A team led by researchers at the 天美影视传媒 has discovered a major cause for a drop in nighttime pollinator activity 鈥� and people are largely to blame.

The researchers found that nitrate radicals (NO3) in the air degrade the scent chemicals released by a common wildflower, drastically reducing the scent-based cues that nighttime pollinators rely on to locate the flower. In the atmosphere, NO3 is produced by chemical reactions among other nitrogen oxides, which are themselves released by the combustion of gas and coal from cars, power plants and other sources. The findings, Feb. 9 in the journal Science, are the first to show how nighttime pollution creates a chain of chemical reactions that degrades scent cues, leaving flowers undetectable by smell. The researchers also determined that pollution likely has worldwide impacts on pollination.

The team 鈥� co-led by , a UW professor of biology, and , a UW professor of atmospheric sciences 鈥� studied the (Oenothera pallida). This wildflower grows in arid environments across the western U.S. They chose this species because its white flowers emit a scent that attracts a diverse group of pollinators, including nocturnal moths, which are one of its most important pollinators.

At field sites in eastern Washington, the researchers collected scent samples from pale evening primrose flowers. Back in the laboratory, they used chemical analysis techniques to identify the dozens of individual chemicals that make up the wildflower鈥檚 scent.

鈥淲hen you smell a rose, you鈥檙e smelling a diverse bouquet composed of different types of chemicals,鈥� said Riffell. 鈥淭he same is true for almost any flower. Each has its own scent made up of a specific chemical recipe.鈥�

Once they had identified the individual chemicals that make up the wildflower鈥檚 scent, the team used a more advanced technique called mass spectrometry to observe how each chemical within the scent reacted to NO3. They found that reacting with NO3 nearly eliminated certain scent chemicals. In particular, the pollutant decimated levels of monoterpene scent compounds, which in separate experiments moths found most attractive.

Moths, which smell through their antennae, have a scent-detection ability that is roughly equivalent to dogs 鈥� and several thousand times more sensitive than the human sense of smell. Research suggests that several moth species can detect scents from miles away, according to Riffell.

Using a wind tunnel and computer-controlled odor-stimulus system, the team investigated how well two moth species 鈥� the (Hyles lineata) and the (Manduca sexta) 鈥� could locate and fly toward scents. When the researchers introduced the pale evening primrose鈥檚 normal scent, both species would readily fly toward the scent source. But when the researchers introduced the scent and NO3 at levels typical for a nighttime urban setting, Manduca鈥檚 accuracy dropped by 50% and Hyles 鈥� one of the chief nocturnal pollinators of this flower 鈥� could not locate the source at all.

Experiments in a natural setting backed up these findings. In field experiments, the team showed that moths visited a fake flower emitting unaltered scent as often as they visited a real one. But, if they treated the scent first with NO3, moth visitation levels dropped by as much as 70%.

鈥淭he NO3 is really reducing a flower鈥檚 鈥榬each鈥� 鈥� how far its scent can travel and attract a pollinator before it gets broken down and is undetectable,鈥� said Riffell.

The team also compared how daytime and nighttime pollution conditions impacted the wildflower鈥檚 scent chemicals. Nighttime pollution had a much more destructive effect on the scent鈥檚 chemical makeup than daytime pollution. The researchers believe this is largely due to sunlight degrading NO3.

The team used a computer model that simulates both global weather patterns and atmospheric chemistry to locate areas most likely to have significant problems with plant-pollinator communication. The areas identified include western North America, much of Europe, the Middle East, Central and South Asia, and southern Africa.

鈥淥utside of human activity, some regions accumulate more NO3 because of natural sources, geography and atmospheric circulation,鈥� said Thornton, who added that natural sources of NO3 include wildfires and lightning. 鈥淏ut human activity is producing more NO3 everywhere. We wanted to understand how those two sources 鈥� natural and human 鈥� combine and where levels could be so high that they could interfere with the ability of pollinators to find flowers.鈥�

The researchers hope their study is just the first of many to help uncover the full scope of pollinator failure.

鈥淥ur approach could serve as a roadmap for others to investigate how pollutants impact plant-pollinator interactions, and to really get at the underlying mechanisms,鈥� said Thornton. 鈥淵ou need this kind of holistic approach, especially if you want to understand how widespread the breakdown in plant-pollinator interactions is and what the consequences will be.鈥�

The study highlights the dangers of human-fueled pollution and its implications for all pollinators as well as the future of agriculture.

鈥淧ollution from human activity is altering the chemical composition of critical scent cues, and altering it to such an extent that the pollinators can no longer recognize it and respond to it,鈥� said Riffell.

Approximately three-quarters of the more than 240,000 species of flowering plants rely on pollinators, Riffell said. And more than听70 species of pollinators are endangered or threatened.

Lead author on the paper is Jeremy Chan, a postdoctoral researcher at the University of Copenhagen who conducted this study as a UW doctoral student in biology. Co-authors are Sriram Parasurama in the UW Department of Biology; Rachel Atlas, a postdoctoral researcher at the Pierre Simon Laplace Institute in France who participated in this study as a UW doctoral student in atmospheric sciences; , a UW doctoral students in atmospheric sciences; Ruochong Xu, a doctoral student at Tsinghua University in China; , a UW professor of atmospheric sciences; and , a professor of chemistry at Seattle University. The research was funded by the Air Force Office of Scientific Research, the National Science Foundation, the National Institutes of Health, the Human Frontiers in Science Program, and the 天美影视传媒.

