Atmospheric scientists have analyzed how the February near-total shutdown of mobility affected the air over China. Results show a striking drop in nitrogen oxides, a gas that comes mainly from tailpipes and is one component of smog.

Learning how behavior shifts due to the COVID-19 pandemic affect air quality is of immediate importance, since the virus attacks human lungs. The event is also a way for Earth scientists to study how the atmosphere responds to sudden changes in emissions.

“During the February 2020 shutdowns in China there was a large and rapid decline in nitrogen dioxide — an air pollutant largely associated with transportation — that is unprecedented in the satellite record,â€� said , a 91̽»¨ doctoral student in atmospheric sciences.

“On the other hand, our analysis shows no dramatic changes in the total amount of aerosol particles in the atmosphere, or in cloud properties. This suggests the immediate climate-related impacts from the shutdown are negligible,� Diamond said.

He is lead author of the published Aug. 19 in Geophysical Research Letters.

While other studies have already looked at air quality during the pandemic, this is the first to take a more rigorous view, using all 15 years of satellite data. It uses a statistical method that compares what was seen in February 2020 to what would have been expected without the pandemic.

“Early in the quarantine period, there was some discussion that the Earth was healing itself, but some of those claims, like the , have turned out to be false,� Diamond said. “The scientific community was interested in documenting what changes actually occurred.�

The authors used data from NASA’s , or OMI, and , or MODIS, which have been monitoring the skies since 2005. These instruments use different wavelengths to monitor quantities like nitrogen oxides, airborne particulates and clouds.

In addition to using a longer record, the model accounted for the expected effects of China’s environmental policies.

“China passed a clean air law in 2013, and ever since you can see that pollution is going down. So just for that reason, we might expect that the pollution in 2020 would be lower than in 2019,� Diamond said.

The analysis also accounted for this past February’s relatively hot and humid weather in China, which made gases more likely to react and form airborne particles.

“You still had some pretty bad smog events happening in the Beijing region, even during the lockdown,� Diamond said.

The authors also considered the atmospheric effects of the Chinese New Year, which is celebrated in either late January or early February and generates both higher particulates from fireworks and lower traffic emissions from people being on holiday.

After accounting for all of these factors, the pandemic’s effect on nitrogen dioxide was a drop of 50% compared to what would be expected for February 2020, a drop unlike any other seen in the satellite observations.

“The difference we see is more than twice as large a drop as anything we saw in the record from 2005 to 2019, including from the 2008 Great Recession. In the statistics of atmospheric science, that’s a giant signal. It is rare to see anything that striking,� Diamond said.

While the change in nitrogen dioxide was dramatic, other quantities showed no significant change. Fine particulate matter, which has a bigger impact on human health and the climate, hardly changed over China during the shutdown. Passenger transportation virtually disappeared during the lockdown, but economic data show that heavy industry and energy production stayed fairly constant, Diamond said.

The fact that some quantities did not change is, for atmospheric scientists, a significant result in itself. Clouds, which are affected by pollution and have the biggest effect on climate, also showed no significant changes.

Co-author , a 91̽»¨professor of atmospheric sciences, and Diamond collaborated on a recent publication that detected cloud changes due to pollution from ships. That study showed that many years of data were required to detect the effect on clouds.

“Our study suggests that since we found little change in particulate pollution due to COVID-19, we are unlikely to see any change in the clouds unless pollution changes over a longer time period due to a prolonged economic downturn,� Wood said.

Overall, the findings agree with a recent study led by the 91̽»¨showing that nitrogen dioxide dropped in several American cities during the peak quarantine period, but levels of other pollutants stayed fairly constant.

The response suggests that future clean air policies can’t focus only on transportation emissions.

“When you’re crafting these clean air strategies, you’re probably not going to be able to attack just one sector; you’ll have to address several sectors at once,� Diamond said.

This research was funded by NASA.

For more information, contact Diamond at diamond2@uw.edu or Wood at robwood2@uw.edu.

New research led by the 91̽»¨ is the first to measure this phenomenon’s effect over years and at a regional scale. Satellite data over a shipping lane in the south Atlantic show that the ships modify clouds to block an additional 2 Watts of solar energy, on average, from reaching each square meter of ocean surface near the shipping lane.

