Request for EPA Concurrence as 

Exceptional Events for the 

February 15–16, 2011,

High Wind PM10 Dust Event 

Affecting High PM10 Concentrations at the Boise Fire 

Station, Ada County and Nampa Fire Station, Canyon 

County, Idaho

State of Idaho

Department of Environmental Quality

September 2013
Printed on recycled paper, DEQ, August 2013, PID 

MPOB, CA code 81630. Costs associated with this 

publication are available from the State of Idaho 

Department of Environmental Quality in accordance 

with Section 60-202, Idaho Code.
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Table of Contents

Acronyms, Abbreviations, and Symbols ...................................................................................... vii

Executive Summary....................................................................................................................... ix

1 Conceptual Model.................................................................................................................... 1

1.1 Overview .......................................................................................................................... 1

1.2 Source Area and Affected Region.................................................................................... 1

1.3 Emissions Process ............................................................................................................ 3

1.4 Contributing Weather Phenomena Synopsis.................................................................... 5

1.5 Path and Timeline from Source Area to Monitors ........................................................... 5

1.6 Concentration Patterns...................................................................................................... 6

2 Not Reasonably Controllable or Preventable (nRCP) ............................................................. 9

2.1 Source Areas Contributing to the Event........................................................................... 9

2.2 Source Area Wind Speeds.............................................................................................. 10

2.3 Basic Controls Analysis ................................................................................................. 10

3 In Excess of Historical Fluctuations (HF) ............................................................................. 11

3.1 Time Series for the Previous Ten Years......................................................................... 11

3.2 Percentile of Concentrations........................................................................................... 15

4 Clear Causal Relationship (CCR).......................................................................................... 16

4.1 Occurrence and Geographic Extent of the Event ........................................................... 16

4.2 Description of Weather Conditions that Created the Event ........................................... 22

4.3 Transport of Emissions Related to the Event in the Direction of the Monitor(s) 

Where Measurements Were Recorded........................................................................ 31

4.4 Spatial Relationship Between the Event, Sources, Transport of Emissions, and 

Recorded Concentrations............................................................................................ 34

4.5 Temporal Relationship Between the High Wind and Elevated PM Concentrations at 

the Monitor(s) in Question.......................................................................................... 34

4.6 Similarity of Chemical Composition of Measured Pollution with that Expected from 

Sources Identified as Upwind ..................................................................................... 34

4.7 Comparison of Event-Affected Days to Specific Nonevent Days—Comparison of 

Area Concentrations and Wind Speeds in the Days Preceding and Following the 

Event ........................................................................................................................... 40

4.8 Alternative Hypotheses .................................................................................................. 40

5 Affects Air Quality (AAQ).................................................................................................... 42

6 Natural Event or Human Activity Unlikely to Recur at the Same Location (NE/HAURL) . 42

7 No Exceedance But For this Event (NEBF).......................................................................... 43

8 Mitigation .............................................................................................................................. 44

9 Procedural Requirements....................................................................................................... 45

10 References.............................................................................................................................. 46
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Appendix A. EPA Completion Checklist ..................................................................................... 50

Appendix B. Supporting Meteorological Data ............................................................................. 52

Appendix C. Hells Canyon IMPROVE Site PM2.5 Speciation..................................................... 63

Appendix D. St. Luke’s Meridian NCORE Site Speciation Data for February 14, 2011 ............ 65

Appendix E. DEQ Air Quality Alerts and Public Education........................................................ 67

Appendix F. News Articles........................................................................................................... 71

List of Tables

Table A. Monitored values Included in this request for concurrence............................................ ix

Table B. Summary of DEQ demonstration in this report meeting Exceptional Event Rule 

elements............................................................................................................................ x

Table 1. Statistics of 24-hour PM10 concentrations recorded in Boise and Nampa, 2002–2011.. 11

Table 2. Percentile statistics with respect to annual and seasonal datasets, with and without 

high wind days, 2002–2011............................................................................................ 16

Table 3. Hourly PM10 concentrations greater than 100 μg/m3at the Nampa fire station for 

winter 2010 and 2011 only. Values related to this dust event are shown in bold (red 

circles in Figure 32)........................................................................................................ 38

Table 4. Comparison of February 14 St. Luke’s monitoring site PM2.5 composition with the 

annual average and winter season historical compositions, 2009–2011. ....................... 39

Table 5. Average, 95th and 99th percentile of PM10 concentrations (μg/m3) in Boise and 

Nampa, 2002–2011, in comparison to recorded values during this event. Statistics 

are shown for all data (top) and winter season (bottom). ............................................... 44

Table 6. DEQ compliance with procedural requirements of the exceptional events rule............. 45

Table A-1. EPA completion checklist. ......................................................................................... 50

Table B-1. Identification of MESOWEST stations used in this report (Horel et al. 2002). ......... 52

Table B-2. Source region weather station data from Mesowest (Horel et al. 2002)..................... 53

Table B-3.Intermediate (Oregon) and affected area weather stations from MESOWEST 

(Horel et al. 2002)........................................................................................................... 55

Table B-4. Weather observations at Lovelock, Boise, and Winnemucca from Mesowest 

(Horel et al. 2002)........................................................................................................... 57

Table B-5. Daily precipitation in source region, January 1–February 15, 2011 (Horel et al. 

2002)............................................................................................................................... 62

Table D-1. St. Luke’s NCORE site speciation for February 14, 2011—XRF elements. ............. 65

List of Figures

Figure 1. Location of Black Rock Playa and Carson Sink Playa source areas, affected PM10 

monitors at Boise and Nampa, and MESOWEST weather stations referenced in this 

report................................................................................................................................. 2

Figure 2. Schematic illustration of relationship between high dust potential and a near-surface 

capillary fringe zone on a wet playa versus a lower dust potential for a dry playa 

(Reynolds et al. 2007)....................................................................................................... 3
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Figure 3. Playa dust storm example near Carson Sink Playa, March 28, 2012. ............................. 4

Figure 4. (a) Boise and Nampa PM10 concentrations, (b) southwest Idaho hourly PM2.5

concentrations, and (c) wind conditions at the Boise airport from MESOWEST

(Horel et al. 2002)............................................................................................................. 7

Figure 5. (a) Surface wind speed, (b) wind gusts, and (c) wind directions at source area sites 

(BLUN2, BUFN2, TR730, and KLOL) and intermediate distances (GSFO3 and 

JVCI1) between source area and affected area. Figure 1 provides locations, and 

Appendix B provides station information and tabular data obtained from 

MESOWEST (Horel et al. 2002)...................................................................................... 8

Figure 6. Twenty-four hour PM2.5 concentration pattern in southwest Idaho on February 12, 

2011, (first bar) through February 17, 2011 (last bar). PM2.5 is a surrogate for PM10. .... 9

Figure 7. Historical PM10 fluctuations at Boise fire station no. 5, 2002–2011. Values over 

120 μg/m3are identified by date along with the maximum 1-hour wind speed/gust 

speed for that day............................................................................................................ 12

Figure 8. Historical PM10 fluctuations at the Nampa fire station, 2002–2011. Values over 

120 μg/m3are identified by date along with the maximum 1-hour wind speed/gust 

speed for that day............................................................................................................ 13

Figure 9. PM10 concentration (blue dots) and paired maximum daily 1-hour wind speed 

(=SKNT, red line) at the Boise fire station, sorted by decreasing wind speed with the 

highest wind speeds to the left........................................................................................ 13

Figure 10. Daily mean PM10 concentration (blue dots) and paired 1-hour maximum wind 

speed (=SKNT, red line) at Nampa fire station sorted by decreasing wind speed with 

the highest wind speeds to the left.................................................................................. 14

Figure 11. PM10 concentration distribution, 2002–2011, at the Boise fire station. ...................... 14

Figure 12. PM10 concentration distribution, 2002–2011, at the Nampa fire station..................... 15

Figure 13. MODIS true color image from the Terra satellite, captured at ~1030 PST on 

February 14, 2011........................................................................................................... 18

Figure 14. MODIS Aqua image captured at ~1330 PST on February 14, 2011........................... 19

Figure 15. MODIS true color image from the Terra satellite, captured at ~1030 PST on 

February 15, 2011........................................................................................................... 20

Figure 16. MODIS Aqua image captured at ~1330 PST on February 15, 2011........................... 21

Figure 17. MODIS Aqua false color images (clouds and snow are blue-tinted; dust is white) 

showing turbulent dust cloud generation on Black Rock Playa (left) and Carson Sink 

Playa (right) as well as dust plumes leaving the playas toward the northeast ~1330 

PST February 15, 2011................................................................................................... 22

Figure 18. Twenty-four hour precipitation totals in the BRP and CSP source region in the 

45 days prior to the event. .............................................................................................. 23

Figure 19. 1800Z (1100 MST) surface analysis February 15, 2011 (National Weather Service 

Hydrometeorological Prediction Center: 

http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml)................................................ 24

Figure 20. 2100Z (0200 MST) surface analysis February 15, 2011 (National Weather Service 

Hydrometeorological Prediction Center: 

http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml)................................................ 24

Figure 21. NCEP/NARR model reanalysis of midlevel winds (meters per second), February 

14–15, 2011 (NOAA/ESRL Physical Science Division, Boulder Colorado: 

http://www.esrl.noaa.gov/psd/). ..................................................................................... 25
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Figure 22. Sounding information for Reno, Nevada, at 18Z (1100 PST) February 15, 2011 

(National Weather Service Upper-Air Observations Program-Global Climate 

Observing System. University of Wyoming Sounding: 

http://weather.uwyo.edu/upperair/sounding.html). ........................................................ 26

Figure 23. Friction velocity for 18Z (1200 MST) February 15, 2012, NARR NAM-ANL 

(National Climatic Data Center National Operational Model Archive and 

Distribution System, NWS-NCEP NAM, 12 km: 

http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)............ 27

Figure 24. Sounding information for Boise, Idaho, at 12Z (0500 MST) February 16, 2011 

(National Weather Service Upper-Air Observations Program-Global Climate 

Observing System. University of Wyoming Sounding: 

http://weather.uwyo.edu/upperair/sounding.html). ........................................................ 28

Figure 25. 1500Z (0800 MST) surface analysis February 16, 2011 (National Weather Service 

Hydrometeorological Prediction Center: 

http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml)................................................ 29

Figure 26. 1800Z (1100 MST) surface analysis February 16, 2011 (National Weather Service 

Hydrometeorological Prediction Center: 

http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml)................................................ 29

Figure 27. Surface winds 1500 MST on February 15, 2011, from MESOWEST (Horel et al. 

2002)............................................................................................................................... 30

Figure 28. HYSPLIT back-trajectories from the 0500–1000 MST PM10 peak at Boise-Nampa 

area on February 15, 2011 (NOAA Ready HYSPLIT model: 

http://ready.arl.noaa.gov/HYSPLIT_traj.php)................................................................ 32

Figure 29. HYSPLIT back-trajectories from the 1600–2400 MST PM10 peak at Boise-Nampa 

area on February 15, 2011 (NOAA Ready HYSPLIT model: 

http://ready.arl.noaa.gov/HYSPLIT_traj.php)................................................................ 33

Figure 30. HYSPLIT back-trajectories for the Boise-Nampa area PM10/PM2.5 impact period 

2100–2300 MST, February 14, 2011 (NOAA Ready HYSPLIT model: 

http://ready.arl.noaa.gov/HYSPLIT_traj.php)................................................................ 35

Figure 31. February 14, 2011, PM2.5 composition (NCORE 2013) compared to Black Rock 

Playa surface soil composition (Gillett 1997). ............................................................... 36

Figure 32. PM 2.5/PM10 ratio at the Nampa fire station sorted from low to high (red line, left 

axis) versus paired 1-hour PM10 concentration (blue dots). ........................................... 38

Figure 33. Event-affected days along with nonevent days before and after the February 14–16, 

2011, event. .................................................................................................................... 40

Figure C-1. Hells Canyon speciation for February 2011, showing high coarse mass (top) and 

elevated soil component on February 14, 2011.............................................................. 63

Figure C-2. Hells Canyon speciation for February 2011 showing higher Si, Fe, Al, and Ca on 

February 14, 2011........................................................................................................... 64
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Acronyms, Abbreviations, and Symbols

μg microgram

μm micrometer

AAQ affects air quality

BRP Black Rock Playa

Ca calcium

CCR clear causal relationship 

CFR Code of Federal Regulations

CSP Carson Sink Playa

DEQ Idaho Department of 

Environmental Quality

EER Exceptional Events Rule

EPA United States Environmental 

Protection Agency

FR Federal Register

FS fire station (Boise and 

Nampa)

HAUR human activity unlikely to 

recur

HAURL human activity unlikely to 

recur at a particular location

HF historical fluctuations

HYSPLIT Hybrid Single Particle 

Lagrangian Integrated 

Trajectory

IMPROVE Interagency Monitoring of 

Protected Visual 

Environments

km kilometer

m meter

mb millibar

mph miles per hour

MODIS Moderate Resolution Imaging 

Spectroradiometer

MST mountain standard time

Na sodium

NAAQS National Ambient Air 

Quality Standard

NAM-ANL North American Mesoscale

Model-Analysis

NASA National Aeronautics and 

Space Administration

NE natural event

NEBF no exceedance but for

NCEP National Center for 

Environmental Prediction

NCORE National Core air monitoring 

network

NOAA National Oceanic and 

Atmospheric Administration

nRCP not reasonably controllable or 

preventable

NWS National Weather Service

PM10 particulate matter 10 

micrometers and smaller

PM2.5 particulate matter 10 

micrometers and smaller

PST Pacific standard time

s second

SIP state implementation plan

TFV threshold friction velocities
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Executive Summary

Northern Ada County is designated as a maintenance area for the National Ambient Air Quality 

Standard (NAAQS) for particulate matter 10 micrometers and smaller (PM10), and the Idaho 

Department of Environmental Quality (DEQ) has just completed the second 10-year 

maintenance plan. While PM10 levels have declined to well below the 150 micrograms per cubic 

meter (g/m3) standard since the last violation in 1991, a white haze settled in the area on 

February 14–16, 2011, causing the PM10 standard to be exceeded on February 15 and 16, 2011,

at the Boise fire station (Boise FS) and on February 15 at the Nampa fire station (Nampa FS). 

To address exceptional events that are not reasonably controllable or preventable, the United 

States Environmental Protection Agency (EPA) promulgated the Exceptional Events Rule (EER) 

in 40 CFR 50 and 51 (72 FR 13560) on March 22, 2007. The EER allows for states to flag air 

quality data as exceptional and exclude those data from use in determining compliance with the 

NAAQS, if EPA concurs with the state’s demonstration that it satisfies the rule requirements.

In accordance with the EER procedures, DEQ flagged two values at the Boise FS monitor and 

one at the Nampa FS monitor as indicated in Table A. DEQ demonstrates in this report, and 

requests EPA concurrence, that these three concentration values occurred as a result of natural 

conditions in another state, not reasonably controllable or preventable by the State of Idaho, fully 

meeting the criteria of the EER. 

Table A. Monitored values Included in this request for concurrence.

Monitor Site: Boise Fire Station No. 5,

Ada County, Idaho

Nampa Fire Station,

Canyon County, Idaho

Monitor ID (AQS#/POC): 16-001-0009 (POC 3) 16-027-0002 (POC 2)

Date PM10 Concentration Recorded, g/m3

2/15/2011 183 174

2/16/2011 156 a

Notes: Particulate matter 10 micrometers or smaller (PM 10); micrograms per cubic meter (g/m3)

a. Elevated PM10 concentrations of 55 and 68 g/m3at the Boise and Nampa fire stations, respectively on February 

14, 2011, and 108 g/m3at the Nampa fire station on February 16, 2011, were also influenced by the same multiday 

high wind event, however, concurrence is not requested for any values below the standard (150 g/m3).

The EER requires that demonstrations to justify data exclusion as exceptional events shall 

provide evidence that the event (a) affects air quality (AAQ); (b) is not reasonably controllable 

or preventable (nRCP), (c) is a natural event or is an event caused by human activity that is 

unlikely to recur at a particular location (NE/HAURL); (d) that there is a clear causal 

relationship (CCR) between the identified source and measurement under consideration; (e) that 

the event is associated with measured concentrations in excess of normal historical fluctuations 

(HF), including background; and (f) that there would have been no exceedance or violation of the 

standard but for the event (NEBF). In addition, the state must document that prompt public

notification procedures and measures to reduce public exposure were followed and that the 

public comment process was followed in reviewing the demonstration. DEQ’s demonstration 

satisfying these elements is summarized in Table B, which identifies the report section 
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containing each element of the demonstration. In addition, EPA’s detailed checklist for specific 

items recommended in the high wind strategy guidance (EPA 2013) is included in Appendix A.

Table B. Summary of DEQ demonstration in this report meeting Exceptional Event Rule elements.

