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# CHAPTER SIX
ATTAINMENT DEMONSTRATION Chapter Six describes the modeling that was performed todemonstrate that attainment of the 24-hour PM-10 standard will be achieved in 2012 . The modeling was conducted to show attainment under high wind conditions since vi olations of the standard under stagnant conditions have not occurred since 2006 (see Chapte r 3 for monitoring data information). A modeling attainment demonstration was performed for a 36 square mile area in the Salt River area, which includes the West 43 rd 

# Avenue monitor that has recorded the most exceedances of the PM-10 standard under high wind c onditions during 2005-2010. A regional attainment demonstration for the entirety of the nonattainment area is also provided in this chapter. Both the modeling demons tration in the Salt River area and the entire nonattainment area are based upon a distance-we ighted rollback approach. Windblown PM-10 emission estimates during high wind hours are calculated from back trajectories while low wind hour emission estimatesare derived from land use distribution within each modeling domain. The benefits of the control measures described in Chapter Five provide the reductions necessary to model atta inment. In addition to the modeling attainment demonstration s, this chapter addresses other requirements of a nonattainment area plan, includin g reasonable further progress, contingency measures, and the onroad motor vehicle emissions budget for conformity. The chapter concludes with a discussion of the control measures in the Five Percent Plan that will reduce PM-10 emissions sufficiently to achieveattainment as expeditiously as practicable and the need for an extension of the attainment date deadline to December 31, 2012. SALT RIVER AREA MODELING This section describes the modeling and results for the attainment demonstration in the Salt River Area. A detailed discussion of the tech nical methods and assumptions used to perform the modeling for the Salt River Area is pro vided in the TSD (Chapter V of Appendix B, Exhibit 1). Design Day Selection PM-10 monitors in the Maricopa County nonattainmentarea recorded 17 exceedances of the 24-hour average PM-10 national ambient air qual ity standard in 2007 (the last year before the control measures in this plan were imple mented). Exceedances were recorded at six monitoring sites in the nonattainment area: Coyote Lakes, Central Phoenix, Durango, Higley, South Phoenix and West 43 rd 

# Avenue. The Buckeye monitor also exceeded the standard on two days in 2007, but this monitor is o utside the nonattainment area and therefore was not modeled in this plan.

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# Of the 17 exceedances recorded within the nonattain ment area in 2007, the West 43 rd



# Avenue monitor recorded the highest number of excee dances with six. The Higley monitor was next highest with five. The remaining exceedin g monitors in the nonattainment area recorded two or less exceedances in 2007. All but one of the exceedances in 2007 occurred under high wind conditions. For the purpo ses of this attainment demonstration, high wind conditions are defined as days when five- minute or hourly average wind speeds are greater than 12 miles per hour. This value is identical to the threshold for windblown dust production as identified in the 2008 PM-10 Per iodic Emissions Inventory (Appendix A, Exhibit 1). Table 6-1 provides a tabulation by monitor of the exceedance days, 24-hour average concentrations and the general meteorologic al conditions associated with the exceedances. The following primary criteria were applied in selecting the design days for PM-10 modeling: 1. Exceedance days with five-minute or hourly averag e wind speeds > 12 miles per hour; and 2. Exceedance days that are unlikely to be considered as a high wind exceptional event. The West 43 rd 

# Avenue monitor recorded six exceedances when hourl y average winds were greater than 12 miles per hour in 2007. Four of th e six exceedance days were associated with high winds from a frontal storm system, while the remaining two days were associated with high winds from monsoon season thunderstorm ou tflows. Days on which thunderstorm outflow activity occurs have been excl uded as candidate days for modeling, as these days are almost always flagged as uncontro llable exceptional events. Two of the four frontal system exceedances days recorded at the West 43 rd 

# Avenue monitor were days in which only the West 43 rd 

# Avenue monitor exceeded the standard (March 27 and May 4). These days suggest that the local sources around the West 43 rd 

# Avenue monitor may have been important contributors to theexceedance value. Of these two dates, May 4, 2007 was chosen as the design day as wind speeds on March 27 th 

# were significantly higher making it a candidate for an ex ceptional event demonstration. For a demonstration of regional attainment across the no nattainment area, the other exceedance days in 2007 were evaluated using the sa me criteria employed to select May 4, 2007 for the Salt River area modeling. All high wind days associated with thunderstorm outflows were removed for consideration due to thei r designation as uncontrollable exceptional events. Of the remaining days with hig h wind days, two days (April 12 and June 6) recorded exceedances at multiple monitors, indicating that the high winds had a more regional effect on PM-10 concentrations. Of t he these two dates, June 6, 2007 was chosen as the design day as April 12, 2007 presente d very strong state-wide high winds indicating this date was also a candidate for an ex ceptional event demonstration. A more

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# Table 6-1

Maricopa County and PM-10 Nonattainment Area 24-Hou r Average PM-10 Standard Exceedance Dates, Measured Concentra tions and Associated Meteorological Conditions in 2007

Monitor Date PM-10 Conc. ( ȝ g/m 3 

# ) Meteorological Conditions Buckeye July 19 195.0 Low Winds

November 15 166.2 Irregular Winds Coyote Lakes July 19 273.4 Thunderstorm Outflow

October 21 312.9 Frontal System High Winds Central Phoenix July 19 267.8 Thunderstorm Outflow Durango Complex November 15 155.7 Irregular Winds Higley ./ 0

1

2 3

4

3

5 6 7 8 9 0

: ;

<

= > ? : 1 @ AB C D

E B0 F ? 

