A California researcher with an appetite for studying atmospheric particles has big investigations underway on aerosols in marine clouds
In a nearly three-decades-long career, University of California, San Diego (UCSD) professor of climate sciences Lynn Russell has studied all manner of aerosols.
These are the tiny particles in the atmosphere, both natural and manmade, that make cloud formation and precipitation possible.
Russell, who teaches at Scripps Institution of Oceanography, a UCSD department, has investigated sea-spray aerosols, which send salts or bits of organic matter into the air by wave action.
Marine aerosols have other sources. She was part of a team that, of all things, studied how guano from sea birds in Antarctica contributes particles to the aerosol-starved atmosphere at the South Pole.
Recently, Russell has been grappling with how stratocumulus clouds along the coast of southern California are influenced by pollution-related particles from Los Angeles and other urbanized areas to the north.
Marine stratocumulus, common all over the world, are known for their net-cooling climate effects. They provide a large fraction of daytime cloud cover worldwide.
“Clouds are the most uncertain part of our understanding of the climate and (represent) where climate models disagree the most,” says Russell. “The kind of clouds we have in San Diego are some of the most important.”
“On top of that,” she adds, pointing to her own expertise, “we know aerosols change cloud properties.”
During her many investigations, Russell has often received funding from Atmospheric System Research (ASR), a program within the U.S. Department of Energy (DOE).
One current ASR project she leads takes aim at improving how sea spray is quantified. It’s based on data from the 2016―2017 Layered Atlantic Smoke Interactions with Clouds (LASIC) field campaign, conducted by DOE’s Atmospheric Radiation Measurement (ARM) user facility.
She and Scripps colleague Dan Lubin designed a 2022 study that leveraged an untouched corner of LASIC data―measurements of sea-spray aerosols.
LASIC has drawn the most attention from researchers because of its measurements of seasonal smoke transported from sub-Saharan Africa. But Russell says she asked herself, “What about the other half of the data?”
What Russell calls the “clean half” of LASIC data involved particles from sea-spray aerosols, the largest reservoir of natural aerosols in the atmosphere, by mass. As such, they have an enormous influence on the clouds that determine how much solar radiation reaches Earth.
Russell is co-leading a second ASR project with modeler Ann Fridlind of the NASA Goddard Institute for Space Studies. They address a key factor in rising surface air temperatures: how warm and mixed-phase shallow clouds respond to a warming earth. They also ask: how is that response modulated by precipitation rates at the base of clouds?
The study so far is focused on northern latitudes, says Russell, and data from a 2019―2020 ARM campaign at the edge of the Norwegian Sea called Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE). Such outbreaks, caused by the passage of cold air over warm water, create shallow convective clouds that evolve into cloud regimes with a big influence on Earth’s energy balance. Aerosols are a factor.
“This is super-exciting for me to learn about cloud processes. I have studied aerosols a lot,” says Russell, “but mostly with warm clouds.”
Russell is leading another project that includes ASR-funded elements: an ambitious, yearlong field campaign starting in mid-February 2023 to investigate manmade aerosol influences on the marine clouds in Russell’s own UCSD backyard in La Jolla, California.
The Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) will leverage the research power of multiple agencies and universities.
The main instruments for EPCAPE come from ARM, which has collected, quality-checked, and archived 24-hour atmospheric data since 1992. It currently operates three fixed atmospheric observatories and three ARM Mobile Facilities (AMF) in climate-critical regions across the world.
ARM’s AMF1 mobile observatory, packed into six containers, is already in place on the Ellen Browning Scripps Memorial Pier. Five instrument containers are midway on the longtime marine observation platform, which juts 330 meters (1,084 feet) into the ocean. A sixth AMF container, for measuring aerosols, is at the ocean end of the pier.
The structure, 33.5 feet above the mean low water level, extends beyond the surf line to deep waters at the head of the La Jolla submarine canyon. That’s far enough out to capture data on genuinely oceanic conditions.
Additional EPCAPE guest instruments, including others from ARM, are in place about a mile away on the peak of Mt. Soledad, elevation 250 meters (820 feet).
