Phytoplankton, Chemistry, Clouds, and Climate

Dr. Patrick R. Veres

NCAR Research Aviation Facility Science and Instrumentation Group, Research Scientist, Group Lead

pveres@ucar.edu

https://airborne-science.com

NCAR ASP Summer Colloquium, July 19, 2023

Atmosphere/Ocean Interactions in the Marine Boundary Layer

Understanding of Earth’s atmosphere requires global observations

We must identify, address, anticipate, and prepare for challenges related to processes within Earth’s atmosphere

Atmospheric measurement programs are overwhelmingly biased to continental regions: instruments can’t swim*, most labs don’t float and remote regions are expensive to reach

Unfortunately oceans cover > 70% of our planet and significantly impact atmospheric composition and climate

• Emissions, chemistry, and climate impacts
• Aerosol nucleation and growth
• Coupling of chemistry and cloud processes

Air-Sea exchange impacts chemistry and cloud processes

Air-Sea exchange of gases and aerosols plays an important role in many atmospherically relevant processes

The recent discovery of hydroperoxymethyl thioformate (HPMTF, Veres et al. 2020, PNAS), a product of dimethyl sulfide (DMS) oxidation, has led to a reevaluation marine sulfur emissions

Dimethyl sulfide (DMS) was a well understood oceanic emission

Marine phytoplankton produce dimethylsulfonium propionate which undergoes enzymatic cleavage to form DMS, to dominant volatile sulfur species in ocean surface water

Until recently, DMS atmospheric chemistry was described in this reduced form:

DMS → 0.6 SO₂ + 0.4 MSA

Zheng et al. 2021, Nature Comms

Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA, 2018)

First Aerosol Characterization Experiment (ACE-1, 1995)

Clark et al. 1998, JGR

For > 20 years we have understood the need to incorporate this chemistry into global models to understand the climate impact of this cycle

Simplified illustration of marine aerosol sources and DMS chemistry circa ~ 2017

DMS in the marine atmosphere and its role in the climate

In 1987, Charlson, Lovelock, Andreae and Warren proposed the CLAW hypothesis

Charlson, R.J., Lovelock, J.E., Andreae, M.O. and Warren, S.G., 1987. Nature

This has prompted extensive research over the last 30+ years, evidence for this feedback is weak and highly debated but not been definitively ruled out.

NASA Atmospheric Tomography Mission (ATom) 2016 - 2018

The NOAA iodide chemical ionization mass spectrometer was deployed during ATom 3&4 (2017/18)

Four global flights on the NASA DC-8 aircraft to provide data in the remote atmosphere for model evaluation

Thompson et al. 2022, BAMS

A new DMS oxidation product hydroperoxymethyl thioformate

Rapidly incorporated into ongoing research, cited 90 times since 2020. The actual implications of this discovery on the fate of marine biogenic sulfur is far more complicated than originally understood

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During ATom a new DMS oxidation product was observed in the atmosphere

(Veres et al. 2020)

Veres et al., 2020, PNAS

HPMTF loss to clouds dominates the fate of maine sulfur

The spatial distribution of of SO₂ and sulfate is significantly altered when accounting for cloud loss → climate impacts

Initial ATom observations of rapid cloud loss were subsequently quantified during the NASA Student Airborne Research Program (SARP, 2019)

Novak et al. evaluated cloud impacts based on one cloud type and incorporated into models through a chemical rate expression that included entrainment into clouds and fractional cloud cover

We can and need to emulate/evaluate what a global model would simulate in various cloud types to better understand the role of clouds on chemistry and climate

Cloud type variability will impact atmospheric composition

Spatial variability of chemical species, fluxes, and conversion rates will depend on cloud type and degree of boundary layer decoupling

Large-eddy simulations (LES) in the marine boundary layer (MBL)

MBL dynamics and circulation are driven by:

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• surface sensible and latent heat fluxes
• radiative heating and cooling
• wind shear

Large eddy simulations represent clouds and turbulent mixing at high resolution

DMS approximation

DMS approximation

Adapted from Brasseur et al. 2023, Atmosphere

LES simulations can be used to probe the impact of boundary layer dynamics on atmospheric processing of gases and aerosols –

we need more data and better computers

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Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA 2023)

Additional field data is needed to advance our understanding

Sulfur emissions and chemistry: Do we understand the source budget and fate of sulfur in the MBL?

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Air/Sea Exchange: What are the fluxes of key gas phase species into and out of the oceans?

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Aerosol Nucleation and Growth: What chemical and microphysical conditions are conducive to this process?

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Coupling of Chemistry and Cloud Processes: How do various cloud types impact the fate of gas-phase species?

AEROMMA flights targeted variable cloud fields and clear sky conditions

Figures by Siyuan Wang (NOAA)

The next chapters are coming soon

Four research flights were conducted from 6/16/23 - 6/23/23

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2023 FARE Users’ Workshop

September 18–22, 2023

Boulder, Colorado

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• FARE Program funded by NSF Division of Atmospheric and Geospace Sciences (AGS)
• Program supports state-of-the-art instruments and facilities for use by geosciences community to carry out field research
• Program includes Lower Atmosphere Observing Facilities (LAOF) and Community Instruments and Facilities (CIF)
• Facilities can be requested through the Facility and Instrumentation Request Process (FIRP) solicitation
• 3 Proposal Tracks: Track 1: E&O | Track 2: Single Facility | Track3: Field Campaign

Facilities for Atmospheric Research and Education (FARE)

Registration ends August 15 !

NSF FARE USERS’ WORKSHOP

September 18 – 22, 2023

Boulder, Colorado

Questions?

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Please contact Brigitte Baeuerle (baeuerle@ucar.edu) or Bart Geerts (geerts@uwyo.edu)

Workshop website: https://www.eol.ucar.edu/fare-users-workshop

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Limited funding is still available to support registration and travel for MSI, PUI, and community college participants

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