2009-034 (2) - Final Supplemental Environmental Impact Report for Fairhaven/Lincoln

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S, Environmental Analysis AIR QUALITY sea breezes. This usually mild weather pattern is interrupted infrequently by periods of extremely hot weather, winter storms, and Santa Ana winds. Temperature and Precipitation The annual average temperature varies little throughout the BocAB, ranging from the lorry to middle 60s, measured in degrees Fahrenheit (OF). With a more pronounced oceanic influence, coastal areas show less variability in annual minimum and maximum temperatures than inland areas. The climatological station nearest to the site in Banta Ana reports a yearly average of 52 °F, The average low is reported at 42.9 °F in ,January while the average high is 84.6 °F in August v RCC 2008). In contrast to a very steady pattern of temperature, rainfall is seasonally and annually highly variable. Almost all rain falls from November through April. Summer rainfall is normally restricted to widely scattered thundershowers near the coast with slightly heavier shower activity in the east and over the mountains. Rainfall averages around 1 3.71 inches per year in the project area, as measured in Santa Ana (WRC C 2008). Humidity Although the BoAB has a semiarid climate, the air near the surface is typically moist because of the presence of a shallow marine layer. Except for infrequent periods when dry, continental air is brought into the o AR by offshore winds, the ocean effect is dominant. Periods of heavy fog, especially along the coastline, are frequent; and low stratus clouds, often referred to as high fog, are a characteristic climatic feature. Annual average humidity is 70 percent at the coast and 57 percent in the east portions of the SoCAB, Wind Wind patterns across the south coastal region are characterized by westerly and southwesterly onshore winds during the day and easterly or northeasterly breezes at night. wind speed is somewhat greater during the dry summer months than during the rainy winter season;. Annually, typical winds in the project area average about 5 to 8 miles per hour during the day and 2 to 5 rn iles per hour during the night. Between periods of wind, periods of air stagnation may occur, both in the morning and evening hours. Air stagnation is one of the critical determinants of air quality conditions on any given day. During the winter and fall months, surface high- pressure systems over the SoCAB, combined with ether meteorological condition , can result in very strong, down slope Santa Ana winds. These winds normally continue a ferny days before predominant meteorological conditions are reestablished. The mountain ranges to the east affect the transport and diffusion of pollutants by inhibiting the eastward transport of pollutants. Air quality in the So AB generally ranges from fair to poor and is similar to air quality in most of coastal southern California. The entire region experiences heavy concentrations of air pollutants during prolonged periods of stable atmospheric conditions. Inversions in conjunction with the two characteristic rrw ind patterns that affect the rate and orientation of horizontal pollu- tant transport, there are two similarly distinct types of temperature inversions that control the vertical depth through which pollutants are rnixed. These inversions are the marine /subsidence inversion and the radiation inversion. The height of the base of the inversion at any given time is no ern as the "mining height." The combination of winds and inversions are critical determinants in leading to the highly degraded air quality in surnmer and the generally good air equality in the winter in the project area. Page .1- a The Planning Center arch 2009 Resolution No. 2009 -034 Page 52 of 130