# High Wind Exceptional Events

And Control Measures for PM 10 

# Areas

Air Quality Division

October 13, 200910-13-09 White Paper High Wind Exceptional Events & Control Measures for PM 10 Areas 

### 1 High Wind Exceptional Events and Control Measures for PM 10 

### Areas

1.0 Background

Under the authority of the Clean Air Act (CAA), th e Environmental Protection Agency (EPA) develops National Ambient Air Quality Standards (NAAQS) fo r each of the criteria pollutants (carbon monoxide, lead, nitrogen oxides, ozone, particulate matter, and sulfur dioxide). For each of these pollutants, EPA

tracks air concentrations based on actual measurement s of pollutant concentrations in the ambient (outside) air at selected monitoring sites throughout the country. Once an air quality standard for a particular pollutant is established, monitors record wh en ambient concentrations of that pollutant exceed a level at which human health is no longer protected. 1 Should these exceedances continue or grow in intensity, the regulatory remedy is to declare the area in violation of the standa rd and designate the area nonattainment for that pollutant. The only time an exceedance would not count toward a violation of a

standard is if that exceedance could be cl assified as an exceptional event.

Exceptional Events impact air quality when their infl uence results in ambient air concentrations of particulate matter that fall outside the range of norma l statistical fluctuations. For particulate matter, these events can be the result of large fires, high wi nds, man-made events such as explosions, or natural events such as volcanic eruptions. In the Western United States, high winds can accompany large storms (e.g., haboobs) that move across a regional or stat e-wide swath of land, or high winds can accompany

“micro-bursts” with or without rain that descend upon a small, localized area. When a monitor within a planning area registers an exceedance of the PM 10 NAAQS – or 150 micrograms per cubic meter ( μ g/m 3 ) over 24 hours – the exceedance is flagged in the EPA Air Quality System (AQS) database and an examination of the event begins to determine if the event could be classified as exceptional. 2 More than three exceedances at the same particulate matter m onitor within three consecutive years add up to a violation of the NAAQS. A violation has a consequen ce to a planning area of either preventing an area from reaching attainment or returning an area to nonattainment that was previously redesignated to attainment. If an exceedance is flagged as an excepti onal event, however, and the EPA’s Regional Office concurs, the exceedance is not counted toward a violation of the NAAQS.

Control measures are established to bring a nonattainme nt area into attainment for a particular NAAQS; the control measures are to remain in place even afte r the area is redesignated to attainment. These

control measures can include Best Available C ontrol Measures (BACM) or Technology (BACT), Reasonable Control Measures (RACM) or Technology (RACT), Most Stringent Measures (MSM), and Lowest Achievable Emission Rate (LAER). Other control measures can be case-by-case control measures or practices that have been shown to be e ffective in reducing pollution from a particular source;

for PM 10 examples include Agricultural Best Manageme nt Practices (AgBMPs), stabilization of vacant lots, or paving unpaved roads or shoulders. A nonattain ment area can be classified as Moderate, Serious, or Severe. The CAA requires areas de signated as serious nonattainment for PM 10 to implement BACM and BACT on all significant sources of PM 10

.

1.1 PM 10 Planning Areas in Arizona

1 A primary NAAQS standard prevents damage to human health; a secondary standard prevents environmental and property damage.

2 Areas redesignated to attainment ar e subject to maintenance pl ans. An exceedance of the NAAQS is treated the same way as a nonattainment area; however, maintenance pl an design values can be flagged as well but are not addressed by the federal Exceptional Events Rule. Maintenance plans are in place for 20 years.10-13-09 White Paper High Wind Exceptional Events & Control Measures for PM 10 Areas 

### 2 Arizona has nine PM 10 planning areas:

Ajo Nonattainment; new plan under development Bullhead City Redesignated to attain ment under a Limited Maintenance Plan Douglas-Paul Spur Nonattainmen t; new plan under development Hayden Nonattainment; plan to be revised 3
Maricopa County Nonattainmen t; under Five Percent Plan 4

Miami Nonattainment; Limited Ma intenance Plan submitted to EPA Nogales Nonattainment; plan to be revised; also nonattainment for PM 2.5 Payson Redesignated to attainment under a Limited Maintenance Plan Rillito Nonattainment; Limited Ma intenance Plan submitted to EPA Yuma Nonattainment; Maintenance Plan submitted to EPA

Detailed information about the planning areas can be obtained by going to ADEQ’s Web site at http://www.azdeq.gov/environ/air/plan/index.html

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1.2 High Wind Exceptional Events Versus Fire Events

As previously stated, exceptional events can includ e among other events, fire events and high wind events. For the purposes of this di scussion, however, the focus is on hi gh wind events as they are often the more prevalent cause of exceedan ces in areas throughout Arizona as well as other parts of the Western United States due to complex terrain and unique weathe r patterns. The characteristics of these high wind events are discussed further in a white paper titled, Impact of Exceptional Events ‘Unusual Winds’ on

PM 10 Concentrations

.

