EXHIBIT 4-2_55A_BRISTOL WIDENING TECHNICAL STUDIES

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3.0 AIR QUALITY ANALYSIS 3.1 Existing Ambient Air Quality Primary pollutants are those emitted directly from a source and include carbon monoxide (CO), nitric oxide and nitrogen dioxide (DTO and NO2), sulfur dioxide (SO2), particulates (TSP), and various hydrocarbons (THC). Secondary pollutants are created with the passage of time, in the air mass, and include ozone (03), photochemical aerosols, peroxyacetylnitrate (PAN), and nitrogen dioxide (NO2). The area of potential environmental impact (APEI) is located within the South Coast Air Basin [SCA.W. The air quality of the basin is determined by the primary pollutant emissions added daily, and by the primary and secondary pollutants already pres- ent,in the air mass. oxidants (90% of which are ozone) represent the major air quality problem basinwide. Ambient air quality in the vicinity of the proposed project is a function of the primary pollutants emitted locally and the exist- ing regional ambient air quality. It is also determined by the meteorological and topographic factors which influence the intru- sion of pollutants into the area from sources outside the im- mediate vicinity. Climate and Meteorology The study area has a mediterranean climate with warm summers, maid winters and moderate rainfall. The land /sea breeze is the primary factor affecting the region's mild climate. The daytime winds are sea breezes predominantly from the west which flow at relatively low velocities. These sea breezes exhibit velocities below 15 mph approximately 95 percent of the time, and below 4 mph about half of the time, with an average velocity of 5 to 7 mph. During the night, the winds across the basin usually reverse direction. These land breezes flow from the east at 1 to 2 miles per hour. l Average monthly temperatures recorded in the vicinity of the APEI at the Santa Ana Fire station range from 57 degrees Fahrenheit in January to 75.8 degrees Fahrenheit in July. Temperature extremes range from a high of 101 degrees during August to a low of 36 degrees in December. Precipitation averages about 12.49 inches annually in the vicinity, with nearly 90 percent occurring be- tween November and March. 1. Source: SCAQM D, "Air Quality Handbook ", December 1983. Refer to page 1 of the Appendix for additional information related to meteorological conditions affecting the disper- sion and transport of air pollutants. 2. Source: NOAA, "Climatological Data Annual Summary ", 1985. t 3 -1