Exceptional Event 

Rule (EER) Element Section Summary

Conceptual model 

(United States 

Environmental 

Protection Agency

guidance, not an EER 

element)

1 The conceptual model describes the source, natural dry lake beds or playas in 

northwest Nevada, high wind conditions, emissions mechanisms leading to 

the event, and transport conditions and concentration patterns. Impact area 

wind conditions contributing to high particulate matter 10 micrometers or 

smaller (PM10) levels remaining in place over portions of 2 days are also 

presented.

Not reasonably 

controllable or 

preventable (nRCP)

2 Pleistocene epoch dry lake bed playa surfaces, including Black Rock Playa 

(BRP) and Carson Sink Playa (CSP) are identified as the source areas. These 

are natural areas in another state that were exposed to winds over the wind 

speed threshold for natural areas and dust generation from them is not 

reasonably controllable or preventable (nRCP). In addition, there are no 

anthropogenic sources capable of contributing dust levels as high as those 

experienced during this event.

Exceeds historical 

fluctuations (HF)

3 The PM10 concentrations on February 15 and 16, 2011, are the highest 24-

hour concentrations observed in over 10 years at the Boise fire station, and 

the February 15 concentration is the second highest observed at the Nampa

fire station in the previous 10 years. A comparison to annual and seasonal 

data sets for the last 10 years is provided showing that normal historical 

fluctuations (HF) are well below these levels.

Clear causal 

relationship (CCR)

4 Evidence provided shows that the playas of northwest Nevada, notably BRP 

and CSP, are the source of dust impacting the Boise-Nampa area on February

15 and 16, 2011. Evidence includes wind data at the source area and at 

monitors; satellite images of dust blowing toward Boise-Nampa; backtrajectories linking BRP and CSP with the monitors in question; and chemical 

composition fingerprinting of the BRP soils that matches National Core 

(NCORE) air monitoring network air filters collected on February 14, 2011, the 

first day of the event. Alternative source hypotheses are discussed and shown 

to be incapable of creating levels this high.

Affects air quality (AAQ) 5 The affects air quality (AAQ) element is met by demonstrating PM10 in excess 

of historical fluctuations (HF) and a clear causal relationship (CCR) between 

source and monitored values.

Natural event or human 

activity unlikely to recur 

(NE/HAUR)

6 The natural event/human activity unlikely to recur (NE/HAUR) criterion is met 

by demonstrating that the event is a natural event that is not reasonably 

controllable or preventable (nRCP) and that there is a clear causal relationship

(CCR) with the identified natural source area. 

No exceedance but for

event (NEBF)

7 Nonevent PM10 levels are typically well below the National Ambient Air Quality 

Standards. A quantitative no exceedance but for (NEBF) analysis for the last 

10 years shows that PM10 levels are typically not more than 23 to 66 

micrograms per cubic meter (g/m3) for Boise and 24 to 78 g/m3for Nampa 

(annual average to 99th percentile). The three PM10 values under 

consideration all exceed the 99th percentile background level by more than 

90 g/m3. No other unusually significant sources were present during the 

event period. Thus, there would be no exceedance but for (NEBF) the high 

wind event involving the BRP and CSP source areas. 

Mitigation 8 DEQ provided prompt public advisories of the elevated levels and advice to 

reduce public health exposure on February 15 and 16, 2011.

EER procedures 9 DEQ met EER procedural requirements for flagging, demonstration, and 

public comment as summarized in this section.
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1 Conceptual Model

1.1 Overview

On February 14 and 15, 2011, high afternoon winds swept 4,000 square kilometers (km2) of the 

flat playa surface covering dry lake beds in northwest Nevada, including the Black Rock Playa

(BRP), and nearby Carson Sink Playa (CSP), entraining a fine white dust and transporting it 

toward the Boise-Nampa area of southwest Idaho. It arrived in the evening of February 15

sending hourly particulate matter 10 micrometers or smaller (PM10) concentrations over 

500 micrograms per cubic meter (g/m3) around midnight. Light winds and a weak surface 

inversion allowed the fine white dust cloud to remain over the most of the valley until it mixed 

out the next morning, causing monitors to exceed the National Ambient Air Quality Standards 

(NAAQS) for PM10 on February 15 and 16 at the Boise fire station (Boise FS) PM10 monitoring 

site and on February 15 at the Nampa fire station (Nampa FS) monitoring site.

1.2 Source Area and Affected Region

The source areas for this event are the flat alkali playas or dry lakebeds, BRP and CSP, and other 

smaller playas located within the Black Rock Desert region of northwest Nevada. The playas of 

western Nevada are clearly capable of producing dust clouds that may affect the Boise-Nampa 

area. Steenburgh et al. (2012) found in a satellite study of episodic dust events impacting the 

Wasatch Front area of Utah, that for most of the dust events in the period 2001–2010, “emission 

sources are located primarily in low-elevation late Pleistocene-Holocene alluvial environments in 

southern and western Utah and southern and western Nevada.” The BRP and CSP of western 

Nevada are approximately 350 miles from the Wasatch front, but only 200–300 miles from the 

Boise-Nampa area so dust emissions and transport from the BRP and CSP to the Boise-Nampa 

area are also likely to occur. The BRP is over 2,600 km2in area, one of the largest flat alkali 

playas on earth (Adams and Sada 2010). It is an arid region of lava beds and playa that lies 

within the footprint of late Pleistocene Lake Lahontan at a mean elevation of 4,000 feet (1,220

meters) above sea level. The CSP is approximately 1,300 km2so the total potentially erodible 

surface, including other smaller playas, is around 4,000 km2(the approximate size of Rhode 

Island).

The affected region around Boise and Nampa is located roughly 250 miles (400 km) northeast of 

the source region, however, elevated particulate levels during the period of February 14–16 

reached from Idaho City, Idaho, to Hells Canyon on the Oregon-Idaho border and as far north as 

Garden Valley, Idaho (possibly even McCall, Idaho). Boise has a mean elevation of 2,700 feet 

(824 meters) above sea level. Figure 1 shows the geographic location of Boise FS and Nampa FS 

monitors, the weather stations referenced in this document, and the BRP and CSP source areas. 

Boise lies within the lower Snake River basin and the smaller Boise River valley and is subject 

to the channeling effect of both of these topographic features. Mean wind flow from either the 

northwest or southeast through the basin is typical when diurnal up/down valley wind flow 

patterns dominate with light synoptic winds. The Nampa FS lies approximately 18 miles west of 

the Boise FS at an elevation of about 2,500 feet (762 meters). It is also in the lower Snake River 
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basin, however, it lies outside the Boise River valley and experiences less of the stagnation and 

terrain-influenced lighter winds that can trap pollutants in the Boise River valley, as occurred on 

the morning of February 16.

Figure 1. Location of Black Rock Playa and Carson Sink Playa source areas, affected PM10 

monitors at Boise and Nampa, and MESOWEST weather stations referenced in this report.
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1.3 Emissions Process

The BRP surface is composed of fine-grained clay and silt sediments mostly smaller than 

3 micrometers (μm) in diameter and dominated by minerals containing silica, aluminum oxide, 

iron, magnesium, and soluble salts (or evaporite minerals). Evaporite minerals include calcite 

(CaCO3), halite (NaCl), and gypsum (CaSO4

.

7H2O), which exhibit shrink-swell properties when 

wetted and dried, thereby making the surface crust looser, less compacted, and more available 

for wind erosion and transport (Adams and Sada 2010; Tollerud and Fantle 2012; Lewis et al. 

2011; and Reynolds et al. 2007, 2009). Reynolds et al. (2007) reports that evaporation of 

rainwater or shallow ground water evaporating through a capillary fringe zone produces fluffy

erodible sediments when salt crystals such as calcite, halite and gypsum grow during 

evaporation. To confirm this process Tollerud and Fantle (2012) exposed BRP sediments to 

wetting and drying cycles by simulating rain in laboratory tests. They found that added quantities 

of the evaporite minerals disrupted the hard clay surface of the sediments through formation and 

expansion of calcite and halite crystals . Reynolds et al. (2007) provides a schematic (Figure 2)

showing that the highest potential for dust emission from playas occurs not on dry playas but on 

wet playas when a very shallow capillary fringe exists near the surface due to a shallow water 

table or to a recent precipitation event. A wet playa is one with ephemeral hydrologic features, 

often even a small residual water body reflecting the presence of a shallow water table. BRP and 

CSP both have such features. Lewis et al. (2011) attributed one BRP dust storm they studied to 

antecedent precipitation 2 weeks prior to passage of a high wind front. 

Once loose unconsolidated minerals and sediments are produced by evaporation of rain or 

shallow ground water, the fluffy or puffy surface materials with increased calcium and sodium 

concentrations are more vulnerable to wind erosion. Ginoux et al. (2012) and Argaman et al. 

(2006) both identify wind erosion thresholds above which dust may become entrained to be 

around 15 miles per hour (mph) (10 meters) for extremely flat surfaces, based on threshold 

surface friction velocity of 0.6 meters per second (m/s) over deserts. Thus for a playa, any 10

meter wind over about 15 mph is likely to begin generating dust. At wind speeds double or triple 

that threshold, significant dust production may be expected. 

Figure 2. Schematic illustration of relationship between high dust potential and a near-surface 

capillary fringe zone on a wet playa versus a lower dust potential for a dry playa (Reynolds et al. 

2007).
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The effect of precipitation on the potential for dust from deserts and playas is complex, and it is 

important to distinguish the effect of antecedent precipitation in the weeks prior to a high wind 

event from antecedent precipitation in the months to years prior to high wind dust storms. The 

former, involving evaporite formation as described by Tollerud and Fantle (2012); Lewis et al. 

(2011); and Reynolds et al. (2007, 2009), relates to precipitation in the weeks prior to the dust 

storm on nonvegetated playas. The latter, involving reduced wind erosion due to increased 

vegetation growth promoted by precipitation months to years antecedent to the high wind 

conditions is also described in the literature (Urban et al. 2009; Holcombe et al. 1997; and 

Pelletier 2005). Both effects are well established, however, the surface mineral changes bringing 

calcium and sodium evaporite minerals to the surface as described by Tollerud and Fantle 

(2012), Lewis et al. (2011), and Reynolds et al. (2007, 2009) are believed to have contributed to 

the dust storm of February 14–16, 2011, on the largely unvegetated BRP and CSP. Nevertheless, 

back-trajectories, satellite images, and chemical composition all point to these playas as the 

source of the dust arriving in Boise-Nampa area on February 14–16, 2011, irrespective of 

mechanism.

During a windy day unrelated to the February 2011 event in question, an Idaho Department of 

Environmental Quality (DEQ) staff person traveling along Interstate I-80 in Nevada observed 

and photographed large white dust clouds arising from the playa (Figure 3) in the CSP area near 

Lovelock, Nevada. The photograph in Figure 3 was taken on March 28, 2012, at approximately 

1300–1400 Pacific standard time (PST) when the hourly winds averaged 22 mph and gusts 

reached 32 mph at two nearby meteorological stations. The white dust in this photograph

suggested to DEQ that the white haze in Boise and Nampa on February 15–16, 2011, might be 

related to these dry lake beds. The photograph is included in this report to help the reader 

conceptualize these dust events and to provide direct, if anecdotal, evidence that such events may 

occur with winds at least as low as 22 mph. 

Figure 3. Playa dust storm example near Carson Sink Playa, March 28, 2012.
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1.4 Contributing Weather Phenomena Synopsis

A relatively snow-free playa surface with unseasonably mild conditions allowing for rainfall in 

the last 2-3 weeks of January 2011 resulted in ideal conditions for developing an extremely large 

(~4,000 km2) erodible surface on the BRP, CSP, and other, smaller playa areas in the region. On 

February 14–16, 2011, a cold front moved through the northwestern Nevada area causing very 

high afternoon winds on each day from the southwest blowing toward the Boise-Nampa area of 

Idaho approximately 200–300 miles away. The dust cloud arrived first on February 14, 2011, 

then again on the morning of February 15, 2011, and finally the most dense cloud of white dust 

arrived on the evening of February 15, 2011, causing hourly PM10 concentrations to reach over 

500 g/m3by 2300 mountain standard time (MST). As the particulate concentrations began to 

climb, the local wind speeds at the Boise airport ranged from calm to 18 mph, well below the 

United States Environmental Protection Agency (EPA) suggested 25 mph threshold velocity for 

entraining dust from local sources such as natural desert, roadways, unvegetated lots, and 

agricultural fields (EPA 2013). The Boise airport winds remained relatively low overnight, 

allowing the dust cloud to remain in the area until morning. The dust was advected out of the 

valley around 0900 MST on February 16, 2011. To summarize, the weather phenomenon 

contributing to this event included (a) antecedent rain 2 to 5 weeks prior, producing a highly 

erodible surface, (b) a cold front with sustained high winds on February 14 and 15, entraining the 

dust from some of the 4,000 km2of playa, (c) transport winds carrying the dust from the playas 

to the Boise-Nampa area; and (d) light winds and a weak surface inversion, which allowed the 

dust cloud to remain in the area overnight, particularly at the Boise site where the surrounding 

foothills tend to somewhat mitigate the valley winds, in comparison to Nampa in the midvalley.

1.5 Path and Timeline from Source Area to Monitors

The time line of dust impacts in southwest Idaho are shown in Figure 4, which combines the (a) 

Boise-Nampa hourly PM10 concentrations, (b) southwest Idaho hourly PM2.5 concentrations, and

(c) Boise airport wind speeds and directions. Figure 5 shows the (a) surface wind speeds, (b) 

wind gusts, and (c) wind directions for selected stations in the source area (BLUN2, BUFN2, 

TR730, and KLOL) and in Oregon along the transport path from the playas to the Boise-Nampa 

area (GSFO3 and JVCI1). Detailed hourly data obtained from the MESOWEST service (Horel et 

al. 2002) are provided in Appendix B, along with station information, and their locations are 

shown in Figure 1. Three distinct periods of dust impacts occurred at the Boise FS and Nampa

FS monitors, typically preceded 8 to 12 hours earlier by high surface winds in the BRP and CSP 

source areas. High surface winds exceeding 25 mph occurred in the source regions on February

14 and 15 from around 1200 to 1600 MST with another period of high winds from 0400 to 0800 

MST on February 15. Wind speeds were well above the site-specific threshold wind speeds (15–

22 mph) for the onset of wind erosion. The path of dust transport suggested by these wind

observations is confirmed by the Hybrid Single Particle Lagrangian Integrated Trajectory 

(HYSPLIT) back-trajectories presented in section 4.3. 
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1.6 Concentration Patterns

Temporal Patterns—The rise in dust concentrations, indicated by the hourly PM10 at Boise and 

Nampa (Figure 4 (a)) and the PM2.5 concentrations at five locations in the southwestern Idaho 

area (Figure 4 (b)) indicates that the dust arrived at the southern edge of the area first (Nampa FS 

and St. Luke’s Meridian monitoring sites) then reached more northerly monitors later, beginning 

with Idaho City, followed by Garden Valley. Garden Valley PM2.5 levels did not increase until 

0200–0400 MST on February 16, suggesting that the dust plume may have passed over Idaho 

City to the east of Garden Valley, then reached Garden Valley from the east with the night time 

valley drainage flows of the South Fork Payette River. The PM2.5 peaks at the McCall monitor 

suggest that dust may have reached McCall, however, the increase is small and cannot be 

positively attributed to the dust storm. These temporal patterns, with southern sites recording 

higher particulate levels before northern sites, suggest that the source is located to the south of 

the Boise-Nampa area. 

Spatial Patterns—The spatial concentration pattern that occurred from February 12 to 17 is 

shown in Figure 6 representing 24-hour averaged PM2.5 concentrations throughout the southwest 

Idaho area. PM2.5 concentrations are shown because there are more PM2.5 monitors than PM10

monitors so they are preferred for reflecting the spatial pattern of the dust. The map in Figure 6

shows that the Boise-Nampa area received the highest concentrations but that the spatial extent 

of the dust cloud was very broad, reaching the mountainous sites at Idaho City and Garden 

Valley. The Interagency Monitoring of Protected Visual Environments (IMPROVE) aerosol 

monitoring site at Hells Canyon on the Oregon-Idaho border (IMPROVE 2013; Hand 2011; and 

NRC 1993) also appears to have elevated PM2.5 on February 14, with higher than normal 

geologic components compared to the other days in February 2011. IMPROVE speciation data 

for Hells Canyon are provided in Appendix C indicating higher PM2.5, higher coarse mass 

(> 2.5 m), and enrichment in the soil component as well as the geologic elements including 

silicon, iron, aluminum, magnesium, and calcium. This broad spatial pattern cannot be explained 

by typical local-scale anthropogenic dust sources such as road dust, construction, or local 

industrial facilities in Ada County, but it suggests a much larger regional-scale dust source 

originating some distance away and widely spread by variable wind directions. 
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Figure 4. (a) Boise and Nampa PM10 concentrations, (b) southwest Idaho hourly PM2.5 concentrations, and (c) wind conditions at the Boise airport from 

MESOWEST (Horel et al. 2002).
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Figure 5. (a) Surface wind speed, (b) wind gusts, and (c) wind directions at source area sites (BLUN2, BUFN2, TR730, and KLOL) and intermediate 

distances (GSFO3 and JVCI1) between source area and affected area. Figure 1 provides locations, and Appendix B provides station information and 

tabular data obtained from MESOWEST (Horel et al. 2002).
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Figure 6. Twenty-four hour PM2.5 concentration pattern in southwest Idaho on February 12, 2011,

(first bar) through February 17, 2011 (last bar). PM2.5 is a surrogate for PM10.

