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  • Preliminary Engineering / Environmental Impact StatementNorthwest Corridor LRT Line to Irving and DFW Airport

    Draft Environmental Impact Statement 3 - 44Chapter 3 Affected Environment

    3.4 AIR QUALITYThis section provides an overview of the airborne pollutants of interest; air quality standards andthe regulatory setting; existing air quality and National Ambient Air Quality Standard (NAAQS)compliance; regional attainment and conformity status; and transit air quality criteria along theDART Northwest Corridor Light Rail Line to Irving/DFW.

    3.4.1 Air Quality Standards and Regulatory Setting

    Airborne PollutantsAmbient air quality is influenced by a number of factors, including climate, topography, windconditions, and the production of airborne pollutants by natural or artificial sources. Tailpipeemissions from cars and trucks produce almost a third of the air pollution in the United States.Vehicles are major sources of carbon monoxide (CO), oxides of nitrogen/nitrogen dioxide(NOx/NO2) and Volatile Organic Compounds (VOCs). CO is the primary component of vehicleexhaust gas and contributes about 60 percent of all CO emission in the United States. Particulatematters (PM10 and PM2.5) and sulfur dioxide (SO2) are also emitted from vehicular traffic; however,the emissions are not as significant as CO and NOx emissions. Ozone (O3), which is not directlyemitted from automobiles (or other sources) is formed in the atmosphere by chemical reactionsinvolving VOCs, NOx, and sunlight. The following is a summary of major airborne pollutants in thestudy area and their health effects:

    Carbon Monoxide (CO) Carbon monoxide is an odorless, colorless gas formed by the burning offuels containing carbon. Motor vehicles are the principal source of CO emissions in urbanareas. Maximum concentrations usually occur near intersections and other areas of trafficcongestion, and they decrease rapidly with distance from the source. It can cause dizzinessand fatigue and can impair central nervous system functions. Exposure to high levels of COcan cause immediate death.

    Particulate Matter (PM2.5 & PM10) Particulate matter enters the air from industrial operations,vehicular traffic and other sources, including fireplaces. Most of the particulate mattergenerated by motor vehicles consists of resuspended road dust. Measurements of particulatematter concentrations include TSP (total suspended particulates), PM10 (particles with adiameter less than or equal to 10 micrometers), and PM2.5 (particles with a diameter lessthan or equal to 2.5 micrometers). Particles of this size can be inhaled, irritating the humanrespiratory tract and aggravating pre-existing respiratory diseases. Certain populations, suchas children, the elderly, exercising adults, and those suffering from asthma or bronchitis, areespecially vulnerable. Very small particles of substances such as Pb, sulfates, and nitratescan cause lung damage directly, can be adsorbed into the blood stream and cause damageelsewhere in the body, and can transport adsorbed gases, such as chlorides or ammoniuminto the lungs and cause injury.

    Ozone (O3) Ozone in the lower atmosphere is a harmful air pollutant and contributes to theformation of smog. It is a secondary pollutant formed by the reaction of volatile organiccompounds and oxides of nitrogen in the presence of strong sunlight. Thus, ozone levels arereduced by minimizing emissions of those precursor pollutants. Ozone causes eye andrespiratory irritation, reduces resistance to lung infections, and may aggravate pulmonaryconditions in individuals with lung disease. Elevated O3 levels cause vegetation damage.

    Volatile Organic Compounds (VOC) Volatile organic compounds (VOC) are a key component inthe formation of ozone. These hydrocarbons are emitted or evaporate into the atmospherefrom a variety of sources, particularly the storage and combustion of fuels in motor vehicles.

  • Preliminary Engineering / Environmental Impact StatementNorthwest Corridor LRT Line to Irving and DFW Airport

    Draft Environmental Impact Statement 3 - 45Chapter 3 Affected Environment

    Oxides of Nitrogen (NOX) is a gaseous mixture of NO and NO2 that damages or irritates thehuman respiratory system, and can exacerbate damage from respiratory disease and otherexisting forms of irritation. NO2 may reduce resistance to certain infections. It is also aprecursor of O3. NO2 is a product of high-temperature combustion, emitted generally by thesame sources as CO. High concentrations of NO2 cause the brown haze readily observed inurban areas during periods of heavy air pollution. Concentrations of NO2 are highest duringlate fall and winter.

    Lead (Pb) Lead is a particulate pollutant that is also a carcinogenic air contaminant. In the past,automobiles were the chief contributors of Pb to the atmosphere in the U.S. Currently, lead isprimarily emitted in U.S. from a relatively small number of point sources such as smelters andbattery plants.

    Sulfur Dioxide (SO2) Sulfur Dioxide is a product of the combustion of high-sulfur fuels, such asmany grades of coal and oil. SO2 is a human respiratory irritant. It combines with moisture inthe atmosphere to form sulfuric acid and damages vegetation and exterior faades ofbuildings.