The result implies that globally, cloud changes caused by particles from all forms of industrial pollution block 1 Watt of solar energy per square meter of Earth’s surface, masking almost a third of the present-day warming from greenhouse gases. The was published March 24 in AGU Advances, a journal of the American Geophysical Union.

“In climate models, if you simulate the world with sulfur emissions from shipping, and you simulate the world without these emissions, there is a sizable cooling effect from changes in the model clouds due to shipping,” said first author , a 91̽»¨doctoral student in atmospheric sciences. “But because there’s so much natural variability it’s been hard to see this effect in observations of the real world.”

The new study uses observations from 2003 to 2015 in spring, the cloudiest season, over the shipping route between Europe and South Africa. This path is also part of a popular open-ocean shipping route between Europe and Asia.

Small particles in exhaust from burning fossil fuels creates “seeds” on which water vapor in the air can condense into cloud droplets. More particles of airborne sulfate or other material leads to clouds with more small droplets, compared to the same amount of water condensed into fewer, bigger droplets. This makes the clouds brighter, or more reflective.

Past attempts to measure this effect from ships had focused on places where the wind blows across the shipping lane, in order to compare the “clean” area upwind with the “polluted” area downstream. But in this study researchers focused on an area that had previously been excluded: a place where the wind blows along the shipping lane, keeping pollution concentrated in that small area.

The study analyzed cloud properties detected over 12 years by the instrument on NASA satellites and the amount of reflected sunlight at the top of the atmosphere from the group of satellite instruments. The authors compared cloud properties inside the shipping route with an estimate of what those cloud properties would have been in the absence of shipping based on statistics from nearby, unpolluted areas.

“The difference inside the shipping lane is small enough that we need about six years of data to confirm that it is real,” said co-author , a 91̽»¨doctoral student in statistics. “However, if this small change occurred worldwide, it would be enough to affect global temperatures.”

Once they could measure the ship emissions’ effect on solar radiation, the researchers used that number to estimate how much cloud brightening from all industrial pollution has affected the climate overall.

Averaged globally, they found changes in low clouds due to pollution from all sources block 1 Watt per square meter of solar energy — compared to the roughly 3 Watts per square meter trapped today by the greenhouse gases also emitted by industrial activities. In other words, without the cooling effect of pollution-seeded clouds, Earth might have already warmed by 1.5 degrees Celsius (2.7 F), a change that the Intergovernmental Panel on Climate Change projects would have significant societal impacts. (For comparison, today the Earth is estimated to have warmed by approximately 1 C, or 1.8 F, since the late 1800s.)

“I think the biggest contribution of this study is our ability to generalize, to calculate a global assessment of the overall impact of sulfate pollution on low clouds,” said co-author , a 91̽»¨professor of atmospheric sciences.

The results also have implications for one possible mechanism of deliberate climate intervention. They suggest that strategies to temporarily slow global warming by spraying salt particles to make low-level marine clouds more reflective, known as marine cloud brightening, might be effective. But they also imply these changes could take years to be easily observed.

“What this study doesn’t tell us at all is: Is marine cloud brightening a good idea? Should we do it? There’s a lot more research that needs to go into that, including from the social sciences and humanities,” Diamond said. “It does tell us that these effects are possible — and on a more cautionary note, that these effects might be difficult to confidently detect.”

Other co-authors are , a 91̽»¨research scientist in atmospheric sciences, and at Goethe University in Frankfurt. The research was funded by NASA and the National Science Foundation.

For more information, contact Diamond at diamond2@uw.edu, Wood at robwood2@uw.edu or Director at direch@uw.edu.

Grants: NASA: NNX-80NSSC17K0404, NNX-15AF98G; NSF: DGE-1256082

What they discover will be used to improve climate models, which routinely underestimate how much solar energy bounces off clouds in that region. Simulating how much solar energy is absorbed or reflected on Earth is key to calculating the future of the planet under climate change.

The Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study, or , could also help scientists understand the very nature of how clouds interact with aerosols — natural or human-made particles that are suspended in the atmosphere. Aerosols can cause clouds to form, change their structure and affect precipitation, all of which affect the amount of energy that reaches the surface.

During the mission, which runs from mid-January through Feb. 25, the scientists are collecting data from air and sea. Observations are being taken from the High-performance Instrumented Airborne Platform for Environmental Research, or HIAPER, a operated by the NSF and the National Center for Atmospheric Research, and the , an Australian deep-ocean research vessel.

“Much of what we currently know about Southern Ocean cloud, aerosol and precipitation properties comes from satellite-based estimates, which are uncertain, and have undergone few comparisons against independent data,” said team member , a 91̽»¨research associate professor of atmospheric sciences. “The data collected during SOCRATES will also enable us to evaluate current satellite data over the Southern Ocean, as well as potentially help in the design of better satellite-based techniques.â€�

The research aircraft based out of Hobart, Tasmania, will make about 16 flights over the Southern Ocean. Instruments will measure the size and distribution of cloud droplets, ice crystals and aerosols. The data will help test the theory that climate models may not be producing enough water — droplets that stay liquid even when the temperature is below freezing.

Measurements will also provide a look back in time to see how the atmosphere behaved in a time when it contained fewer human pollutants.

“It can be difficult to find truly pristine conditions in the Northern Hemisphere,â€� said , a 91̽»¨professor of atmospheric sciences. “By studying the more pristine Southern Ocean region, we hope to be able to learn about what conditions may have been like in the Northern Hemisphere in the pre-industrial period.”

The measurements taken from the sky will be complemented by data collected from the R/V Investigator.  The ship’s team will launch soundings every six hours, and sometimes more often, throughout the campaign.

The U.S. portion of SOCRATES is largely funded by the National Science Foundation.

“The Southern Ocean is famously remote and stormy and it’s hard to imagine a worse place to do a field campaign. But a vast, stormy ocean is a great laboratory for studying clouds, and it’s clear from our models that we have a lot to learn about them,â€� said Eric DeWeaver, program director in NSF’s geoscience directorate.

SOCRATES investigators will also incorporate other ocean measurements and data from that 91̽»¨scientists installed in 2016.

“SOCRATES will allow for some of the best observations of clouds, aerosols, radiation, and precipitation that have ever been collected over the Southern Ocean,” said principal investigator , at the University of Oklahoma. “These data will provide us with critical insight into the physics of cloud formation in the region, information we can use to improve global climate models.”

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Based on a National Center for Atmospheric Research . For more information, contact Marchand at rojmarch@uw.edu.

A new 91̽»¨ study looks at the idea of , which a 91̽»¨group is investigating as a promising strategy to offset global warming. The strategy would spray saltwater into the air to make marine clouds reflect more incoming solar rays.

Small-scale tests of marine cloud brightening would also help answer scientific questions about clouds and aerosols, two 91̽»¨atmospheric scientists say in a published in July in the journal . This dual goal for early-stage geoengineering tests would follow the U.S. National Academies of Sciences’ 2015 recommendation that any tests of geoengineering also yield a scientific benefit.

“A major, unsolved question in climate science is: How much do aerosol particles cool the planet?,” said lead author , a 91̽»¨professor of atmospheric sciences. “A controlled test would measure the extent to which we are able to alter clouds, and test an important component of climate models.”

Other co-authors are , a 91̽»¨professor of atmospheric sciences, Philip Rasch at the Department of Energy’s Pacific Northwest National Laboratory and Kelly Wanser.

The authors are part of a that is proposing to spray saltwater over oceans to cause a small increase in the brightness of marine clouds and boost their capacity to reflect sunlight. Doing so could be a short-term measure to offset global warming in a possible future emergency situation. In the meantime, it could also further understanding of the climate system.

One of the biggest uncertainties in climate models is the clouds, which reflect sunlight in unpredictable ways. Water droplets can only condense on airborne particles, such as smoke, salt or human pollution. When the air contains more particles the same amount of moisture can form smaller droplets, which creates whiter, brighter, more reflective clouds. Climate scientists believe pollution since the Industrial Revolution has created brighter clouds that reflect more sunlight, offsetting the warming from greenhouse gases, which trap long-wave radiation. But they can’t pin down the size of the effect or predict how much it might change in the future.

