Air Quality & Pollution

Scientists observe first signs of healing in the Antarctic ozone layer

NCAR scientists Doug Kinnison and Michael Mills are co-authors on a new study published today in the journal Science. This is an excerpt from a news release by the Massachusetts Institute of Technology, a UCAR member institution, about the study.This animation shows the opening and closing of the Antarctic ozone hole (dark blue) in 2015. (Animation courtesy of NASA.)June 30, 2016 | Scientists at MIT and elsewhere have identified the “first fingerprints of healing” of the Antarctic ozone layer, published today in the journal Science.The team found that the September ozone hole has shrunk by more than 4 million square kilometers — about half the area of the contiguous United States — since 2000, when ozone depletion was at its peak. The team also showed for the first time that this recovery has slowed somewhat at times, due to the effects of volcanic eruptions from year to year. Overall, however, the ozone hole appears to be on a healing path.The authors used “fingerprints” of the ozone changes with season and altitude to attribute the ozone’s recovery to the continuing decline of atmospheric chlorine originating from chlorofluorocarbons (CFCs). These chemical compounds were once emitted by dry cleaning processes, old refrigerators, and aerosols such as hairspray. In 1987, virtually every country in the world signed on to the Montreal Protocol in a concerted effort to ban the use of CFCs and repair the ozone hole.“We can now be confident that the things we’ve done have put the planet on a path to heal,” says lead author Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT. “Which is pretty good for us, isn’t it? Aren’t we amazing humans, that we did something that created a situation that we decided collectively, as a world, ‘Let’s get rid of these molecules’? We got rid of them, and now we’re seeing the planet respond.”Solomon’s co-authors include Diane Ivy, research scientist in the Department of Earth, Atmospheric and Planetary Sciences, along with researchers at the National Center for Atmospheric Research in Boulder, Colorado, and the University of Leeds in the U.K.Read the full release at MIT News.About the articleTitle: Emergence of Healing in the Antarctic Ozone Layer Authors: Susan Solomon, Diane J. Ivy, Doug Kinnison, Michael J. Mills, Ryan R. Neely, and Anja SchmidtJournal: Science, DOI: 10.1126/science.aae0061

Planes, ships and satellites: Investigating air quality in Korea

May 12, 2016 | Scientists from the National Center for Atmospheric Research are on the ground in South Korea as part of a field campaign to investigate the region's air quality. Between May 1 and June 12, NCAR scientists and their colleagues from NASA, U.S. and South Korean universities, and South Korea’s National Institute of Environmental Research (NIER) will collect observations from airborne labs, ships, satellites, and ground-based instruments. The campaign, which involves more than 580 researchers from 72 institutions, is called KORUS-AQ (Korea U.S.-Air Quality study). "These observations will help us develop a much better understanding of the various complex factors controlling air quality over the Korean Peninsula," said NCAR scientist Louisa Emmons, who is on site with KORUS-AQ. "The observations will help improve air quality models, and in turn, those models will help us interpret the current, as well as future, observations." This 2007 NASA satellite image shows a swath of air pollution sweeping east across the Korean peninsula to Japan. (Image courtesy NASA.) South Korea offers a rare opportunity to separate the diverse factors that contribute to air quality. For example, Seoul, the capital of South Korea, is one of the world's five most-populated metropolitan areas, but it is surrounded by rural, forested land. This stark separation gives scientists the ability to differentiate the components of pollution that originate from factories, tailpipes, and other human-related sources of pollution from those that originate from natural areas, including volatile organic compounds emitted by vegetation. Because the Korean Peninsula is largely isolated by bodies of water, scientists can also more easily determine what kinds of pollution blow into the region—dust and industrial pollution from China, for example—as well as what kinds of pollution blow out of the region toward Japan. From left: NCAR scientists Sam Hall, Benjamin Gaubert, Pablo Saide, Deedee Montzka, Louisa Emmons, and Andy Weinheimer. (Photo courtesy Sam Hall.) NCAR scientists are contributing to the effort in several ways. A team led by Emmons is issuing chemical forecasts of pollution transport and formation so that the scientists taking airborne measurements can decide where, or whether, to fly. The planes being used during KORUS-AQ include a NASA DC-8, a NASA King Air, and a Korean King Air operated by Hanseo University and NIER.  Two NCAR research groups from the Atmospheric Chemistry Observations  and Modeling lab are also flying instruments onboard the DC-8. One team, led by NCAR scientist Sam Hall, is measuring the amount of light available to break down compounds in the atmosphere. The second, led by NCAR scientist Andy Weinheimer, is measuring ozone and nitrogen oxides in the atmosphere. In combination with other instruments on the aircraft, these help to characterize the photochemical history, processes, and evolution of air pollution along the flight path. Follow what's happening with KORUS-AQ at the NASA Earth Expeditions blog, or watch a video about the campaign here. Writer/contactLaura Snider, Senior Science Writer and Public Information Officer

