Updated 3 December 2007

Atmospheric Composition
Highlights of Recent Research

Atmospheric Composition

Overview

Recent Accomplishments

Near-Term Plans

Archived News Postings (June 2000 - July 2005)

Related Sites

Calls for Proposals

For long term plans, see Atmospheric Composition Chapter of the draft Strategic Plan posted on web site of US Climate Change Science Program

Additional Past Accomplishments:

The following are selected highlights of recent research supported by CCSP participating agencies (as reported in the fiscal year 2008 edition of the annual report, Our Changing Planet).

Protecting Earth's Ozone Layer Also Helped Slow Climate Change. 1

A 1987 international agreement to reduce ozone-depleting chemicals has also slowed global warming by years, according to a new study by CCSP scientists and their colleagues. The double effect occurred because compounds that destroy the atmosphere's ozone layer also act as greenhouse gases. The ozone layer shields the Earth from harmful ultraviolet radiation. To protect this layer, nations around the world signed the Montreal Protocol in 1987 to control the production and use of ozone-depleting substances. While protecting the ozone layer, the Montreal Protocol and its Amendments have also cut in half the amount of greenhouse warming caused by ozone-destroying chemicals that would have occurred by 2010 had these substances continued to build unabated in Earth's atmosphere. The amount of warming that was avoided is equivalent to 7 to 12 years of rise in carbon dioxide (CO2) concentrations in the atmosphere during the 2000 to 2010 time frame. Earlier studies showed that continued growth in ozone-depleting substances would lead to significant warming of Earth's climate. The new analysis quantifies the near-term climate benefits of controlling these substances (see Figure 1).

Figure 1: Effectiveness of the 1987 Montreal Protocol Agreement. Past, present, and projected future abundances of ozone-depleting substances in the stratosphere show the effectiveness of the 1987 Montreal Protocol agreement that reduced worldwide use of these substances (panel a). Because ozone-depleting substances are also greenhouse gases, the Montreal Protocol and its amendments gave an early start to slowing climate warming (panel b). The left axis (Climate Warming Ability) gives the climate forcing in units of watts per meter squared (Wm-2). Credit: G.J.M. Velders, Netherlands Environmental Assessment Agency; S.O. Andersen, USEPA; J.S. Daniel, NOAA; D.W. Fahey, NOAA; and M. McFarland, DuPont Fluoroproducts.

Satellite Studies of Water Vapor and Ozone-Depleting Gas Transport. 2

Analyses of Aura satellite observations of water vapor and carbon monoxide at high altitudes, and their comparison with model calculations, show that thunderstorms over Tibet provide a pathway for water vapor and chemicals to travel from the lower atmosphere into the stratosphere. Since water vapor has a strong influence on climate, learning how it reaches the stratosphere can help improve climate prediction models. Similarly, understanding the pathways that ozone-depleting chemicals can take to reach the stratosphere is essential for understanding future threats to the ozone layer.

Improved Estimates of the Recovery of the Antarctic Ozone Hole. 3

CCSP research has improved our understanding of atmospheric motions that transport ozone-depleting substances from the lower atmosphere to the Antarctic stratosphere, showing that this transport is slower than previously estimated. As a result, the revised estimate for recovery of Antarctic ozone will occur about 15 years later than previously thought, in approximately 2065 instead of 2050. Such research during the ozone layer's recovery phase is crucial for policymakers.

Completion of International Assessment of the Ozone Layer. 4

The Scientific Assessment of Ozone Depletion: 2006

Scientific Assessment of Ozone Depletion 2006 Executive Summary

CCSP researchers played key roles in the completion of the international state-of-understanding assessment of the ozone layer, which was provided in FY 2007 to the over 190 nations (including the United States) that are Parties to the United Nations Montreal Protocol on Substances that Deplete the Ozone Layer. The Scientific Assessment of Ozone Depletion: 2006 summarizes current understanding regarding the extent of ozone depletion globally and at the poles, describes the current abundances of ozone-depleting gases in the atmosphere, assesses the future expectations for the recovery of the ozone layer and its relation to possible future climate change, and updates the past, current, and expected future status of ultraviolet radiation at the Earth's surface. CCSP researchers were prominent in the leadership, preparation, and review of the assessment—a 2-year endeavor that involved over 300 scientists from 31 countries around the globe. Global decisionmakers will consider the information in the over 500 pages of the report as they discuss possible future actions to protect the stratospheric ozone layer.

Field and Laboratory Investigations on Atmospheric Composition and Climate. 5, 6, 7

A combination of field experiments for the Mexico City area, the northeastern United States, and other regions, together with laboratory studies, have better defined aerosol formation processes, their properties, and their abundances. The studies have shown a higher than expected formation of organic aerosols within the atmosphere, which could potentially have a cooling effect. The research has also demonstrated the influence of aging and composition on aerosol properties, and the ubiquity of absorbing (warming) aerosols and black carbon in the atmosphere. The information will enable more accurate calculation of aerosol influences on climate through their absorption and scattering of light; results that will ultimately lead to more accurate model estimates of the climatic role of aerosols.

