The Environmental Protection Agency is proposing to strengthen its air quality standards for sulfur dioxide — a change that reflects new concerns about the health effects of exposure to the gas.

Sulfur dioxide is one of the major components in volcanic emissions.

The new standard would revise the amount of sulfur dioxide considered safe over different periods, doing away with an annual and 24-hour standard and instead measuring one-hour levels.

The current 24-hour average standard for sulfur dioxide is 140 parts per billion and the annual average standard is 30 parts per billion. In an effort to monitor sulfur dioxide levels over shorter periods, EPA is proposing the new hourly standard be set as low as 50 parts per billion.

The changes to the National Ambient Air Quality Standard raise new health concerns for residents on the Big Island, where sulfur dioxide levels from volcanic emissions have regularly been well above current EPA standards since March 2008, when a new vent opened at Kīlauea.

ADVERSE EFFECTS

EPA officials say the proposed standards are in response to evidence linking short-term exposure to high levels of sulfur dioxide "with a range of adverse respiratory effects," increased visits to emergency rooms and hospital admissions for respiratory illnesses, especially in at-risk populations.

The effects of long-term exposure to sulfur dioxide are unknown.

The EPA last revised its air quality standards for sulfur dioxide in 1996. The guidelines are intended to alert the public when sulfur dioxide concentrations in the air start affecting health, especially in children, the elderly and those with respiratory diseases.

On the Mainland, most sulfur dioxide emissions are from power plants and industrial facilities, and the standards help the EPA clamp down on big polluters. Though there is nothing EPA officials can do to curtail emissions from Kī- lauea, which is the largest producer of sulfur dioxide in the United States, the standards help put the sulfur dioxide levels recorded in Big Island communities in context.

Those communities, including Pāhala, Na'alehu and Ocean View, get some of the highest concentrations of sulfur dioxide in the nation — and the new standards suggest that the public health concerns from that exposure could be even more worrisome than originally believed.

EPA officials stress that people shouldn't panic. Meredith Kurpius, acting chief of air quality analysis office in EPA's Region 9, which includes Hawai'i, cautioned that the standards are set at levels that protect the most vulnerable — so healthy people may not see any health effects at the current standard or the tougher proposed standard.

But, she said, the new one-hour standard would allow for fewer "peaks" during which sulfur dioxide levels are very high — since averaging those peaks out over an hour would still equate to a significant concentration (compared to averaging them out over 24 hours).

The state Health Department also computes a three-hour average, with a standard of 500 parts per billion.

From Jan. 1 to March 21, there were 190 instances on the Big Island, mostly in communities downwind of the new Kīlauea vent, when sulfur dioxide levels were recorded above EPA or state standards.

The highest recorded levels were on Jan. 20, in Pāhala, when the 24-hour average hit 520 parts per billion and a three-hour average from 3 to 6 a.m. was 1,000 parts per billion.

DATA COLLECTION

Kurpius said the new one-hour standard comes as the EPA is taking a harder look at sulfur dioxide emissions from natural sources. The EPA collects data on emissions during "exceptional events," which includes everything from volcanoes to wildfires, but does nothing with those figures.

Officials are trying to determine whether they should. That role might come in the form of ensuring states are taking the right steps to protect and educate residents about hazardous emissions.

"I do think we need to start going in that direction," Kurpius said.

"We have situations like wildfires, where they are reoccurring. If the air quality is not good, what can we do about that?"