# July 19 199.5 Thunderstorm Outflow August 16 195.6 Thunderstorm Outflow August 23 230.4 Thunderstorm Outflow October 24 174.8 Frontal System High Winds South Phoenix April 12 171.1 Frontal System High Winds

August 13 159.5 Thunderstorm Outflow 

# West 43 rd 

# Avenue March 27 227.9 Frontal System High Winds

April 12 202.7 Frontal System High Winds G H I

J K

L

M N

O P Q R S

T H

U

V I W T XY Z [ \ ] ^ [ S _ W ` a S X b c c d N M P Q R S

T H

U

V I W T X

Y Z [ \] ^ [ S _ W 

# July 19 178.0 Thunderstorm Outflow August 16 215.1 Thunderstorm Outflow Note: The selected design days are highlighted in b old italics. The Buckeye monitor is located outsid e the PM10 nonattainment area and is not part of the attainment demonstration. The Coyote Lakes monitor was a special purpose monitor that no longer operates and has since been replaced by the Zuni Hills monitor in late 2009. As such, the Coyote Lakes monitor is not a g ood candidate for producing a design day.



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# detailed discussion on design day selection is pres ented in the TSD (Chapter V of

Appendix B, Exhibit 1). Plots of hourly wind speed and PM-10 concentration for the high wind design days of May 4, 2007 and June 6, 2007 at the West 43 rd 

# Avenue and Higley monitors are shown in Figure 6-1 through 6-3. Modeling Domain On a high wind design day, the areal extent impacti ng monitors is largely a function of wind speed. As such it is necessary to divide the selected design days into high and low wind hours. High wind hours are represented by sources located along back trajectories and low wind hours are represented by sources within a mode ling domain surrounding the selected monitoring site. The basis for distinguishing betw een high and low wind hours is the 12 mph windblown dust aerodynamic entrainment threshol d established in the 2008 PM-10 Periodic Emissions Inventory (Appendix A, Exhibit 1 ). Five-minute average wind speed and direction as mea sured at the West 43 rd 

# Avenue monitor is employed to construct the back trajector ies for each high wind hour. Past modeling of back trajectories indicate that the lands sig nificantly contributing to elevated PM-10 concentrations recorded at the monitor lie general ly within a mile of either side of the path of the upwind back trajectories (see Secti on entitled “Establishing the Boundaries of a High Wind Domain” in Chapter V of Appendix B, Exhibit 1). The modeling domain used during the low wind hours for the West 43 rd 

# Avenue monitor is similar to the area initially defined in the ADEQ T SD for the 2005 PM-10 attainment plan and is bounded by Van Buren Street to the north, Ba seline Road to the south, 59 th

# Avenue to the west and 7 th

# Street to the east. Due to the diversity and numb er of PM-10 sources in the Salt River area, it is considered to be a wo rst-case representation of sources throughout the nonattainment area. Figure 6-4 shows the low wind domain and the high w ind back trajectories on May 4, 2007 as originating from the West 43 rd 

# Avenue monitor. The highlighted area surrounding the back trajectories represent the land use domain use d for calculating windblown PM-10 emissions during the high wind hours. Inventory Development For the high wind hours, hourly windblown PM-10 emi ssions are calculated based upon the land uses that fall within the hourly back trajectory. Emiss ions from the land uses within each hourly back trajectory are calculated per the methodology described in the 2008 PM10 Periodic Emissions Inventory. Initially, the la nd uses within each back trajectory are evaluated for their potential to emit windblown dus t. Some land uses are assumed to have no windblown dust emissions (office/retail), some a re partially emissive (commercial/industrial) and others are assumed to be 1 00% emissive (vacant lands).
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# Figure 6-1 Summary of the Monitoring Conditions at West 43 rd

# Avenue

on the High Wind Design Day (May 4, 2007)

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# Figure 6-2 Summary of the Monitoring Conditions at West 43rd Avenue

on the High Wind Design Day (June 6, 2007)

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# Figure 6-3 Summary of the Monitoring Conditions at Higley

on the High Wind Design Day (June 6, 2007)

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# Figure 6-4 Salt River Area Low Wind Domain and May 4, 2007 Hourly High Wind Back Trajectories and Associated Domains as Originating from West 43 rd