For more information, contact Riffell at 206-348-0789 or jriffell@uw.edu and Thornton at 206-543-4010 or joelt@uw.edu.

Despite their invisibly small size, ultrafine particles have become a massive concern for air pollution experts. These tiny pollutants 鈥� typically spread through wildfire smoke, vehicle exhaust, industrial emissions and airplane fumes 鈥� can bypass some of the body鈥檚 built-in defenses, carrying toxins to every organ or burrowing deep in the lungs.听听

New research from the 天美影视传媒 found that those effects aren鈥檛 felt equitably in Seattle. The most comprehensive study yet of long-term ultrafine particle exposure found that concentrations of this tiny pollutant reflect the city鈥檚 decades-old racial and economic divides. 听

The study, 听in Environmental Health Perspectives, also found that racial and socioeconomic disparities in ultrafine particle exposure are larger than those observed in more commonly studied pollutants, like fine particles (PM 2.5) and nitrogen dioxide (NO2).听

The study used mobile monitoring 鈥� a car loaded with air pollution sensors driving around the city for the better part of a year 鈥� to examine long-term average levels of four pollutants: soot (or black carbon), fine particles (PM 2.5), nitrogen dioxide (NO2) and ultrafine particles. Researchers found the highest concentrations of all four pollutants on census blocks with median household incomes under $20,000 and those with proportionately larger Black populations. 听

Disparities in concentrations of ultrafine particles 鈥� which are less than 0.1 micron in diameter, or 700 times thinner than the width of a single human hair 鈥� were especially stark. Blocks with median incomes under $20,000 had long-term UFP concentrations 40% higher than average. Blocks where median incomes are over $110,000, meanwhile, saw UFP concentrations 16% lower than average.听听

鈥淲e found greater disparities with this pollutant of emerging interest, a pollutant that hasn鈥檛 been well-characterized. That鈥檚 very interesting,” said senior author , a UW professor in the Department of Environmental and Occupational Health Sciences. 鈥淥ur work has shown the highest ultrafine particle concentrations are north of the airport and below common aircraft landing paths, downtown, and south of downtown where there are port and other industrial activities.”听

The study also found that modern-day air pollution disparities mirror Seattle鈥檚 history of redlining, the racist practice that denied racial minorities and low-income residents access to bank loans, homeownership and other wealth-building opportunities in more 鈥渄esirable鈥� areas. The practice shaped American cities throughout the early 20th century, building a foundation of segregation and environmental racism.听

Today, neighborhoods once classified as 鈥渉azardous鈥� are still exposed to higher concentrations of pollution than those once labeled 鈥渄esirable,鈥� the study found. This was true for all sizes of particles. The spatial disparities were largest, however, in Seattle neighborhoods that received no label because they were once considered industrial areas.听

In those previously industrial areas, ultrafine particle concentrations were 49% above average.听听

鈥淭hese results are important because air pollution exposure has been shown to lead to detrimental health effects, and these health effects disproportionately impact racialized and low-income communities,鈥� said , the study鈥檚 lead author, who graduated from the UW in 2022 with a degree in industrial and systems engineering. 鈥淣otably, air pollution is just one factor, and there are plenty of other examples of how systemic racism is detrimental to people’s health and well-being.鈥�听

Bramble said the results didn鈥檛 surprise her. She was raised in Tacoma, in a neighborhood near Interstate 5, where the constant crush of cars and diesel trucks spewed pollution into the air. And as a student journalist at the UW, she researched the relationship between redlining, green spaces, heat and air pollution.听听

鈥淚n the case of air pollution exposures, these policies affect the health of real people. I think at a time where the teaching of systemic racism is a controversial topic in this country, being ignorant is not going to reduce the number of children who suffer from asthma due to air pollution,鈥� Bramble said. 鈥淚nstead, I hope we can have conversations about how past policies affect us today, to drive efforts toward a healthier, sustainable society.鈥�听

Bramble proposed and carried out this study for the grant program, which provides National Institute of Environmental Health Sciences funding and mentorship to undergraduates from underrepresented backgrounds to pursue research. She joined the program in June 2020 under Sheppard鈥檚 mentorship.听听

Other UW authors are Magali Blanco, Annie Doubleday and Amanda Gassett of the Department of Environmental and Occupational Health Sciences, Anjum Hajat of the Department of Epidemiology and Julian Marshall of the Department of Civil and Environmental Engineering.听听

For more information, contact Sheppard at sheppard@uw.edu.听

The air in the United States and Western Europe is much cleaner than even a decade ago. Low-sulfur oil standards and regulations on power plants have successfully cut sulfate concentrations in the air, reducing the fine particulate matter that harms human health and cleaning up the environmental hazard of acid rain.

Despite these successes, sulfate levels in the atmosphere have declined more slowly than sulfur dioxide emissions, especially in wintertime. This unexpected phenomenon suggests sulfur dioxide emission reductions are less efficient than expected for cutting sulfate aerosols. A new study led by the Tokyo Institute of Technology, Hokkaido University and the 天美影视传媒 explains why. The was published May 5 in Science Advances.