2 Not Reasonably Controllable or Preventable (nRCP)

2.1 Source Areas Contributing to the Event

The BRP is approximately 2,600 km2in surface area and extends approximately 100 km in 

length, trending northeasterly such that winds approaching it from 220 degrees and eroding dust 

along its entire length are aligned to carry the dust directly toward the Boise-Nampa area. The 

BRP is a dry alkali lakebed remnant of the Pleistocene epoch Lake Lahontan that covered much 

of northwest Nevada approximately 15,000 years ago (Adams and Sada 2010). Numerous other 

playas in the area, including CSP, are also remnants of Lake Lahontan. They presumably have 
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similar mineral composition and are likely to also contribute to the dust reaching southwest 

Idaho, including during the February 15–16 event. Thus, it is clear that BRP, CSP, and other 

playas are natural, having originated before modern human habitation in the area. Section 2.3

shows that these playas are not significantly altered by modern human activities. 

2.2 Source Area Wind Speeds

EPA will generally accept 25 mph as a high wind threshold as stated in the May 2013 interim 

guidance on high wind exceptional events (EPA 2013):

The high wind threshold is the minimum threshold wind speed capable of overwhelming reasonable 

controls on anthropogenic sources (i.e., significant emissions from controlled sources) or causing emissions 

from natural undisturbed areas. The EPA recommends that air agencies establish area-specific high wind 

thresholds based on local or applicable conditions and information. If an agency is unable to develop an 

area-specific high wind threshold, the EPA will generally accept a threshold of a sustained wind of 25 mph 

for areas in the West provided the agencies submit evidence of this as the level at which they expect stable 

surfaces (i.e., controlled anthropogenic and undisturbed natural surfaces) to be overwhelmed.

However, for extremely flat surfaces with disturbed or loose fine surface soils, the literature 

suggests that steady winds over 15 mph may cause blowing dust (Ginoux et al. 2012; Argaman

et al. 2006). This is consistent with the 22 mph wind speed that occurred when DEQ 

photographed a large turbulent dust storm on CSP. Together, the literature and DEQ observation 

establish an area-specific wind threshold range for entraining fine playa dust from 15 to 22 mph.

Wind speeds in Nevada on February 14–16, 2011, are shown in Figure 5 and provided in detail 

in Appendix B along with station identification and quality control information. All wind data 

were obtained from MESOWEST (Horel et al. 2002), which gathers data from meteorological 

networks throughout the west. Measured sustained winds at the southwest end of BRP (BLUN2),

northeast of BRP (TR730), and at Lovelock, Nevada, in the vicinity of the CSP (KLOL) 

exceeded 28 mph on February 15 (Figure 5), reaching 35 mph at the TR730 station north of the 

BRP and 31 mph at Lovelock, near the CSP. These 1-hour sustained wind speeds are well above 

the 15 mph sustained wind threshold established in the literature for extremely flat surfaces such 

as playas, above the 22 mph site-specific level documented when DEQ photographed turbulent 

dust clouds on the CSP and above the EPA default windspeed (25 mph) for natural undisturbed 

areas in the west. Wind gust speeds exceeded 30 mph at all the source region sites and reached or 

exceeded 45 mph at two of them (KLOL and TR730).

2.3 Basic Controls Analysis

Human activities that occur on the BRP include recreational vehicle traffic, gypsum mining, and 

periodic large but temporary gatherings such as amateur rocketry launches. The largest event, the 

annual Burning Man performance art festival is held at a temporary Black Rock City on the last 

week of August of each year. The Burning Man festival disturbs only about 1% of the playa 

surface (BLM 2012). Together with all other human activities, up to 7% of the playa surface is 

estimated to be disturbed by humans each year. However, the BLM concludes in the 2012 

Environmental Assessment for the Burning Man 2012–2016 Special Recreation Permit (BLM 

2012) that the weathering processes that occur in the fall and winter following the Burning Man 

festival “promote the formation of a surface crust on the playa, which would decrease the ability 
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of the winds to move dust.” If the human-disturbed playa surface contributed in any significant 

manner to dust from the BRP, the dust impacts would be expected to occur near the end of the 

summer during or shortly after the Burning Man festival when human disturbance peaks, rather 

than 6 months later in February. The winter season sees a minimum of human activity, due to 

harsh winter conditions, so the February 14–16 dust storm is not likely to be related to human 

activity. In addition, if human activity related to the Burning Man event was the primary cause of 

dust generation, the large turbulent dust clouds visible from space would be restricted to that 

location near the left-central portion of the BRP where Black Rock City is located and would not 

occur so broadly on the BRP and on the CSP, as seen in section 4.1, Figure 17. In conclusion, the 

dust storm of February 14–16, 2011 is a natural event with very little if any contribution from 

human activity.

Regardless of the conclusion that the February 14–16, 2011, dust storm is a natural event, it is 

also clear that even if human activity did contribute to a portion of the wind erosion on the playa

during this event, making it in a small part not a natural event, such human activity would be 

beyond the State of Idaho’s jurisdiction, and for the purposes of the EER demonstration and 

Idaho’s responsibility, the event would still remain not reasonably controllable or preventable

(nRCP). 

3 In Excess of Historical Fluctuations (HF)

Analysis and observations showed that high winds may create dust storms and elevate PM10

concentrations in the Boise-Nampa area but not often. Table 1 shows the statistics of the PM10

concentration at the Boise FS and Nampa FS monitors during the 10-year period from 2002 

through 2011 (EPA 2012). The mean annual 24-hour PM10 concentrations are 22.9 and 24.5 

μg/m3at Boise and Nampa, respectively 

Table 1. Statistics of 24-hour PM10 concentrations recorded in Boise and Nampa, 2002–2011.

Statistics Boise Nampa

Mean PM10 concentration (μg/m3) 22.9 24.5

Median PM10 concentration (μg/m3) 21.0 20.0

Mode PM10 concentration (μg/m3) 14.0 15.0

Standard deviation (μg/m3) 13.7 17.1

Count 3,325 2,852

Notes: Micrograms per cubic meter (μg/m3)

3.1 Time Series for the Previous Ten Years

High wind events usually last a short time. Therefore, the impact on the 24-hour average PM10

concentrations is very limited most of the time. Figure 7 and Figure 8 show the 24-hour PM10

concentrations from 2002 through 2011 at Boise and Nampa. There were only two days in which 

the PM10 concentrations were higher than 120 μg/m3in Boise (February 15 and 16, 2011), and 

five days in Nampa (including February 15, 2011). Days in which the PM10 exceeded 120 μg/m3

(an arbitrary break point for discussion only) are identified along with the maximum 1-hour wind 
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speed and 2-minute gust speed, recorded at the Boise airport for that day. These graphs indicate 

that local wind speeds over 30 mph and gusts over 40 mph are typically required in order for 

local dust sources to produce concentrations approaching the standard—speeds well above those 

recorded at Boise Air Terminal (KBOI) on February 15. Higher winds did occur on February 16, 

however, those winds did not generate the dust; they occurred after 0800 MST and served to 

blow the dust out of the valley, ending the high PM10 event. 

Figure 9 and Figure 10 show the 24-hour PM10 concentrations at Boise and Nampa monitoring

sites respectively, along with maximum daily 1-hour wind speeds, measured at the Boise airport, 

from 2002 through 2011. In these plots the wind speeds (red line) and paired 24-hour PM10

concentrations (blue dots) were sorted from highest to lowest wind speed to demonstrate that

when the maximum 1-hour wind speed is below about 30 mph, the general pattern does not show 

any apparent correlation between maximum wind speeds and PM10 concentrations, and PM10

concentrations never exceed 120 μg/m3(an arbitrary dividing point between normal fluctuations 

and extreme events). If the traditional local dust sources were a problem in the Boise-Nampa 

area, many more of the PM10 concentrations in Figure 9 and Figure 10 would increase on the far 

left as the highest winds occur. 

Figure 11 and Figure 12 show PM10 concentration distributions for Boise and Nampa, 

respectively. Both figures show that all the 24-hour average PM10 concentrations over 120 μg/m3

are isolated from the main distribution range. These distributions indicate that the February 2011

exceedance days are exceptional with respect to the sample distribution over the previous 

10 years. 

Figure 7. Historical PM10 fluctuations at Boise fire station no. 5, 2002–2011. Values over 120 μg/m3

are identified by date along with the maximum 1-hour wind speed/gust speed for that day.
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Figure 8. Historical PM10 fluctuations at the Nampa fire station, 2002–2011. Values over 120 μg/m3

are identified by date along with the maximum 1-hour wind speed/gust speed for that day.

Figure 9. PM10 concentration (blue dots) and paired maximum daily 1-hour wind speed (=SKNT, 

red line) at the Boise fire station, sorted by decreasing wind speed with the highest wind speeds 

to the left. The orange boxes indicate the February 15 and 16, 2011, exceedances. The wind 

speeds were measured at the Boise airport. Note that the high wind on February 16 occurred after

the event when a cold front blew the dust out.
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Figure 10. Daily mean PM10 concentration (blue dots) and paired 1-hour maximum wind speed 

(=SKNT, red line) at Nampa fire station sorted by decreasing wind speed with the highest wind 

speeds to the left. The orange box indicates the February 15, 2011, exceedance. 

Figure 11. PM10 concentration distribution, 2002–2011, at the Boise fire station.
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Figure 12. PM10 concentration distribution, 2002–2011, at the Nampa fire station.

3.2 Percentile of Concentrations

The exceptional concentrations on February 15 and 16, 2011, of 183 and 156 μg/m3respectively, 

are the highest and second highest values recorded at the Boise FS in the 10-year dataset from 

2002 to 2011. The February 15, 2011, concentration of 174 μg/m3at the Nampa FS was the 

second highest in the 2002–2011 annual dataset, just 1 μg/m3lower than the highest value 

(175 μg/m3) recorded on October 29, 2003. The percentile statistics for these values relative to 

the annual dataset for 2002–2011, and the 2002–2011 seasonal winter (December, January, and 

February) data set are summarized in Table 2. The percentiles with and without all high wind 

days are also shown. For the analysis summarized in Table 2, high wind days are defined as days 

with at least 1 hour in which the wind speed exceeded 25 mph, as recorded at the Boise airport’s

National Weather Service (NWS) station, KBOI. Finally, in the last column, the percentile 

ranking for each February exceedance is shown relative to the set of only the high wind days 

from 2002 through 2011 (days with maximum 1-hour wind speed > 25 mph). In comparison, the 

daily maximum 1-hour wind speed of 20.7 mph on February 15 at 1000 MST, was the 83rd 

percentile value for the 10-year period, with 610 of 3,647 days having a higher maximum hourly 

wind speed. This demonstrates the disconnect between this event and local winds.

It is clear from these statistics that the extreme PM10 concentrations observed February 15 and 

16, 2011, are exceptionally high amongst any subset of Boise and Nampa data, largely 

independent of season or wind conditions in the Boise-Nampa area.
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Table 2. Percentile statistics with respect to annual and seasonal datasets, with and without high 

wind days, 2002–2011.

Site Date PM10 

(μg/m3)

Percentile Relative to

Annual 

Dataa

Annual Data 

without High 

Wind Days

(> 25 mph)b

Winter 

Season 

Datac

Winter Data 

without High 

Wind Days

(> 25 mph)d

All High Wind 

Days with 

Maximum

1-hour Wind 

Speed

(> 25 mph)

e

Number of Boise fire 

station observations 3,322 3,112 809 769 208

Boise fire 

station 2/15 183 99.970% 99.968% 99.88% 99.87% 99.52%

Boise fire 

station 2/16 156 99.940% 99.936% 99.75% 99.74% 99.52%

Number of Nampa fire 

station observations 2,820 2,647 757 724 173

Nampa fire 

station 2/15 174 99.18% 99.96% 99.87% 99.86% 98.84%

Notes: Particulate matter 10 micrometers or smaller (PM10); micrograms per cubic meter (μg/m3); miles per hour 

(mph)

a. Annual data including all observations, 2002–2011

b. Annual data excluding all days with the maximum hourly wind speed above 25 mph

c. Winter data including all observations in December, January, and February, 2002–2011

d. Winter data excluding all days with the maximum hourly wind speed above 25 mph

e. High wind days including the 2002–2011 annual dataset after removing all days with a maximum daily 1-hour wind 

speed less than 25 mph

4 Clear Causal Relationship (CCR)

4.1 Occurrence and Geographic Extent of the Event

Occurrence—The dust that settled on the Boise-Nampa area on February 15, 2011, arrived 

briefly from 0800 to 1000 MST, and then again in the evening when it was trapped until the cold 

front blew it out of the area around 0800 to 0900 MST the morning of February 16. Since the 

area was dark for most of that time, the haze was not widely noticed beyond the NWS weather

observations indicating haze and not reported in the media other than to report the DEQ 

advisories (Appendix F). NWS entries identifying the haze are provided in Appendix B.

Geographic Extent—The geographic extent of the event can be seen in the PM2.5 concentration 

pattern represented in Figure 6. The dust was composed of 82%–96% coarse particles (2.5–

10 μm in size) and only 4%–18% in the fine mode, less than 2.5 μm in aerodynamic diameter. So 

PM2.5 levels are not as extreme as PM10 levels, however DEQ operates mostly PM2.5 monitors so 

PM2.5 is used as a surrogate for PM10 to show the spatial concentration patterns. Figure 6 shows 

that the highest particulate concentrations occurred at Nampa and Meridian on February 15 and 

16 but also reached the cities of Idaho City and Garden Valley in the mountains to the north of 

the Boise-Nampa area. Finally, the Hells Canyon IMPROVE site appears to also have been 
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impacted on February 14 (Appendix C), however, IMPROVE samples were not collected on 

February 15 or 16. 

MODIS Satellite Evidence—MODIS (Moderate Resolution Imaging Spectroradiometer)

satellite imagery of the source area (NOAA 2013) confirms that major dust plumes were 

generated over the BRP and CSP areas on February 14 and 15, 2011, and travelled in the 

direction of the Boise-Nampa area of southwest Idaho. The playa areas can be seen without 

significant dust generation on the morning of February 14, 2011 (Figure 13), which shows a 

MODIS true color image from the Terra satellite taken at approximately 1030 PST.

The increasing winds on February 14, 2011, began to generate significant dust clouds in the 

afternoon, as seen in the MODIS Aqua satellite image shown in Figure 14 taken around 

1330 PST. Turbulent dust clouds can be seen on the BRP and CSP, and white haze is visible 

trailing toward the northeast. The dust eroded from the BRP and CSP on February 14 first 

arrived in the Boise-Nampa area on February 14 around 1800 to 1900 MST, peaking around 

2200 MST as seen in the time series chart in Figure 4(a). Although the hourly PM10

concentration nearly reached 300 μg/m3on the evening of February 14, the 24-hour 

concentration was only 55 μg/m3at the Boise FS monitor and 68 μg/m3at the Nampa FS

monitor, so the NAAQS was not threatened and exceptional event concurrence is not requested. 

Nevertheless, the dust impact on February 14 is important to note, because the only National 

Core (NCORE) air monitoring network PM2.5 speciation samples collected during this 3-day 

wind episode, were collected on February 14. PM2.5 reached 24-hour levels around 25 μg/m3on 

this day at Nampa and Idaho City, well above the levels typical for this time of year. The 

February 14 speciation is discussed in section 4.6. 

On February 15, dust entrainment on the BRP and CSP started earlier in the day and can be seen 

in the ~1030 PST MODIS Terra image (Figure 15), already streaming to the northeast from the 

BRP and other smaller dry lakebeds and crossing the Nevada-Oregon border. By the time the 

afternoon MODIS Aqua image was taken (Figure 16), dust again streamed to the northeast, and 

turbulent puffy dust clouds are visible on both the BRP and CSP. To verify that the puffy clouds 

on the BRP and CSP are dust rather than water vapor condensation clouds, false color

magnifications of the February 15 afternoon MODIS image are shown for the BRP (left side of

Figure 17) and CSP (right side of Figure 17). Puffy, white-tan turbulent dust clouds can be seen 

on both playas, distinct from the blue-tinted moisture clouds in the area and are reminiscent of 

the dust clouds photographed by DEQ (Figure 3) near the CSP in March 2012. 
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Figure 13. MODIS true color image from the Terra satellite, captured at ~1030 PST on February 14, 

2011.
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Figure 14. MODIS Aqua image captured at ~1330 PST on February 14, 2011.
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Figure 15. MODIS true color image from the Terra satellite, captured at ~1030 PST on February 15, 

2011.
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Figure 16. MODIS Aqua image captured at ~1330 PST on February 15, 2011.
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Figure 17. MODIS Aqua false color images (clouds and snow are blue-tinted; dust is white) 

showing turbulent dust cloud generation on Black Rock Playa (left) and Carson Sink Playa (right) 

as well as dust plumes leaving the playas toward the northeast ~1330 PST February 15, 2011.

