrangian trajectories through the simulated cloud and use these trajectories as a basis for offline box / parcel model calculations using the University of Manchester Aerosol Cloud and Precipitation Interactions Model parcel model (ACPIM19). Within the ACPIM-trajectory simulations we will also consider the gas-phase and aqueous chemistry relevant to this project, which eventually lead to the irreversible ‘loss’ of sulfur species via dissolution, dissociation, and oxidation to S(VI) within the cloud water. These ACPIM-trajectories will then be ensemble averaged to produce a vertical profile of the concentrations of relevant species, therefore addressing the importance of cloud processes to this problem.
References
- Wohl et al., Biogeosciences, 17, 2020 ↩︎
- Lawson et al., Atmos. Chem. Phys, 20(5), 2020 ↩︎
- Yang et al., PNAS, 110, 2013 ↩︎
- Yang et al., J. Geophys. Res.-Oceans, 119, 2014 ↩︎
- Yang, et al., Sci Rep, 11, 2021 ↩︎
- Porter et al., GRL, 47, 2020 ↩︎
- Hodshire et al., Atmos. Chem. Phys., 19, 2019 ↩︎
- Lee et al., Environmental Science: Atmospheres, 2021 ↩︎
- Rollins et al., Atmos. Meas. Tech., 9, 2016 ↩︎
- Rollins, et al., Atmos. Meas. Tech., 13, 2020 ↩︎
- Novak, et al., Atmos. Chem. Phys. Discuss., 2021 ↩︎
- Sellar, et al., J.A.M.E.S., 11, 2019 ↩︎
- Archer‐Nicholls et al., J.A.M.E.S., 13(5), 2021 ↩︎
- Hoesly et al., Geosci. Model Dev., 11, 2018 ↩︎
- Chen et al. The Journal of Phys. Chem. A, 2021 ↩︎
- Berndt et al., Journal Phys. Chem. Let., 10(21), 2019 ↩︎
- Veres et al., PNAS, 117(9), 2020 ↩︎
- Hoffmann et al., PNAS, 113(42), 2016 ↩︎
- Connolly et al., Atmos. Chem. Phys., 13, 2013 ↩︎
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