Tracking air quality from high in the sky

October 21, 2015 | NCAR scientists have demonstrated how new types of satellite data could improve how agencies monitor and forecast air quality, both globally and by region. The scientists used computer simulations to test a method that combines analysis of chemistry-climate model output with the kind of data that could be obtained from a planned fleet of geostationary satellites, each of which would view a large area of Earth on a continuous basis from high orbit. For example, with a constellation of satellites, the system could be used to measure, track, and predict the effects of pollution emitted in Asia and transported to the western U.S., or the impacts of wildfires in the Pacific Northwest on air quality in the Midwest. A high-orbit geostationary satellite could view a large area of the Earth, such as North America in this illustration, on a continuous basis. (Image courtesy NASA/Langley Research Center). "We think the new perspective made possible by geostationary sensors would provide data that is useful for everyday air quality forecasting, as well as for early warnings about extreme events, like the effects of wildfires," said NCAR scientist Helen Worden, one of the members of the research team. The NCAR team reported their test of the system's potential in a paper co-authored with a NASA scientist that appears in the journal Atmospheric Environment. Current observations are mostly taken from low-elevation, globally orbiting satellites that provide only one or two measurements over a given location per day, thus limiting critical air quality observations, such as vehicle emissions during rush hour. ­One exception is an air quality forecasting system at the National Oceanic and Atmospheric Administration that uses geostationary sensors to provide information about tiny polluting particles known as aerosols. But that system doesn't track carbon monoxide, a primary indicator of air pollution that serves as a good chemical tracer for observing how pollutants are emitted and dispersed in the atmosphere. "Carbon monoxide lives long enough—a month or two—that you can track it around the Earth," Worden said. To fill in the data gap, several countries and space agencies plan to deploy geostationary satellites by the end of the decade to observe and monitor air pollutants over North America, Europe, and East Asia. Proof of concept The team members applied a statistical technique that they and colleagues have developed over the years to analyze data obtained by an instrument aboard NASA's globally orbiting Terra spacecraft called MOPITT (Measurement of Pollution in the Troposphere). A collaboration between the University of Toronto and NCAR, MOPITT pioneered the measurement of carbon monoxide from space. Starting with MOPITT's real-world observations, the scientists then produced a data set of hypothetical observations representative of those potentially obtainable from a constellation of geostationary satellites. They visualized their results on high-resolution maps, producing results for areas as small as 2.7 miles (7 kilometers) wide that extend as high as 7.5 miles (12 kilometers) into the atmosphere. Measurements of carbon monoxide in April 2014 from the MOPITT instrument  (Measurement of Pollution in the Troposphere) aboard NASA's globally orbiting Terra spacecraft. The boxes show the observing domains for geostationary satellites and red colors indicate high levels of carbon monoxide. (©UCAR. Image courtesy Helen Worden, NCAR. This image is freely available for media & nonprofit use.) When it comes to speed and cost, the NCAR method has several advantages. A month's worth of data, about 200 million data points, can be produced in less than 12 hours using a standard desktop computer. "The model produced very realistic results on high-resolution maps at a low computational cost," said NCAR scientist Jerome Barre, who led the study. The scientists caution that there are limitations to the new system when viewing extremely polluted areas. The team accounted for the impact of clouds in their model to simulate the most realistic measurements.  Next steps A geostationary satellite positioned at about 22,000 miles above the equator will orbit in sync with the Earth’s rotation, thus remaining fixed above the same region. Measurements by the satellite's instruments can be taken many times a day. A constellation of such satellites would provide the coverage over populated regions needed to provide enough data to analyze air quality and atmospheric composition, determine whether the pollution is human-made or natural, and track its movement. In addition to carbon monoxide, instruments on these satellites would gather data on other pollutants, such as nitrogen dioxide and ozone. "Combined, those will give you good indications of the chemical conditions of the atmosphere," Barre said. That would enable scientists to track pollutants both vertically and horizontally in our atmosphere, he said, and that is "what's really needed to monitor, forecast, and manage air quality on a daily basis." About the article Jerome Barre, David P. Edwards, Helen M. Worden, Arlindo Da Silva, and William Lahoz, 2015: On the feasibility of monitoring carbon monoxide in the lower troposphere from a constellation of Northern Hemisphere geostationary satellites. (Part 1). Atmospheric Environment, 113, 63-77, doi:10.1016/j.atmosenv.2015.04.069 Writer/ContactJeff Smith, Science Writer and Public Information Officer Collaborating organizations NASA Norwegian Institute for Air Research FundersNational Science FoundationNASA

What's driving soot across India?

