EXHIBIT 4-2_55A_BRISTOL WIDENING TECHNICAL STUDIES

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AMBIENT AIR QUALITY STANDARDS AND DATA The four pages that follow present: (1) the currently adopted ambient air quality standards, (2) episode criteria, (3) avail- able episode data, and (4) ambient air quality data from the most representative monitoring station for the most recent three years in terms of both state and federal standards. Irregularities caused by changes in the standards are discussed below. The California Air Resources Board (CARE) periodically reviews the state's ambient air quality standards considering new health effect studies and recommendations by the Department of Health Services. On September, 1982, new sea level carbon monoxide standards were adopted by the CARE. The one -hour standard was revised downward from 40 to 20 ppm. The 12 -hour standard of 10 ppm was dropped in favor of an 8-hour standard of 9.0 ppm. These revised standards were designed to prevent carboxyhemoglobin concentrations from exceeding 2% in the blood and thereby avoid adverse health effects in persons with heart disease, chronic obstructive pulmonary disease, anemia or pregnant women and their unborn fetuses. The national ambient carbon monoxide standards are also under review by the United States Environmental Protection Agency (EPA). They are currently set at 35 ppm for one -hour averages and 9.0 ppm for an eight -hour average. The state 24 -hour standard for total suspended part Sculates (TSP4 was changed (effective July 1, 1983) from 100 ug /m to 50 uglm for particulate matter with an aerodynamic d, eter equal to or less than 10 microns. In addition, the 60 ug�m annual geometric mean (AGM) standard for TSP was replaced by a 30 ug /m3 standard for total thoracic particulates (TTP). Both of these changes reflect health concerns related to smaller particles that pene- trate deeply into the human respiratory tract and the effect of these particles on visibility. F