Research Indicates Importance of Anthropogenic Secondary Organic Aerosol. 5

Organic aerosol particles produced within the atmosphere, called "secondary organic aerosol" (SOA), are important to climate because they interact with sunlight and affect the energy balance of Earth's atmosphere. About 90% of secondary organic aerosol is currently believed to arise from the oxidation of natural volatile organic compounds of biological origin. Volatile organic compounds produced by human activity have therefore not been included in most modeling studies that assess the relevance of SOA to climate forcing. However, a recent study examining aerosol production in Mexico City indicates the presence of SOA production pathways not currently accounted for, and suggests that the human-caused sources of SOA are much more important than had been thought. Findings from this study (see Figure 2) show that amounts of SOA produced for any reacted amount of anthropogenic volatile organic compounds are as much as eight times greater than predicted by current models. The research will enable modelers to more accurately represent the atmospheric processes related to SOA, ultimately leading to improved climate projections.

Figure 2: Secondary Organic Aerosol (SOA) Formation in Mexico City. Current state-of-the-art models under-predict the rapid formation of large amounts of SOA. Here, data are shown from Mexico City on 9 April 2003. Solid dots indicate observations and shaded areas indicate the predicted SOA-mass concentration attributed to classes of anthropogenic volatile organic compounds, such as aromatics (red), alkenes (green), and alkanes (black). Credit: R. Volkamer, University of California, San Diego; J.L. Jimenez, University of Colorado; F. San Martini, National Academy of Sciences; K. Dzepina, University of Colorado; Q. Zhang, SUNY Albany; D. Salcedo, Universidad Autónoma del Estado de Morelos, Cuernavaca, Mexico; L.T. Molina, University of California, San Diego; D.R. Worsnop, Aerodyne Research; and M.J. Molina, University of California, San Diego (redrawn from Geophysical Research Letters with permission from the American Geophysical Union).

First Analyses from the Gulf of Mexico Climate Study. 8

Several Federal agencies, with significant university, private, and non-profit sector participation, completed a major field mission, the Gulf of Mexico Atmospheric Composition and Climate Study, in early FY 2007 and started analyzing the wealth of data that resulted from the mission. This intensive field study took place in August through October 2006 in the Texas/ northwestern Gulf of Mexico region and was focused on providing a better understanding of the sources and atmospheric processes responsible for the formation and distribution of ozone and aerosols in the atmosphere and the influence that these species have on the radiative forcing of climate regionally and globally, as well as their impact on air quality, human health, and regional haze. Rapid synthesis reports on the data were produced within the first few weeks after completion of the mission, an unprecedented turnaround time for communication of the results of a field mission. Early findings are helping to improve the simulation of the radiative forcing of climate change by lower atmosphere ozone and aerosols.

Models Evaluated Using Saharan Dust Storm Data. 9

A large Saharan dust storm raged across the North African desert in March 2006, the largest storm in the last several years. The event was captured by ground-based instruments of the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) that were deployed in Niamey, Niger, during 2006, as well as by instruments flown onboard the Meteosat-8 geostationary satellite platform, and instruments onboard the Terra and Aqua polar-orbiting satellite platforms. The combination of AMF and satellite observations provides the first well- sampled direct evaluations of the effects of the dust storm on solar and thermal radiation across the atmosphere, allowing researchers to test their understanding of how dust affects the radiant energy budget of the atmospheric column. This information is a key component in computer models that simulate both regional and global weather and climate.

Field and Modeling Studies of Aerosols and Clouds. 10,11, 12

A significant but inadequately understood area of climate research involves the effects of aerosol on cloud formation, cloud properties, and cloud lifetimes. An analysis of results from an interagency field experiment, the Cloud Indirect Forcing Experiment, indicates that an increase in aerosol produces higher concentrations of small drops in certain types of maritime clouds. Aircraft and satellite observations of the changes to the maritime clouds show that these microphysical effects result in brighter clouds that have a cooling effect by reflecting more of the incident sunlight back to space. In other CCSP studies, modeling of the effect of carbonaceous (soot-like) aerosol showed a reduction in cloudiness with increasing aerosol amount, as a result of aerosol absorption modifying the heating of the surface and the atmosphere. Finally, another modeling study showed no evidence for aerosol increasing the lifetime of individual cumulus clouds as is usually hypothesized. CCSP researchers also completed a FY 2007 field campaign over the U.S. Southern Great Plains to study the interactions of atmospheric aerosols and fair weather cumulus clouds downstream of a midsize urban area (Oklahoma City), the Cumulus Humilis Aerosol Processing Study (CHAPS). Observations from this campaign will aid in development and evaluation of climate model parameterizations of cloud-aerosol processes. CHAPS involved coordination of experiments between the CCSP Atmospheric Composition and Global Water Cycle Interagency Working Groups.