October 12, 2015 | As a teenager in the 1990s, NCAR postdoctoral scientist Rajesh Kumar bicycled five miles from his village north of Delhi to school. He remembers riding through clear skies and fog, but not smog. Today, Delhi ranks as the most polluted city in the world with 12 additional Indian cities in the notorious top 20, according to the urban air database released last year by the World Health Organization. In Delhi alone, small particulates averaged six times the recommended maximum, a hazard to the health especially of children and the elderly. Smog also contributes to climate change by trapping heat that otherwise would escape the atmosphere. Scientists have identified the sources and transport patterns of black carbon soot, a health and visibility problem for a dozen Indian cities, including Delhi, shown here enveloped in smog. (Photo by Jean-Etienne Minh-Duy Poirrier, Creative Commons [CC BY-SA 2.0], via Flickr.) Experiencing increased air pollution in his home country has inspired Kumar to understand more about its driving forces and remedies. Most recently, the researcher was lead author on a paper concluding that black carbon emissions—fine particles or soot caused by the incomplete burning of fossil fuels and biomass from plant or animal waste—are transported in the atmosphere across India. Only 5 percent of the emissions at any given time blow in from outside the country.   Black carbon emissions from northern India, for example, contribute up to 30 percent to black carbon pollution in southern India during the winter, the study found, while southern India makes a similar contribution to northern India during the summer monsoon season. While human activity—agricultural waste burning, use of household cook stoves, industry and vehicles—is the cause of most black carbon emissions, the seasonal cycle is driven by the monsoon weather. "What this means is that India has the power to reduce black carbon emissions significantly—but only if individual states and regions work together on mitigation strategies," said Kumar. The paper appears in the Journal of Geophysical Research – Atmospheres. A research team headed by Kumar now is conducting a simulation of how air quality is likely to change in South Asia overall by mid-century, a topic he will discuss at the American Geophysical Union’s fall meeting in December. Haze from urban and industrial pollution, as well as agricultural and wildland fires (red dots), can be seen over northern India below the Himalayan mountain range in this satellite image from October 2014. (Photo courtesy NASA.) Shining a spotlight on soot Co-author Mary Barth, an NCAR scientist, noted that attention to black carbon emissions has grown as more is known about its ability to strongly absorb solar radiation. The issue is especially of concern in densely populated areas such as the Indo-Gangetic Plain, which consists of Bangladesh and swaths of India and Pakistan. There is concern not only due to black carbon's atmospheric impacts, but also because soot that settles on snow absorbs more heat from the Sun and thus accelerates melting. Emission levels are so high in that region that there is concern about glacier melt in the Himalayas—the region's primary storehouse of water. "If you curtail black carbon emissions, you can reduce heat over the short term," Barth said. "It's something you can do while working to reduce carbon dioxide levels in the atmosphere." Black carbon has a short life span of only a week or two, while carbon dioxide molecules remain in the atmosphere for about 100 years. Prior studies have provided important information about black carbon pollution in parts of India, but they didn't detail the specifics of how the particles are transported across the country. For their observational database, the research team used monthly average black carbon concentrations reported from 21 sites representing a range of environments, including cities, semi-urban areas, and coastal areas. They also took meteorological data into account. The team then developed models for tracking air pollutants that were combined with the NCAR-based Weather Research and Forecasting Model. NCAR researcher Rajesh Kumar studies black carbon emission levels. (©UCAR. Photo by Carlye Calvin. This image is freely available for media & nonprofit use. While the computer model reproduced the seasonal cycle of black carbon emissions fairly well, it was more difficult to capture that seasonality in the complex terrain of the Himalayan region. Kumar, who also has studied the impact of ozone pollution on India's agriculture production, notes that India is taking steps to improve its air quality. Efforts include national programs to promote liquefied petroleum gas for cooking and solar power for energy production and irrigation. "I hope that in 20 years or so, India will be able to talk about its good air quality, not its pollution," Kumar said.  About the article Rajesh Kumar, M. C. Barth, G. G. Pfister, V. S. Nair, Sachin D. Ghude, and N. Ojha, 2015: What controls the seasonal cycle of black carbon aerosols in India? Journal of Geophysical Research - Atmospheres, 120, 7788-7812, DOI: 10.1002/2015JD023298 | OpenSky Dive Deeper Variability in emission levels was simulated by applying a tagging technique developed by Kumar. The technique consists of assigning 10 different values or "tracers" to standard black carbon particles in order to track the emissions from different regions and sources. For example, separate tracers were assigned to emissions from four regions of India and from outside the country to determine geographic variability. Traditionally, researchers would have done a separate simulation for each tracer, or variable. Putting all 10 tracers in the model at the same time saved a tremendous amount of computing time, Kumar said. The data, crunched by the NCAR-Wyoming Supercomputing Center's Yellowstone system, took only about a tenth the time of the traditional method. Writer/contact Jeff Smith, Science Writer and Public Information Officer Collaborating organizations Indian Institute of Tropical Meteorology Max Planck Institute for Chemistry, Germany Vikram Sarabhai Space Center, India. Funder National Science Foundation