# Avenue Monitor

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# Land uses that are conservatively assumed to have 1 00% of their acreage available for

windblown dust production include: vacant and open lands, sand and gravel/mining lands, lands under development, landfills and unpav ed automotive test tracks. Land uses where only portions of the acreage is availabl e for windblown dust production include: agricultural lands, industrial lands, comm ercial lands and large public lands. Windblown PM-10 emissions from these land uses are calculated by use of emission factors based upon wind speed and the disturbance le vel of each land use. The disturbance level of each land use is derived from rule effectiveness studies of the fugitive dust rules that regulate the various land uses. The effectiveness of the rule is assumed to be an approximate surrogate for the average level of disturbance of each regulated land use. The details of the calculation of the windblown PM-10 emissions are provided in the TSD (Chapter V of Appendix B, E xhibit 1). Since there have been no stagnation violations of t he 24-hour PM-10 standard since 2006, detailed low wind design-day specific emissio n inventories are not needed. However, emissions reductions achieved as a result o f controls in this plan during the low wind hours of the high wind design days are qua ntifiable and a necessary part of the attainment demonstration. In order to account for these emissions reductions, annual low wind emission inventories for the PM-10 nonattainment area are allocated to the Salt River area domain based upon land use dist ribution. This allows for representation of the low wind emissions, and assoc iated control measure benefits, in the Salt River area domain without having to createa design day inventory. The details on how low wind emissions are allocated to the SaltRiver area domain based upon land use is included in the TSD (Chapter V of Appendix B , Exhibit 1). Distance-Weighted Rollback Modeling The fundamental assumption underlying any rollback method is that pollutant concentrations are directly proportional to total emissions ove r the area of interest. A weighted rollback approach applies a distance reduct ion factor to the emissions of each source in the modeling domain to help assess the impa ct of emissions as distance from the monitor increases. The reduction factor is cal culated based upon the distance between each source and the impacting monitor. An investigation of results from a limited-term (20 10-mid 2011) saturation monitoring study conducted in the Salt River area and beyond u nder high wind conditions suggested the need to account for distance between emission sources and the impacted monitor. Further testing of different wei ghting factors through the analysis of dispersion model AERMOD confirmed that a 1/d weight ing factor proved to be the best form of weight to use in adjusting PM-10 emissions developed through the back trajectory domains (See section entitled “Source Weighting” i n Chapter V of Appendix B, Exhibit 1 for more information). Thus, all high wi nd design day emissions inventories were weighted to account for a 1/d distance from the model ed monitor.

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# Distance weighting was not applied to the low wind domain, as the low wind domain

primarily serves to identify the predominant land u ses near the monitor and thus the predominant low wind emissions associated with the land uses. The overall reduction in low wind emissions gained through the implementatio n of control measures was applied as the reduction factor to the low wind hourly conc entrations without the need to weight these reductions by distance. A detailed explanation of the saturation monitoring study and the AERMOD evaluation can be found in the TSD (Chapter V of Appendix B, E xhibit 1). Background Concentrations The temporary saturation monitoring study also prov ided insights into nonanthropogenic levels of PM-10 within the nonattainm ent area. These background values were established by comparing monitored readings un der high and low wind conditions at the temporary, rural Arlington School monitor an d the existing Buckeye monitor located just outside the western edge of the nonatt ainment area. The Arlington School monitor was located approximately 11 miles west of the Buckeye monitor, surrounded by mostly natural desert land. Under high wind conditions (> 12 mph), when the win d is coming primarily from the west, the Arlington monitor consistently recorded lower P M-10 concentrations than the Buckeye monitor, which is primarily impacted by PM- 10 emissions from agricultural activities. The median value under high wind condi tions at the Arlington monitor was found to be 21.9 ȝ g/m 3

# and is assumed to be the non-anthropogenic backgro und PM-10 concentration for the PM-10 nonattainment area unde r high wind conditions. A similar comparison under low wind conditions yielded a medi an value of 14.9 ȝ g/m 3

# and is assumed to be the non-anthropogenic background PM-1 0 concentration for the PM-10 nonattainment area under low wind conditions. A detail ed explanation of the methods and data used to develop the background values can be found in the TSD (Chapter V of Appendix B, Exhibit 1). Control Measure Analysis To assess the benefits of the control measures unde r high wind conditions, separate hourly windblown PM-10 inventories were developed a long back trajectory domains using base case soil disturbance rates in 2007 and then compared against inventories developed using the predicted soil disturbance rates in 2012. The high wind inventories are then weighted by distance from the monitor to m ore accurately represent the lessening impact of emission sources that are farther awa y from the modeled monitor. The reductions seen during the high wind hours is s trictly due to the benefits of control measures in this plan, as land use is held constantbetween 2007 and 2012. Table 6-2 provides a summary of the hourly high wind inventor ies for 2007 and 2012.

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