When concentrations of acidic sulfate from fossil fuel emissions decrease while the concentration of more basic ammonium molecules in the atmosphere stay constant, liquid water droplets in clouds become less acidic. This makes conversion of sulfur dioxide to sulfate more efficient. So, even though air quality regulations have reduced the supply of sulfur dioxide from power plants and shipping, the total amount of sulfate particulates that harm human health has dropped more slowly.

鈥淚t does not mean that the emissions reductions aren鈥檛 working. It鈥檚 just that there is a reaction which partially mitigates the reductions,鈥� said co-author , a UW professor of atmospheric sciences. 鈥淲e need to understand this multiphase chemistry in the atmosphere to make an efficient strategy to manage air pollution and accurately predict future air pollution and climate change impacts.鈥�

During most of the 20^th century, sulfur dioxide emissions increased with industrialization in many parts of the world. But recently that trend has reversed in response to regulations, while ammonium emissions from animals and agriculture continue at the same rate. These trends are expected to continue.

Data from an ice core in Greenland that preserves past years鈥� atmospheres show that the proportion of sulfate containing oxygen with one extra neutron, or oxygen-17, increased in the 1980s after countries began to regulate emissions. The authors鈥� analysis shows this is due to faster sulfate formation in the liquid phase in the atmosphere, which occurs largely within clouds, under less-acidic conditions.

鈥淎fter the SO₂ emission control, relatively lower atmospheric acidity promotes the efficiency of sulfate production in the atmosphere, which weakens the response of sulfate level to the SO₂ reduction,鈥� said lead author at the Tokyo Institute of Technology. 鈥淥ur unique isotopic techniques applied for the Greenland ice core records identify the key process of the weakened response of sulfate to SO₂ emissions reduction.鈥�

The data came from an ice core drilled in southeast Greenland (SE-Dome) as part of a project led by Hokkaido University. The oxygen trapped in this ice provided evidence of sulfate composition from 1959 to 2015, without contamination from local pollution.

鈥淏ased on a continuous and high-resolution ice core record from SE-Dome, we could obtain reliable records for atmospheric aerosols without second modification after deposition,鈥� said co-author and leader of SE-Dome ice core project at Hokkaido University. 鈥淲e plan to drill a second ice core at the same location this year, and try to reconstruct the aerosol history back to the 1750s.鈥�

The ice core does not contain separate data for summer and winter, but models show that other, gas-phase chemical reactions for sulfur dioxide become more important in summer, reducing the summertime impact of changing cloud acidity. Knowing how these molecules react will help improve the atmospheric models used to forecast air quality and project climate change.

The research was funded by the Japan Society for the Promotion of Science and the National Science Foundation. , a graduate student in atmospheric sciences at the UW, is among the other co-authors.

For more information, contact Alexander at beckya@uw.edu or Hattori at hattori.s.ab@m.titech.ac.jp.

Adapted from a press release by Tokyo Institute of Technology.

Wildfires burning in the West affect not only the areas burned, but the wider regions covered by smoke. Recent years have seen hazy skies and hazardous air quality become regular features of the late summer weather.

Many factors are causing Western wildfires to grow bigger and to generate larger, longer-lasting smoke plumes that can stretch across the continent. An analysis led by the 天美影视传媒 looks at the most detailed observations to date from the interiors of West Coast wildfire smoke plumes.

The multi-institutional team tracked and flew through wildfire plumes from the source to collect data on how the chemical composition of smoke changed over time. A resulting , published Nov. 2 in the Proceedings of the National Academy of the Sciences, shows that smoke forecasts may incorrectly predict the amount of particles in staler smoke.

The new results could significantly change the estimate for particles in staler smoke, which could be the difference between 鈥渕oderate鈥� and 鈥渦nhealthy鈥� air quality in regions downwind of the fire.

鈥淲ildfires are getting larger and more frequent, and smoke is becoming a more important contributor to overall air pollution,鈥� said lead author , a UW professor of atmospheric sciences. 鈥淲e really targeted the smoke plumes close to the source to try better understand what’s emitted and then how it can transform as it goes downwind.鈥�

Knowing how newly generated wildfire smoke transitions to stale, dissipated smoke could lead to better forecasts for air quality. Communities can use those forecasts to prepare by moving outdoor activities inside or rescheduling in cases where the air will be unsafe to be outdoors, as well as limiting other polluting activities such as wood-burning fires.

鈥淭here are two aspects that go into smoke forecasts,鈥� said first author , a UW postdoctoral researcher in atmospheric sciences. 鈥淥ne is just where is the smoke plume going to go, based on dynamics of how air moves in the atmosphere. But the other question is: How much smoke gets transported 鈥� how far downwind is air quality going to be bad? That鈥檚 the question our work helps to address.鈥�

When trees, grass and foliage burns at high temperatures they generate soot, or black carbon, as well as organic particles and vapors, called organic aerosols, that are more reactive than soot. Fires can also produce 鈥溾�� aerosol, a less-well-understood form of organic aerosol that gives skies a brownish haze.

Once in the air, the organic aerosols can react with oxygen or other molecules already in the atmosphere to form new chemical compounds. Air temperature, sunlight and concentration of smoke affect these reactions and thus alter the properties of the older smoke plume.

The multi-institutional team measured these reactions by flying through wildfire plumes in July and August 2018 as part of WE-CAN, or the field campaign led by Colorado State University.