2.0 Control Measures

The development of a state implementation plan (S IP) for an area designated as nonattainment for PM 10 includes at the minimum:

 a review of all relevant monitoring sites and ambient monitoring data;

 development of an emissions invent ory of all contributing sources of PM 10 ;

 application of emission factors to the ambient con centrations recorded in the emissions inventory; any controls already in place for PM 10 emissions;

 any controls in place in areas throughout the country, particularly the West, with similar characteristics to the planning area;

 any current research on effective control measures; current level of enforcement for any control measures already in place;

 and any modeling that shows the effectiveness of control measures on PM 10 emissions.

Fortunately, there is a moderate amount of information about control measures for PM 10 ; unfortunately, much of the information is source and area-specific. Information on the relative effectiveness of control measures is not as abundant, nor is it easily applicab le to the specific conditions in most of the PM 10 planning areas in Arizona. Because the demonstr ations required to obtain a concurrence on an exceptional event should account for the relative complexity of the emitting source mix, parsing out a specific source or source category along with the a pplicable control measure for a determination of relative effectiveness can be difficult and may even be counter-productive. This is compounded by the

3 The Hayden area was previously included with the Mi ami area; split into two planning areas later approved by

EPA.

4 Maricopa County nonattainment area also include Apache Junction portion of Pinal County.10-13-09 White Paper High Wind Exceptional Events & Control Measures for PM 10 Areas 

### 3 fact that PM 10 cannot be characterized by a specific source category through routine examination of the particulates deposited on a monitor’s filter. Through the SIP development process, however, the overall make-up of the planning area is known and fairly reliable assumptions about source contribution and implemented control measure effectiveness can be made in most cases.

2.1 Evaluating the Effectiveness of Contro l Measures; Implementation and Enforcement

There are several ways to evaluate the effectiveness of a control measure. The most direct approach is actual field testing. Planners can also query re presentatives of other planning areas for examples of effective control measures, sharing testing data, or rep licating specific field tests. Another approach is to research control measures that have been recognized as BACM by EPA, other states, source emitters, or in some cases by the courts. Regardless of how a c ontrol measure is chosen and its relative effectiveness evaluated, it is often subjected to a computer mo del to demonstrate whether the control measure or measures actually show a reduction in emissions or pr event an increase in the concentration of emissions (i.e., reasonable further progress toward attaining the NAAQS).

Optimum effectiveness is measured by the degree of c ontrol efficiency; efficiency can be a set percentage or a range (i.e., the range can represent how the c ontrol measure is to be implemented over time) in relation to the level of compliance, or control effici ency multiplied by the compliance level. In the case where a control measure is a one-time, succinct acti on such as paving an unpaved road, the effectiveness should be high. 5 Other calculations of effectiveness can be less straightforward due to the variables in implementation and enforcement. Degree, range an d timing of control measure implementation coupled

with a variable level of enforcement make field in spections of vital importance to determine the true

effectiveness of certain control measures. Without reliable or complete reporting of the implementation of control measures, the lower or low est range of control efficiency is most likely reflective of actual field

situations. It is difficult to calculate other types of control measure effectiveness when the implementation is more qualitative than quantitative in nature, even though the measure has proven effective in field tests (e.g., actions required only when special circumstances arise, or actions that rely on training and advanced communication). Field insp ections, reporting, and a noticeable reduction in emissions provide verification of projected control effi ciency for a particular control measure. A pattern of non-compliance would provide verification that the control efficiency has been compromised or the control measure itself was perhaps unenforceable as currently designed or implemented.

Due to the varied nature of control measures, a pl anning approach that commits to a series of control measures rather than relying solely on only a few is of ten the best way to gain an overall high level of control effectiveness for a planning area. The commitm ent to implement these measures suggests that an optimal level of enforcement will be in place, often strengthened further by permit conditions, rules, and ordinances with specific consequences for non-compliance. Control measures that are voluntary in nature can also have a high degree of effectiveness but often rely on ongoing outreach and inspections. Contingency measures are designed to provide a dditional emission reductio ns should the committed control measures fail to provide sufficient reductions . These measures are often not modeled toward progress in reducing emissions of a particular pollutant , but they can be effective should sources not wish to move to the higher degree of control these measures can represent.

By considering a control measure or suite of contro l measures in place around the time of an exceptional event, such as those triggered by high winds, it should be possible to determine the following: either (a)

the control measure effectiveness w as insufficient to control the background concentration of emissions thereby contributing to cumulative emissions suffici ent to exceed the NAAQS wh en coupled with high

5 In areas where a maintenance plan is in place, contro l measures that may appear permanent must be routinely revisited to assure that they are in good condition, or authority to enforce certain measures is still in place.10-13-09 White Paper High Wind Exceptional Events & Control Measures for PM 10 Areas 

### 4 winds, or (b) the wind conditions were unique a nd severe enough to overwhelm the control measures regardless of control effectiveness.

