Volcano Watch — How does East Hawaii get vog?

Over the past several weeks, many east Hawaii residents have noticed the high frequency of days with poor air quality. People traveling on Highway 11 through the Glenwood/Volcano area have encountered such severe bog that they had to turn on their car lights to navigate through the hazy gloom.

Last week in Volcano Watch, we discussed volcanic gases produced by Kīlauea and the impact of volcanic smog or “vog” on the Kona side of the island during steady tradewind (northeasterly) conditions. This week we will discuss the effects of volcanic gases on air quality, focusing on information from a local air-quality monitoring project and what it tells us about the conditions that intensify vog in east Hawai‘i.

Air Quality on the Big Island became a significant issue in 1986, when the eruption of Kīlauea Volcano changed from a state of periodic fountaining of lava and gas at Pu‘u ‘Ō‘ō to one of continuous effusive activity which persists through today. During the episodic activity of Pu‘u ‘Ō‘ō, enough time elapsed between fountaining events for trade winds to blow any collection of volcanic gas away from the island. Currently, the daily release of roughly 350-1,600 tons of SO₂ from Kīlauea provides a continuous supply of gas from several degassing sources that accumulates and results in volcanic air pollution. For comparison with man-made pollution, Environmental Protection Agency regulations call a source that emits as little as 0.25 tons per day a “major source” of pollution.

One graphic example of the effects of SO₂ on the environment can be seen in Ka‘ū Desert. Although this area is sparsely vegetated, the average annual rainfall is between 40 and 50 inches, roughly the same as the Nā‘ālehu/Wai‘ōhinu area. The desert conditions in this case are not due to an arid environment, but a number of factors, including the acidity of the rain that falls in this area. During prevailing trade-wind conditions, SO₂and other gases from the caldera area blow over the Ka‘ū desert. The SO₂ is oxidized to sulfuric acid, and rain with a pH as low as 2.0 is created.

Sulfur dioxide is considered an irritant that can cause inflammation of lung tissue. Health effects include bronchial constriction and reduced mucus clearance from the lungs. These effects reportedly occur at higher concentrations and for longer periods of exposure than are normally experience din the publicly accessible areas of the volcano. The health effects of vog, formed when SO₂ reacts chemically to form a mixture of sulfate-aerosols, sulfuric acid and other oxidized sulfur species, are not well documented. However, on Hawaii, many people report headaches and tiredness during extended periods of poor air quality.

The U.S. Geological Survey, in cooperation with the National Park Service, operates on air quality monitoring station that was established in 1986. This site, located behind park headquarters in Hawai‘i Volcanoes National Park, is part of a nationwide network of stations intended to monitor man-made air pollution, However, in our case, continuous monitoring of SO₂ gas, wind speed, and wind direction near the actively degassing areas of the Kīlauea summit provides an important record of the effects of eruptive activity on air quality.

The data from this monitoring project show that high SO₂ days at this site are accompanied by low-speed winds from the southwest or east, confirming that wind speed and direction have a critical effect on SO₂ levels. Halema‘uma‘u crater is just 4 km to the southwest of the station, and the current east rift eruptive site is 16 km to the east-southeast, so when winds blow from either of these directions, the station is directly downwind. When wind speed is persistently low, gas is able to accumulate hour after hour without being dispersed, resulting in high levels of SO₂.

From 1997-1991, SO₂ levels at the NPS-USGS air quality monitoring station exceeded the EPA primary health standard of 0.14 parts per million (ppm) on 40 separate occasions. In the past three weeks, persistently light variable winds and Kona winds have caused levels at this site to exceed this standard twice. On Sept. 22 and Oct. 4, 24-hour averages were 0.20 ppm and 0.28 ppm, respectively, the most frequent occurrence of extreme levels of SO₂ in the past two years.

Conditions that cause high SO₂ levels at the monitoring site in the National Park also create conditions for vog in east Hawaii. The major degassing vents on Kīlauea are south and southwest of the Hilo, Kea‘au and Pāhoa areas, so when winds are from the south and southwest, these areas—although farther form the source—are also downwind of the fume. Vog episodes that affect the Hilo area are generally not as intense along the Hāmākua coast because of the greater distance from the vents and because of the local wind patterns. The persistently light, variable winds of the past several weeks are also conducive to vog conditions and are responsible for the high frequency of voggy days recently in east Hawai‘i.

Here is an easy method for approximating low wind speeds and forecasting vog conditions east east Hawai‘i. When the wind is 4-7 mph, leaves at the tops of the trees will rustle, and a breeze can be felt on your face. If the wind speed is so low that these conditions are not detected, and the wind direction is persistently from Kona or variable, the chances are good that east Hawai‘i will experience vog.