Research flights from Boise, Idaho, used a C-130 aircraft to observe the smoke. The study flew through levels of 2,000 micrograms per cubic meter, or about seven times the worst air experienced in Seattle this summer. Seals on the aircraft kept the air inside the craft much cleaner, though researchers said it was like flying through campfire smoke.

鈥淲e tried to find a nice, organized plume where we could start as close to the fire as possible,鈥� Palm said. 鈥淭hen using the wind speed we would try to sample the same air on subsequent transects as it was traveling downwind.鈥�

The analysis in the new paper focused on nine well-defined smoke plumes generated by the in southwestern Oregon, the Bear Trap fire in Utah, the Goldstone fire in Montana, the South Sugarloaf fire in Nevada, and the Sharps, Kiwah, Beaver Creek and Rabbit Foot wildfires in Idaho.

鈥淵ou can’t really reproduce large wildfires in a laboratory,鈥� Palm said. 鈥淚n general, we tried to sample the smoke as it was aging to investigate the chemistry, the physical transformations that are happening.鈥�

The researchers found that one class of wildfire emissions, phenols, make up only 4% of the burned material but about one-third of the light-absorbing 鈥渂rown carbon鈥� molecules in fresh smoke. They found evidence of complex transformations within the plume: Vapors are condensing into particles, but at the same time and almost the same rate, particulate components are evaporating back into gases. The balance determines how much particulate matter survives, and thus the air quality, as the plume travels downwind.

鈥淥ne of the interesting aspects was illustrating just how dynamic the smoke is,鈥� Palm said. 鈥淲ith competing processes, previous measurements made it look like nothing was changing. But with our measurements we could really illustrate the dynamic nature of the smoke.鈥�

The researchers found that these changes to chemical composition happen faster than expected. As soon as the smoke is in the air, even as it鈥檚 moving and dissipating, it starts to evaporate and react with the surrounding gases in the atmosphere.

鈥淲hen smoke plumes are fresh, they鈥檙e almost like a low-grade extension of a fire, because there鈥檚 so much chemical activity going on in those first few hours,鈥� Thornton said.

The authors also performed a set of inside a research chamber in Boulder, Colorado, that looked at how the ingredients in smoke react in daytime and nighttime conditions. Wildfires tend to grow in the afternoon winds when sunlight speeds up chemical reactions, then die down and smolder at night. But very large wildfires can continue to blaze overnight when darker skies change the chemistry.

Understanding the composition of the smoke could also improve weather forecasts, because smoke cools the air underneath and can even change wind patterns.

鈥淚n Seattle, there are some thoughts that the smoke changed the weather,鈥� Thornton said. 鈥淭hose kinds of feedbacks with the smoke interacting with the sunlight are really interesting going forward.鈥�

The research was funded by the National Science Foundation and the National Oceanic and Atmospheric Administration. Other co-authors are graduate students and and research scientist in the UW Department of Atmospheric Sciences; Lauren Garofalo, Matson Pothier, Delphine Farmer, Sonia Kreidenweis and Emily Fischer at Colorado State University; Rudra Pokhrel, Yingjie Shen and Shane Murphy at the University of Wyoming; Wade Permar and Lu Hu at the University of Montana; and Teresa Campos, Samuel Hall, Kirk Ullmann, Xuan Zhang and Frank Flocke at the National Center for Atmospheric Research in Boulder, Colorado.

For more information, contact Thornton at joelt@uw.edu or Palm at bbpalm@uw.edu.

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.

鈥淒uring the February 2020 shutdowns in China there was a large and rapid decline in nitrogen dioxide 鈥� an air pollutant largely associated with transportation 鈥� that is unprecedented in the satellite record,鈥� said , a 天美影视传媒 doctoral student in atmospheric sciences.

鈥淥n 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,鈥� 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.

鈥淓arly 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,鈥� Diamond said. 鈥淭he scientific community was interested in documenting what changes actually occurred.鈥�

The authors used data from NASA鈥檚 , 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鈥檚 environmental policies.

鈥淐hina 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,鈥� Diamond said.

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

鈥淵ou still had some pretty bad smog events happening in the Beijing region, even during the lockdown,鈥� 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鈥檚 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.

鈥淭he 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鈥檚 a giant signal. It is rare to see anything that striking,鈥� 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 UW 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.

鈥淥ur 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,鈥� Wood said.

Overall, the findings agree with a recent study led by the UW 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鈥檛 focus only on transportation emissions.

鈥淲hen you鈥檙e crafting these clean air strategies, you鈥檙e probably not going to be able to attack just one sector; you鈥檒l have to address several sectors at once,鈥� Diamond said.

This research was funded by NASA.

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

Regulators can now breathe easier. A 天美影视传媒-led study, published in March in the , provides a fuller picture of the relationship between nitrogen oxides 鈥� the tailpipe-generated particles at the center of the Volkswagen scandal, also known as NOx, 鈥� and PM2.5, the microscopic particles that can lodge in lungs.

Results show that declining NOx due to tighter standards does ultimately lead to cleaner air 鈥� it just might take longer.

A key finding is how the concentration of NOx affects the formation of PM2.5, found in smog, by changing the chemistry of the hydrocarbon vapors that transform into the particles less than 2.5 microns across, or about 3 percent the width of a human hair.