Russell lives near the pier and low-lying Mt. Soledad―a prominence still high enough to permit measurements from within cloud cover. Living at that interface of land and ocean has given her a unique view of how valuable aerosol studies there can be. She began looking into it more than a decade ago.
SOLEDAD and E-PEACE
Russell was part of an earlier series of small, incremental studies to investigate coastal marine stratocumulus clouds, all of which influenced the shape and direction of EPCAPE.
In 2012, Russell collaborated with Richard Leaitch of Environment and Climate Change Canada to lead a 49-day experiment called SOLEDAD―Stratocumulus Observations of Los Angeles Emissions-Derived Aerosol Droplets. Ground-based instruments near the peak of Mt. Soledad took in data on the chemical composition and size distribution of cloud-forming droplets. They found that both elemental carbon and salt particles from the ocean contributed to the cloud droplets.
Gaps and questions left over from SOLEDAD, says Russell, will be taken up during EPCAPE.
In one 2015 paper, on marine aerosol-cloud interactions, SOLEDAD was paired with another campaign that investigated marine clouds similar to those targeted by EPCAPE: the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE), funded by the National Science Foundation and the Office of Naval Research.
The same two experiments were central to a 2016 paper on marine cloud microphysical properties related to cloud reflectivity.
E-PEACE was ambitious. There was a 12-day research cruise and 30 research flights over 40 days.
Russell pointed to a related paper showing that organic aerosol particles from a smoke generator mounted on the research vessel could be sufficiently hygroscopic to form a ship track – a zig-zagging line of brightness in the satellite cloud imagery.
MAGIC and More
Both SOLEDAD and E-PEACE were informed by an even earlier field program, in July 2001, called Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II), led by Bjorn Stevens, then at the University of California, Los Angeles. (He is now managing director of the Max Planck Institute of Meteorology in Hamburg, Germany.)
This study of drizzle, cloud microstructure, and aerosols involved a month of nighttime C-130 flights starting in San Diego, for which Russell measured aerosol composition. The National Center for Atmospheric Research (NCAR) in Colorado operated the aircraft.
In the realm of ARM, Russell pointed to a couple of ARM field campaigns that took a grander, wider view of marine clouds in the northeastern Pacific.
In 2012 and 2013, ARM mounted instruments on a container ship making transects between California and Hawaii during an operation called the Marine ARM GPCI Investigation of Clouds (MAGIC).
In 2015, ARM operated an air-and-sea field campaign called the ARM Cloud Aerosol Precipitation Experiment (ACAPEX). Based on the California coast, ACAPEX included flights that swung from across the land to over the ocean. Its research targets were the large-scale dynamics of cloud, precipitation, and aerosol processes.
The design of EPCAPE and its science questions also owe a debt to investigations that took place far from the California coastline, in Antarctica and the North Atlantic.
Russell was a co-investigator during the 2015―2017 ARM West Antarctic Radiation Experiment (AWARE), led by Lubin, her Scripps colleague, who is now an EPCAPE co-investigator.
“It was just like EPCAPE,” she said of the campaign in Antarctica. “Both locations provide unique opportunities to characterize clouds, aerosols, and cloud-aerosol interactions.”
AWARE’s main site was at McMurdo Station on Ross Island, where Russell had ARM technicians collect filter samples. To target (among many other things) Antarctic aerosols and cloud microphysics at McMurdo, AMF2 included cloud radars, high-resolution lidars, and a complete suite of aerosol instruments.
Russell helped co-author a 2020 summary paper that showed the striking differences between arctic and antarctic annual cycles.
The campaign also looked at biogenic aerosols―another topic in which Russell has a fierce interest.
Along coastal Antarctica, the Ross Sea is the most biologically active feature of the southern polar region. Biogenic influences include not only marine sea spray, but emissions of ammonia and nitrogen from penguin colonies rife with guano. Russell’s graduate student Jun Liu led a 2018 paper on such aerosol influences during the summer.
In the Atlantic Ocean, clouds have some of the same characteristics as those in coastal California.
Russell gained insights on marine aerosol composition from a NASA research campaign called the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES), a multidisciplinary, multi-platform exercise.