4.2 Description of Weather Conditions that Created the Event

Antecedent Conditions—As described in section 1.3, precipitation in the weeks prior to a wind 

event produces loose, highly erodible evaporite minerals on the surface of certain alkali playas 

such a BRP and CSP. Once loose materials are present on the surface, wind gusts may initiate 

saltation of small particles. Daily precipitation data at sites in the BRP and CSP source region for 

the period from January 1 through February 15, 2011, are shown in Figure 18 and are provided

in tabular form in Appendix B. Rain fell at Lovelock and Fallon, near the CSP and north of the 

BRP (TEXN2) on January 30, two weeks prior to the event, and relatively heavy rains fell at all 

sites around the BRP (BUFN2, BLUN2, TR730 and TEXN2) between January 12 and 16, 2011,

four weeks prior to the event. The two weeks prior to the event were dry at all stations except for 

TEXN2, a higher elevation station north of the BRP, which received 0.07 inches on February 5, 

still leaving nine days for drying and surface evaporite formation. DEQ believes that these 

precipitation patterns are ideal for enhancing the near-surface water table or moisture layer in the 

weeks prior to the high wind dust event and for causing significant surface evaporite mineral 

formation.
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Figure 18. Twenty-four hour precipitation totals in the BRP and CSP source region in the 45 days 

prior to the event.

Event Conditions—Also important for dust episodes stemming from the BRP and CSP are the 

passage of cold fronts (or baroclinic troughs) and geostrophic adjustment (Steenburgh et al.

2012). A trough passed through around 1100 MST on February 15, 2011, and propagated

eastward with the jet stream. This jet contributed to a rapid rate of pressure change as the 

atmosphere adjusted to geostrophic imbalance (Kaplan et al. 2010). It is possible to note the 

marked decrease in pressure of about 1 millibar per hour (mb*hr-1) at several stations in northern 

Nevada, such as Fallon and Elko, southern Idaho, and Ontario in eastern Oregon, associated with 

this passage when one compares Figure 19 and Figure 20.
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Figure 19. 1800Z (1100 MST) surface analysis February 15, 2011 (National Weather Service 

Hydrometeorological Prediction Center: http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml).

Figure 20. 2100Z (0200 MST) surface analysis February 15, 2011 (National Weather Service 

Hydrometeorological Prediction Center: http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml).
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High wind speeds can be observed across eastern Oregon and northwest Nevada preceding and 

on the event day using National Center for Environmental Prediction (NCEP)/North American 

Regional Reanalysis (NARR) model data (Mesinger et al. 2006, accessed November 23, 2012 

from http://www.esrl.noaa.gov/psd/ data/gridded/data.narr.html). The BRP lies along the edge 

of this boundary and experienced winds aloft of 25 m/s (56 mph) as shown in Figure 21.

Figure 21. NCEP/NARR model reanalysis of midlevel winds (meters per second), February 14–15, 

2011 (NOAA/ESRL Physical Science Division, Boulder Colorado: http://www.esrl.noaa.gov/psd/).

Steenburgh et al. (2012) noted that sustained winds of 10 m/s (22 mph) are strong enough to 

elevate dust, while Argaman et al. (2006) and Ginoux et al. (2012) suggest that 15 mph is an 

appropriate threshold velocity for wind erosion on flat surfaces with disturbed or loose material. 

After the morning inversion broke, the momentum associated with this midlevel flow would 

have mixed down to the surface and enhanced winds related to the baroclinic trough passage. 

Figure 22 shows the 1100 PST sounding information for Reno, Nevada. The figure indicates that 

not only had the inversion broken, but vertical mixing occurred as the temperature profile 

parallels the dry adiabat curve to around 690 millibar (mb). At this height, another inversion set

in and prevented any further mixing.
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Figure 22. Sounding information for Reno, Nevada, at 18Z (1100 PST) February 15, 2011 (National 

Weather Service Upper-Air Observations Program-Global Climate Observing System. University of 

Wyoming Sounding: http://weather.uwyo.edu/upperair/sounding.html).

Surface observations taken from stations across the desert and Great Basin on February 14 and 

15, 2011, indicate sustained wind speeds greater than 10 m/s (22 mph) for multiple consecutive 

hours across both days. Coupled with this were sufficiently high threshold friction velocities

(TFV). TFV values greater than 0.8 m/s are generally strong enough to erode both disturbed and 

undisturbed dust (Marticorena et al., 1997); however, Holcombe et al. (1997) noted that TVF 

values of 0.3–0.5 m/s are strong enough to lift disturbed particles, which are expected to be 

present on the playas. TFV is a measure for conditions necessary for blowing dust and is higher 

for undisturbed soils and lower for disturbed soils. Friction velocities have been calculated for 

18Z February 15 (1100 MST) using the NAM12 model. As illustrated in Figure 23, the TFV 

exceeds 0.4 m/s and is between 0.8 and 1.2 m/s across the source region indicating that the 

minimum TFV required to lift dust are met and exceeded for both disturbed and undisturbed 

crust. 
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Figure 23. Friction velocity for 18Z (1200 MST) February 15, 2012, NARR NAM-ANL (National 

Climatic Data Center National Operational Model Archive and Distribution System, NWS-NCEP 

NAM, 12 km: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets).

Presented with the following information, it is possible to relate observed meteorological 

conditions and atmospheric measurements to such a conceptual model. Observations taken from 

MESOWEST stations at KBOI (Boise, ID), KLOL (Lovelock, NV), and KWMC (Winnemucca, 

NV), provided in Appendix B, all indicate poor visibility and haze throughout the period of 

February 15–16, 2011. Weather conditions in Boise during the event promoted the containment 

and accumulation of particulate in the valley as a result of weak surface winds overnight and a 

weak surface inversion, as indicated in the February 16, 2011, morning (12Z) sounding shown in 

Figure 24 taken at Boise, Idaho.
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Figure 24. Sounding information for Boise, Idaho, at 12Z (0500 MST) February 16, 2011 (National 

Weather Service Upper-Air Observations Program-Global Climate Observing System. University of 

Wyoming Sounding: http://weather.uwyo.edu/upperair/sounding.html).

Winds the evening of February 15, 2011, ranged from calm to 18 mph over the time period of 

1900 to 0700 MST the morning of February 16, with observations of haze from 2200 to 0800 

MST. At 0900 MST a cold front associated with the trough axis responsible for the event passed 

through the area quickly removing any residual airborne dust. After that, conditions were 

reported as mostly clear as winds shifted from the southeast to the northwest, surface 

temperatures dropped from 48 oF to 33 oF, and snow began to fall. Figure 25 indicates the 

position of the cold front to be slightly west of Boise, Idaho, at 15Z on February 16, 2011 (0800 

MST), and Figure 26 indicates the position of the cold front to be east of Boise, Idaho, at 1800Z

on February 16, 2011 (1100 MST).
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Figure 25. 1500Z (0800 MST) surface analysis February 16, 2011 (National Weather Service 

Hydrometeorological Prediction Center: http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml).

Figure 26. 1800Z (1100 MST) surface analysis February 16, 2011 (National Weather Service 

Hydrometeorological Prediction Center: http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml).
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The observed surface winds during the afternoon of February 15, 2011 (1500 MST) are shown 

for the NWS and United States Department of Agriculture Forest Service/Bureau of Land 

Management remote automatic weather (RAWS) stations reporting to the MESOWEST service 

(Horel et al. 2002) in Figure 27. Winds in the source region around the playas are generally in 

the 20 to 28 mph range, and gusts reach up to 46 mph. Surface wind speeds between the BRP

and CSP area and Boise and Nampa monitors remain elevated but then decrease to around 

13 mph only after reaching the Snake River and Boise River valleys.

Figure 27. Surface winds 1500 MST on February 15, 2011, from MESOWEST (Horel et al. 2002).

Wind barbs point in the direction toward which the wind is blowing. Number on left of dot 

indicates hourly sustained wind speed, and number on right indicates the maximum 2-minute 

wind gust for that hour, both in miles per hour.
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4.3 Transport of Emissions Related to the Event in the Direction of 

the Monitor(s) Where Measurements Were Recorded

The transport of emissions from the source area to the monitors where the particulate 

measurements were recorded are shown graphically using back-trajectory plots, which begin at 

the monitors at the time that the PM10 levels are rising through the time that they either peak or 

pass. The back-trajectories are an established methodology that utilizes archived model 

meteorological fields, including a wind speed and wind direction vector for every hour and every 

12 km distance and links them backward in time, delineating the path that the air mass has taken 

in the previous 24 hours prior to its arrival at the monitor. Using this approach, whenever the 

suspected source area or areas occur along one or more of the back-trajectory lines, this is 

evidence linking the source area to the monitored peak concentrations, a key element 

demonstrating the causal relationship. 

Back-trajectories were computed using the National Oceanic and Atmospheric Administration’s 

(NOAA’s) Ready HYSPLIT modeling tool (Draxler and Rolph 2003). The archived NAM 12km

meteorological model was used to compute 24-hour long back-trajectories with modeled vertical 

motion, and starting elevations at 0, 500, and 1,000 meters aboveground level, ending at the 

Boise FS monitor (which is also reasonably representative of the Nampa FS monitor).

For the February 15–16, 2011, dust episode, two periods of time occurred in which the dust from 

the playas of northwest Nevada arrived in the Boise-Nampa area. The back-trajectories are 

designed to show the origin of the winds reaching Boise at these times. These two impact periods 

are visible in the PM10 time series plot in Figure 4:

 0500 to 1000 MST February 15—This was a smaller impact, with 1-hour PM10 

concentrations in the 200 to 330 μg/m3range, but it did contribute significantly to the 

recorded 24-hour PM10 concentration. The back-trajectories for this period, shown in 

Figure 28, indicate that the 500 meter and 1,000 meter trajectories pass near the BRP, 

closely paralleling the visible blowing dust trending toward Boise. 

 1600 to 2400 MST February 15—This is the major impact period when dust from 

Nevada reached hourly concentrations around 500 μg/m3, then remained trapped in the 

valley overnight until the dust was advected out of the valley around 0900 to 1000 MST 

on February 16. As a result, the high PM10 concentrations persisted for nearly 10 hours, 

exceeding the standard on both February 15 and 16 at the Boise FS monitor and on 

February 15 at the Nampa FS monitor. The back-trajectories for the period of rising PM10

concentrations on the evening of February 15, 2011, between 1600 and 2400 MST are 

shown in Figure 29. For the air mass arriving in Boise during this period, it appears that 

the surface level air may have passed over the CSP, while the 500 meter and 1,000 meter

air passed directly over the BRP. Thus, it appears that either or both playas may have 

contributed.

In summary, the back-trajectories for the dust impact periods on February 15 and 16, 2011,

corroborate the blowing dust visible in the MODIS satellite images for the same time frame and 

are consistent with the measured surface wind directions shown in Figure 27.
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Figure 28. HYSPLIT back-trajectories from the 0500–1000 MST PM10 peak at Boise-Nampa area on 

February 15, 2011 (NOAA Ready HYSPLIT model: http://ready.arl.noaa.gov/HYSPLIT_traj.php).
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Figure 29. HYSPLIT back-trajectories from the 1600–2400 MST PM10 peak at Boise-Nampa area on 

February 15, 2011 (NOAA Ready HYSPLIT model: http://ready.arl.noaa.gov/HYSPLIT_traj.php).
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4.4 Spatial Relationship Between the Event, Sources, Transport of 

Emissions, and Recorded Concentrations.

The spatial relationship between the wind erosion event at the BRP and CSP source areas, and 

the transport winds are depicted in Figure 28 and Figure 29 where back-trajectories lead directly 

from the impacted area of the Boise-Nampa monitors to the source areas. These modeled backtrajectories are confirmed by the recorded surface observations throughout the source and 

transport region, depicted graphically in Figure 27, as well as the MODIS satellite images in 

Figure 14 through Figure 16, which show dust blowing from the BRP and CSP source areas 

directly toward the Boise-Nampa area along the same 210 to 230 degrees bearing (from true 

north). 

4.5 Temporal Relationship Between the High Wind and Elevated PM 

Concentrations at the Monitor(s) in Question

Time series charts combining source area winds and wind directions, and Boise-Nampa area 

hourly PM10 monitor data and winds are shown in Figure 4 and Figure 5. These time series charts

show high afternoon winds in the source areas in Nevada blowing dust toward the Boise-Nampa 

area on the afternoon of February 14 and throughout most of the day on February 15, 2011. The 

dust, indicated by PM10 concentrations at Boise FS and Nampa FS monitors, peaked on February 

14 at 1900–2200 MST, and again on February 15 at 0500–1000 MST and 1600–2400 MST,

where it appeared to be trapped by reduced wind speeds until the increasing winds associated 

with the cold front blew it out of the valley the following morning. 

4.6 Similarity of Chemical Composition of Measured Pollution with 

that Expected from Sources Identified as Upwind

Chemical Similarity—The PM10 monitors indicated unusually high concentrations peaking at 

1900–2200 MST on February 14, 2011. Although the NAAQS was not threatened, the PM10

impacts are of interest on February 14 because that is the only day of the multiday high wind 

episode in Nevada for which a speciation sample was collected at the NCORE speciation site 

located at St. Luke’s Medical Center, Meridian, Idaho, sampling location, situated between the 

Boise FS and Nampa FS. The St. Luke’s speciation filters are routinely submitted to an EPA 

laboratory for extensive chemical analysis, thus providing a chemical composition for the dust. 

The PM10 at the Boise and Nampa FS monitoring sites and the PM2.5 at the St. Luke’s monitoring

site all reached unusually high levels on the evening of February 14, suggesting dust impacts. 

DEQ investigated the potential sources to see if the same source mechanisms and transport 

conditions occurred on February 14 as DEQ documented on February 15 and 16. 

First, winds in the source areas of northwest Nevada were obtained, verifying winds around 

25 mph with gusts exceeding 40 mph occurred for the entire afternoon from 1200 through 1800 

MST, with additional high wind periods around 2100 and 2300 MST (Figure 5). Next, MODIS 

satellite images were obtained showing that while visible dust was not blowing during the 

~1030 PST MODIS Terra satellite pass (Figure 13), visible dust blowing off the BRP toward the 

Boise-Nampa area was visible in the afternoon during the MODIS Aqua satellite pass at 

~1330 PST (Figure 14). 
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Finally, HYSPLIT back-trajectories were simulated, as described earlier, starting at Boise FS

during the peak PM10 hours, 1900–2300 MST, on February 14. As shown in Figure 30, surface 

level back-trajectories appear to pass over the CSP area where MODIS satellite images show 

vigorous puffy dust clouds indicative of turbulent wind erosion. The 500 meter and 1,000 meter

trajectories pass very near the western edge of the BRP suggesting that while CSP is a very 

likely source, BRP is potentially also a contributing source area on February 14.

Figure 30. HYSPLIT back-trajectories for the Boise-Nampa area PM10/PM2.5 impact period 2100–

2300 MST, February 14, 2011 (NOAA Ready HYSPLIT model:

http://ready.arl.noaa.gov/HYSPLIT_traj.php).

Based on the additional wind speed data, satellite images, and back-trajectories presented for 

February 14, DEQ concluded that the same source areas and transport conditions brought 

elevated PM10 and PM2.5 to the Boise-Nampa area on February 14 as was demonstrated for the 
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higher impacts observed on February 15–16, 2011, and therefore the chemical composition of 

the February 14 sample is a fingerprint of the same dust that caused the NAAQS violations on 

February 15–16, 2011. 

NCORE speciation data for February 14, 2011, is provided in Appendix D and is compared in 

Figure 31 to a literature composition for the BRP surface soils analysis (Gillett 1997). The 

February 14 St. Luke’s PM2.5 fingerprint matches the BRP surface soils composition very well

(Figure 31) but is slightly enriched in calcium (Ca) and sodium (Na). These are indicators of the 

water soluble evaporite minerals identified by Tollerud and Fantle (2012), and their enrichment 

in the February 14 NCORE samples supports the conceptual model mechanism involving wind 

erosion of calcium enriched evaporite minerals (along with clays and silts) made more erodible 

by antecedent precipitation in the weeks prior to the event.

Figure 31. February 14, 2011, PM2.5 composition (NCORE 2013) compared to Black Rock Playa 

surface soil composition (Gillett 1997).

It should be noted, as anecdotal weight-of-evidence, that the February 14, 2011, NCORE 

speciation represents the second highest geologic composition observed at the St. Luke’s 

NCORE site. An examination of the highest geologic component in the 2006–2011 database, 

which was recorded on November 22, 2006, indicates a remarkably similar composition to the 

February 14 sample, in that the calcium content was unusually high. DEQ examined winds in 

Nevada on November 22, 2006, developed back-trajectories, and concluded that the dust 

reaching the Boise-Nampa area on that day, while not approaching the PM10 standard in 

magnitude, also originated in the playa region of northwest Nevada under high wind conditions. 

