<b><font size="4">Sulfur Dioxide Advisory Levels</font></b>

COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS

Emergency Management Office

Office of the Governor

Benigno R. Fitial, Governor

Timothy P. Villagomez, Lt. Governor

Mark S. Pangelinan

Acting Director

Sulfur Dioxide Advisory Levels

The SO₂ concentrations measured at the two monitoring sites are reviewed every 15 minutes and one of four advisory levels of health concern are assigned for that 15-minute period for each site. The four possible advisory levels are Good (with an associated advisory color of green), Moderate (yellow), Unhealthy for Sensitive People (Orange), and Unhealthy (Red). Each advisory level is associated with an increasing level of concern for human health. The meaning of the four levels are:

Good	Unusually sensitive individuals may want to limit their exposure in this area.
Moderate	Sensitive individuals may want to limit outdoor exertion, or stay indoors or in an air conditioned environment.
Unhealthy For Sensitive People	Physically active and sensitive individuals may want to limit outdoor exertion, or stay indoors or in an air conditioned environment.
Unhealthy	All individuals should limit or avoid outdoor exertion, or stay indoors or in an air conditioned environment.

Sensitive individuals can include children, the elderly, people with asthma or heart or lung disease.

Criteria for Setting Sulfur Dioxide Advisory Levels

The advisory level is determined every 15 minutes and is initially set based on the current 15-minute average SO₂ concentration at each monitoring site. If the SO₂ average is less than 300 parts per billion (ppb) the advisory level is initially set to Good (Green); if less than 500 ppb the level is Moderate (Yellow); if less than 1000 ppb the level is Unhealthy For Sensitive Groups (Orange); and if greater than or equal to 1000 ppb the level is Unhealthy (Red). The next level of checks is performed according to the criteria in the table below.

Criteria for Setting the Advisory Condition Level
Condition	SO₂ Concentration	Time Duration	Details
Good	<300 ppb	15-minute average	Can be >300 ppb for single 15-minute average
Moderate	≥300 ppb	30-minute average	Requires two consecutive 15-minute averages >300 ppb
Unhealthy for Sensitve People	≥500 ppb	15-minute average	Requires just one 15-minute average
Unhealthy	≥1000 ppb	15-minute average	Requires just one 15-minute average

For example, if the current and previous 15-minute average SO₂ concentrations are ≥300 ppb then the advisory condition is set at Moderate (Yellow) AND IT REMAINS at the Yellow level until the conditions for downgrading the advisory to a lower level in the following table are met. Similarly, if the current 15-minute average concentration is ≥ 500 ppb or ≥ 1000 ppb then the advisory is set at the Orange or Red levels, respectively. These levels also persist until the conditions for downgrading the advisory level are met.

Criteria for Downgrading Advisory Condition Level
From Condition	SO₂ Concentration	Time Duration	Details
Moderate	<300 ppb	1 hour	Downgrades to green after 1 hour if green condition (<300 ppb) persists
Unhealthy for Sensitve People	<500 ppb	1 hour	Downgrades to yellow after 1 hour if yellow condition (<500 ppb) persists
Unhealthy	<1000 ppb	3 hours	Downgrades to orange or yellow after 3 hours if orange (<1000 ppb) or yellow (<500 ppb) conditions persist

The advisory color/level resulting after all these checks are performed and the the current 15-minute average SO₂ concentration are posted on the Hawai`i Volcanoes Current Conditions web page. If this advisory color code does not appear to match the color expected from the SO₂ concentration based on the color scale on the Current Condtions web page it is due to the above advisory criteria being applied. These time durations and persistence criteria are used to limit switching between color conditions multiple times each hour.

Update: Thursday, October 04, 2007 01:42:56 PM
By:gg