A heads up on air quality

March 11, 2015 | Air pollution in the United States costs thousands of lives and billions of dollars every year. But what if forecasters could issue detailed air quality forecasts days in advance? Such forecasts may be coming. NCAR and its research partners recently received a $1.3 million grant from NASA to develop the capability to produce detailed 48-hour forecasts of ground-level ozone and fine particulate matter. Summer smog obscures Los Angeles. NCAR scientists are working to create a system to produce more detailed air pollution forecasts. (Photo by Massimo Catarinella via Wikipedia Commons.) This will provide an important advance to air quality forecasts, which are issued by the National Oceanic and Atmospheric Administration, or NOAA. The current forecasts provide just a single-value prediction. A forecast might state, for example, that concentrations of ozone (the chief ingredient in smog) are expected to be in the “moderate” category on the following day. But it will not specify how likely it is that ozone levels will actually turn out to be moderate. The goal for the new, three-year project is to generate more detailed, probabilistic forecasts. Just as a weather forecast, for example, might warn of a 60 percent chance of rain in the afternoon, new air quality forecasts might warn of a 60 percent chance of high ozone levels during certain times of the day. These improved forecasts offer the promise of significant benefits for society. High concentrations of ozone and fine particulates (with a diameter of 2.5 microns or less) cause respiratory and cardiovascular problems and even premature death, as well as costs associated with health care, missed work, and damage to crops and forests. Poor air quality in the United States causes as many as 60,000 premature deaths each year and costs $100–$150 billion per year, according to NOAA estimates. More detailed forecasts would enable people to plan their outdoor activities for periods of better air quality. “If the forecasts can reduce the impacts of these pollutants by even 1 percent, that would save 600 lives and more than $1 billion each year,” said NCAR scientist Luca Delle Monache, who is leading the project. “That would be more lives saved than are lost in an average year by all severe weather events combined, including tornadoes, hurricanes, and floods.” Leveraging the past to predict the future The new technology will use advanced computer models and atmospheric observations, including NASA satellite sensors. It will also incorporate a powerful technique that Delle Monache and his colleagues have developed over the past several years and successfully applied to fine-scale prediction of certain weather phenomena. The technique is being used to forecast the atmospheric conditions most conducive to generating solar and wind power, for example. The technique, known as an analog ensemble, draws on a multitude of past computer model predictions and observations to create a database of situations that are comparable to the current one. It analyzes how well those past predictions performed. The information is then applied to the current situation. This results in more detailed and accurate predictions. If all goes as planned, the research team will begin testing the new prediction technology next year. Air quality officials say they are looking forward to getting more detailed forecasts, including the first-ever estimates of probability within NOAA-issued air quality predictions. “NCAR's new forecast system promises to expand the forecasting capabilities in Delaware and the continental United States,” said Ali Mirzakhalili, director of the Delaware Division of Air Quality. “This will improve the decision making process for protecting the public health.” Writer/contactDavid Hosansky CollaboratorsNCARNASANOAAUniversity of Colorado BoulderUniversity of Maryland FunderNASA              

