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4 Environmental Analysis 4.3 Air Quality The Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (USEPA) to set National Ambient Air Quality Standards (NAAQS)for six common air pollutants. The USEPA calls these "criteria" air pollutants because it regulates them by developing health-based (primary) or environmentally based (secondary)standards. Criteria pollutants that are a concern in the SJVAB are described below. Ozone (03) is a respiratory irritant and oxidant that increases susceptibility to respiratory infections and can cause substantial damage to vegetation and other materials. Ozone is not emitted directly into the atmosphere, but is a secondary air pollutant produced in the atmosphere through a complex series of photochemical reactions involving precursor organic compounds and nitrogen oxides (NOx). Volatile organic compounds (also called reactive organic gases [ROG]) and NOx are known as precursor compounds for ozone. Significant ozone production generally requires ozone precursors to be present in a stable atmosphere with strong sunlight for approximately 3 hours. Ozone exists naturally in the stratosphere, shielding earth from harmful ultraviolet radiation. However, at ground level, ozone causes adverse health effects and is a major component of smog. High concentrations have been tied to respiratory ailments and cardiovascular disease, as well as damage to natural ecosystems, agricultural crops, and materials such as rubber, paint, and plastics. The main sources of NOx and ROGs, often referred to as ozone precursors, are combustion processes (including motor vehicle engines), the evaporation of solvents, paints, and fuels, and biogenic sources. Ozone levels usually build up during the day and peak in the afternoon hours. Ozone levels are usually highest on hot, windless summer afternoons, especially in inland valleys. Since weather conditions have a strong impact on ozone formation, ozone levels can vary significantly from day to day or from one summer to the next. Nitrogen dioxide (NO2) is an air quality pollutant of concern because it acts as a respiratory irritant. NO2 is a major component of the group of gaseous nitrogen compounds commonly referred to as NOx. A precursor t003 formation, NOx is produced by fuel combustion in motor vehicles, industrial stationary sources (such as industrial activities), ships, aircraft, and rail transit. Typically, NOx emitted from fuel combustion is in the form of nitric oxide (NO) and NO2. NO is often converted to NO2 when it reacts with 03 or undergoes photochemical reactions in the atmosphere. Aside from its contribution to 03 formation, NO2 can increase the risk of acute and chronic respiratory disease and reduce visibility. NO2 may be visible as a coloring component of the air on high pollution days, especially in conjunction with high 03 levels. The main sources of NOx emissions in the region are on-road and off-road motor vehicles and fuel combustion (SJVAPCD 2015a). Particulate Matter (PM) comprises solid particles and liquid droplets, including smoke, dust, organic compounds, soil particles, and aerosols. Particles that are 10 micrometers in diameter or smaller (also called respirable particles) are a potential human health concern because they can enter the lungs, which can affect the heart and cause adverse health effects. They can be emitted directly to the atmosphere as well as be formed in the atmosphere by chemical reactions among precursors. Some sources of PM, such as demolition and construction activities, are local in nature, while others, such as vehicular traffic, have a more regional effect. Very small particles of certain substances (e.g., sulfates and nitrates) can cause lung damage directly, or can contain adsorbed gases (e.g., chlorides or ammonium) that may be injurious to health. Particulates also can damage materials and reduce visibility. Research has indicated that there are associations Griffith Energy Storage Project 4.3-2 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023