Air Quality Division: Assessment: Air Quality Modeling: SIP Modeling

The Air Quality Division typically develops a State Implementation Plan (SIP) after an area (usually a municipality but sometimes a large industrial facility affecting a region) has recorded violations of the federal health standards for ambient air quality, known as National Ambient Air Quality Standards (NAAQS). A SIP describes the area affected, the nature of the air pollution problem, the sources of air pollution and their contribution to violations of the federal NAAQS, and the enforceable air pollution control strategies that will be implemented to bring the area back into attainment for the particular federal health standard that has been exceeded. Upon completion, the SIP is submitted to U.S. EPA Region 9 for review and approval of the methodology and assumptions used to demonstrate that an area's air quality will meet the NAAQS.

Bullhead City PM10 SIP

Bullhead City is in non-attainment for the federal based PM10 health standard for exceedances of the 24-hour PM10 (particulate matter less than 10 microns) standard. ADEQ Air Assessment and Planning staff developed a PM10 State Implementation Plan (SIP) for the Bullhead City area and this SIP was submitted to U.S. EPA in June of 1995.

Analyses of the meteorological conditions, the emissions inventory and the results of dispersion modeling for the June 21, 1989, PM10 exceedance day in Bullhead City indicate that it was a combination of three relatively large construction projects and a 30+ mph north wind occurring together on June 21, 1989, that caused the June 21, 1989 PM10 exceedance in Bullhead City. The date of the previous PM10 exceedance in Bullhead City, May 30, 1991, was also a regional high PM10 episode which caused PM10 exceedances not only in Bullhead City but also at eight other monitoring stations in California and Nevada.

Both the 24-hour PM10 levels and the annual PM10 levels in the Bullhead City area have shown a downward trend since the occurrence of the May 30, 1991, PM10 exceedance. In addition, dispersion modeling of the Bullhead City area for the Year 2001, predicts that Bullhead City will be in attainment for both the 24-hour PM10 Health Standard and the annual PM10 Health Standard when control measures such as "just in time" grading and paving of a number of unpaved roads in the Bullhead City area are implemented.

Payson PM10 SIP

Payson is also in non-attainment for the federal based PM10 health standard for exceedances of the 24-hour PM10 standard. ADEQ Air Assessment and Planning staff developed a PM10 State Implementation Plan (SIP) for the Payson area which was submitted to U.S. EPA in June of 1995.

Analyses of the meteorological conditions, the emissions inventory and the results of dispersion modeling for for the Dec. 7, 1990 PM10 exceedance day in Payson indicate that it was woodsmoke from residential fireplaces/woodstoves and industrial source emissions combined with a strong thermal inversion that caused this exceedance. The calm, stagnant air conditions that led to the PM10 exceedance in Payson are almost opposite of the conditions that led to the PM10 exceedance in Bullhead City - high wind speeds that resulted in wind erosion of the soil. Dispersion modeling, with PM10 control measures, predicts that Payson will be in attainment for both the 24-hour PM10 Health Standard and the Annual PM10 Health Standard by the Year 2001 The major changes responsible for the improvement in air quality (i.e., decrease in ambient PM10 levels) from 1990 to 2001 for Payson appear to be:

  • Closing and dismantling of the Kaibab Industries facility as of Sept. 1, 1993.
  • Move of a portable crushing/screening plant from south of Payson to northeast of Payson on State Route 260 (Payson Concrete and Material).
  • Replacement of old wood stoves and fireplaces (non-U.S. EPA-approved) with cleaner, U.S. EPA approved wood stoves and fireplace inserts.
  • New wood stoves installed in residences after 1992 are the cleaner, U.S. EPA approved wood stoves.
  • Implementation of the Town of Payson's restriction on wood stoves being the sole source of heat in new housing construction
  • New zoning laws by Town of Payson requiring new parking lots be paved.
  • Application of dust palliatives on unpaved roads by the Town of Payson.
  • Additional miles of paving of unpaved roads and unpaved shoulders of paved roads by the Town of Payson and Gila County.

The attainment of the PM10 health standard by the Year 2001 is in spite of the projected increases in population and in vehicle traffic in Payson by the Year 2001.

Maricopa County PM10 SIP (Microscale)

The Maricopa County PM10 Nonattainment Area encompasses approximately 2,880 square miles in Maricopa County. This nonattainment area was delineated based on historical ambient measurements of Total Suspended Particulates (TSP) and PM10 that exceeded the National Ambient Air Quality Standards (NAAQS). Exceedances of both the 24-hour and annual PM10 NAAQS have been measured in Maricopa County since 1989. (The 24-hour PM10 NAAQS is 150 micrograms per cubic meter (g/m3) and the annual PM10 NAAQS is 50 g/m3.)

In order to deal with the specific causes and formulate the necessary control measures for 24-hour exceedances, a microscale field study for the Maricopa County PM10 Nonattainment Area ("Phoenix PM10 Microscale Study") was designed in 1994 and conducted throughout 1995.

In Oct. 1996, U.S. EPA Region 9 and ADEQ agreed that the PM10 Serious Area Plan for Maricopa County be managed in two parts: a microscale plan developed by ADEQ to address 24-hour PM10 exceedances and a regional plan developed by Maricopa Association of Governments (MAG) to address exceedances of the annual PM10 standard. (ADEQ completed the microscale plan and MAG is currently working on the regional plan.)

PM10 sources in Maricopa County include urban sources (i.e., vehicle traffic, industry), rural sources (agriculture, unpaved roads) and the transition zone between urban land use and rural land use which is typically associated with various types of construction activities. A total of 22 PM10 exceedances were measured by the entire Maricopa County Environmental Services DU.S. EPArtment (MCESD) high volume (hi-vol) PM10 network during the 1995 field study. The majority of the exceedances, 16, occurred at the Salt River monitor.

Based on the emissions inventories, meteorological conditions and dispersion modeling, done for the April 9, 1995, PM10 /wind blown exceedance day, it appears that cleared areas (whether the cleared areas are due to agriculture, road construction or housing construction) combined with an average wind speed greater than 15 miles per hour, were the cause of the PM10 exceedances recorded at three sites in metropolitan Phoenix on April 9, 1995: West Chandler, Gilbert and Maryvale.

It appears that fugitive PM10 emissions from earth moving activities and other activities that disturb the soil on cleared and vacant lands (i.e., industrial, surface mining, and disturbed land under construction) were the major cause of the 24-hour exceedances recorded at the Salt River site - based on the emissions inventories, meteorological conditions and dispersion modeling, done for the Salt River site.

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