Cold facts of air pollution

February 2, 2015 | The difference between a breath of cold air and a breath of warm air isn’t just the temperature. It’s also the pollutants they might contain. Until now, wintertime air pollution hasn’t been studied in much detail. Scientists have focused more on warm air, partly because summertime's stagnant atmospheric conditions and intense sunshine tend to worsen ozone pollution. But that's about to change as researchers turn their attention to winter air quality in the eastern United States. The WINTER field project will focus on the Northeast urban corridor, Ohio River Valley, and Southeast Mid-Atlantic. (©UCAR. Image by Alison Rockwell, NCAR, based on NASA satellite map. This image is freely available for media & nonprofit use.) This month, a major air quality project known as WINTER (Wintertime Investigation of Transport, Emissions, and Reactivity) takes to the air to examine pollutants across the Northeast urban corridor, Ohio River Valley, and Southeast Mid-Atlantic. Scientists will home in on wintertime emissions from urban areas, power plants, and farmland, and seek to better understand the chemical processes that take place as pollutants move through an atmosphere that is not only colder but also darker than in summer. The field campaign, which runs from February 1 to March 15, is being led by scientists at the University of Washington, NOAA's Earth System Research Laboratory, University of California Berkeley, Georgia Institute of Technology, University of Colorado Boulder, and the University of New Hampshire. The research team will use the NSF/NCAR C-130, a flying laboratory equipped with more than 20 instruments to measure gases and particles. The aircraft is owned by the National Science Foundation and operated by NCAR. NCAR is also managing the project, including coordinating research flights and providing data services. Flight operations will be based at the NASA Langley Research Center in Hampton, Virginia. "Aircraft missions will occur at different times during the campaign so that the pollutant gases and reactions can be observed during the day, at night, from night into day, and day into night,” said NCAR project manager Cory Wolff. WINTER's regional differences NCAR scientist Alan Hills (right) and University of California, Irvine, graduate student Jason Schroeder operate instruments for the WINTER field project aboard the NSF/NCAR C-130. (©UCAR. Photo by Alison Rockwell, NCAR. This image is freely available for media & nonprofit use.) A number of factors affect wintertime air: colder temperatures, snow cover, lower absolute humidity, and fewer hours of sunlight. Plants tend to emit fewer chemicals, while people may emit more as they burn heating oil and other fuels to heat their homes. In addition, pollutants may travel farther because chemical reactions take place more slowly in cold air. By flying over several regions, the WINTER research team will better understand the atmospheric impacts created by different types of emissions from major cities in the Northeast and coal-fired power plants in the Ohio River Valley. The scientists will compare those emissions with data they gather in the Southeast, where winters are milder, plants have a more pronounced influence on the atmosphere, and emissions come from agricultural burning. The project’s findings will be used to provide more detailed information to decision makers and improve computer models of the atmosphere. “Wintertime pollution has not been the focus of many campaigns—most are during the spring and summer months when the Sun has maximum impact,” said Wolff. “By sampling the air in the cold and darkness of winter, the science team can get a better sense of the atmospheric chemistry of the eastern United States and compare that to other times of year. " Writer/contactDavid Hosansky CollaboratorsUniversity of WashingtonNOAA's Earth System Research LaboratoryUniversity of California BerkeleyGeorgia Institute of TechnologyUniversity of Colorado BoulderUniversity of New Hampshire FundersNational Science Foundation (NSF)National Oceanic and Atmospheric Administration (NOAA)        