DEQ concludes that high geologic component, enriched in calcium is a signature of the playa 

dust from the BRP, CSP, and other playas in northwest Nevada.
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Size Similarity—In addition to the chemical similarity between the dust reaching the BoiseNampa area on February 14, 2011, and BRP surface sediments, the size distribution provides 

additional information about the nature of potential sources. Wind-blown dust is known to be 

mostly larger than 2.5 μm in size, while most other sources of atmospheric particulate air 

pollution generate particles smaller than 2.5 μm. Smoke particles from combustion sources, 

including fires, residential wood combustion, gas and diesel vehicle exhaust, and industrial 

combustion sources are typically smaller than 1 μm in size. Secondary organic aerosols formed 

by condensation of gaseous organic compounds such as terpenes or polyaromatic hydrocarbons 

are also less than 2.5 μm in size. Finally, secondary inorganic aerosol species including 

ammonium nitrate and ammonium sulfate, formed when nitrogen oxides and sulfur oxides 

oxidize in the atmosphere and combine with ammonia are less than 2.5 μm. Careful examination 

of PM2.5 and PM10 hourly concentrations in Figure 4 indicates that the PM10 dust that arrived on 

February 15 was composed of approximately 4% to 18% PM2.5 (the remainder, 82% to 96% was 

in the coarse particle fraction, 2.5 to 10 μm in size).

Analysis of historical PM2.5/PM10 ratios data suggests that the event of February 14–16, 2011,

was a dust event. Figure 32 shows the PM2.5/PM10 ratio measured at the Nampa FS monitoring 

site in winter months over the previous 2 years (red line) sorted by increasing the PM2.5/PM10

ratio, along with the paired 1-hour PM10 concentration (blue squares). The data show that for the 

all samples with PM10 hourly concentrations higher than 100 μg/m3, the PM2.5/PM10 ratio is 

lower than ~0.2 (or 20%), indicating that the main component is coarse particulates, the character 

of dust particles, while the majority of winter hours have more than 20% PM2.5 indicating that 

they consist largely of smoke and secondary aerosol species typical of a winter speciation. Table 

3 shows that 18 of the 25 highest hourly PM10 concentrations (greater than 100 μg/m3) in the 

winter 2010 and 2011 dataset at the Nampa FS (circled red in Figure 32) were measured during 

the February 14–16 event. The other seven hourly PM10 concentrations above 100 μg/m3

occurred on days when the Boise airport winds were in the 22–25 mph range with gusts from 32 

to 39 mph, all higher than the winds recorded during the February 15 event. These nonevent

hourly observations reflect local dust transported a much shorter distance, allowing less of the 

larger particles to settle out, therefore having a more coarse composition and a lower 

PM2.5/PM10 ratio. The 24-hour averages that included the other hourly values never exceeded 

48 μg/m3at the Nampa FS or 21 μg/m3at the Boise FS, more typical of windy winter days where 

local sources dominate. In conclusion, the size information demonstrates that there is very little 

contribution from sources of fine particulate (PM2.5) during the event, such as car exhaust, 

burning, industrial combustion, and secondary aerosol formation but a somewhat greater 

PM2.5/PM10 ratio than expected during high wind dust storms originating from local sources.
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Figure 32. PM 2.5/PM10 ratio at the Nampa fire station sorted from low to high (red line, left axis) 

versus paired 1-hour PM10 concentration (blue dots).Hourly values above 100 μg/m3that occurred 

during the February 14–16 event are circled in red

Table 3. Hourly PM10 concentrations greater than 100 μg/m3at the Nampa fire station for winter 

2010 and 2011 only. Values related to this dust event are shown in bold (red circles in Figure 32).

Date

Hourly 

PM10

(μg/m3)

Date

Hourly 

PM10

(μg/m3)

Date

Hourly 

PM10 

(μg/m3)

1/19/2011 101 2/15/2011 141 2/16/2011 260

2/14/2011 285 2/15/2011 117 2/16/2011 202

2/14/2011 181 2/15/2011 103 2/16/2011 169

2/14/2011 151 2/15/2011 103 11/1/2011 139

2/15/2011 282 2/15/2011 101 11/3/2011 116

2/15/2011 231 2/16/2011 532 12/2/2011 339

2/15/2011 179 2/16/2011 328 12/2/2011 147

2/15/2011 162 2/16/2011 264 12/21/2011 282

— — — — 12/21/2011 228

Notes: Particulate matter 10 micrometers or smaller (PM10); micrograms per cubic 

meter (μg/m3). 

Difference in Composition from Typical Boise-Nampa Aerosol—The NCORE speciation 

sample captured on February 14 includes approximately 5 hours of elevated dust impacts

attributed to the BRP and CSP wind erosion source, while the remainder of the day exhibits

somewhat normal PM10 and PM2.5 concentrations, based on the time series chart presented in 
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Figure 4. DEQ transformed the NCORE speciation into the routine classifications of fine 

particulate matter (< 2.5 μm): elemental carbon (EC), organic carbon (OC), ammonium sulfate

((NH4)2SO4), ammonium nitrate (NH4NO3), and geologic (GEO) as shown in Table 4. The fine 

particulate matter in western cities is usually classified into these five categories and their sum 

should approximate the total PM2.5 mass. 

In addition to the February 14 composition, Table 4 shows that the average composition of the 

Boise-Nampa airshed averaged over 2009–2011, which is typically dominated by organic matter 

and ammonium nitrate, a secondary aerosol pollutant formed from photochemical reactions of 

nitrogen oxides to form nitrates and combine with ammonia. The winter speciation is similar to 

the annual speciation, with the exception that the ammonium nitrate is much higher and the 

geologic component is generally lower. On February 14, the ammonium nitrate and organic 

matter were lower than usual, and the geologic portion of the PM2.5 was much higher, 

comprising 37.7% of the mass, 10 times higher than the normal geologic composition in winter 

(3.7%). Most of the geologic particulate mass probably arrived mostly during 5 hours on the 

evening of February 14 when the PM10 peaked, while the remainder of the hours on that day 

apparently contributed organic matter and smaller amounts of other species reflective of near 

normal wintertime speciation.

Table 4. Comparison of February 14 St. Luke’s monitoring site PM2.5 composition with the annual 

average and winter season historical compositions, 2009–2011.

February 14, 2011, 24-hour Speciation Sample

Species OM EC (NH4)2SO4 NH4NO3 GEO PM2.5

Concentration 

(μg/m3)

1.4 0.2 0.3 0.3 2.3 6.1

% 22.7% 4.0% 5.2% 5.7% 37.7%

3-year Annual Average Speciation, 2009–2011

Species OM EC (NH4)2SO4 NH4NO3 GEO PM2.5

Concentration 

(μg/m3)

2.8 0.4 0.7 1.4 0.7 7.1

% 41.2% 5.4% 10.1% 20.7% 10.5% —

3-year Winter Average Speciation, 2009–2011

Species OM EC (NH4)2SO4 NH4NO3 GEO PM2.5

Concentration 

(μg/m3)

3.8 0.5 1.1 3.4 0.3 9.4

% 41.3% 5.3% 12.3% 36.3% 3.7% —

Notes: Organic carbon (OC); elemental carbon (EC); ammonium sulfate ((NH4)2SO4); ammonium nitrate 

(NH4NO3); geologic (GEO); particulate matter 2.5 micrometers or smaller (PM2.5); micrograms per cubic 

meter (μg/m3)
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4.7 Comparison of Event-Affected Days to Specific Nonevent Days—

Comparison of Area Concentrations and Wind Speeds in the 

Days Preceding and Following the Event

The high winds over the playas of northwestern Nevada lasted from about noon on February 14 

through the afternoon on February 15, 2011, and affected the Boise-Nampa area PM10

concentrations on February 14, 15, and 16. The elevated PM10 concentrations on these three days 

at the Boise FS and Nampa FS monitors are compared to the nonevent days before and after the 

event in Figure 33. This figure shows that the normal winter season PM10 concentrations are 

typically around 10–30 μg/m3even when the local winds are higher than those experienced on 

February 14 and 15 when the dust was transported to the area. The high wind speed on February 

16 is not associated with the dust event that persisted through the early morning hours but 

occurred later on that day when the cold front moved through the valley after about 0800 MST 

effectively blowing the dust out of the valley. Finally, it appears obvious from Figure 33 that the 

elevated PM10 concentrations on February 14 and 16 were also part of the same multiday wind 

event that peaked on February 15 although they are not included in this exception request.

Figure 33. Event-affected days along with nonevent days before and after the February 14–16, 

2011, event.

4.8 Alternative Hypotheses

The analysis presented in this report demonstrates that the elevated PM10 particulate matter 

impacting the Boise and Nampa FS monitors is composed of over 82% of coarse particulate 

(larger than 2.5 μm and smaller than 10 μm), predominately geologic in composition with some 

enrichment in evaporite mineral constituents calcium and sodium. Very little elemental carbon,
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ammonium sulfate, and ammonium nitrate particulate is present as is common in many 

wintertime western urban airsheds, including the Boise-Nampa airshed (section 4.6). It is 

therefore clear that the normal urban sources such as residential wood combustion, vehicle 

exhaust, industrial combustion, and outdoor burning are not contributors to any significant 

extent, but rather, the source is geologic in nature. In addition, the lack of significant elemental 

carbon, along with the timing in the winter season indicate that neither wildfires nor agricultural 

fires contributed to the PM10 levels during this event. 

Potential geologic particulate sources include road dust, construction dust, industrial emissions, 

agricultural dust, and wind erosion from nonagricultural lands, either those surrounding the 

Boise-Nampa area, or regional sources located outside the Treasure Valley of Idaho. All these 

potential sources are inherently included in the statistics for the previous 10 years provided in 

Section 3, “In Excess of Historical Fluctuations” and Section 7, “No Exceedance But For This 

Event,” and therefore are already excluded as probable sources since, historically, they rarely 

produced concentrations as high as those recorded on February 15 and 16. Nevertheless, DEQ 

considered each of these sources as a potential source category for coarse geologic dust and 

discusses each below. 

 Road Dust—Road dust emissions vary with the quantity of fine particles or silt on the 

roadway and the amount of vehicle traffic. The quantity of silt varies with season and is 

typically higher in the winter due to antiskid road sanding operations. However, road 

sanding agreements and cleanup documented in the Northern Ada County PM10 State 

Implementation Plan (SIP) (DEQ 2004) provide reasonable control of silt loadings 

resulting from winter antiskid treatment. In addition, the period from January 1 through 

February 15, 2011, just prior to this event, had the second lowest snowfall of any 

January 1–February 15 period in the previous 10 years, so road-sanding-related silt on the 

road should have been lower than most of the years included in the PM10 statistics 

described in section 3.1.

 Construction Dust—No major new construction projects were in progress in the vicinity 

of either the Boise FS or Nampa FS monitors in February 2011. February is also 

generally too early in the spring for any significant new construction elsewhere in the 

valley. Finally, it is unlikely that a location-specific source category such as construction 

would affect both sites similarly, not to mention the Idaho City and Garden Valley sites 

in the mountains to the north.

 Industrial Emissions—Idaho’s New Source Review Permitting Program limits industrial 

emissions. Air quality permits for 13 significant sources of dust were revised to limit 

allowable PM10 emissions in the 2004 Northern Ada County PM10 SIP (DEQ 2004). 

Thus, a decline in allowed industrial particulate emissions has occurred over the last 

10 years, and no sudden increase in industrial emissions appears to have occurred that is

large enough to reach the dust levels observed during this event.

 Agricultural Activity—Agricultural areas surround the city of Nampa and are not too far 

from the city of Boise and are a potential source of fugitive dust from tilling and 

harvesting or from wind erosion from bare fields that have been recently disturbed. 

Harvesting in the Treasure Valley occurs in the fall with the last harvest date for any 

major Idaho crop ending by November 10, while the earliest planting date for any major 

Idaho crop is March 21 (USDA 2010). Thus, soil-disturbing agricultural activities are at a 

minimum level in the winter, and 3 months of wintertime weather should serve to 
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minimize the freshly disturbed surface amenable to wind erosion. Finally, wind speeds at 

the Boise airport did not exceed 21 mph on February 15, so significant wind erosion from 

agricultural land is not likely to have contributed noticeably to the PM10 concentrations 

during this event.

 Nonagricultural Lands—The winds in the Boise area during this event did not exceed 

21 mph, with gusts no greater than 25 mph, much lower than other wind storms over the 

last 10 years that never produced PM10 concentrations approaching the standard, so it is 

very unlikely that natural, nonagricultural lands such as desert and rangeland in Idaho 

contributed significantly to the dust events of February 14–16, 2011.

Alternative source categories such as those described above are generally already characterized 

in the normal PM10 historical fluctuations (section 3) over the past 10 years, and no significant 

variation in any of these source categories is known that could cause an extreme PM10 episode of 

the magnitude and geographic extent observed February 14–16, 2011.

5 Affects Air Quality (AAQ)

The EER requires agencies to document that the identified source of an exceptional event truly 

affected air quality at the location of the monitor in question. However, EPA’s interim high wind 

guidance (EPA 2013) indicates that if historical fluctuations (HF) and a clear causal relationship

(CCR) have been adequately demonstrated, then the affects air quality (AAQ) element will have 

been met. 

The PM10 concentrations reached at the Boise FS on February 15 and 16, 2011, exceed any 

reached in the previous 10 years, far exceeding all normal historical fluctuations (section 3). 

Similarly, the February 15 PM10 concentration at the Nampa FS monitor exceeded all but one 

value in the previous 10 years demonstrating both sites exceeded normal historical fluctuations. 

In addition, a clear causal relationship has been demonstrated through back-trajectories, satellite 

images, and composition, linking dry lake beds in Nevada to these events (section 4). Therefore 

the high wind events originating at the BRP and/or CSP in Nevada clearly affected air quality at 

the Boise FS and Nampa FS monitoring sites on February 15 and 16, and DEQ has satisfied the 

affects air quality criterion. 

6 Natural Event or Human Activity Unlikely to Recur at the 

Same Location (NE/HAURL)

The EER requires agencies to document that the identified source of an exceptional event is 

either a natural event (NE) or a human activity unlikely to recur at the same location (HAURL) 

and affects the monitors in question again. However, EPA’s interim high wind guidance (EPA 

2013) indicates that if an agency has adequately demonstrated that the source is a natural event 

or, if not natural, is not reasonably controllable or preventable and that there is a clear causal 

relationship between the identified source and the affected monitor, then the natural event/human 

activity unlikely to recur at the same location criterion is also satisfied. 
Request for Concurrence PM10 Exceptional Events

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DEQ demonstrated in section 4 that there is a clear causal relationship between the BRP and CSP 

source areas in Nevada and the extremely high PM10 levels at the Boise FS and Nampa FS

monitors on February 15 and 16, 2011. DEQ showed in section 2 that these Pleistocene-era dry 

lakebeds are not only natural sources, with a natural dust generation mechanism minimally 

influenced by human activity, but also that even if human activity was considered significant 

enough to term the playa emissions in some small part not natural, Idaho has no control over any 

human activity occurring on federal lands in another state, and therefore from an Idaho 

perspective, the source would remain not reasonably controllable or preventable.

7 No Exceedance But For this Event (NEBF)

The EER 40 CFR 50.14(b)(1) directs EPA to exclude data only where an agency demonstrates an 

exceptional event caused a concentration in excess of a NAAQS. It must be shown that the 

concentrations at the monitor would have been below the standard if the event had not occurred 

(i.e., but for the event).

EPA guidance (EPA 2013) suggests that if nonevent pollution levels are typically significantly 

below the NAAQS during the season of the event, then a qualitative no exceedance but for

(NEBF) may be adequate. The very low 95th and 99th percentile values in Table 5 demonstrate 

that this is the case. The discussion of particle size in section 4.6 demonstrating that fire and 

secondary aerosol cannot be responsible, and the discussion of alternative local dust sources in 

section 4.8 demonstrate qualitatively that no other local sources could cause PM10 concentrations 

as high as those recorded during this event. A quantitative no exceedance but for analysis is 

provided below in addition to the qualitative discussion.

Quantitative No Exceedance But For Analysis—The clear causal relationship with the Nevada 

playas has already been established in section 4. Table 5 shows the PM10 concentrations at the 

Boise FS and Nampa FS monitoring sites representing the average, 95th and 99th percentile 

concentration values for historical annual and winter season monitoring data, 2002–2011. While 

the most probable upper end of the range of concentrations expected at Boise FS and Nampa FS 

monitors may be represented by the average and 95th percentile values (EPA 2013), DEQ will 

assume that the normal background fluctuations could have been as high as the 99th percentile

historical value, to be conservative.