In four separate experiments between 2015 and 2018, NAAMES deployed satellite sensors, high- and low-flying aircraft, a Woods Hole Oceanographic Institution research vessel, and autonomous floats suspended below, in the sea.
The mission was to collect measurements on the marine environment’s biogenic aerosols, which influence marine clouds and―ultimately―the climate. Helping out was Sea Sweep, a ship-side device that generates bubbles to capture uncontaminated samples of freshly emitted particles from the sea surface.
“It’s a clever approach to quantifying sea spray over the real ocean,” says Russell, and was designed by Patricia Quinn and Timothy Bates at the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory.
As for ARM influences in the Atlantic, Russell points to the user facility’s Eastern North Atlantic (ENA) atmospheric observatory in the Azores; the 2017―2018 Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign; and the LASIC campaign, which figures in her ASR project on sea-spray aerosols.
Sea-spray aerosols are among a multitude of influences at play during EPCAPE, where the goal is to inform better climate models.
“We need better observations,” says Russell. “Better observations make models better at predicting future clouds.”
Russell was born in Oakland, California, the daughter of a chemical engineer whose father left his native Vienna, Austria, in 1938, after the Nazi regime confiscated his business and home.
During her girlhood, Russell and the family moved every few years, courtesy of her father’s numerous Shell Oil postings.
Russell remembers living in Houston “a few times” (she graduated from high school there), as well as a memorable five years in Modesto, California.
“It was a lot of fun,” she says of the Central Valley city once known for its drag-cruising and hot-car culture. “I’ll just put that plug out there, even though I was too young to drag McHenry Avenue.”
For two of her high school years, the family lived in Germany―a place she revisited while writing her honors thesis at Stanford University (B.S. Chemical Engineering, A.B. International Relations, 1991).
“I got to breathe a lot of aerosols and study aerosols too,” she says of her 1990 summer in East and West Germany.
That was just months after the Berlin Wall came down.
“The environmental pollution was terrible” in East Germany, says Russell, whose thesis was on the effects of burning coal in the formerly communist country. “The pollution would just sit, the statues would decay, and the people would suffer the consequences.”
As a chemical engineering major, she gave industry a try, including one summertime stint of boiling hexane for a chemical company in Germany.
Says Russell, “I learned a lot about precision and accuracy there.”
Following Russell’s junior year in college, however, aerosols (previously a mystery to her) became the central theme of her life as a scientist. She went on to study with a world expert, atmospheric chemist John Seinfeld, during PhD studies at the California Institute of Technology (PhD, Chemical Engineering, 1995).
In June 1992, within a year of starting graduate school at Caltech, “I was in the middle of the Atlantic,” says Russell, during a multinational field campaign called the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE). The three-ship, two-island, one-plane marine field campaign was led by Barry Huebert, now an emeritus professor at the University of Hawai’i at Manoa.
Aboard the R/V Oceanus, Russell undertook shipboard scans on a differential mobility analyzer to measure the size distributions of marine aerosols―the subject of her eventual dissertation.
ASTEX/MAGE, she says, “is how I knew I’d found something I was interested in pursuing.”
Challenges and success in the mid-Atlantic also gave Russell an immense appetite for fieldwork. Over the years, she has been on the job in far-flung locales, including stops in Australia, Japan (part of her globe-spanning travels to study dust and haze), Sweden, Mexico, and the North Slope of Alaska.
Then there was a research trip to Alert, Nunavut, Canada. This northernmost settlement in the world, about 500 miles from the North Pole, “is almost at the end of the world,” she says.
After Caltech came a postdoctoral stint at NCAR and then a faculty spot at Princeton University from 1997 to 2003. From there, after a research sabbatical in Sweden, Russell moved to UCSD and La Jolla.
Along the way, Russell has been the only scientist to be part of both the first and second DOE-NOAA reports (in 2015 and 2022) on the feasibility of brightening marine clouds so they would reflect more solar radiation to cool a warming Earth.
“It’s definitely a stupid idea,” she says. “But it may be better than doing nothing.”# # #
Author: Corydon Ireland, Science Writer, Pacific Northwest National Laboratory
This work was supported by the U.S. Department of Energy’s Office of Science, through the Biological and Environmental Research program as part of the Atmospheric System Research program.