Not just rain: thunderstorms also pour down ozone

January 7, 2015 | A new study in Geophysical Research Letters offers for the first time unequivocal evidence that large storms move significant amounts of ozone from the stratosphere down to the troposphere, the lowest part of the atmosphere. The finding has implications for global climate because tropospheric ozone is a powerful greenhouse gas as well as a pollutant that affects human health and the environment. The research, led by NCAR scientist Laura Pan, means that scientists may have to re-evaluate climate models with regard to the transport of ozone. Those models generally do not include the role of thunderstorms, as they deal with larger and longer-range phenomena. It was already well established that tropospheric ozone originates in significant measure in the stratosphere. But the transport was primarily attributed to jet streams and other sources of circulation. The new study has its roots in a 2012 field project, known as the Deep Convective Clouds and Chemistry Experiment (DC3), that was based in the Great Plains and focused on the impact of storms on chemical composition of the atmosphere. On the night of May 30, the research aircraft flew through a line of large thunderstorms over Kansas. One of the research aircraft, the NASA DC-8, flew just above the storms in the lower stratosphere, carrying an instrument known as a Differential Absorption Lidar, or DIAL, to measure ozone levels. A rotating supercell thunderstorm moves across northeast Colorado. Thunderstorms such as this move ozone down from the stratosphere into the lower atmosphere. (©UCAR. Photo by Bob Henson.) Pan subsequently discovered that, during that flight, the DIAL instrument recorded a phenomenon that was only hinted before but never observed in an unambiguous fashion. Above the leading edge of the eastward moving storm, DIAL registered a curtain of ozone dipping below the stratosphere, where it was relatively abundant, into the troposphere. On a graph, this ozone-rich air resembled a ram’s horn whose wide end was pushed eastward ahead of the storm and whose narrow end curved westward into the storm. By examining the DIAL data and those from other instruments, the scientists determined that the “ram’s horn,” containing 150 parts per billion by volume (ppbv) of ozone, extended down to an altitude of about 8 km—or about 4 km (~2.5 miles) into the troposphere. At the same altitudes, but away from the storm system, ozone accounted for only 60 to 100 ppbv. In addition, thin filaments of the enhanced ozone extended about 100 km from the cloud’s edge. The researchers then set out to study the ozone transport process by numerically simulating the May 30 storm. Their simulation reproduced the ram’s horn and other observations made during the flight, demonstrating that deep convective storms like the one studied are capable of perturbing the tropopause, normally a stable barrier between stratosphere and troposphere. The authors say that the phenomenon challenges global chemistry climate models, since hundreds of storms like the one observed occur over the United States every summer, adding an as yet undermined quantity of ozone into the troposphere. Further, they say, as storm behavior may change in an evolving climate, it is important to understand and incorporate this process into global chemistry-climate models. Laura L. Pan, Cameron R. Homeyer, Shawn Honomichl, Brian A. Ridley, Morris Weisman, Mary C. Barth, Johnathan W. Hair, Marta A. Fenn, Carolyn Butler, Glenn S. Diskin, James H. Crawford, Thomas B. Ryerson, Ilana Pollack, Jeff Peischl, and Heidi Huntrieser (2014), Thunderstorms Enhance Tropospheric Ozone by Wrapping and Shedding Stratospheric Air, Geophysical Research Letters, 41, 7785-7790, doi: 10.1002/2014GL061921 WriterHarvey Leifert ContactDavid Hosansky, NCAR/UCAR Communications Collaborating institutionsNASA Langley Research CenterNational Oceanic and Atmospheric Administration Earth System Research LaboratoryCooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USAInstitute of Atmospheric Physics, German Aerospace Center FunderNational Science Foundation    

Chlorine makes a comeback

November 5, 2014 | Concentrations of hydrogen chloride (HCl), the main reservoir of chlorine in the stratosphere, have increased by several percent over much of the Northern Hemisphere since 2007, a new study finds. The observed buildup in HCl is attributed to a temporary shift in atmospheric circulation, rather than to any increased emission of the chlorine-containing, ozone-destroying compounds that are banned by the Montreal Protocol. Ozone concentrations above the Arctic in March 2011 (shown above in Dobson units) reveal significant depletion. In mid-March, more than 40% of the ozone above some locations was removed.  The loss was produced by excess hydrogen chloride and persistent cold temperatures. Ozone loss over the Antarctic, often referred to as the "ozone hole," has similar chemical origins. (NASA image courtesy James Hannigan, NCAR.) A team of researchers from 15 institutions in 9 countries conducted the analysis, published in Nature this week. The authors include NCAR’s Michael Coffey and James Hannigan. Atmospheric chlorine is closely monitored because of the danger it poses to the stratospheric ozone layer, which protects people and ecosystems from harmful ultraviolet radiation. For more than 20 years, the Montreal Protocol and its extensions have restricted emissions of the chemicals most likely to damage the ozone layer, including chlorofluorocarbons (CFCs), which release chlorine atoms when they break up. “We found no evidence that new sources of chlorine are responsible for the increase in HCl,” says NCAR’s Hannigan.  “This suggests that the Montreal Protocol continues to be effective in reducing chlorine emissions, although we may see natural variations from time to time in the amount of chlorine held in the atmosphere.” The culprit for the HCl increase appears to be a temporary slowing of the Brewer-Dobson circulation, which brings stratospheric air downward over middle and high latitudes of the Northern Hemisphere in winter. As a result of this slowdown, the wintertime stratosphere air has been “older”—refreshed about every 3.4 years rather than every 3 years. This has provided more time for a larger fraction of the CFCs within the aged air to be converted into HCl. The unexpected increase in stratospheric HCl was found at a variety of latitudes across the Northern Hemisphere through the globe-spanning Network for the Detection of Atmospheric Composition Change. The result was corroborated by satellite observations and analyzed with model simulations. In the Southern Hemisphere, HCl in the stratosphere continues to decrease as expected. The study left for further analysis the question of what may be causing the post-2007 stratospheric circulation slowdown, cautioning that “such variability and its causes will have to be thoroughly characterized and carefully accounted for when evaluating trends or searching for ozone recovery.” Regardless of its origin, Hannigan noted, the current path to excess chlorine in the Arctic stratosphere creates a situation where high ozone loss can still occur. In a report issued in September, the World Meteorological Organization confirmed that most of the substances regulated under the Montreal Protocol continue to decrease. Scientists expect that ozone levels will have recovered to 1980-era values by midcentury over the Arctic and above midlatitudes in both hemispheres, with the recovery delayed somewhat over the Antarctic. E. Mahieu, M.P. Chipperfield, J. Notholt, T. Reddmann, J. Anderson, P.F. Bernath, T. Blumenstock, M.T. Coffey, S.S. Dhomse, W. Feng, B. Franco, L. Froidevaux, D.W.T. Griffith, J.W. Hannigan, F. Hase, R. Hossaini, N.B. Jones, I. Morino, I. Murata, H. Nakajima, M. Palm, C. Paton-Walsh, J.M. Russell III, M. Schneider, C. Servais, D. Smale, and K.A. Walker, Recent Northern Hemisphere stratospheric HCl increase due to atmospheric circulation changes, Nature, doi: 10.1038/nature13857 Writer/contactBob Henson, UCAR/NCAR CommunicationsCollaborating institutionsHampton UniversityJet Propulsion LaboratoryKarlsruhe Institute of TechnologyNational Center for Atmospheric ResearchNational Institute for Environmental Studies, JapanNational Institute of Water and Atmospheric Research, JapanOld Dominion UniversityTohoku UniversityUniversity of BremenUniversity of LeedsUniversity of LiègeUniversity of WollongongUniversity of TorontoUniversity of WaterlooUniversity of York FundersAustralian Research CouncilAWI BremerhavenBelgian Science Policy OfficeCanadian Space AgencyDanish Meteorological InstituteFederation Wallonie–BruxellesFonds de la Recherche Scientifique, BelgiumInternational Foundation High Altitude Research Stations Jungfraujoch and GornergraMeteoSwiss Ministry of Business, Innovation and Employment, New ZealandNASA National Oceanic and Atmospheric ResearchNational Science FoundationState Meteorological Agency, SpainUK National Environment Research Council    

