Tuesday, July 22, 2014

7/22/2014 Using Visibility to Estimate Air Quality Conditions

In Washington, we are fortunate that so much of our state is represented by air quality monitors although it would be impossible to have an instrument in every community or every area that may experience smoke impacts.  This post describes an alternative of using visibility to roughly estimate air quality.  (Remember that data from an actual monitor is always far more accurate.)

Our neighbors to the south (Oregon) make use of a simple method to estimate air quality conditions using visibility when you are not near a monitor (or if the nearest monitor is off line).  

Estimating visibility using the 5-3-1 Index

Determine the limit of your visual range by looking for distant targets or familiar landmarks such as mountains, mesas, hills, or buildings at known distances (miles). The visual range is that point at which these targets are no longer visible. Ideally, the viewing of any distance targets should be made with the sun behind you. Looking into the sun or at an angle increases the ability of sunlight to reflect off of the smoke, and thus making the visibility estimate less reliable. 

Once distance has been determined, follow this simple guide:
    If over 15 miles:  The air quality is generally good.

    Between 5-15 miles:  Air quality is moderate and beginning to deteriorate, and is generally healthy, except possibly for smoke sensitive persons. The general public should avoid prolonged exposure if conditions are smoky to the point where visibility is closer to the 5 mile range.

    If under 5 miles:  The air quality is unhealthy for young children, adults over age 65, pregnant women, and people with heart and/or lung disease, asthma or other respiratory illness. These people should minimize outdoor activity.

    If under 3 miles:  The air quality is unhealthy for everyone. Young children, adults over age 65, pregnant women, and people with heart and/or lung disease, asthma or other respiratory illness should avoid all outdoor activities.

    If under 1 mile:  The air quality is very unhealthy, and in some cases may be hazardous. Everyone should avoid all outdoor activities. 
Using the 5-3-1 Visibility Index
Distance you can see*
You are:
You have:
An adult 
A teenager 
An older child

Age 65 and over 
A young child

Respiratory illness 
Lung or heart disease

5 milescheck visibilityminimize outdoor activity
3 milesminimize outdoor activitystay inside
1 milestay insidestay inside

No matter how far you can see, if you feel like you are having health effects from smoke exposure, take extra care to stay inside or get to an area with better air quality.You should also see your doctor or other health professional as needed.
* less reliable under high humidity conditions

Source: Oregon Wildfire Response Protocol for Severe Smoke Episodes, version 2.0, June 3, 2014

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