    Federal Clean Air ActThe Federal Clean Air Act (CAA) was enacted in 1970 and was last amended in 1990 with thepurpose of controlling air pollution and providing a framework for national, state, and local airquality control efforts. The CAA Amendments of 1990 (CAAA) requires the EnvironmentalProtection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for widespreadpollutants considered harmful to public health and the environment. EPA has set NAAQS for sixprincipal or criteria pollutants; Ozone (O3), Particulate Matter (PM10), Carbon Monoxide (CO),Sulfur Dioxide (SO2), Oxides of Nitrogen (NOx), and Lead (Pb). The EPA has established primaryand secondary standards for these pollutants. The primary air quality standards are defined asthe levels of air quality necessary, with an adequate margin of safety, to protect the public health.Secondary standards are the levels of air quality necessary to protect the public welfare from anyknown or anticipated adverse effects of a pollutant on property, material, and vegetation.

    In July 1997, the EPA amended NAAQS to include an 8-hour standard for O3 and to adopt anNAAQS for PM2.5. EPA issued official designations for the PM2.5 standard on December 17, 2004and made modifications in April 2005 (EPA, 2005). Ambient air quality standards for criteriapollutants are presented in Table 3-20 lists the criteria pollutants, their relative primary andsecondary standards, and the condition required for each standard to be met (standard threshold).

    Attainment StatusThe EPA designates geographic areas in a state with respect to meeting the NAAQS asattainment, nonattainment, or unclassifiable. Areas transitioning from nonattainment to attainmentare termed maintenance areas. The nonattainment areas are designated based on the degree ofviolation of the NAAQS. For O3 the designations are extreme, severe, moderate, or marginal. OnApril 15, 2004, EPA designated several counties in the North Central Texas area as nonattainmentunder the new 8-Hour NAAQS for ozone (O3) as mandated by Section 181(b)(2)(A) of the CAAA.

    North Central Texas newly designated nine-county ozone nonattainment area covers all of Collin,Dallas, Denton, and Rockwall counties; and portions of Ellis, Johnson, Kaufman, and Parkercounties. Figure 3-16 shows the nine-county O3 nonattainment area. Based on the magnitude ofozone pollution in these nine counties, the nonattainment area was classified as Moderate.

  • Preliminary Engineering / Environmental Impact StatementNorthwest Corridor LRT Line to Irving and DFW Airport

    Draft Environmental Impact Statement 3 - 46Chapter 3 Affected Environment

    TABLE 3-20NATIONAL AMBIENT AIR QUALITY STANDARDS

    Criteria Pollutant AveragingTimesPrimary

    StandardSecondaryStandard Threshold for Standard

    8-hour9 ppm

    (10 mg/m3)None

    Not to be exceeded more than once ayear.

    Carbon Monoxide(CO)

    1-hour35 ppm

    (40 mg/m3)None

    Not to be exceeded more than once ayear.

    Nitrogen Dioxide(NO2)

    Annual(Arithmetic Mean)

    0.053 ppm(150 g/m

    3)

    Same as Primary -------

    1-hour Average 0.12 ppm Same as Primary

    Areas not attaining the 1- hour standardby the end of 1997 must attain thatstandard before demonstratingattainment with the 8-hour standard.

    Ozone(O3)

    8-hour Average 0.08 ppm Same as Primary

    3-year average of the fourth-highest dailymaximum 8-hour average ozoneconcentrations measured at eachmonitor within an area over each yearmust not exceed 0.08 ppm.

    Lead(Pb)

    Quarterly(Arithmetic Mean)

    1.5 g/m3

    Same as Primary -------

    Annual(Arithmetic Mean)

    50 g/m3

    3-year average of the weighted annualmean PM10 concentration at eachmonitor within an area must not exceed50 g/m

    3.

    Particulate < 10micrometers(PM10)

    24-hour Average 150 g/m3

    Same as Primary

    3-year average of annual 98th percentilevalues not to be exceeded more thanonce a year.

    Annual(Arithmetic Mean)

    15 g/m3 Same as Primary

    3-year average of the weighted annualmean PM2.5concentrations from singleor multiple community-oriented monitorsmust not exceed 15.0 g/m

    3.

    Particulate < 2.5micrometers(PM2.5)

    24-hour Average 65 g/m3 -------

    3-year average of the 98th percentile of24-hour concentrations at eachpopulation-oriented monitor within anarea must not exceed 65 g/m

    3.

    Annual(Arithmetic Mean)

    0.03 ppm ------- -------

    24-hour Average 0.14 ppm -------Not to be exceeded more than once ayear.

    Sulfur Dioxide(SO2)

    3-hour