Where's the atmosphere's self-cleaning power?

September 12, 2014 | In a finding that could alter how scientists quantify emissions of certain pollutants, a new study in Nature concludes that the self-cleaning power of the atmosphere does not differ substantially between the northern and southern hemispheres. The finding was surprising, as model simulations generally show that the hydroxyl molecule (OH)—the dominant “detergent” of the atmosphere that removes many pollutants by oxidizing them—is more common in the Northern Hemisphere. “This suggests we still have more to learn about this aspect of atmospheric chemistry,” said NCAR scientist Britton Stephens, a co-author of the paper. The Sun rises over Antarctica during HIPPO with the wing of the NSF/NCAR HIAPER research aircraft in the foreground. During a three-year field project, HIPPO researchers sent the Gulfstream V jet from the Arctic to the Antarctic, gathering the most extensive airborne sampling of carbon dioxide and other greenhouse gases to date. Data from HIPPO has contributed to new findings about the geographic distribution of the hydroxyl molecule, which removes many natural pollutants from the atmosphere. (©UCAR. Photo by Andrew Watt. This image is freely available for media & nonprofit use.) Because massive amounts of nitrogen oxides are emitted in the Northern Hemisphere by motor vehicles, industry, and other human-related activities concentrated there, OH has been thought to be more common in that region. The nitrogen oxides promote the formation of ozone, which in turn can react with water vapor molecules in the presence of sunlight to form OH. OH is highly difficult to measure because it exists in low concentrations and lasts for just about a second on average before reacting with pollutants and other gases. The new study, led by Prabir Patra of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), inferred OH concentrations by using measurements of methyl chloroform, a human-made chemical that is chiefly removed from the atmosphere by OH. The measurements came from two long-term, ground-based observation networks as well as from a 2009–2011 field project that deployed an advanced research aircraft owned by the National Science Foundation and operated by NCAR. The HIAPER Pole-to Pole Observations project, or HIPPO, flew from the Arctic to Antarctic, taking detailed observations of the atmosphere at a range of altitudes. The new study also drew on an advanced JAMSTEC atmospheric chemistry model. The results indicate that the northern/southern hemisphere ratio of OH is nearly equivalent at about .97, plus or minus .12. In contrast, state-of-the-art models have predicted an OH concentration that is 13-42% higher in the Northern Hemisphere. The ratio is significant as scientists have relied on OH concentration to estimate emissions of certain gases, such as methane and carbon monoxide. The estimates of these emissions in the Northern Hemisphere may need to be revised if concentrations of OH are approximately the same as in the Southern Hemisphere, the authors said. P. K. Patra, M.C. Krol, S. A. Montzka, T. Arnold, E. L. Atlas, B.R. Lintner, B.B. Stephens, B. Xiang, J. W. Elkins, P. J. Fraser, A. Ghosh, E. J. Hintsa, D. F. Hurst, K. Ishijima, P. B. Krummel, B.R. Miller, K. Miyazaki, F.L. Moore, J. Mühle, S. O’Doherty, R.G. Prinn, L.P. Steele, M. Takigawa, . J. Wang, R.F. Weiss, S.C. Wofsy, and D. Young, Observational evidence for interhemispheric hydroxyl-radical parity, Nature, doi:10.1038/nature13721 Writer/contactDavid Hosansky, NCAR & UCAR Communications Collaborating institutionsJAMSTEC, Tohoku University, Wageningen University, National Oceanic and Atmospheric Administration, Scripps Institution of Oceanography, University of Miami, Rutgers (The State University of New Jersey), National Center for Atmospheric Research, Harvard University, Centre for Australian Weather and Climate Research (Commonwealth Scientific and Industrial Research Organisation, or CSIRO), National Institute of Polar Research, Cooperative Institute for Research in the Environmental Sciences, University of Bristol, Massachusetts Institute of Technology, Georgia Institute of Technology FundersJapan Society for the Promotion of Science/Grants-in-Aid for Scientific ResearchJapan Ministry of Education, Culture, Sports, Science and TechnologyNational Science FoundationNASAEuropean Union FP7 project PEGASOSNational Oceanic and Atmospheric AdministrationCSIROU.K. Department of Energy and Climate Change                  

