|
4.3 AIR QUALITY
<br /> This section includes a description of existing air quality, a summary of applicable regulations, and analyses of
<br /> potential short-term and long-term air quality impacts of the proposed project. The methods of analysis for short-
<br /> term construction, long-term regional(operational), local mobile source, odor, and toxic air contaminant(TAC)
<br /> emissions are consistent with the recommendations of the San Joaquin Valley Air Pollution Control District
<br /> (SJVAPCD). Mitigation measures are recommended, as necessary,to reduce significant air quality impacts.
<br /> 4.3.1 ENVIRONMENTAL SETTING
<br /> The project site is located in San Joaquin County,which is within the San Joaquin Valley Air Basin(SJVAB).
<br /> The SJVAB also comprises all of Fresno,Kings,Madera,Merced, San Joaquin, Stanislaus, and Tulare counties,
<br /> and the valley portion of Kern County. Ambient concentrations of air pollutants are determined by the amount of
<br /> emissions released by pollutant sources and the atmosphere's ability to transport and dilute such emissions.
<br /> Natural factors which affect transport and dilution include terrain,wind, atmospheric stability, and the presence of
<br /> sunlight. Therefore, existing air quality conditions in the area are determined by such natural factors as
<br /> topography,meteorology, and climate, in addition to the amount of emissions released by existing air pollutant
<br /> sources, as discussed separately below.
<br /> TOPOGRAPHY, METEOROLOGY,AND CLIMATE
<br /> The SJVAB,which occupies the southern half of the Central Valley, is approximately 250 miles long and, on
<br /> average, 35 miles wide. The SJVAB is a well-defined climatic region with distinct topographic features on three
<br /> sides. The Coast Range,which has an average elevation of 3,000 feet, is located on the western border of the
<br /> SJVAB. The San Emigdio Mountains,which are part of the Coast Range, and the Tehachapi Mountains,which
<br /> are part of the Sierra Nevada, are both located on the south side of the SJVAB. The Sierra Nevada forms the
<br /> eastern border of the SJVAB. The northernmost portion of the SJVAB is San Joaquin County. There is no
<br /> topographic feature delineating the northern edge of the basin. The SJVAB can be considered a"bowl"open only
<br /> to the north.
<br /> The SJVAB is basically flat with a downward gradient in terrain to the northwest. Air flows into the SJVAB
<br /> through the Carquinez Strait,the only breach in the western mountain barrier, and moves across the Sacramento—
<br /> San Joaquin Delta(Delta)from the San Francisco Bay Area. The mountains surrounding the SJVAB create a
<br /> barrier to airflow,which leads to the entrapment of air pollutants when meteorological conditions are unfavorable
<br /> for transport and dilution.As a result,the SJVAB is highly susceptible to pollutant accumulation over time.
<br /> The inland Mediterranean climate type of the SJVAB is characterized by hot, dry summers and cool,rainy
<br /> winters. The climate is a result of the topography and the strength and location of a semipermanent, subtropical
<br /> high-pressure cell. During summer,the Pacific high-pressure cell is centered over the northeastern Pacific Ocean,
<br /> resulting in stable meteorological conditions and a steady northwesterly wind flow.Upwellings of cold ocean
<br /> water from below to the surface,because of the northwesterly flow,produce a band of cold water off the
<br /> California coast. Daily summer high temperatures often exceed 100°F, averaging in the low 90s in the north and
<br /> high 90s in the south. In the entire SJVAB, daily summer high temperatures average 95°F. Over the last 30 years,
<br /> temperatures in the SJVAB averaged 90°F or higher for 106 days a year, and 100°F or higher for 40 days a year.
<br /> The daily summer temperature variation can be as high as 30°F (SJVAPCD 2002). In winter,the Pacific high-
<br /> pressure cell weakens and shifts southward,resulting in wind flow offshore,the absence of upwelling, and storms.
<br /> Average high temperatures in the winter are in the 50s,but lows in the 30s and 40s can occur on days with
<br /> persistent fog and low cloudiness. The average daily low temperature in the winter is 45°F(SJVAPCD 2002).
<br /> Temperature and solar radiation are particularly important in the chemistry of ozone formation,which is a
<br /> photochemical reaction requiring sunlight. Generally,the higher the temperature,the more ozone is formed,
<br /> Manteca WQCF and Collection System Master Plans EIR EDAW
<br /> City of Manteca 4.3-1 Air Quality
<br />
|