Categorized | Sci-Tech

Volcano Watch: Reduced sulfur dioxide emissions from Kilauea’s east rift

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

Like the delicate interplay between the Spanish and Dutch soccer players in the final game of the World Cup, competing forces shape our island environment and control prevailing conditions.

For example, volcanic air pollution in Hawaii is a function of the amount and location of sulfur dioxide (SO2) and other gases emitted from Kilauea, and of the weather conditions controlling the geographic fate of these emissions.

Recent data suggest that a period of improved air quality in leeward Hawaii has persisted since late spring, as compared with that of the previous six months. This reprieve is coincident with a notable decrease in SO2 gas emissions measured from east rift eruptive vents.

Gas emissions from the eruptive vent within Halemaumau Crater at Kilauea’s summit have not changed significantly during this time. The current combined SO2 emissions from the summit and rift of Kilauea are similar to those measured previously; however, the relative contribution of SO2 from the east rift has decreased, and those from the summit have increased.

The change in gas release distribution has altered the severity of the impact on communities.

Not surprisingly, episodes of improved air quality in Kona have occurred during previous lulls in activity from the east rift zone. Reports from observant Kona residents during a 12-day eruptive pause and decrease in emissions in June 2007 suggest improved air quality on the leeward coast.

Generally, during decreased east rift activity, no lava flows enter the sea; thus, the acidic ocean entry plume is absent, as well. And while this plume predominantly impacts the environment within a few miles of the entry, the absence of an ocean entry plume cannot be ruled out as a contributing factor to improved air quality farther downwind.

A reduction in the Halemaumau summit vent activity may also contribute to improved air quality downwind. The period of quiet at the summit vent from July to mid-August 2009 coincided with steady summer trade winds, which blow emissions to communities such as Pahala and Kona. Hawaii State Department of Health data show that very poor air quality days for these communities from July through August 2009 were far fewer than during the same period in 2008.

One objective measure of air-quality conditions is the number of days that the federal health standards for sulfur dioxide gas and fine particulate matter (PM2.5) are exceeded in various communities. The composition of volcanic pollution varies in the relative amounts of SO2 gas and particulate matter, depending upon distance from volcanic vents and atmospheric conditions.

The Kona communities are predominantly exposed to particulates, because of the chemical conversion of gas to particles on the many-mile journey to the leeward side of the island.

West Hawaii residents recently breathed a clean air sigh of relief. From April through June 2010, there were no days during which the PM2.5 standard was exceeded at the monitoring site in South Kona. This contrasts with the previous 6 months, when the PM2.5 health standard was exceeded on 10 days. For as many as 7-8 of these days, wild fires contributed to the particulate load, as well.

Since the summit vent opened in March 2008, exceedances of the PM2.5 standard have ranged from zero to 6 days each quarter. While the readily visible particles have repeatedly exceeded federal standards, the SO2 gas standard has not been exceeded in South Kona.

Pahala also had improved air quality during the 2nd quarter of 2010, with no exceedances of the PM2.5 standard and only 8 days on which the SO2 standard was exceeded. This contrasts with the previous 6-month period, when the SO2 standard was exceeded on 31 days and the particle standard exceeded on one day.

In Pahala, exceedances of the gas and particle standard have ranged from 1 to 17 days and 0 to 9 days, respectively, on a quarterly basis. Prior to the opening of the summit vent, no exceedances of federal health standards were measured in Pahala or in Kona.

For more information on the exceedance of air quality standards, see the Hawaii State Department of Health’s web page at hawaii.gov/health/environmenta…

A list of protective actions for reducing the impacts of volcanic air pollution is posted by the American Lung Association at www.ala-hawaii.org

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