Ground-level ozone's toll in India

September 9, 2014 | Ozone pollution in India is damaging millions of tons of the country’s major crops, according to a new study by an international team of researchers. The pollution caused losses of more than $1 billion in a single year, destroying enough food to feed tens of millions of people living in poverty in the country. The study used crop production data and a powerful, NCAR-based computer model to estimate the impacts of ozone. It was led by scientists at the Indian Institute of Tropical Meteorology (IITM) in Pune, India, with co-authors from the Scripps Institution of Oceanography and NCAR. The research was published last month in Geophysical Research Letters, a journal of the American Geophysical Union. The researchers looked at the agricultural effects in 2005 of high levels of ground-level ozone, which damages plants and affects human health as well. They estimated that the pollutant ruined 6.7 million U.S. tons (6 million metric tons) of India’s wheat, rice, soybean, and cotton crops that year. India could feed 94 million people with the lost wheat and rice crops, about one-third of the country’s population living in poverty, according to Sachin Ghude, an atmospheric scientist at the Indian Institute of Tropical Meteorology and lead author of the new study. A traffic jam in Delhi, India. Automobile emissions in the presence of sunlight contribute to the formation of low-level ozone, a significant threat to human health and crop productivity. (Wikimedia Commons image courtesy NOMAD.) Despite air quality standards passed in the 1980s that were designed to curb industrial and vehicle emissions, pollution remains a major challenge for India. Long-term measurements of surface ozone across India—measured on the ground or by aircraft—are not available, making it difficult to get a clear picture of how levels of the pollutant have changed. But satellite-based studies show ozone has increased in the last two decades, Ghude said. To estimate ozone levels over specific regions of the country, the researchers turned to the chemistry version of the NCAR-based Weather Research and Forecasting (WRF) model. This powerful software tool enabled the researchers to simulate hourly ozone levels, based on six estimates of emissions. They then calculated the impact on yields of wheat, soybeans, cotton, and rice. Although previous studies had looked at ozone damage at local levels, the study’s authors set out to conduct the first comprehensive look at how ozone pollution has affected agriculture in India on a national level. Ghude said the new paper could help policymakers craft new ozone pollution standards and plan mitigation strategies to reduce damage to plants. NCAR postdoctoral researcher Rajesh Kumar, a co-author of the study, said India's ozone problems will likely get worse with climate change. Research has shown that warmer temperatures tend to produce higher levels of ozone. “This is a huge impact, but what we have now is not the worst-case scenario,” he said. “It will most likely get worse.” Ghude, S. D., C. Jena, D. M. Chate, G. Beig, G. G. Pfister, R. Kumar, and V. Ramanathan (2014), Reductions in India's crop yield due to ozone, Geophysical Research Letters, 41, 5685–5691, doi:10.1002/2014GL060930. Writer/ContactDavid Hosansky, NCAR/UCAR Communications Collaborating institutionsIndian Institute of Tropical Meteorology National Center for Atmospheric Research Scripps Institution of Oceanography FunderNational Science Foundation  

Pages

Subscribe to Air Quality & Pollution