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	Summer 2006

Clearing the air: DRI faculty study causes and chemistry of haze

Dr. Doug Lowenthal, left, and Dr. Mark Green work hard to change views on haze, so we can all see more clearly. Photo by Heather Emmons

Air pollution—we all know it when we see it, smell it or when it affects our health. Air pollution even may be affecting global climate, with different forms of air pollutants thought to be contributing to raising, or lowering, global temperatures. Many DRI faculty in the Division of Atmospheric Sciences (DAS) are examining the particles and chemical components that make up air pollution—specifically, haze. These researchers, along with many collaborators outside of DRI, are working to determine how to measure the various chemical and physical components found in haze and how these tiny particles interact with each other. Their research includes taking direct measurements of pollutants in the field, remotely monitoring air quality and using historical air quality data. They also are combining their findings with previous studies to complete a picture of how haze forms, how it interferes with health and visibility and even how it plays a role in the global climate.

When the weather is described as hazy, most people know that means it will be a day where you may not be able to see distant objects very well. If you live in a city, it can be a day where the tops of tall buildings are obscured, or you cannot see far down the streets. Surprisingly, although people tend to think that the air is better in the countryside, hazy days can and do occur in rural areas. In some of the more remote areas of the country, such as western Texas and Maine, haze obscures the view of areas of natural beauty, even though there may be no obvious nearby sources of air pollution.

Besides obscuring visibility, haze can affect human health and the environment. People with weak respiratory systems often are asked to stay inside on very hazy days and limit their physical exertion. Exposure to tiny particles found in different types of air pollution has been linked to increased respiratory illnesses, decreased lung function and even premature death in susceptible individuals. In addition, certain particles found in haze and other forms of air pollution can contribute to the formation of acid rain, which damages trees and plants, and makes waters unsuitable for many forms of aquatic life. Acid rain also can etch and erode limestone and marble facades of buildings and historical monuments, and can even ruin paint on cars.

Air pollutants that contribute to haze can come from natural sources, such as dust or soot from wildfires, and manmade sources, including car and truck exhaust and burning of fuel for industry, manufacturing and power generation. Haze is a form of air pollution that can be thought of as a complicated chemical stew of different kinds of tiny airborne particles which, when they interact together, act to scatter light. When light is scattered, the outlines of objects become less distinct, and this means that visibility is reduced. Because haze scatters light, it also has an impact on Earth’s radiation balance and, therefore, on climate. When sunlight is scattered by haze, it cannot penetrate Earth’s atmosphere as effectively; thus, haze may play a role in regulating temperatures around the globe.

DAS faculty member Dr. Douglas Lowenthal has been studying various aspects of haze for 15 years. He started working with fellow DAS faculty member Dr. Judith Chow studying haze in the urban areas of Tucson and Phoenix, Ariz., in the 1990s. Moving from urban to more rural haze studies, Lowenthal’s current research is focused on regional haze and the impact it has on U.S. national parks. Many of the beautiful landscapes that people have come to see in the national parks can be partially or completely obscured by haze. Imagine visiting the Grand Canyon and not being able to see across the canyon, or going to the Smoky Mountains and not being able to see the mountains. That is the impact haze can have on these vistas.

	Left: Hazy and clear days at Big Bend NationalPark in Texas. Right: Jarbidge Wilderness Area, Nev., with a visual range of less than 25 miles. Big Bend images courtesy of the National Park Service and Jarbidge images courtesy of the USDA Forest Service.

With funding from the Electric Power Research Institute (EPRI) and the U.S. Environmental Protection Agency (EPA), Lowenthal specifically studies sources and chemical and physical properties of the tiny atmospheric particles that can cause haze. Lowenthal says that one of the most important findings of his research on haze to date has to do with a new law called the EPA Regional Haze Rule. The Regional Haze Rule calls for state and federal agencies to work together to improve visibility in U.S. National Parks and Wilderness Areas. This law mandates that haze in the national parks must be reduced to natural levels by 2064—effectively restoring views in the parks that currently are obscured by haze. This law also requires states and federal agencies to develop and implement air-quality protection plans to reduce emissions of the pollutants that cause haze. The EPA is using both the chemical and physical properties of haze to check for compliance with this new law.

Because haze is a mixture of tiny particles that are in aerosol form, it has distinctive chemical and physical properties depending on what kinds of particles are present. A long-standing protocol, called IMPROVE (Interagency Monitoring of PROtected Visual Environments), estimates how hazy it is using these chemical and physical properties. Results from Lowenthal’s studies show that the way current IMPROVE protocols estimate haze needs to be changed.

“These changes are related to how we apportion haze to various sources as well as the costs of reducing pollution emissions from those sources,” Lowenthal said.

The results from Lowenthal’s research will help industries that emit pollutants determine how much they need to remediate their emissions.

Lowenthal currently is working on a project that will evaluate models used to reduce source emissions for the new EPA Regional Haze Rule. In addition, he is starting a six-year project sponsored by EPRI for detailed aerosol studies at several national parks to better define the chemical and physical properties that determine haze levels at these sites.

Another major contributor to haze studies at DRI is Dr. Mark Green, who also works on haze studies in National Parks and Wilderness Areas. Green was involved in managing the Big Bend Regional Aerosol and Visibility Observational Study (BRAVO), a field and data-analysis study to determine sources of haze at Big Bend National Park in Texas. DRI also hosts a website for the Causes of Haze Assessment (COHA) project, found at www.coha.dri.edu, which Green heads. This site gives an introduction to haze studies and presents results from data analysis of haze in U.S. National Parks and Wilderness Areas. The purpose of this site is to provide researchers with data, models and results of studies so they can understand causes of visibility impairment for more than 100 U.S. National Parks and Wilderness Areas. The information, combined with modeling results, is used to form conceptual models of causes of haze in each area.

By working with private industry, federal and state agencies, and a large number of collaborators, including other DRI faculty members, Lowenthal, Green and their co-workers are helping others understand haze and to clear the air at U.S. national parks.