The statistics shown in Table 5 indicate that the normal year-round concentrations at the Boise 

FS, but for the BRP and CSP playa dust on February 15 and 16, 2011, would have been at or 

below the range 23–45 μg/m3and 99% of the time it would have been 66 μg/m3or less. The 

Boise FS concentrations on February 15 and 16 were 183 μg/m3and 156 μg/m3, respectively, so 

it is clear that the playa dust contributed at least 117 μg/m3on February 15 (183 − 66 = 117) and 

90 μg/m3on February 16 (156 − 66 = 90). Thus, the event contributed more than half the PM10

on these two days, and it is clear that the NAAQS (150 μg/m3) would not have been exceeded 

but for the regional transport event from the playas as described in this document. 

At the Nampa FS, the normal concentrations, but for the BRP and CSP playa dust would have 

been in the range 24–56 μg/m3, and 99% of the time, it would have been less than 78 μg/m3

based on the annual values in Table 5. Again, it is clear, that at the Nampa FS, over half the PM10

concentration of 174 μg/m3 measured on February 15 resulted from the regional playa dust event 
Request for Concurrence PM10 Exceptional Events

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and that at least 96 μg/m3(174 − 78 = 96) or 55% of the February 15 concentration may be 

attributed to the playa dust. Therefore, the NAAQS would not have been exceeded on that day 

but for the regional transport event from the playas. 

The seasonal statistics shown in the bottom of Table 5 are very similar to the annual percentiles, 

indicating again no significant seasonal variation and no substantial difference in the but for

demonstration.

Table 5. Average, 95th and 99th percentile of PM10 concentrations (μg/m3) in Boise and Nampa, 

2002–2011, in comparison to recorded values during this event. Statistics are shown for all data 

(top) and winter season (bottom).

Site Annual 

Average

Annual 95th

Percentile

Annual 99th

Percentile

Recorded Values

Feb. 15 Feb. 16

Boise 23 45 66 183 156

Nampa 24 56 78 174

Site Seasonal 

Average

Seasonal 95th

Percentile

Seasonal 99th

Percentile

Recorded Values

Feb. 15 Feb. 16

Boise 20 41 65 183 156

Nampa 19 40 80 174 —

8 Mitigation

The mitigation provisions of the EER (40 CFR 51.930) require that (EPA 2013):

(a) A State requesting to exclude air quality data due to exceptional events must take appropriate and 

reasonable actions to protect public health from exceedances or violations of the national ambient air 

quality standards. At a minimum, the State must:

(1) Provide for prompt public notification whenever air quality concentrations exceed or are expected to 

exceed an applicable ambient air quality standard;

(2) Provide for public education concerning actions that individuals may take to reduce exposures to 

unhealthy levels of air quality during and following an exceptional event; and

(3) Provide for the implementation of appropriate measures to protect public health from exceedances or 

violations of ambient air quality standards caused by exceptional events.

The dust event of February 15 and 16, 2011, arrived mostly in the evening, without the warning 

signs that usually accompany high winds such as thunderstorms or very windy conditions. 

Nevertheless, DEQ’s Boise Regional Office issued air quality alerts at 1023 MST on February 

15 and again at 0909 MST on February 16, alerting the public to the high particulate levels and 

providing public advisory information concerning actions that individuals may take to reduce 

exposures to unhealthy levels of particulate dust in the air. Given the sudden nature of the event, 

and the prompt dispersal of the dust on the morning of February 16, there was no time nor need 

for additional advisories or educational material. DEQ’s public advisory messages and associated 

public health educational material are provided in Appendix E. News stories based on DEQ 

advisories that also contributed to informing the public are provided in Appendix F.

In conclusion, the DEQ public notification process successfully alerted the public during this 

event and in view of the very low frequency of occurrence in the prior 10 years, DEQ believes 
Request for Concurrence PM10 Exceptional Events

45

that additional public notification measures are not necessary and source mitigation is not 

feasible.

9 Procedural Requirements

The EER establishes specific procedural requirements that an air agency must follow to request 

data exclusion (EPA 2013). Those requirements and DEQ’s actions to meet them are 

summarized in Table 6. 

Table 6. DEQ compliance with procedural requirements of the exceptional events rule.

Exceptional Event Rule Procedural Requirements DEQ Action/Intended Action

A State shall notify EPA of its intent to exclude one or more 

measured exceedances of an applicable ambient air quality standard 

as being due to an exceptional event by placing a flag in the 

appropriate field for the data record of concern which has been 

submitted to the AQS database... 40 CFR 50.14(c)(2)(i)

DEQ placed flags on the three 

samples described in this report 

in prior to July 2012.

The placement of the flags and the submittal of an initial event 

description must be done not later than July 1st of the calendar year 

following the year in which the flagged measurement occurred. 40 

CFR 50.14(c)(2)(iii)

DEQ placed flags on the three 

samples described in this report 

in prior to July 2012.

A State that has flagged data as being due to an exceptional event 

and is requesting exclusion of the affected measurement data shall, 

after notice and opportunity for public comment, submit a 

demonstration to justify data exclusion to EPA not later than the 

lesser of, 3 years following the end of the calendar quarter in which 

the flagged concentration was recorded or, 12 months prior to the 

date that a regulatory decision must be made by EPA. A State must 

submit the public comments it received along with its demonstration 

to EPA. 40 CFR (50.14(c)(3)(i))

DEQ submitted this package for 

public comment on August 5, 

2013. It received no comments in 

the 30 day public comment 

period. DEQ is now submitting it 

to EPA for concurrence, less than 

3 years following the first quarter 

of 2011, when the event 

occurred. 

With the submission of the demonstration, the air agency must 

document that the public comment process was followed. 40 CFR 

(50.14(c)(3)(iv))

DEQ presented this 

demonstration for public 

comment August 5, 2013 for a 

period of at least 30 days. No 

public comments were received 

and no changes were made in 

the document with the exception 

of updates in this table.
Request for Concurrence PM10 Exceptional Events

46

10 References

Adams, K.D. and D.W. Sada. 2010. Black Rock Playa, Northwestern Nevada: Physical 

Processes and Aquatic Life. Desert Research Institute.

Argaman, E., A. Singer, and H. Tsoar. 2006. “Erodibility of Some Crust Forming 

Soils/Sediments from the Southern Aral Sea Basin as Determined in a Wind Tunnel.” 

Earth Surface Processes and Landforms 31:47-63.

BLM (United States Bureau of Land Management). 2012. “Burning Man 2012–2016 Special 

Recreation Permit NVW03500-12-01 Final Environmental Assessment.” Winnemucca, 

NV: BLM, Winnemucca District Office. DOI-BLM-NV-W030-2012-0007-EA.

DEQ (Idaho Department of Environmental Quality). 2004. Northern Ada County PM10 State 

Implementation Plan. Boise ID: DEQ.

Draxler, R.R. and G.D. Rolph. 2003. HYSPLIT (HYbrid Single-Particle Lagrangian Integrated 

Trajectory) Model Access via NOAA ARL READY Website. National Oceanic and 

Atmospheric Administration, Air Resources Laboratory.

http://ready.arl.noaa.gov/HYSPLIT_traj.php

EPA (United States Environmental Protection Agency). 2013. Interim Guidance on the 

Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality 

Data Affected by High Winds Under the Exceptional Events Rule. Washington, DC: EPA.

Gillett, S.L., 1997. Toward a Silicate-based Molecular Nanotechnology. Presented at the Fifth 

Foresight Conference on Molecular Nanotechnology, November 8. Palo Alto, CA. 

Accessed October 17, 2012. 

http://www.foresight.org/Conferences/MNT05/Papers/Gillett1/

Ginoux, P., J.M. Prospero, T.E. Gill, N.C. Hsu, and M. Zhao. 2012. “Global-Scale Attribution of 

Anthropogenic and Natural Dust Sources and Their Emission Rates Based on MODIS 

Deep Blue Aerosol Products.” Reviews of Geophysics 50. RG3005, 

doi:10.1029/2012RG000388.

Hand J.L. et al. 2011. IMPROVE, Interagency Monitoring of Protected Visual Environments: 

Spatial and Seasonal Patterns and Temporal Variability of Haze and its Constituents in 

the United States. Fort Collins, CO: Cooperative Institute for Research in the 

Atmosphere. Colorado State University. Report V. ISSN 0737-5352-87.

Holcombe, T.L., T. Ley, and D.A. Gillette. 1997. “Effects of Prior Precipitation and Source Area 

Characteristics on Threshold Wind Velocities for Blowing Dust Episodes, Sonoran 

Desert 1948-78.” Journal of Applied Meteorology 36: 1160-1175.

Horel, J. et al. 2002. “Mesowest: Cooperative Mesonets in the Western United States.” Bulletin

of the American Meteorlogical Society 83: 211–225. http://mesowest.utah.edu/
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47

IMPROVE (Interagency Monitoring of Protected Visual Environments). 2013. “IMPROVE 

Aerosol Data.”. http://vista.cira.colostate.edu/improve/Data/IMPROVE/AsciiData.aspx

Kaplan, M.L., R. Vellore, and J.M. Lewis. 2010. “Dust Storm Over the Black Rock Desert, Part 

II: Mesoscale Subgeostrophic Jet Streak Circulations Organizing the Deep Convective 

Boundary Layer.” Journal of Geophysical Research. Submitted.

Lewis, J.M., M.L. Kaplan, R. Vellore, R.M. Rabin, J. Hallett, and S.A. Cohn. 2011. “Dust Storm 

Over the Black Rock Desert: Larger‐Scale Dynamic Signatures.” Journal of Geophysical 

Research 116. D06113, doi:10.1029/2010JD014784.

Marticorena, B., G. Bergametti, D. Gillette, and J. Belnap. 1997. “Factors Controlling Threshold 

Friction Velocity in Semiarid and Arid Areas of the United States.” Journal of 

Geophysical Research 102: 23, 277–23, 287.

Mesinger, F. et al. 2006. “North American Regional Reanalysis: A Long-Term, Consistent, 

High-Resolution Climate Dataset for the North American Domain, as a Major 

Improvement Upon the Earlier Global Reanalysis Datasets in Both Resolution and 

Accuracy.” Bulletin of the American Meteorological Society. 87, 3, p. 343. March 2006.

National Climatic Data Center. 2012. “National Operational Model Archive and Distribution 

System, NWS-NCEP NAM, 12 km.” Accessed December 6, 2012. 

http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets

National Weather Service. 2012. “Hydrometeorological Prediction Center Surface Analysis 

Archive.” Accessed November 23, 2012. 

http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml

National Weather Service. 2012. “Upper-Air Observations Program-Global Climate Observing 

System (GCOS).” University of Wyoming Sounding. Assessed November 23, 2012. 

http://weather.uwyo.edu/upperair/sounding.html

NOAA (National Oceanic and Atmospheric Administration). 2012. “NOAA/ESRL Physical 

Science Division.” Earth Systems Research Laboratory. Boulder, CO. Accessed 

November 23, 2012. http://www.esrl.noaa.gov/psd/

NOAA (National Oceanic and Atmospheric Administration). 2013. “MODIS Satellite Images.”

Accessed April 2013. http://ge.ssec.wisc.edu/modis-today/

NOAA (National Oceanic and Atmospheric Administration). No date. “Ready HYSPLIT 

Model.” http://ready.arl.noaa.gov/HYSPLIT_traj.php

NRC (National Research Council). 1993. Protecting Visibility in National Parks and Wilderness

Areas. Washington, DC: The National Academies Press, 1993.

Pelletier, J.D. 2006. Sensitivity of Playa Windblown-Dust Emissions to Climactic and 

Anthropogenic Change.” Journal of Arid Environments 66: 62-75.
Request for Concurrence PM10 Exceptional Events

48

Reynolds, R.L., J.C. Yount, M. Reheis, H. Goldstein, P.Chavez, Jr., R. Fulton, J.Whitney, 

C. Fuller, and R.M. Forester. 2007. “Dust Emission from Wet and Dry Playas in the 

Mojave Desert, USA.” Earth Surface Processes Landforms 32:1811-1827.

Reynolds, R.L., R. Bogle, J. Vogel, H. Goldstein, and J. Yount. 2009. "Dust Emission at 

Franklin Lake Playa, Mojave Desert (USA). Response to Meteorological and Hydrologic 

Changes 2005-2008." Natural Resources and Environmental Issues 15(18). 

Steenburgh, W.J., J.D. Massey, and T.H. Painter. 2012. “Episodic Dust Events of Utah's 

Wasatch Front and Adjoining Region.” Journal of Applied Meteorology and Climatology

51: 1654–1669.

Tollerud, H.J. and M.S. Fantle. 2012. “Temporal Development of Surface Roughness and its 

Relationship with Water in a Playa Dust Source: The Impact of Precipitation and 

Inundation on Surface Properties.” American Geophysical Union. Fall Meeting. Poster 

Abstract A33E-0208.

Urban, F.E., R.L. Reynolds, and R. Fulton. 2009. The Dynamic Interaction of Climate, 

Vegetation, and Dust Emission, Mojave Desert, USA.” in Arid Environments and Wind 

Erosion. A. Fernandez-Bernal and M.A. De La Rosa eds. Nova Science Publishers. ISBN 

978-1-60692-411-2.

USDA (United States Department of Agriculture). 2010. “Field Crops Usual Planting and 

Harvesting Dates.” Agricultural Handbook. Number 628. National Agricultural Statistics 

Service.
Request for Concurrence PM10 Exceptional Events

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Request for Concurrence PM10 Exceptional Events

50

Appendix A. EPA Completion Checklist

Completeness Checklist for High Wind Dust Exceptional Events Demonstration:

Site Name/AQS ID: Boise FS 16-001-0009 POC3 and Nampa FS: 10-027-0002 POC2

Pollutant: PM10

Date(s): Boise FS: February 15 and 16, 2011. Nampa FS: February 15, 2011

Table A-1. EPA completion checklist.

Procedural Criteria EPA Use

Did an exceedance of the NAAQS occur? Yes

Were data flagged by July 1st of following year (or by another appropriate deadline 

associated with a new or revised NAAQS)?

Yes

Was there a 30-day public comment period?

Is documentation for the comment period included?

Aug 2013

Will be

If public comments were received, are the public comments and responses 

included?

Will 

be

Was the package submitted within 3 years of the end of the quarter in which 

the event occurred and 12 months prior to the date that any regulatory decision 

must be made by the EPA (or by another appropriate deadline associated with a 

new or revised NAAQS)?

Will 

be

Evidence Information Included Page(s) E

P

A

U

s

e

Conceptual Model p. 1-8

-description of weather phenomena resulting in high 

wind

Yes p. 5

p. 23-30

-description of what sources were likely 

entrained by the high wind

Yes p. 1, 3, 4

-explanation of the path by which the dust 

reached the monitor(s)

Yes p. 5, 31-34

-map showing relevant monitors, topography, other 

relevant geographic features

Yes p. 2

-description of how the event day differs from nonevent days

Yes p. 38-40

-description of concentration and wind patterns for 

the exceeding monitor(s) and surrounding area

Yes p. 5 - 8

Wind Statistics

-max sustained wind (Hourly avg) 35 mph in Nevada p. 7, 8 & 

App. B

- max sustained wind (1-5 min avg) 48 mph in Nevada p. 7, 8 & 

App. B

-max gust (1 min avg) 49 mph in Nevada p. 7, 8 & 

App. B

-wind trajectories included? Yes p. 32 - 33
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-other: Modeled Friction 

Velocities

p. 26, 27

nRCP

-Area-specific high wind threshold (default = 

25mph)

15 - 22 mph for flat 

playas

p. 3, 4

-sources contributing to event identified, 

including anthropogenic vs. natural?

Yes - Natural p. 1, 10, 11

-controls identified for anthropogenic sources? (note: 

level of control analysis depends on wind speed)

Not applicable – no

anthropogenic sources

N/A

-are natural sources not reasonably controllable? Yes p. 10, 11

-was a High Wind Action Plan included? No – Not applicable N/A

HF

-were time-series analyses for concentration and wind 

data included?

Yes p. 7, 8

-annual comparison to historical data (wind and 

concentrations)

> 99%ile for all 3 

concentration values. 

83%tile for Boise wind

p. 15, 16

-seasonal comparison to historical data (wind and 

concentrations)

> 99%ile for all 3 

concentration values. 

Local wind no relevant

p. 15, 16

CCR (=> AAQ & / Natural Event)

-were spatial analyses included, establishing a spatial 

relationship between the event, sources, transport of 

emissions, and recorded concentrations?

Yes: a)Satellite Images 

and b)Hysplit Backtrajectories

 a)Fig 6,

 b)p. 31-33

-were temporal analyses included, establishing a 

temporal relationship between the high wind and 

elevated PM concentrations at the monitor?

Yes

p. 5-8

p. 31

-comparison of event-affected day(s) to specific nonevent days?

Yes p. 38, 39, 40

-was the dust shown to be from the sources 

discussed in the nRCP section?

Yes Sec 4 CCR

p. 16-41

-were alternative hypotheses discussed? Yes p. 40-42

-was a causal (not just correlational) relationship 

established?

Yes Sec 4 CCR

p. 16-41

NEBF

-was a “but for” analysis included? Yes p. 43-44
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Appendix B. Supporting Meteorological Data 

Table B-1. Identification of MESOWEST stations used in this report (Horel et al. 2002).

