Colorado State Scientists Study Sun’s Radiation to Track Pollution Sources

Colorado State University scientists are studying the reduction of solar ultraviolet radiation by atmospheric particles to learn how the various sources of pollution – biomass burning, auto exhaust and oil refining – affect the atmospheric chemistry and air quality of Mexico City. This particular technique will be used along with data retrieval from satellites around the world to study the influence of pollution on global warming and climate change.

This research allows Colorado State scientists to trace the location of where the air people breathe originally came from by studying the optical properties of aerosols along with computer forecast models.

Aerosols are tiny airborne solid particles consisting of acids, water, black carbon or dust. The aerosols change the amount of solar radiation reaching the earth’s surface as well as modify the heating and circulation in the atmosphere. Scientists emphasize the importance of distinguishing naturally occurring aerosols from volcanoes, dust storms, sea salt spray and forest fires as opposed to aerosols induced by human activity such as burning fossil fuels.

"Aerosols contribute to human health problems such as emphysema and respiratory problems," said Jim Slusser, Colorado State senior scientist and director of the UVB Monitoring and Research Program. "It is only when strict mitigation, regulatory standards and stiff fines for non-compliance were pushed through Congress that U.S. cities began to reduce harmful sulfur and black carbon aerosols. The data from our research will help decision makers in Mexico choose between various mitigation and adaptation strategies in regards to the dense pollution."

Since 1992, Colorado State scientists have created research stations in 26 states to measure ultraviolet radiation and to determine its effects on agriculture and human health. The U.S. Department of Agriculture funds the $1.85 million UVB Monitoring and Research Program, or UVMRP, in Colorado State’s Natural Resource Ecology Laboratory, based in the Warner College of Natural Resources.

Solar measurements from the UV to the near infrared are made every three minutes at 36 climate stations established by Colorado State. This critical information – unavailable from any other source – is used by researchers at USDA, NASA, NOAA and EPA.

In early March 2006, scientists from all over the world and more than 80 academic institutions and federal agencies made measurements to quantify the various chemical, radiative and dynamical factors associated with air quality in Mexico City. The project is funded by a National Science Foundation grant.

As a nation, Mexico has very little regulation on emissions from oil refineries, transportation, biomass burning and power generation. As a result, Mexico City often is engulfed in ozone and aerosol pollution. At times, even surrounding rural areas are extremely hazy due to biomass burns. Ozone results when solar UV rays are absorbed by hydrocarbons and nitrogen oxides.

Slusser and Andres Hernandez, a graduate student in Mexico City, collected measurements of the optical properties of aerosols from three sites within 50 kilometers of Mexico City.

The unique instrumentation of the UVMRP allows separate measurement of the direct sun beam as well as scattered radiation from the rest of the sky. These capabilities allow scientists to deduce the optical properties of aerosols and in many cases identify the point sources of air pollution.

"Aerosols can either cool or warm the planet depending largely on the amount and proportion of radiation that they scatter rather than absorb. With sufficient sites, we can use our instrumentation, combined with satellite retrievals, to make measurements to validate global models on mitigation strategies for reducing the greenhouse warming aerosols around the world. As in the case of ozone depletion, this effort will require participation with scientists, government and industry.

"Less absorbing aerosols will result in more damaging UV and greater production of tropospheric ozone. The Mexicans are in a dilemma in that even if they cleaned up the soot and black carbon from the diesel exhaust, the now scattering aerosol will result in more potential damaging UVB and ozone," Slusser said.

In the next 10 years, scientists hope to apply this technique to a broad global network of major cities and provide information to policy makers and other scientists about human-induced climate change.

"The aerosol work that we performed in Mexico City is relevant to climate modelers who need to understand the influence of mega cities in developing countries such as Mexico on climate change. Climate modelers will need our UVB and visible solar radiation data to validate their computer models. Most models predict greater and greater extremes in weather – precipitation, wind, storms and temperature.

"The UVMRP produces the world’s most extensive time series of solar radiation. This record becomes ever more useful as it is extended. Eventually we will be able to separate cyclical influences such as El Nino and the solar cycle from trends and year-to-year variability," Slusser said.

In November 2006, Slusser and Barry Lefer from the University of Houston were awarded a grant from the EPA to study Houston’s pollution using the pollution aerosols technique.

UVB is a narrow range of the sun’s energy that is only partially absorbed by the ozone layer and can damage biological organisms. Ultraviolet light is a more energetic portion of the spectrum than light that is visible to the naked eye. It is separated into three groups: UVA, which is not damaging to organisms; UVB, which is known to damage DNA and result in mutations; and UVC. Unlike UVB, harmful UVC rays are absorbed entirely by the ozone.

During the past 11 years as director of the UVMRP, Slusser has doubled the number of staff and published more than 40 peer reviewed research papers. He obtained his doctoral degree in atmospheric science at the University of Alaska where he studied trace gas influence on artic ozone depletion. He completed his post-doctorate work in atmospheric chemistry at Cambridge, England. His interests include aerosol/cloud interaction, changes in cloud cover and precipitation and blues guitar.