How are Burn Days Decided

Placer County is divided among three different air basins, Sacramento Valley, Mountain Counties, and Lake Tahoe. The California Air Resources Board (ARB), uses specific criteria (California Code of Regulations-Title 17) to determine the burn day decisions. The Placer County Air Pollution Control District provides this information, on permissive burn days, to the public daily in the afternoon.

The criteria are based on a meteorological value called 500-millibar (mb) heights.

• The height values are obtained from 500-mb forecast weather charts.
• 500-mb heights typically average 18,300 feet above sea level.
• High 500-mb heights are related to sinking air through the air column, which tends to be more stable.
• Stability is a measure of the atmosphere’s ability to lift smoke away from the ground. A more stable atmosphere indicates less plume rise, whereas an unstable atmosphere suggests good conditions for plume rise.

Mountain Counties & Lake Tahoe Air Basin

• A no burn day is declared for the following day if the 500-millibar heights are forecasted to be greater than or equal to the specified 500-millibar height criteria listed in Title 17.
• A no burn day may be declared if there are significant smoke or ozone impacts.
• Air Resources Board Meteorologists may also declare a no burn day if he/she establishes other factors that are not conducive to burning.

Sacramento Valley Air Basin

• The stability of the atmosphere is determined by comparing minimum morning surface temperatures to temperatures aloft.
• Temperatures aloft are measured by daily aircraft soundings.
• Morning stability is calculated from the 3,000 foot temperature minus minimum surface temperature.
• Pollutant levels are also a factor in determining a no burn day. Particulate measurements are gathered throughout the Sacramento Valley.
• If the stability of the atmosphere is greater than 17° Fahrenheit and particulate measurements are elevated, a no burn day is declared.
• A no burn day may also be declared if ozone concentrations are forecasted to be unhealthy.

Rainy days are usually associated with lower 500-millibar heights. Good smoke dispersion with smoke rising upward. Rain-washes smoke particles out of the air.

Burning is allowed only on a permissive burn day and in those areas of Placer County that allow burning.

• For the Greater Auburn Area (within 12 miles) (or for cell phones) call 530-889-6868.
• All other areas of Placer County (land lines only) call 800-998-2876 toll-free.
• The Air District has established a policy in making some holidays during the burn season no burn days in Placer County.

On days when the fire danger is increased, the Air District works very closely with local fire officials to include their information in the burn day message. For more information, contact the Placer County Air Pollution Control District at 530-745-2330.