Station 

ID

Station Name Mesonet 

ID

Latitude Longitude Elevation, 

ft

BUFN2 BUFFALO CREEK RAWS 40.5806 -119.7888 3940

BLUN2 BLUEWING MOUNTAIN RAWS 40.5015 -119.1216 4570

TR730 DOUBLE H RAWS 41.6525 -118.0442 6380

JVCI1 JORDAN VALLEY CWMA SCAN 42.9500 -117.0100 4508

GSFO3 GRASSY MOUNTAIN RAWS 42.6261 -117.3951 4560

TEXN2 TEXAS SPRINGS RAWS 41.8009 -118.4514 5760

KBOI BOISE AIR TERMINAL NWS/FAA 43.5670 -116.2405 2822

KLOL LOVELOCK, DERBY FIELD AIRPT NWS/FAA 40.0684 -118.5702 3901

KNFL FALLON, NAVAL AIR STATION NWS/FAA 39.43222 -118.686 3934

KWMC WINNEMUCCA MUNICIPAL AIRPT NWS/FAA 40.9019 -117.8072 4301

All meteorological data were obtained from MESOWEST at http://mesowest.utah.edu/

This study was made possible in part due to the data made available by the governmental 

agencies, commercial firms, and educational institutions participating in MesoWest.

Data quality control information for individual networks and additional overall quality control

checks implemented by MESOWEST is identified below.

Quality control for NWS/FAA stations:

Federal Meteorological Handbook No. 1 - Surface Weather Observations and Reports September 

2005: http://www.ofcm.gov/fmh-1/fmh1.htm

Quality control for USDA RAWS stations: 

http://raws.fam.nwcg.gov/nfdrs/WeatherStationStandards.pdf

SCAN, Soil Climate Analysis Network, Natural Resources Conservation Service, USDA:

http://www.wcc.nrcs.usda.gov/scan/

MESOWEST Quality Control: http://mesowest.utah.edu/html/help/qc.html
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Table B-2. Source region weather station data from Mesowest (Horel et al. 2002).

Date/ 

Time, 

MST

BLUN2 

WS 

mph

BLUN2 

GUST 

mph

BLUN2 

DRCT 

°

BUFN2 

WS 

mph

BUFN2 

GUST 

mph

BUFN2 

DRCT 

°

TR730 

WS 

mph

TR730 

GUST 

mph

TR730 

DRCT 

°

KLOL 

WS 

mph

KLOL 

GUST 

mph

KLOL 

DRCT 

°

2/14 02:00 4 6 302 10 16 221 20 24 185 4.6 180

2/14 03:00 1 5 118 8 17 202 24 30 193 5.8 110

2/14 04:00 0 8 244 5 13 244 22 32 191 4.6 340

2/14 05:00 3 7 281 3 8 290 24 32 197 3.5 120

2/14 06:00 0 6 305 8 19 215 20 32 194 0

2/14 07:00 0 5 325 16 30 211 16 25 200 0

2/14 08:00 2 8 170 12 29 217 20 26 197 0

2/14 09:00 0 6 33 6 17 277 19 27 201 0

2/14 10:00 3 7 132 16 26 213 16 25 220 8.1 190

2/14 11:00 7 16 195 8 22 204 12 22 221 12.7 230

2/14 12:00 23 35 197 8 21 210 11 18 214 26.5 32.2 220

2/14 13:00 18 34 200 20 35 225 18 23 215 25.3 38 250

2/14 14:00 19 32 222 22 41 232 21 38 227 24.2 36.8 250

2/14 15:00 21 34 233 22 44 230 22 30 226 13.8 21.9 240

2/14 16:00 22 39 250 21 36 218 25 37 224 16.1 250

2/14 17:00 19 30 234 18 31 229 26 45 229 25.3 32.2 250

2/14 18:00 13 31 238 22 29 238 20 33 225 21.9 31.1 260

2/14 19:00 8 20 243 20 34 230 18 27 219 10.4 260

2/14 20:00 7 17 239 12 33 232 20 32 207 4.6

2/14 21:00 6 11 195 7 17 249 27 38 208 12.7 270

2/14 22:00 8 14 229 5 10 259 20 34 229 6.9 190

2/14 23:00 8 15 203 3 9 273 20 31 221 4.6 140

2/14 24:00 4 14 128 5 9 359 21 31 213 0

2/15 01:00 5 18 184 7 15 213 21 41 209 4.6

2/15 02:00 13 26 217 5 11 263 22 30 199 4.6 70

2/15 03:00 18 33 216 7 18 191 24 33 197 4.6 330

2/15 04:00 27 38 214 2 18 310 29 39 203 8.1 200

2/15 05:00 27 44 212 5 12 45 32 44 201 0

2/15 06:00 21 32 211 3 9 206 29 43 200 5.8 300

2/15 07:00 18 33 205 3 12 300 23 42 195 3.5

2/15 08:00 9 31 164 2 6 169 26 34 197 4.6 210

2/15 09:00 11 21 172 4 8 355 31 38 201 3.5 240

2/15 10:00 16 23 183 4 10 184 32 42 200 8.1 250

2/15 11:00 24 34 198 15 28 216 28 41 206 11.5 230

2/15 12:00 23 36 212 16 29 199 28 39 200 10.4 250

2/15 13:00 23 37 199 22 34 220 35 46 203 19.6 26.5 190

2/15 14:00 23 33 204 22 40 222 33 45 211 16.1 24.2 220

2/15 15:00 28 45 216 20 34 212 33 46 225 19.6 27.6 240

2/15 16:00 25 43 210 19 33 215 33 48 223 31.1 36.8 260

2/15 17:00 23 40 214 18 34 215 24 40 233 23 32.2 240

2/15 18:00 25 38 218 12 32 222 22 32 228 25.3 32.2 230

2/15 19:00 17 31 213 18 30 213 18 30 220 24.2 38 230

2/15 20:00 23 37 211 10 26 217 14 23 222 15 240

2/15 21:00 12 35 191 10 32 220 20 30 221 21.9 230

2/15 22:00 12 29 189 8 26 236 16 25 213 18.4 27.6 240

2/15 23:00 11 29 175 5 29 133 19 29 211 9.2 240

2/15 24:00 19 32 189 10 20 155 18 24 205 0

2/16 01:00 6 23 217 6 23 165 18 26 188 0

2/16 02:00 4 18 137 4 17 156 14 21 168 5.8

2/16 03:00 13 23 204 12 31 208 28 36 196 3.5 150

2/16 04:00 20 35 211 12 21 216 28 40 194 18.4 240
Request for Concurrence PM10 Exceptional Events

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Date/ 

Time, 

MST

BLUN2 

WS 

mph

BLUN2 

GUST 

mph

BLUN2 

DRCT 

°

BUFN2 

WS 

mph

BUFN2 

GUST 

mph

BUFN2 

DRCT 

°

TR730 

WS 

mph

TR730 

GUST 

mph

TR730 

DRCT 

°

KLOL 

WS 

mph

KLOL 

GUST 

mph

KLOL 

DRCT 

°

2/16 05:00 24 40 218 8 24 201 30 40 194 23 36.8 240

2/16 06:00 20 33 207 12 21 204 33 49 205 13.8 230

2/16 07:00 16 37 210 17 25 241 29 49 203 16.1 240

2/16 08:00 22 35 240 12 35 263 32 43 196 20.7 260

2/16 09:00 10 37 242 17 33 268 30 41 229 10.4 270

2/16 10:00 17 29 259 13 29 266 17 43 256 13.8 21.9 290

2/16 11:00 19.6 260

2/16 12:00 21 36 238 7 22 240 12 21 223 23 29.9 270

2/16 13:00 18 32 228 15 23 235 21 27 227 32.2 36.8 270

2/16 14:00 16 27 233 14 23 235 28 37 227 20.7 31.1 260

2/16 15:00 14 26 217 13 32 239 29 39 228 24.2 33.4 280

2/16 16:00 19 28 229 16 28 240 21 43 257 19.6 32.2 260

2/16 17:00 15 30 217 15 26 232 26 37 226 17.3 25.3 250

2/16 18:00 13 29 216 7 29 48 15 30 251 23 29.9 260

2/16 19:00 15 29 212 7 17 170 15 260

2/16 20:00 13 27 212 10 17 203 23 42 222 15 300

2/16 21:00 11 22 210 1 12 192 19 31 214 5.8 200

2/16 22:00 10 21 216 8 14 193 22 34 222 5.8 210

2/16 23:00 2 12 235 2 10 237 27 37 226 8.1 200

2/16 24:00 0 5 160 3 6 352 23 38 226 9.2 210

2/16 01:00 3 11 151 3 5 23 14 26 224 8.1 220
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Table B-3.Intermediate (Oregon) and affected area weather stations from MESOWEST (Horel et al. 

2002).

Date/ Hour 

MST

GSFO3 

WS 

mph

GSFO3 

GUST 

mph

GSFO3 

DRCT °

JVCI1 

WS 

mph

JVCI1 

GUST 

mph

JVCI1 

DRCT °

KBOI 

WS 

mph

KBOI 

GUST 

mph

KBOI 

DRCT °

2/14 02:00 16 20 128 6.3 12.3 148 12.7 170

2/14 03:00 15 23 133 4.9 9.7 158 13.8 160

2/14 04:00 15 20 129 2.7 9.2 166 10.4 170

2/14 05:00 17 24 124 1.4 3.8 11 18.4 150

2/14 06:00 16 23 124 2 5.5 341 16.1 150

2/14 07:00 10 20 134 1.4 4.7 58 15 160

2/14 08:00 12 17 137 2.8 7 99 13.8 160

2/14 09:00 13 19 147 5.4 11.3 147 4.6 100

2/14 10:00 12 19 154 7.3 9.6 142 11.5 160

2/14 11:00 13 19 180 4.9 8.1 144 3.5 110

2/14 12:00 6 19 218 7 18.6 162 11.5 150

2/14 13:00 10 22 207 12.7 18.4 178 16.1 21.9 140

2/14 14:00 17 27 206 12.4 18.8 183 19.6 23 130

2/14 15:00 27 38 215 17.7 27.7 201 18.4 150

2/14 16:00 22 36 209 18.2 28.9 213 12.7 140

2/14 17:00 19 33 219 16.9 26.2 220 10.4 140

2/14 18:00 18 29 216 13.6 20.4 203 10.4 140

2/14 19:00 13 21 191 12.2 19 195 12.7 130

2/14 20:00 11 18 193 13 22.1 195 11.5 140

2/14 21:00 12 17 185 9.7 17.9 175 10.4 140

2/14 22:00 10 15 199 8.5 13.7 159 13.8 130

2/14 23:00 16 25 192 8.7 14 168 12.7 140

2/14 24:00 26 38 208 8.4 13 163 9.2 130

2/15 01:00 14 34 183 11.2 16.2 161 15 130

2/15 02:00 14 24 154 8.1 13.8 156 11.5 120

2/15 03:00 10 21 134 7.5 11.4 154 16.1 140

2/15 04:00 10 19 157 7.7 11.8 155 12.7 120

2/15 05:00 8 16 198 10.9 16.6 167 15 130

2/15 06:00 0 14 243 5.5 13.7 147 13.8 24.2 120

2/15 07:00 10 19 149 6.9 10 147 15 130

2/15 08:00 11 19 154 5.5 9.7 150 12.7 120

2/15 09:00 13 20 171 8.2 11.5 160 12.7 120

2/15 10:00 14 24 193 7.6 12.2 162 20.7 140

2/15 11:00 23 32 207 9.4 20.8 181 16.1 25.3 150

2/15 12:00 25 38 209 14.6 24.6 193 16.1 140

2/15 13:00 27 41 217 17.1 26.2 199 17.3 23 160

2/15 14:00 28 46 222 18.3 26.5 199 13.8 24.2 140

2/15 15:00 28 48 220 16.8 25 204 12.7 190

2/15 16:00 28 43 217 11.6 20.8 201 13.8 180

2/15 17:00 26 41 210 14.8 24.5 218 18.4 200

2/15 18:00 20 34 219 16.3 27.9 211 12.7 200

2/15 19:00 17 33 219 13.8 23.4 214 4.6 170

2/15 20:00 15 28 218 8.3 14.7 189 5.8 140

2/15 21:00 15 28 193 5.5 8.8 170 0

2/15 22:00 12 23 201 7.1 11.9 171 8.1 160

2/15 23:00 10 17 198 9.5 14.2 166 11.5 150

2/15 24:00 9 17 147 9.5 14 173 12.7 150

2/16 0100 12 25 149 8 13 169 10.4 160

2/16 0200 10 21 147 9.7 14.8 174 15.0 140

2/16 0300 8 18 156 6.2 10.2 161 9.2 130
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Date/ Hour 

MST

GSFO3 

WS 

mph

GSFO3 

GUST 

mph

GSFO3 

DRCT °

JVCI1 

WS 

mph

JVCI1 

GUST 

mph

JVCI1 

DRCT °

KBOI 

WS 

mph

KBOI 

GUST 

mph

KBOI 

DRCT °

2/16 04:00 11 18 151 6.2 9.9 166 10.4 130

2/16 05:00 16 23 206 6.2 13 174 11.5 140

2/16 06:00 14 25 206 8.7 17 181 18.4 140

2/16 07:00 14 26 202 6.7 15.7 173 5.8 170

2/16 08:00 17 30 204 8.9 15.7 176 10.4 270

2/16 09:00 20 27 196 12.5 20.9 188 6.9 40

2/16 10:00 26 37 243 11.9 18.5 179 13.8 280

2/16 11:00 13.3 30.7 205 15.6 23 295

2/16 12:00 7.7 18 321 9.0 303

2/16 13:00 6 14 181 3.5 7.8 250 2.6 355

2/16 14:00 13 21 235 3.3 6.6 163 3.5 200

2/16 15:00 19 27 238 3.1 9 179 4.6 100

2/16 16:00 25 46 258 10.8 22 213 6.9 120

2/16 17:00 17 37 278 15.5 29.1 282 14.7 32.2 258

2/16 18:00 18 29 273 9.1 17.2 282 8.1 70

2/16 19:00 8 26 277 7.3 12.1 286 3.5 90

2/16 20:00 4 12 267 3.4 10.2 316 5.8 120

2/16 21:00 3 11 175 1.6 3.8 82 8.1 60

2/16 22:00 16 24 181 2.8 6.7 147 5.8 110

2/16 23:00 18 28 251 5.7 17.9 153 5.8 120

2/16 24:00 3 20 229 8.6 25.9 175 4.6 170
Request for Concurrence PM10 Exceptional Events

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Table B-4. Weather observations at Lovelock, Boise, and Winnemucca from Mesowest (Horel et al. 

2002).