“We found that there are two different regimes of PM2.5 formation,” said first author , a UW professor of atmospheric sciences. “One where adding NOx enhances PM2.5, and one where adding NOx suppresses PM2.5.”

The findings could help explain why air quality appears to have stagnated in recent years over some parts of North America, even as emissions of all types have been dropping. Regulators are concerned because air pollution is a leading human health hazard, especially among children, the elderly and those with respiratory or heart problems.

Officials knew to expect slow progress on reducing ozone, another component of smog, because of a somewhat similar role that NO_x plays in ozone formation. But the recent concern was that PM2.5 concentrations might be different, and would just continue to go up with decreasing NOx emissions.

“We’re basically saying: ‘Hold on, don’t worry. Things might look like they’re getting worse, in some places, but overall they should get better,'” Thornton said.

The discovery of this complex relationship could also help atmospheric scientists predict how air will change as emissions drop further.

Hydrocarbon vapors 鈥� carbon-based compounds from either natural sources or fossil fuels 鈥� do not readily convert to PM2.5. Only through a set of chemical reactions in the air that involve free radicals, which are produced by sunlight and modulated by NOx, are hydrocarbon vapors converted into particulates.

The research combines observations from a 2013 that measured emissions plumes in the air above Southeastern U.S. cities as well as experiments conducted at the Pacific Northwest National Laboratory.

The ease with which hydrocarbons convert to PM2.5 shifts with the availability of the different ingredients, and the reaction rates also change. Both must be considered to understand the effect on regional PM2.5, the new study shows. Even though the process of PM2.5 formation from hydrocarbons gets easier as NO_x drops, the chemical reactions slow down. Together the two effects mean that, eventually, drops in nitrogen oxides will lead to drops in PM2.5.

“You could be in a regime where it gets worse, but if you push past it, it gets better,” Thornton said. “In most urban areas in the U.S., the NOx levels are low enough that we are past this point already.”

Previous research from Thornton’s group has shown why is more resistant to emissions regulations than summer smog: because different temperatures provide seasonal conditions that send the chemistry down distinct paths.

The research was funded by the Department of Energy, the Environmental Protection Agency and the National Science Foundation. The aircraft study was funded by the National Oceanic and Atmospheric Administration. The other lead author is at the Environmental Protection Agency, who was a visiting scientist at the 天美影视传媒. Other co-authors are from the UW Department of Atmospheric Sciences; Pacific Northwest National Laboratory; the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory; and the University of Colorado, Boulder.

###

For more information, contact Thornton at 206-543-4010 or thornton@atmos.uw.edu.

The air in the United States is much cleaner than even a decade ago. But those improvements have come mainly in summer, the season that used to be the poster child for haze-containing particles that cause asthma, lung cancer and other illnesses.

A led by the 天美影视传媒 shows why winter air pollution levels have remained high, despite overall lower levels of harmful emissions from power plants and vehicles throughout the year.

“In the past 10 years or so, the summer air pollution levels have decreased rapidly, whereas the winter air pollution levels have not. Air quality in summer is now almost the same as in winter in the eastern U.S.,” said corresponding author , who did the work as part of his UW doctorate in atmospheric sciences. “We have pinpointed the chemical processes that explain the seasonal difference in response to emissions reductions.”

The study, published the week of July 23 in the Proceedings of the National Academy of Sciences, shows that the particles follow different pathways in the winter.

Results came from analyzing observations collected during the 2015 (WINTER) campaign. During that UW-led effort, researchers spent six weeks in winter flying through pollution plumes over New York City, Baltimore, Cincinnati, Columbus, Pittsburgh, Washington, D.C., and along the coal-fired power plants of the Ohio River Valley.

The study was funded by the National Science Foundation, with in-kind support from NASA and the National Oceanic and Atmospheric Administration.

Particles that form smog come in different flavors. Two important ones are sulfates, from sulfur dioxide emitted mainly by coal-fired power plants, and nitrates, created from nitrogen oxides known collectively as NOx. Air-quality regulations have lowered sulfur dioxide in the U.S. by 68 percent between 2007 and 2015, and NOx by about a third during that time.

Summertime levels of particulates 鈥� when the two flavors of oxides clump up into watery packets of nitrates and sulfates that create beautiful sunsets but harm human health 鈥� have dropped in the eastern U.S. by about a third during that time. But the winter concentrations of particulates have decreased by only half as much, for reasons that had been unclear.

“The air quality models that we use to understand the origin of air pollution perform quite well in summer, but have some issues in the wintertime. Before this study, we could not reproduce the observed particulate composition in winter,” said , who was second author on the paper and co-principal investigator of the field campaign. “We now have a better tool to look at what is the best strategy to improve wintertime air quality on regional scales in the eastern U.S., and potentially other places, like Europe and Asia.”

In the summer, some of the emitted NOx and sulfur dioxide remains in the gas phase and gets zapped by sunlight or deposited on land, and the rest forms particulates in the form of nitrates and sulfates. As the primary ingredients drop, so do the levels of particulates.

But the new analysis shows that the chemistry of wintertime air follows a more complex path. With less sunlight and colder temperatures, more of the chemistry happens in the liquid phase, on the surfaces of existing particulates or liquid and ice clouds. In that phase, as the primary ingredients drop, the efficiency of converting sulfur dioxide to sulfate rises, because more oxidants are available. And as sulfate goes down, the particulates become less acidic, making NOx convert more easily to nitrates.