3.0 Effect of Exceptional Events (High Winds ) on Control Measures; Overwhelmed Controls

In parts of the Western United States high wind events can generally be classified as one of two types: mesoscale events or synoptic scale events. M esoscale high winds associated with thunderstorm development are localized events that are often initia lly devoid of rain and cause a reduction in visibility due to lofted particles from disturbed arid land or certa in soil types. Synoptic scale high wind events, on the other hand, have a greater tendency to transport particles over long distances. Both types of high wind events are capable of transporting particles into an area from distances outside of a specific planning area. This paper does not attempt to explain in detail the eff ect of these types of high winds, but in relation to planning area control measures it is important to note that at times these winds can overwhelm or greatly

reduce the effectiveness of a control measure or suite of control measures.

Unfortunately, information on the effects of high wi nd events on control measures, specifically measures for the control of particulate matter, is not readily av ailable. Most of the information is anecdotal in nature, observations after the fact. There are studies on the effects of high winds on particulate matter itself – effects of particle size bombardment and par ticle size relative to transport – but the information does not always translate well to control measure appli cations or is too case-specific. More to the point, however, is an understanding that certain measured high wind speeds do cause lifting of certain soil types or increase background concentrations of already ex isting particulates. There is a fair amount of agreement and observations to support that high winds over a certain speed can overwhelm most controls regardless of the level of implementation or enfo rcement. The phenomenon is discussed further in a corresponding white paper titled, Impact of Exceptional Events ‘Unusual Winds’ on PM 10

Concentrations

.

4.0 Tracking Relative Effectiveness of Impl emented Control Measures During High Winds

As stated previously, it is essential that the control m easures for a planning area be routinely inspected for implementation and level of enfor cement in order to have a meaningful sense of control measure effectiveness. Text of permit conditions needs to be periodically reviewed, dust complaints need to be properly logged and the subject of timely and appr opriate response, inspections and any enforcement actions that resulted need to be reported, along w ith any other action necessary to determine the full implementation of a control measure. When comparing the control measures to the effects of a high wind event, it is helpful to know what the conditions were on the ground and in the air prior to the high wind event, the day of the high wind event, and after th e high wind event. The time before the event can determine possible contributors to elevated PM 10 concentrations while the time after the event could expose non-compliance patterns that would not othe rwise be directly tied to the event.

In order to obtain a better picture of what control measures are in place during the intervals of a high wind event, a simple reporting form has been constructed. This form, when reviewed by analysts of the high wind event, should provide a clearer picture of what could have contributed to the exceedance and could add to an argument that the event was indeed exceptional. The form requires several pieces of useful information. (1) Because some, but not all, planning areas have High Pollution Advisory (HPA) notification procedures, including high wind watches fo r particulate matter pollution, noting the existence of a HPA action on the day of or days prior to the event is important. 6 (2) Complaints are useful bits of

6 For areas that do not have a HP A program in place, the Na tional Weather Service issues storm watches and warnings to alert the public to possible heavy rain, flooding, gusty winds and blowing dust. Airports, both large and small regional air fields, also have data sources that regi ster high winds and reduced visibility so aircraft warnings

can be issued.10-13-09 White Paper High Wind Exceptional Events & Control Measures for PM 10 Areas 

### 5 information as they often reveal insufficient impl ementation or enforcement of control measures, especially if the complaints are for the same source or group of sources; in the case of voluntary measures they can be the only available measure of effectiv eness. (3) Inspections co mpleted routinely or for special purposes (e.g., nighttime inspections) give sp ecific information on what is happening in and around the planning area, particularly inspections requi red during a HPA. (4) Finally, any record of

notices or actual enforcement actions on a source in the planning area tells a story of serious noncompliance with implemented control measures, or it tells of control measures that have been insufficiently implemented.

A sample form is attached to this paper. Each party responsible (i.e., State, County, or any other relevant public officer/agency) for sources in the planning ar ea would complete the form, which would then be reviewed by those preparing the analysis that dem onstrates whether the high wind event is truly an exceptional event. For those events that are obviously of such severity that control measures would be overwhelmed, it is still useful to note the control m easure actions for the planning area, especially an issuance of a HPA or pertinent weather forecast. Th e reverse side of the form contains the committed control measures for the planning area. Control meas ures can vary considerably for particular planning areas, but including them on the form reminds everyone that they need to be c onsidered in the exceptional event analysis.

5.0 Conclusion

A demonstration that a high wind event is in fact an exceptional event requires a robust analysis of the wind conditions coupled with an examination of the control measures in place in and around the area in which the monitor registered an exceedance. This demonstration must not only pass the scrutiny of regulators but also the general public. Should the high wind event that caused the exceedance truly reflect

an influence that resulted in ambient air concentrations of particulate matter that fell outside the range of normal statistical fluctuations, then EPA’s concurrence with the dem onstration allows for a focus on PM 10 emissions that can be controlled.