3.12 Air Quality
AIR QUALITY
3.12
This section provides an overview of the air quality in the San Diego region. It is not necessary or possible
to describe air quality at each of the specific borrow sites or receiver sites. Since potential air quality
impacts are addressed in terms of compliance with federal or state regulations, those regulations are
discussed in this section.
3.12.1 Environmental Setting, Climate and Meteorology
The receiver and borrow sites are located in the San Diego Air Basin (SDAB), which is contiguous with
San Diego County. The climate of San Diego County is characterized by warm, dry summers and mild,
wet winters. One of the main determinants of the climatology is a semi-permanent high-pressure area (the
Pacific High) in the eastern Pacific Ocean. In the summer, this pressure center is located well to the north,
causing storm tracks to be directed north of California. This high-pressure cell maintains clear skies for
much of the year. When the Pacific High moves southward during the winter, this pattern chances, and
low-pressure storms are brought into the region, causing widespread precipitation. In San Diego County,
the months of heaviest precipitation are November through April, averaging about 9 to 14 inches annually.
The mean temperature is 62.2F, and the mean maximum and mean minimum temperatures are 75.7F and
48.5F, respectively.
The Pacific High also influences the wind patterns of California. The predominant wind directions at
MCAS Miramar are westerly and west-southwesterly during all four seasons, and the average annual wind
speed is 5.6 mph.
A common atmospheric condition known as a temperature inversion affects air quality in San Diego.
During an inversion, air temperatures get warmer with increasing height rather than cooler. Subsidence
inversions occur during the warmer months (May through October) as descending air associated with the
Pacific high-pressure cell comes into contact with cool marine air. The boundary between the layers of air
represents a temperature inversion which traps pollutants below it. The inversion layer is approximately
2,000 feet MSL during the months of May through October. However, during the winter months
(November through April), the temperature inversion is approximately 3,000 feet MSL. Inversion layers
are important elements of local air quality because they inhibit the dispersion of pollutants, thus resulting in
a temporary degradation of air quality.
Regional Beach Sand Project EIR/EA
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