2014-069 - Final Environmental Impact Report No. 2014-01

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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR CITY OF SANTA ANA 5. Environmental Analysis AIR QUALITY Wind Wind patterns across the south coastal region are characterized by westerly or southwesterly onshore winds during the day and by easterly or northeasterly breezes at night. Wind speed is somewhat greater during the dry summer months than during the rainy winter season. 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 other meteorological conditions, can result in very strong, downslope Santa Ana winds. These winds normally continue a few days before predominant meteorological conditions are reestablished. The mountain ranges to the east affect the transport and diffusion of pollutants by inhibiting their eastward transport. Air quality in the SoCAB 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 (SCAQMD 2005). Inversions In conjunction with the two characteristic wind patterns that affect the rate and orientation of horizontal pollutant transport, there are two similarly distinct types of temperature inversions that control the vertical depth through which pollutants are mixed. These are the marine /subsidence inversion and the radiation inversion. The combination of winds and inversions are critical determinants in leading to the highly degraded air quality in summer and the generally good air quality in the winter in the project area (SCAQMD 2005). Air Pollutants of Concern Criteria Air Pollutants Pollutants emitted into the ambient air by stationary and mobile sources are regulated by federal and state law Air pollutants are categorized as primary or secondary. Primary air pollutants are emitted directly from sources. Carbon monoxide (CO), volatile organic compounds (VOC), nitrogen dioxide (NO2), sulfur dioxide (SO2), coarse inhalable particulate matter (PMio), fine inhalable particulate matter (PMzs), and lead (Pb) are primary air pollutants. Of these, CO, SO2, NO2, PM10, and PM25 are "criteria air pollutants," which means that ambient air quality standards (AAQS) have been established for them. VOC and oxides of nitrogen (NO�) are air pollutant precursors that form secondary criteria pollutants through chemical and photochemical reactions in the atmosphere. Ozone (Oz) and NOz are the principal secondary pollutants. A description of each of the primary and secondary criteria air pollutants and their known health effects is presented below. Carbon Monoxide (CO) is a colorless, odorless, toxic gas produced by incomplete combustion of carbon substances, such as gasoline or diesel fuel. CO is a primary criteria au pollutant. CO concentrations tend to be the highest during winter mornings with little to no wind, when surface based inversions trap the pollutant at ground levels. Because CO is emitted directly from internal combustion, engines and motor vehicles Page 5.2 -2 PlaceWorkr