“Testing out marine cloud brightening would actually have some major benefits for addressing both questions,” Wood said. “Can we perturb the clouds in this way, and are the climate models correctly representing the relationship between clouds and aerosols?”

The proposal is now waiting on funding from government or private donors. For several years, 91̽»¨researchers have been working with a group of engineers in California’s Bay Area to that turns saltwater into tiny particles that could be sprayed high into the marine cloud layer. It’s the first in a series of steps needed to implement the roughly three-year plan. The researchers propose to:

• Produce a sprayer that is able to eject trillions of aerosol particles per second
• Conduct initial lab tests of the sprayer ( 91̽»¨research scientist helped conduct wind-tunnel testing of a prototype nozzle in 2015 in the Bay Area)
• Do preliminary outdoor tests in a coastal area that is fairly flat, relatively free of air pollution and prone to marine clouds (the group is currently seeking funding for in Monterey Bay)
• Move to small-scale offshore tests

If tests were successful, people might someday decide whether to use a scaled-up version to create a small increase in the reflection of sunlight over large swaths of the world’s oceans.

“We’re talking about some kind of new world in terms of the ethical issues,” Ackerman said. “But for climate, we’re no longer in an era of ‘do no harm.’ We are altering the climate already. It’s now a case of ‘the lesser of two evils.'”

Ackerman will speak July 27 in Newry, Maine, at the first about the proposed testing plan. Another speaker is the leader of a Harvard University test of an alternate proposal to spray reflective particles high in the atmosphere.

In addition to the paper on the scientific benefits of testing marine cloud brightening, a group of 91̽»¨graduate students and professors published a recent with a scientific and ethical analysis of how the climate would respond to particles injected into the stratosphere. Authors include 91̽»¨graduate students and faculty in philosophy, atmospheric science and civil engineering who were part of an interdisciplinary 91̽»¨ — among the first of its kind.

The class was taught last winter by Ackerman and , a 91̽»¨philosophy professor who wrote a on the ethics of deliberately tinkering with the planet’s atmosphere. Ackerman has since written an about the teaching experience. He believes the interdisciplinary approach is the right way to proceed with geoengineering.

“There’s a science question about can we do it, but there’s also an ethical question about should we do it, and a policy question about how would we do it,” Ackerman said. “I’m an agnostic on this. I want to test geoengineering and see if it works. But the whole time we’re working on this, I think we need to still be asking ourselves: ‘Should we do it?'”

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For more information, contact Wood at robwood2@uw.edu or 206-543-1203 and Ackerman at tpa2@uw.edu or 206-221-2767.

Tiny aerosol particles, emitted by everything from tailpipes to trees, float above us reflecting sunlight, seeding clouds and absorbing solar heat. How exactly this happens – and how it might change in the future – is one of the biggest uncertainties in how humans are influencing climate.

91̽»¨ scientists are part of a NASA field campaign, , or ORACLES, that is flying research planes around clouds off the coast of Namibia to see how smoke and clouds interact.

“The Namibians are being wonderful hosts and are really helping to make this a success,” said deputy principal investigator , a 91̽»¨professor of atmospheric sciences.

Wood plans to be in the field until late September. , a research scientist with the 91̽»¨Joint Institute for the Study of the Atmosphere and Ocean, is also among the roughly 100 participating scientists.

Fires burning on African savannas generate smoke that contains aerosol particles. This smoke rises high in the atmosphere and blows west off the coast, then drops down toward the cloud layer. The interaction between air moisture and smoke pollution is complex and not well understood.

“We still have a lot of pretty fundamental questions unanswered, such as whether the smoke and cloud layers are clearly separated, or, alternatively, if smoke particles end up mixing into the cloud deck and changing the clouds’ properties,” said , a graduate student in Wood’s group who is participating in the campaign.

From August 29 through late September, NASA’s ER-2 and P-3 research aircraft will take off roughly every other day from the project’s base in Walvis Bay, Namibia. The planes will fly at altitudes between sea level and about 3 miles elevation with instruments that look up and down to see how smoke and clouds interact. The team plans to return for follow-up measurements in 2017 and 2018.

