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7.B. - Page 67 Redwood City Chapter 4.Environmental Impact Analysis Environmental Setting Climate The project site is located in San Mateo County within the San Francisco Bay Area Air Basin (SFBAAB).Climate within the SFBAAB is characterized by moderately wet winters and dry summers.Climate in the project area is affected by marine air flow and the County's close proximity to the San Francisco Bay. Bay breezes push air onshore during the daytime and draw air from the land offshore at night.During the summer months,the Bay helps to cool the warm onshore flows, while during the winter months,it warms the air.This mediating effect keeps temperatures relatively consistent throughout the year. However,the Bay wind patterns can concentrate and carry pollutants from other cities to the area,adding to the locally emitted pollutant mix(Bay Area Air Quality Management District 2011). Overview of Pollutants The air quality management agencies of direct importance in the project area are the U.S. Environmental Protection Agency(EPA),the California Air Resources Board (ARB),and BAAQMD. The EPA and ARB have established national ambient air quality standards (NAAQS) and California ambient air quality standards (CAAQS),respectively,for the following six criteria pollutants: carbon monoxide (CO); nitrogen dioxide (NOa); sulfur dioxide(SOa); ozone (03);lead; and particulate matter(PM),including PM less than or equal to 10 microns in diameter(PM10) and PM less than or equal to 2.5 microns in diameter(PM2.5). Ozone and NOa are considered to be regional pollutants, as these pollutants affect air quality on a regional scale.Pollutants such as CO3 SOa,and lead are considered to be local pollutants.PM is considered both a regional and a local pollutant. The pollutants of concern in the San Mateo County are ozone and PM because they are designated as nonattainment for the NAAQS and CAAQS in the San Mateo County.The following discussion describes these criteria pollutants.Toxic air contaminants (TACs) are also discussed,although there are no established federal or state standards for these pollutants. Ozone is a nearly colorless,odorless gas that irritates the lungs and damages materials and vegetation. Ozone is not emitted directly into the air,but is formed by a photochemical reaction in the atmosphere.Ozone precursors,which include reactive organic gases (ROG) and nitrogen oxides (NOx),react in the atmosphere in the presence of sunlight to form ozone. Because photochemical reaction rates depend on the intensity of ultraviolet light and air temperature,ozone is primarily a summer air pollution problem. ROG and NOx are emitted by mobile sources and by stationary combustion equipment. Carbon monoxide is a highly toxic,odorless,colorless gas that binds to hemoglobin in the bloodstream in the place of oxygen molecules. By reducing the oxygen-carrying potential of blood, CO causes heart difficulties in people with chronic diseases,reduces lung capacity,impairs mental functioning by interfering with the transfer of oxygen to the brain,and may aggravate arteriosclerosis.Motor vehicles are the dominant source of CO emissions in most areas.High CO levels develop primarily during winter when periods of light winds combine with the formation of ground-level temperature inversions (typically from the evening through early morning).These conditions result in reduced dispersion of vehicle emissions. Motor vehicles also exhibit increased CO emission rates at low air temperatures. Addendum No.2 to the Environmental Impact Report for 4 ZZ September 2012 the Redwood City Costco Wholesale Project ICF 00154.12