When it comes to air quality, few places can top Hawai’i. But if this year is like most others, in coming weeks, the islands will be visited by a high, thick brown cloud of pollutants, making its annual springtime trek from Asia to North America and points east. And precisely because Hawai’i’s high-elevation air is so clear, it provides scientists with one of the best spots in the world to view the brown cloud.
The two-mile-thick cocktail of particulates, formed during spring dust storms in the Gobi Desert, is at times dense enough to spoil the view between the neighboring summits of Mauna Loa and Mauna Kea. From the Gobi, it picks up pollutants and soot from the industrial centers of East Asia. Carried by strong westerly winds and high pressure zones, most years the plume reaches Hawai’i about a week after its creation in Asia. Two years ago the cloud missed Hawai’i altogether and headed straight across the Northern Pacific to the U.S. mainland.
Dr. John Barnes of Mauna Loa Observatory is among many to notice the brown springtime haze in the upper air of Hawai’i. Mauna Loa Observatory, operated by the National Oceanic and Atmospheric Administration, records the daily path of the plume and obtains particulate samples. Even though Hawai’i usually suffers a direct hit from the Asian cloud, it remains an ideal site for collecting information about global air pollution.
No Place Like Home
An unearthly landscape of rough ‘a’a lava blankets the terrain that lines the road to the Mauna Loa Observatory high on the northern slope of Mauna Loa, the largest active volcano in the world. At 11,000 feet above sea level and 30 miles southwest of Hilo, the observatory has been operating since 1957 as a baseline station for NOAA’s Climate Monitoring and Diagnostics Laboratory (CMDL), headquartered in Boulder, Colorado.
The lava surrounding the observatory supports little vegetation, creating near desert-like conditions. Any locally generated pollution that lingers during the day is cleared out at night by clean, cool air – called ‘free troposphere’ by scientists – that sinks down from high altitudes. These properties are unique to Mauna Loa among CMDL’s five observatories.
The observatory has four ongoing activities on the Island of Hawai’i, including an administration office in Hilo and the principal site at Mauna Loa. A third operation involves sampling air at Cape Kumukahi, the easternmost tip of the island, where trade winds, traveling thousands of miles across the open ocean, deliver air relatively untouched by land-based pollution. The fourth regular activity is collection of daily rainfall data at the Old Hilo Airport, where the observatory also launches weekly sondes, or balloons, that record ozone levels up to 37 kilometers above sea level.
The two researchers who staff the Hilo office, Barnes and physical scientist Steve Ryan, send the data collected at MLO to Boulder. The laboratory’s main mission is to obtain long-term observations and conduct research on atmospheric change. “CMDL has the largest monitoring program world-wide for both ozone destroying chemicals and greenhouse gases,” Barnes says.
Record Holders
Among atmospheric scientists, MLO enjoys respect as providing the longest continuous record of carbon dioxide concentrations. Its data, which date back to 1958, have helped scientists determine rates of increase in CO2 concentration in the global atmosphere. Having a long-term record is vital for understanding atmospheric changes. Says Barnes, “You need measurement records that are at least a few times longer than natural cycles in order to see man-made effects and know that they aren’t just natural variations. In order to measure things like global warming that have small changes, you need even longer records to be sure.”
Barnes notes that natural, or background, concentrations of CO2 are around 280 parts per million (ppm). Since the dawn of the industrial age, combustion of fossil fuels has elevated CO2 concentrations to around 350 ppm. A plot of the monthly measurements of CO2 concentrations measured at MLO shows a sawtoothed line climbing ever upwards. The annual highs occur in winter months in the northern hemisphere, when less carbon is bound up in vegetation and when cold leads to in combustion of more fossil fuels. The troughs represent summer concentrations, when more carbon is tied up in vegetation.
The MLO data have been especially useful to climate modelers wanting to show the impact of fossil fuel combustion on global warming. Their models use CO2 trends observed at MLO to predict climate change over the next 50 to 100 years based on a variety of emission scenarios.
Ozone Zone
The observatory’s measurements are not limited to carbon dioxide. It also provides much of the information used in many current studies of stratospheric ozone. The observatory measures levels of ozone from sea level to the upper limits of the stratosphere, some 25 miles out. In the years since 1964, when MLO began making ozone observations, it has recorded a 4 percent drop in stratospheric ozone levels. Altogether, the amount of stratospheric ozone has dropped about 6 percent globally since pre-industrial levels, Barnes says, adding: “We expect it to decrease another 2 percent total in the next 15 to 10 years, and then start to recover.” Over time, complete recovery of stratospheric ozone levels is possible, he says.
A key factor in recovery of ozone levels is the reduction of chlorofluorocarbons and related chemicals in the stratosphere. These chemicals, which were once widely used as aerosol propellants, refrigerants, and in the manufacture of Styrofoam, insulation, and fire extinguishers, destroy ozone when they reach the stratosphere. Curbs in their production were mandated by an international agreement in 1987, known as the Montreal Protocol. Once again, data from MLO helped document the need for the agreement. “MLO was just one site, although one of the most important, where the data were collected,” Barnes says.
— Loretta Sherwood
Loretta, a student at Ohio State University, was working with Environment Hawai`i as an intern when she wrote this article.
— Volume 14, Number 10 April 2004