Observations could help understand, for example, how forest fires burning inland affect the coastal cloud layer in other parts of the world, and how changes in air quality and global warming will act together on regional weather patterns.

The principal investigator is Jens Redemann of NASA’s Ames Research Center. Other partners on the $30 million, five-year NASA project include the Namibia University of Science and Technology and Namibia’s Gobabeb Research & Training Centre.

“This is a fantastic opportunity to interact with and learn from scientists not only from across the United States, but also from Namibia and South Africa,” Diamond said.

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For more information, contact Wood at robwood@atmos.washington.edu and Diamond at diamond2@uw.edu.

New research led by the 91̽»¨ and the Pacific Northwest National Laboratory suggest tiny ocean life in vast stretches of the Southern Ocean play a significant role in generating brighter clouds overhead. The were published July 17 in the online, open-access journal .

The study shows that plankton, the tiny drifting organisms in the sea, produce airborne gases and organic matter to seed cloud droplets, which lead to brighter clouds that reflect more sunlight.

“The clouds over the Southern Ocean reflect significantly more sunlight in the summertime than they would without these huge plankton blooms,” said co-lead author , a 91̽»¨doctoral student in atmospheric sciences. “In the summer, we get about double the concentration of cloud droplets as we would if it were a biologically dead ocean.”

Although remote, the oceans in the study area between 35 and 55 degrees south is an important region for Earth’s climate. Results of the study show that averaged over a year, the increased brightness reflects about 4 watts of solar energy per square meter.

“Life in the ocean has a big effect on clouds,” said co-author , a 91̽»¨professor of atmospheric sciences.

“This idea has been floating out there as a hypothesis, but there hasn’t been much evidence,” said cloud expert , a 91̽»¨professor of atmospheric sciences.

McCoy and co-author , now at the University of Leeds, began this research as 91̽»¨in 2014 looking at NASA satellite data for clouds over the parts of the Southern Ocean that are not covered in sea ice and have year-round satellite data. The space agency launched the first Moderate Resolution Imaging Spectroradiometer, or , instrument in 1999 to measure the cloud droplet size for all Earth’s skies.

Clouds reflect sunlight based on both the amount of liquid suspended in the cloud and the size of the drops, which range from tiny mist spanning less than a hundredth of an inch (0.1 mm) to large drops about half an inch (10 mm) across. Each droplet begins by growing on an aerosol particle, and the same amount of liquid spread across more droplets will reflect more sunlight.

Using the NASA satellite data, the 91̽»¨team in 2014 that Southern Ocean clouds are composed of smaller droplets in the summertime. But that doesn’t make sense, since the stormy seas calm down in summer and generate less sea spray to create airborne salts.

The new study looked more closely at what else might be making the clouds more reflective. Co-lead author , a scientist at the Pacific Northwest National Lab in Richland, Washington, used an ocean biology model to see whether biological matter could be responsible.

Marine life can affect clouds in two ways. The first is by emitting a gas, such as dimethyl sulfide released by Sulfitobacter bacteria and phytoplankton such as , which creates the distinctive sulfurous smell of the sea and also produces particles to seed marine cloud droplets.

The second way is directly through organic matter that collects at the water’s surface, forming a bubbly scum that can get whipped up and lofted into the air as tiny particles of dead plant and animal material.

By matching the cloud droplet concentration with ocean biology models, the team found correlations with the sulfate aerosols, which in that region come mainly from phytoplankton, and with the amount of organic matter in the sea spray.

“The dimethyl sulfide produced by the phytoplankton gets transported up into higher levels of the atmosphere and then gets chemically transformed and produces aerosols further downwind, and that tends to happen more in the northern part of the domain we studied,” Burrows said. “In the southern part of the domain there is more effect from the organics, because that’s where the big phytoplankton blooms happen.”

Taken together, these two mechanisms roughly double the droplet concentration in summer months.