So, even though air quality regulations have reduced both types of primary emissions, the total amount of particulates that harm human health has dropped more slowly.

“It’s not that the reductions aren’t working. It’s just that the reductions have a cancelling effect, and the cancelling effect has a set strength,” said Shah, who is now a postdoctoral researcher at Harvard University. “We need to make further reductions. Once the reductions become larger than the cancelling effect, then winter will start behaving more like summer.”

The study predicts that unless emissions reductions outpace current forecasts, air quality in winter will continue to improve only gradually until at least 2023. At this rate it would be several years before emissions reach levels when wintertime pollution starts to drop more quickly.

“This paper shows that understanding the underlying atmospheric chemistry that converts primary pollutants into fine particulate matter is critical for calibrating our expectations about what emissions reductions will accomplish, and therefore for how to optimize future emissions reductions to continue getting the ‘biggest bang for the buck’ in terms of reducing fine particulate matter concentrations,” said third author , who was the principal investigator on the field campaign.

The findings suggest that more emissions reductions, of both sulfur and nitrogen oxides, will be needed to improve wintertime air quality in the Eastern U.S. and other cold climates.

“This research helps explain why emissions controls to reduce air pollution substances, such as sulfate and nitrate, have not been as successful as expected in the eastern U.S. in winter,” said Sylvia Edgerton, program director in the NSF’s Division of Atmospheric and Geospace Sciences, which funded the research. “The WINTER field campaign produced a unique set of winter observations. They demonstrate that chemical feedbacks during winter months counteract expected reductions in air pollution due to reduced emissions.”

Other co-authors are and at the UW; Jason Schroder, Pedro Campuzano-Jost, and Jose Jimenez at the University of Colorado Boulder; Hongyu Guo and Rodney Weber at Georgia Institute of Technology; Amy Sullivan at Colorado State University; Jaime Green, Marc Fiddler and Solomon Bililign at North Carolina A&T State University; Teresa Campos, Meghan Stell, Andrew Weinheimer and Denise Montzka at the National Center for Atmospheric Research in Boulder; and Steven Brown at the National Oceanic and Atmospheric Administration in Boulder.

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For more information, contact Shah at 412-736-0062 听or vshah@uw.edu, Jaegle at 206-685-2679 or jaegle@uw.edu and Thornton at 206-543-4010 or joelt@uw.edu.

NSF grants: AGS-1360745, AGS-1360834, AGS-1360730. NASA: NNX15AT96G

Now, a probiotic bacteria for trees can boost the speed and effectiveness of this natural cycle, providing a microbial partner to help protect trees from the toxic effects of the pollutants and break down the听toxic pollutants plants bring in from contaminated groundwater.

Researchers from the 天美影视传媒 and several small companies have conducted the first large-scale experiment on a Superfund site using poplar trees fortified with a probiotic 鈥� or natural microbe 鈥� to clean up groundwater contaminated with (TCE), a common pollutant found in industrial areas that is harmful to humans when ingested through water or inhaled from the air. Their were published in final form Aug. 11 in the journal .

The successful field trial could be a game changer to quickly and effectively clean up Superfund sites around the country and polluted sites abroad that have high levels of TCE, the authors say.

“These results open the door,” said corresponding author , a UW professor in the School of Environmental and Forest Sciences. “We have known about this process for a long time from our laboratory research, but it hasn’t been used in practice because there were no field results. Now, engineering companies can start using this in real life.”

Contaminated sites containing TCE and other pollutants can be expensive to clean up when using engineering methods such as excavating or pumping toxic pollutants听from underground. As a result, many sites sit untreated. This new method allows contaminated sites to be dealt with more effectively, often at lower costs, promoting human health.

Doty’s lab worked to find the best microbe strain that could effectively break down TCE and boost tree growth. Jun Won Kang, a former UW graduate student, had obtained poplar wood from a site in the Midwest where trees were already growing in TCE-contaminated soil. After grinding down small samples of the trees and isolating over a hundred different microbes, each strain was then placed in a flask containing high levels of TCE.

The microbe that ultimately was selected eliminated nearly all of the TCE in its flask. The researchers had a clear winner.

“The poplar at the older site in the Midwest selected for the best microbes to help it do its job,” Doty explained. “We took advantage of that natural selection process. We just had to find the best ones that the plant already chose.”

The pollutant TCE has been used widely as a degreaser and a solvent in industrial manufacturing sites across the country. The U.S. Environmental Protection Agency cites TCE as one of the most common pollutants in soil or water, and it is present in more than 1,000 sites the agency lists as priorities for cleanup. TCE is a known carcinogen to humans, affecting the liver and even transferring the toxic pollutant to nursing babies .

Given the prevalence and toxicity of TCE, the researchers used the chemical to test the ability of poplar trees infused with microbes to clean up groundwater in the Superfund research area in California’s Silicon Valley after it had subsequently flowed into the NASA Research Park at NASA’s Ames Research Center. At NASA Ames, in coordination with NASA Ames’ Environmental Division, the researchers planted rows of young poplar trees 鈥� some inoculated with the specific microbe, and others without 鈥� on a field above a known groundwater plume contaminated with TCE.