Phytoplankton Emissions and Cloud Properties over the Southern Ocean. 13

Researchers have long thought that emissions from marine phytoplankton influence aerosols and clouds, but evidence for how this natural process occurs has been scarce. With satellite remote-sensing data and a cloud parcel model, CCSP researchers have shown that over a large area of the Southern Ocean, phytoplankton blooms are correlated in space and time with increases in cloud droplet concentrations and decreases in effective cloud droplet radius. The modeling study showed that the changes in cloud properties could be attributed to the formation of organic aerosol particles arising from the oxidation of a hydrocarbon (isoprene) that is emitted by phytoplankton. This effect seems to act in concert with sulfur emissions from phytoplankton, which have previously received much greater attention.

Ocean

Additional Past Accomplishments:

References

1) Velders, G.J.M., S.O. Andersen, J.S. Daniel, D.W. Fahey, and M. McFarland, 2007: The importance of the Montreal Protocol in protecting climate. Proceedings of the National Academy of Sciences, 104, 4814-4819, doi:10.1073/pnas.0610328104.

2) Fu, R., Y. Hu, J.S. Wright, J.H. Jiang, R.E. Dickinson, M. Chen, M. Filipiak, W.G. Read, J.W. Waters, and D.L. Wu, 2006: Short circuit of water vapor and polluted air to the global stratosphere by convective transport over the Tibetan Plateau. Proceedings of the National Academy of Sciences, 103, 5664-5669.

3) Newman, P.A., E.R. Nash, S.R. Kawa, S.A. Montzka, and S.M. Schauffler, 2006: When will the Antarctic ozone hole recover? Geophysical Research Letters, 33, doi:10.1029.2005GL025232.

4) WMO, 2007: Scientific Assessment of Ozone Depletion: 2006. Global Ozone Research and Monitoring Project–Report No. 50. World Meteorological Organization, Geneva, Switzerland, 572 pp.

5) Volkamer, R., J.L. Jimenez, F. San Martini, K. Dzepina, Q. Zhang, D. Salcedo, L.T. Molina, D.R. Worsnop, and M.J. Molina, 2006: Secondary organic aerosol formation from anthropogenic air pollution: Rapid and higher than expected. Geophysical Research Letters, 33, L17811, doi:10.1029/2006GL026899.

6) Quinn, P.K., T.S. Bates, D. Coffman, T.B. Onasch, D. Worsnop, P.D. Goldan, W.C. Kuster, T. Baynard, J.A. de Gouw, J.M. Roberts, B. Lerner, and A. Stohl, 2006: Impact of sources and aging on submicrometer aerosol properties in the marine boundary layer across the Gulf of Maine. Journal of Geophysical Research, 111, D23S36, doi: 10.1029/2006JD007582.

7) Gao, R.S., J.P. Schwartz, K.K. Kelly, D.W. Fahey, L.A. Watts, T.L. Thompson, J.R. Spackman, J.G. Slowik, E.S. Cross, J.-H. Han, P. Davidovits, T.B. Onasch, and D.R. Worsnop, 2007: A novel method for estimating light-scattering properties of soot aerosols using a modified single-particle soot photometer. Aerosol Science and Technology, 41, 125-135.

8) See esrl.noaa.gov/csd/2006.

9) Slingo, A., T.P. Ackerman, R.P. Allan, E.I. Kassianov, S.A. McFarlane, G.J. Robinson, J.C. Barnard, M.A. Miller, J.E. Harries, J.E. Russell, and S. Dewitte, 2006: Observations of the impact of a major Saharan dust storm on the Earth's radiation budget. Geophysical Research Letters, 33, L24817, doi:10.1029/2006GL027869.

10) Jiang, H. and G. Feingold, 2006: Effect of aerosol on warm convective clouds: Aerosol-cloud- surface flux feedbacks in a new coupled large eddy model. Journal of Geophysical Research, 111, doi:10.1029/2005JD006138.

11) Jiang, H., A. Xue, G. Teller, G. Feingold, and Z. Levin, 2006: Aerosol effects on lifetime of shallow cumulus. Geophysical Research Letters, 33, doi:10.1029/2006GL026024.

12) Wilcox, E.M., G. Roberts, and V. Ramanathan, 2006: Influence of aerosols on the shortwave cloud radiative forcing from North Pacific oceanic clouds: Results from the Cloud Indirect Forcing Experiment (CIFEX). Geophysical Research Letters, 33, L21804, doi:10.1029/2006GL027150.

13) Meskhidze, N. and A. Nenes, 2006: Phytoplankton and cloudiness in the Southern Ocean. Science, 314, 5804, doi:10.1126/science.1131779.

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Atmospheric Composition Highlights of Recent Research