The Southern Ocean is a unique environment for studying clouds. Unlike in other places, the effects of marine life there are not swamped out by aerosols from forests or pollution. The authors say it is likely that similar processes could occur in the Northern Hemisphere, but they would be harder to measure and may have a smaller effect since aerosol particles from other sources are so plentiful.

Wood is part of a larger team developing a field program to take direct measurements of Southern Ocean clouds and aerosols.

“We have really poor observations of everything in the Southern Ocean, and it’s a really important region,” Wood said. “It also provides a glimpse of how a pristine, pre-industrial area might behave.”

The research was funded by NASA, the U.S. Department of Energy and a graduate fellowship from the Air Force Office of Scientific Research. Other co-authors are and at Pacific Northwest National Laboratory and at Los Alamos National Laboratory.

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For more information, contact McCoy at 206-395-6041 or dtmccoy@atmos.uw.edu; Burrows at susannah.burrows@pnnl.gov; Hartmann at 206-543-7460 or dhartm@uw.edu; and Wood at 206-543-1203 or robwood@atmos.washington.edu. Also see the PNNL .

91̽»¨ researchers led the three-year project to gather leading thinkers and publish a snapshot of a field that they say is rapidly gaining credibility in the scientific community.

“In the past five years or so, geoengineering has moved from the realm of quackery to being the subject of scientific research,” said co-editor , a 91̽»¨associate professor of atmospheric sciences. “We wanted to contribute to a serious intellectual discourse.”

Creating clouds over the ocean that would reflect back sunlight is the subject of a by Wood, whose research is on the interaction among air pollution, clouds and climate. He and co-author Tom Ackerman, a 91̽»¨atmospheric sciences professor, look at what it would take to test the idea with a field experiment.

“I don’t want to prove it right, I just want to know if it’s feasible,” Wood said. “If you look at the projections for how much the Earth’s air temperature is supposed to warm over the next century, it is frightening. We should at least know the options. Is geoengineering feasible if there were to be what people call a ‘climate emergency’?”

Also explored in the journal issue is the idea of injecting reflective particles into the stratosphere, subject of a 2006 in Climatic Change by Nobel Prize-winning chemist Paul Crutzen and central to Seattle entrepreneur Nathan Myhrvold’s proposed . Yet another idea is of ocean microbes, though Wood said preliminary tests suggest this is not as successful at drawing carbon dioxide out of the atmosphere as its proponents had originally thought.

How to govern geoengineering is a topic of hot debate. In one , U.K. authors flesh out the so-called , which suggest how geoengineering could be regulated as a global public good. The five principles described in the paper concern the research, publication, assessment and deployment of geoengineering techniques.

Many of the authors spoke at the 91̽»¨during a , and more attended a 2012 workshop where they developed their paper ideas.

While discussions were civil, Wood said, the contributors didn’t all agree. A 91̽»¨philosopher questions whether geoengineering can even be described in the Oxford Principles as a global public good.

“Just spraying sulfates into the stratosphere is not the kind of thing that necessarily benefits everyone, so in that sense it seems a mistake to call it a global public good,” said co-editor , a 91̽»¨philosophy professor who has written a book on ethics and climate change. There are decisions about how to conduct sulfate spraying, he writes, and potential tradeoffs between short-term benefits and long-term risks.

Gardiner also questions whether something should be done in people’s benefit but without their permission, and if accepting geoengineering as a necessary evil ignores other science or policy options.

He’s not the only social scientist to be looking at climate issues.

“A lot of people, from across the academy, are getting interested in the Anthropocene – the idea that we may have entered a new geological era where human influence is a dominant feature, and what that means for various issues,” Gardiner said.

The collection aims to prompt a serious academic discussion the editors say has so far been lacking.

“It’s an interdisciplinary discussion with an emphasis on the research angle – whether and how we should be researching geoengineering,” said co-editor Lauren Hartzell-Nichols, a 91̽»¨lecturer in philosophy. “We hope it helps people think about this issue in a more interdisciplinary and integrated way.”

The seminars and workshop that led to the issue’s creation were supported by the 91̽»¨College of the Environment.

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For more information, contact Wood at 206-543-1203 or robwood@atmos.washington.edu and Gardiner at 206-221-6459 or smgard@uw.edu.