After only a year, the trees given the microbe were bigger and healthier than the poplars with no special treatment. After three years, the inoculated trees were still more robust, and a sample of tree trunks revealed greatly reduced levels of TCE inside the trees.

When trees take up and degrade chemicals, called phytoremediation, it often comes at the expense of their own health. This manifests as stunted growth, yellow leaves, withering brown leaves and branches, and sometimes death as the pollutant hampers the tree’s ability to survive. But when the microbe selected specifically to deal with TCE is introduced, the trees destroyed the TCE 鈥� and experienced more robust growth and increased survival rates, clear benefits of the probiotic.

“The real goal is to try to improve performance,” said co-author , president and CEO of Edenspace Systems Corporation in Virginia. “If we have something that speeds up and improves performance and makes it so the trees can grow better, that’s really what we were trying to accomplish with this project.”

Additionally, the researchers found that groundwater samples taken directly downstream from the test site showed much lower levels of the pollutant, compared with higher levels up-gradient from the testing area. They also found evidence of increased chloride in the soil around the poplar roots, a harmless, naturally occurring element and byproduct of TCE as it is degraded by the bacteria inside trees.

A number of organizations have expressed interest in using this technology, said co-author , chief science officer for Intrinsyx Technologies Corporation based at NASA’s Research Park. And landowners hampered by the high costs associated with traditional clean-up methods are starting to use the technology.

“This has the potential to make a huge impact on a lot of legacy sites where you have contaminated groundwater issues, including TCE, and where funding is currently less available,” Freeman said. “This is definitely a big cost savings to everyone involved. It’s a real win-win situation because it’s green, it’s long-term sustainable, publicly acceptable and it’s solar powered by the trees themselves.”

Other co-authors are Christopher Cohu of Phytoremediation and Phytomining Consultants United; Joel Burken of Missouri University of Science and Technology; Andrea Firrincieli of Tuscia University in Italy; Andrew Simon of Edenspace Systems Corporation; Zareen Khan of the UW; Jud Isebrands of Environmental Forestry Consultants; and Joseph Lukas of Earth Resources Technology.

The work was funded by the National Institutes of Health through a Small Business Innovation Research grant. Support for Doty’s research was also provided by the Byron and Alice Lockwood Foundation.

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For more information, contact Doty at sldoty@uw.edu or 206-616-6255; Blaylock at blaylock@edenspace.com or 703-961-8700; and Freeman at Jfreeman@intrinsyx.com or 650-210-9219.

NIH grant: R44ES020099

By analyzing samples from the Greenland ice sheet, 天美影视传媒 atmospheric scientists found clear evidence of the U.S. Clean Air Act. They also discovered a link between air acidity and how nitrogen is preserved in layers of snow, according to a published this week in the .

Forty-five years ago, acid rain was killing fish and dissolving stone monuments on the East Coast. Air pollution rose beginning with the Industrial Revolution and started to improve when the U.S. Clean Air Act of 1970 required coal power plants and other polluters to scrub sulfur out of their smokestacks.

UW researchers began their study of ice cores interested in smog, not acid rain. They discovered a link between the two forms of pollution in the geologic record.

Nitrogen is emitted as a short-lived compound, NOx, which causes ground-level ozone, the main ingredient in smog, and relates to compounds that are the “detergent” of the atmosphere. Sources of NOx include smokestacks and vehicle tailpipes, as well as wildfires, soil microbes or reactions triggered by lightning strikes.

Teasing out the sources of NOx through history might tell us about the atmosphere of the past, how methane, ozone and other chemicals change in the atmosphere, and also provide a measure of global human emissions.

“How much the nitrate concentrations in ice core records can tell about NOx and the chemistry in the past atmosphere is a longstanding question in the ice-core community,” said lead author , a UW postdoctoral researcher in atmospheric sciences.

Unlike other gases, short-lived NOx can’t be measured directly from air bubbles trapped in ice cores. Within a day or two most of the NOx changes into nitrate, a water-soluble molecule essential to life that gets deposited in soil and snow.

by co-author , a UW professor of Earth and space sciences, suggested that comparing amounts of the two stable forms of nitrogen 鈥� nitrogen-15 and nitrogen-14 鈥� in nitrate could pinpoint the emission sources of NOx. Ice cores from Greenland and North American lake sediments showed the nitrogen-15 ratio gradually decreasing since 1850, suggesting a corresponding rise in human emissions.

The new research says: not so fast. The detailed measurements of nitrate, NOx and sulfur show the nitrogen isotope ratio leveling off in 1970, and suggests that ratio is sensitive to the same chemicals that cause acid rain.

“This shows that the relationship between emissions and the isotopes is less direct than we thought, and the final signal recorded in the Greenland ice cores is actually not just the nitrogen emission, but the combined effect of sulfur and nitrogen emissions,” Steig said.

The ice cores used in the study were collected in 2007 at Summit Station, Greenland. Total amounts of nitrate for each year were measured and calculated at South Dakota State University, where Geng did his doctoral work. The different forms, or isotopes, were measured in UW鈥檚 .

Geng’s work showed that the long-term decrease in the nitrogen-15 isotope since 1850, and its leveling off in 1970, are linked to changes in air chemistry. Airborne nitrate can exist as a gas or a particle, and nitrate with lighter isotopes tends to exist as a gas. But he found that the total fraction of nitrate present as gas or particle varies with the acidity of the atmosphere, and the acidic air causes more of the light isotopes to exist as a gas.

“The isotope records really closely follow the atmospheric acidity trends,” said co-author , a UW associate professor of atmospheric sciences. “You can really see the effect of the Clean Air Act in 1970, which had the most dramatic impact on emission of acid from coal-fired power plants.”

What’s more, airborne nitrate dissolves in water and falls at the poles as snow. While that snow sits on the ground, sunlight bouncing off the surface triggers chemical reactions that send some of it back into a gas form. Acid air can also influence the reactivity of nitrate in snow and thus the preservation of nitrate in ice cores.

Other ice core records might also be affected by acidity in air, Alexander said. No effect would be expected for stable gases like carbon dioxide and oxygen, or for the water molecules used to calculate temperature variations through time. But acidity in air could influence deposition and preservation of other volatile compounds such as chlorine, mercury or organic materials in ice cores.

Eventually, better understanding of the air chemistry during formation of the layers could allow researchers to correct for the effect, extracting better information of the past from these compounds in the geologic record.

The research was funded by the National Science Foundation. Other co-authors are Eric Sofen and Andrew Schauer at the UW, Jihong Cole-Dai at South Dakota State University and Jo毛l Savarino at University of Grenoble in France.

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For more information, contact Geng at 206-543-4596 and leigeng@uw.edu, Alexander at 206-543-0164 or beckya@uw.edu or Steig at 206-685-3715 or steig@uw.edu.

is a 天美影视传媒 doctoral student in political science and author of the new book “.” She answered a few questions about the book for UW Today.

Q: What’s the basic concept behind this book?

A: As Prince William Sound emerged from a cloak of darkness on March 24, 1989, shades of pale spring light marked the dawning of a tragic day in Alaskan and American history. Oil boiled from the bowels of the supertanker Exxon Valdez, grounded on Bligh Reef, while a fisherman, Bobby Day, readied his boat for a herring season that would never open. The book centers on his story and gives voice to the 10,000 fishermen who struggled to hold Exxon accountable in the wake of the spill. The book brings to life the personal and environmental consequences of this disaster, while tracing the regulatory and governance failures that gave rise to the spill.

“Red light to starboard” was the final warning delivered by the lookout on the Exxon Valdez on that fateful night. That admonition also serves as a metaphor for many missed signals that a major spill in Prince William Sound was inevitable. This story reveals the regulatory and governance failures that gave rise to the spill, politics surrounding oil development, coziness between the government and oil industry, and unheeded warnings by local citizens and industry insiders.听 As those contributing factors emerge, the book develops an implicit thesis that citizens and local resource users, or groups representing the public interest, can and should have a formal mechanism for oversight in the regulatory process.

Q: You have a personal connection with this material. Would you explain?

A: Even before I came to have a personal connection with this disaster, the Exxon Valdez oil spill was a defining event in my life. Like other Americans, I was astounded that an accident like this could happen, and heartbroken by the images of environmental devastation I saw nightly on the news.

When I met my husband 鈥� the fisherman at the center of this story 鈥� I came to a deeper understanding of the spill’s impacts and I wanted others to come to know and feel those impacts as I had. I also found myself driven by a more profound question of why the spill had happened. The more I began to try and answer this question, the more complexities I discovered. Weaving all of these pieces of evidence into a narrative became a challenging task, but the personal connection and intriguing history made this a book I had to write.

Q: You state in your epilogue that one lesson that could be learned from the disaster is that 鈥渁ssigning blame, putting a dollar value on a pristine environment, and cleaning up an environmental disaster are all fruitless efforts.鈥� Why do you feel this is true?

A: Once loosed in the cold, clear waters of Prince William Sound, eleven million gallons of oil proved impossible to recover. The commitments outlined in the industry’s contingency plans may have met their legal obligations, but they were of little value in the struggle to contain crude oil as it was carried on the tides and embedded in the gravel beaches of Prince William Sound where it can still be found today.

Cleaning up the spill proved as futile as the efforts of the fishermen to hold Exxon to account for the harm done to their way of life and place on earth. Their class action lawsuit against what would become the largest and most profitable corporation in the world, failed to deliver the emotional and financial justice the fishermen sought. By 2008, when the Supreme Court’s final ruling brought an end to the legal battle, nearly 20 percent of the original plaintiffs had passed away. The ruling whittled down the punitive damages originally granted by an Anchorage jury to 10 cents on the dollar.

The fishermen’s case embodies the structural disadvantages of individuals versus powerful, repeat players in our legal and political system. Those inequities are as real as the physical properties of oil and water that makes them impossible to separate.

Q: Despite the above, you wrote that “hope arose” out of the Valdez disaster “like a phoenix from the oiled beaches of the Sound.” Would you explain?

A: After the spill, the Oil Pollution Act of 1990 mandated the formation of a Regional Citizens’ Advisory Council, funded by the oil industry. The Council brings balance to the interaction among citizens, industry and regulators. It could serve as a model for preventing future accidents in energy exploration, production and transport.

Q: Finally, what do you hope readers take away from the book?

A: I hope that readers will finish the book having been drawn in to the story of a fisherman and other Alaskans whose lives were changed by a manmade disaster 鈥� and enlightened by facts that illuminate broader problems of governance and their potential solutions.

• “” was published this month by Washington State University Press.