Lovelock Nevada, KLOL Boise, ID KBOI Winnemucca, NV KWMC

Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs

2-14-2011 0:53 PST clear 2-14-2011 0:53 MST clear 2-14-2011 0:56 PST clear

2-14-2011 1:53 PST clear 2-14-2011 1:53 MST clear 2-14-2011 1:56 PST clear

2-14-2011 2:53 PST clear 2-14-2011 2:53 MST clear 2-14-2011 2:56 PST clear

2-14-2011 3:53 PST clear 2-14-2011 3:53 MST clear 2-14-2011 3:56 PST clear

2-14-2011 4:53 PST clear 2-14-2011 4:53 MST clear 2-14-2011 4:56 PST clear

2-14-2011 5:53 PST clear 2-14-2011 5:53 MST clear 2-14-2011 5:56 PST clear

2-14-2011 6:53 PST clear 2-14-2011 6:53 MST clear 2-14-2011 6:56 PST clear

2-14-2011 7:53 PST clear 2-14-2011 7:53 MST clear 2-14-2011 7:56 PST clear

2-14-2011 8:53 PST mostly clear 2-14-2011 8:53 MST clear 2-14-2011 8:56 PST clear

2-14-2011 9:53 PST haze 2-14-2011 9:53 MST clear 2-14-2011 9:56 PST overcast

2-14-2011 9:55 PST haze 2-14-2011 10:53 MST clear 2-14-2011 10:56 PST partly cloudy

2-14-2011 10:03 PST haze 2-14-2011 11:53 MST clear 2-14-2011 11:56 PST clear

2-14-2011 10:12 PST haze 2-14-2011 12:53 MST clear 2-14-2011 12:56 PST partly cloudy

2-14-2011 10:24 PST haze 2-14-2011 13:53 MST clear 2-14-2011 13:32 PST haze

2-14-2011 10:28 PST haze 2-14-2011 14:53 MST mostly clear 2-14-2011 13:41 PST haze

2-14-2011 10:39 PST haze 2-14-2011 15:53 MST mostly cloudy 2-14-2011 13:50 PST haze

2-14-2011 10:51 PST haze 2-14-2011 16:53 MST mostly cloudy 2-14-2011 13:56 PST partly cloudy

2-14-2011 10:53 PST haze 2-14-2011 17:53 MST overcast 2-14-2011 14:56 PST haze

2-14-2011 11:24 PST lt rain 2-14-2011 18:53 MST overcast 2-14-2011 15:45 PST partly cloudy

2-14-2011 11:53 PST lt rain 2-14-2011 19:53 MST overcast 2-14-2011 15:56 PST clear

2-14-2011 12:08 PST lt rain 2-14-2011 20:53 MST clear 2-14-2011 16:56 PST haze

2-14-2011 12:26 PST lt rain 2-14-2011 21:53 MST mostly clear 2-14-2011 17:13 PST haze

2-14-2011 12:33 PST lt rain 2-14-2011 22:53 MST mostly cloudy 2-14-2011 17:56 PST partly cloudy

2-14-2011 12:53 PST haze 2-14-2011 23:53 MST clear 2-14-2011 18:56 PST clear

2-14-2011 13:06 PST haze 2-15-2011 0:53 MST clear 2-14-2011 19:56 PST clear

2-14-2011 13:13 PST haze 2-15-2011 1:53 MST clear 2-14-2011 20:56 PST clear

2-14-2011 13:31 PST haze 2-15-2011 2:53 MST clear 2-14-2011 21:56 PST clear

2-14-2011 13:53 PST haze 2-15-2011 3:53 MST clear 2-14-2011 22:56 PST clear

2-14-2011 14:37 PST haze 2-15-2011 4:53 MST clear 2-14-2011 23:56 PST clear

2-14-2011 14:49 PST haze 2-15-2011 5:53 MST clear 2-15-2011 0:56 PST clear

2-14-2011 14:53 PST haze 2-15-2011 6:53 MST clear 2-15-2011 1:56 PST clear

2-14-2011 15:29 PST haze 2-15-2011 7:53 MST haze 2-15-2011 2:56 PST clear

2-14-2011 15:51 PST haze 2-15-2011 8:53 MST haze 2-15-2011 3:56 PST clear

2-14-2011 15:53 PST haze 2-15-2011 9:53 MST haze 2-15-2011 4:56 PST clear

2-14-2011 16:00 PST haze 2-15-2011 10:53 MST clear 2-15-2011 5:56 PST clear

2-14-2011 16:13 PST haze 2-15-2011 11:53 MST clear 2-15-2011 6:56 PST clear

2-14-2011 16:21 PST haze 2-15-2011 12:53 MST clear 2-15-2011 7:56 PST clear

2-14-2011 16:43 PST haze 2-15-2011 13:53 MST partly cloudy 2-15-2011 8:56 PST clear

2-14-2011 16:45 PST haze 2-15-2011 14:53 MST mostly clear 2-15-2011 9:56 PST clear

2-14-2011 16:53 PST haze 2-15-2011 15:53 MST clear 2-15-2011 10:56 PST clear

2-14-2011 17:01 PST haze 2-15-2011 16:53 MST mostly clear 2-15-2011 11:56 PST clear

2-14-2011 17:03 PST haze 2-15-2011 17:53 MST mostly clear 2-15-2011 12:56 PST clear

2-14-2011 17:53 PST clear 2-15-2011 18:53 MST mostly cloudy 2-15-2011 13:56 PST clear

2-14-2011 18:53 PST clear 2-15-2011 19:53 MST clear 2-15-2011 14:56 PST haze

2-14-2011 19:53 PST clear 2-15-2011 20:53 MST clear 2-15-2011 15:56 PST clear

2-14-2011 20:53 PST haze 2-15-2011 21:53 MST haze 2-15-2011 16:32 PST Haze
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Lovelock Nevada, KLOL Boise, ID KBOI Winnemucca, NV KWMC

Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs

2-14-2011 21:53 PST clear 2-15-2011 22:53 MST clear 2-15-2011 16:41 PST haze

2-14-2011 22:53 PST clear 2-15-2011 23:53 MST haze 2-15-2011 16:51 PST haze

2-14-2011 23:53 PST clear 2-16-2011 0:53 MST haze 2-15-2011 16:56 PST haze

2-15-2011 0:53 PST clear 2-16-2011 1:53 MST haze 2-15-2011 17:03 PST haze

2-15-2011 1:53 PST clear 2-16-2011 2:53 MST haze 2-15-2011 17:15 PST haze

2-15-2011 2:53 PST clear 2-16-2011 3:53 MST haze 2-15-2011 17:56 PST haze

2-15-2011 3:53 PST clear 2-16-2011 4:53 MST haze 2-15-2011 18:15 PST haze

2-15-2011 4:53 PST clear 2-16-2011 5:53 MST haze 2-15-2011 18:45 PST haze

2-15-2011 5:53 PST clear 2-16-2011 6:53 MST haze 2-15-2011 18:56 PST haze

2-15-2011 6:53 PST clear 2-16-2011 7:53 MST haze 2-15-2011 19:56 PST clear

2-15-2011 7:53 PST clear 2-16-2011 8:53 MST mostly clear 2-15-2011 20:19 PST haze

2-15-2011 8:53 PST clear 2-16-2011 9:53 MST clear 2-15-2011 20:34 PST haze

2-15-2011 9:53 PST clear 2-16-2011 10:42 MST overcast 2-15-2011 20:56 PST haze

2-15-2011 10:31 PST haze 2-16-2011 10:53 MST overcast 2-15-2011 21:56 PST haze

2-15-2011 10:40 PST haze 2-16-2011 11:16 MST lt snow; fog 2-15-2011 22:56 PST haze

2-15-2011 10:44 PST mostly cloudy 2-16-2011 11:18 MST lt snow; fog 2-15-2011 23:56 PST clear

2-15-2011 10:46 PST haze 2-16-2011 11:26 MST lt snow; fog 2-16-2011 0:56 PST mostly clear

2-15-2011 10:53 PST haze 2-16-2011 11:40 MST lt snow; fog 2-16-2011 1:56 PST mostly clear

2-15-2011 11:09 PST haze 2-16-2011 11:48 MST lt snow; fog 2-16-2011 2:56 PST mostly cloudy

2-15-2011 11:22 PST haze 2-16-2011 11:53 MST lt snow; fog 2-16-2011 3:56 PST mostly cloudy

2-15-2011 11:31 PST haze 2-16-2011 12:06 MST lt snow; fog 2-16-2011 4:56 PST overcast

2-15-2011 11:44 PST haze 2-16-2011 12:14 MST lt snow; fog 2-16-2011 5:56 PST overcast

2-15-2011 11:53 PST clear 2-16-2011 12:51 MST mostly cloudy 2-16-2011 6:56 PST lt rain

2-15-2011 12:12 PST haze 2-16-2011 12:53 MST partly cloudy 2-16-2011 7:58 PST mod rain

2-15-2011 12:19 PST haze 2-16-2011 13:53 MST clear 2-16-2011 8:01 PST lt snow; fog

2-15-2011 12:33 PST haze 2-16-2011 14:53 MST partly cloudy 2-16-2011 8:10 PST mod snow; fog

2-15-2011 12:38 PST haze 2-16-2011 15:53 MST partly cloudy 2-16-2011 8:31 PST lt snow; fog

2-15-2011 12:51 PST haze 2-16-2011 16:03 MST thunder 2-16-2011 8:36 PST lt snow; fog

2-15-2011 12:53 PST haze 2-16-2011 16:12 MST lt snow shwr; squalls 2-16-2011 8:41 PST lt snow; fog

2-15-2011 12:57 PST haze 2-16-2011 16:20 MST mod snow; fog 2-16-2011 8:56 PST lt snow

2-15-2011 13:07 PST partly cloudy 2-16-2011 16:25 MST mostly cloudy 2-16-2011 9:56 PST overcast

2-15-2011 13:24 PST haze 2-16-2011 16:30 MST mostly cloudy 2-16-2011 10:13 PST lt snow; fog

2-15-2011 13:39 PST haze 2-16-2011 16:31 MST mostly cloudy 2-16-2011 10:23 PST lt snow; fog

2-15-2011 13:53 PST haze 2-16-2011 16:34 MST mostly cloudy 2-16-2011 10:30 PST lt snow; fog

2-15-2011 14:01 PST haze 2-16-2011 16:40 MST partly cloudy 2-16-2011 10:39 PST lt snow; fog

2-15-2011 14:10 PST haze 2-16-2011 16:42 MST mostly cloudy 2-16-2011 10:47 PST lt snow; fog

2-15-2011 14:41 PST lt rain 2-16-2011 16:49 MST mostly cloudy 2-16-2011 10:53 PST lt snow; fog

2-15-2011 14:53 PST lt rain 2-16-2011 16:53 MST mostly cloudy 2-16-2011 10:56 PST lt snow; fog

2-15-2011 15:12 PST haze 2-16-2011 17:53 MST clear 2-16-2011 11:02 PST lt snow

2-15-2011 15:14 PST haze 2-16-2011 18:53 MST clear 2-16-2011 11:10 PST lt snow

2-15-2011 15:33 PST haze 2-16-2011 19:53 MST clear 2-16-2011 11:29 PST mostly cloudy

2-15-2011 15:42 PST haze 2-16-2011 20:53 MST clear 2-16-2011 11:56 PST mostly clear

2-15-2011 15:53 PST haze 2-16-2011 21:53 MST clear 2-16-2011 12:56 PST clear

2-15-2011 16:06 PST haze 2-16-2011 22:53 MST mostly cloudy 2-16-2011 13:56 PST mostly clear
Request for Concurrence PM10 Exceptional Events

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Lovelock Nevada, KLOL Boise, ID KBOI Winnemucca, NV KWMC

Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs

2-15-2011 16:53 PST haze 2-16-2011 23:53 MST overcast 2-16-2011 14:56 PST mostly cloudy

2-15-2011 17:51 PST haze 2-16-2011 15:56 PST clear

2-15-2011 17:53 PST haze 2-16-2011 16:56 PST clear

2-15-2011 18:09 PST haze 2-16-2011 17:56 PST clear

2-15-2011 18:36 PST haze 2-16-2011 18:56 PST mostly clear

2-15-2011 18:40 PST haze 2-16-2011 19:56 PST partly cloudy

2-15-2011 18:53 PST haze 2-16-2011 20:56 PST clear

2-15-2011 19:03 PST haze 2-16-2011 21:56 PST clear

2-15-2011 19:06 PST haze 2-16-2011 22:56 PST partly cloudy

2-15-2011 19:16 PST haze 2-16-2011 23:56 PST overcast

Lovelock Nevada, KLOL (cont)

Date & Time of Observation

Weather 

Obs

2-15-2011 19:25 PST haze

2-15-2011 19:42 PST haze

2-15-2011 19:50 PST haze

2-15-2011 19:53 PST haze

2-15-2011 20:36 PST haze

2-15-2011 20:46 PST haze

2-15-2011 20:53 PST haze

2-15-2011 21:02 PST haze

2-15-2011 21:16 PST haze

2-15-2011 21:22 PST haze

2-15-2011 21:29 PST haze

2-15-2011 21:36 PST haze

2-15-2011 21:42 PST haze

2-15-2011 21:53 PST haze

2-15-2011 21:58 PST haze

2-15-2011 22:10 PST haze

2-15-2011 22:16 PST haze

2-15-2011 22:23 PST haze

2-15-2011 22:32 PST haze

2-15-2011 22:47 PST haze

2-15-2011 22:53 PST haze

2-15-2011 23:20 PST haze

2-15-2011 23:36 PST haze

2-15-2011 23:49 PST haze

2-15-2011 23:53 PST haze

2-16-2011 0:10 PST haze

2-16-2011 0:43 PST haze

2-16-2011 0:53 PST haze

2-16-2011 1:00 PST haze

2-16-2011 1:05 PST haze

2-16-2011 1:36 PST haze

2-16-2011 1:43 PST haze
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Lovelock Nevada, KLOL Boise, ID KBOI Winnemucca, NV KWMC

Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs

Lovelock Nevada, KLOL (cont)

Date & Time of Observation

Weather 

Obs

2-16-2011 1:53 PST haze

2-16-2011 2:14 PST haze

2-16-2011 2:22 PST haze

2-16-2011 2:31 PST haze

2-16-2011 2:36 PST haze

2-16-2011 2:53 PST haze

2-16-2011 3:22 PST haze

2-16-2011 3:28 PST haze

2-16-2011 3:35 PST haze

2-16-2011 3:37 PST haze

2-16-2011 3:48 PST haze

2-16-2011 3:49 PST haze

2-16-2011 4:20 PST haze

2-16-2011 4:23 PST haze

2-16-2011 4:51 PST haze

2-16-2011 4:53 PST haze

2-16-2011 5:07 PST haze

2-16-2011 5:14 PST haze

2-16-2011 5:25 PST haze

2-16-2011 5:29 PST haze

2-16-2011 5:31 PST haze

2-16-2011 5:38 PST mostly cloudy

2-16-2011 5:53 PST overcast

2-16-2011 6:16 PST haze

2-16-2011 6:23 PST haze

2-16-2011 6:30 PST haze

2-16-2011 6:53 PST overcast

2-16-2011 7:20 PST mod rain; fog

2-16-2011 7:45 PST partly cloudy

2-16-2011 7:53 PST mostly clear

2-16-2011 8:53 PST clear

2-16-2011 9:53 PST clear

2-16-2011 10:53 PST clear

2-16-2011 11:53 PST mostly clear

2-16-2011 12:53 PST clear

2-16-2011 13:53 PST clear

2-16-2011 14:53 PST mostly clear

2-16-2011 15:53 PST mostly clear

2-16-2011 16:53 PST clear

2-16-2011 17:53 PST partly cloudy

2-16-2011 18:53 PST clear

2-16-2011 19:53 PST clear
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Lovelock Nevada, KLOL Boise, ID KBOI Winnemucca, NV KWMC

Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs Date/Time of Obs Weather Obs

2-16-2011 20:53 PST clear

2-16-2011 21:53 PST clear
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Table B-5. Daily precipitation in source region, January 1–February 15, 2011 (Horel et al. 2002).

Date BUFN2 BLUN2 TR730 TEXN2 KNFL KLOL

1/1/2011 0 0 0 0 0.04 0

1/2/2011 0.01 0.02 0.04 0.01 0 0

1/3/2011 0 0 0 0.04 0 0

1/4/2011 0 0 0.01 0 0 0

1/5/2011 0 0 0 0 0 0

1/6/2011 0 0 0 0 0 0

1/7/2011 0 0 0.01 0.05 0 0

1/8/2011 0 0 0 0 0.01 0

1/9/2011 0 0 0 0 0 0

1/10/2011 0 0 0 0 0 0

1/11/2011 0 0 0 0 0 0.08

1/12/2011 0.06 0.04 0 0 0 0

1/13/2011 0.02 0 0 0.16 0 0

1/14/2011 0 0 0.07 0.08 0 0

1/15/2011 0 0 0.13 0.24 0 0

1/16/2011 0 0 0.01 0.09 0 0

1/17/2011 0 0 0 0 0 0

1/18/2011 0 0 0 0 0 0

1/19/2011 0 0 0 0 0 0

1/20/2011 0 0 0 0 0 0

1/21/2011 0 0 0 0 0 0

1/22/2011 0 0 0 0 0 0

1/23/2011 0 0 0 0 0 0

1/24/2011 0 0 0 0 0.01 0

1/25/2011 0 0 0 0 0 0

1/26/2011 0 0 0 0 0 0

1/27/2011 0 0 0 0 0 0

1/28/2011 0 0 0 0 0 0

1/29/2011 0 0 0 0 0 0

1/30/2011 0 0 0 0.03 0.05 0.01

1/31/2011 0 0 0 0 0 0

2/1/2011 0 0 0 0 0 0

2/2/2011 0 0 0 0 0 0

2/3/2011 0 0 0 0 0 0

2/4/2011 0 0 0 0 0 0

2/5/2011 0 0 0 0.07 0 0

2/6/2011 0 0 0 0 0 0

2/7/2011 0 0 0 0 0 0

2/8/2011 0 0 0 0 0 0

2/9/2011 0 0 0 0 0 0

2/10/2011 0 0 0 0 0 0

2/11/2011 0 0 0 0 0 0

2/12/2011 0 0 0 0 0 0

2/13/2011 0 0 0 0 0 0

2/14/2011 0 0 0 0 0 0

2/15/2011 0 0 0 0 0 0
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Appendix C. Hells Canyon IMPROVE Site PM2.5 Speciation

Figure C-1. Hells Canyon speciation for February 2011, showing high coarse mass (top) and elevated soil component on February 14, 

2011. In top panel, MT = total mass, MF = fine mass, CM = coarse mass. In bottom panel, OCf = fine organic carbon, SO4f = fine sulfate, 

NO3f = fine nitrate, Opf = fine pyrolysis carbon, Sf = fine sulfur, soilf = fine soil/geologic mass, CHLf = fine chloride, and ECf = fine 

elemental carbon (IMPROVE 2013).
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Figure C-2. Hells Canyon speciation for February 2011 showing higher Si, Fe, Al, and Ca on February 14, 2011. In top panel, NAf = fine 

sodium, SIf = fine silicon, Fef = fine iron, Kf = fine potassium, Alf = fine aluminum, MGf = fine magnesium, CAf = fine calcium. In bottom 

panel, Tif = fine titanium, BRf = fine bromine, ZNf = fine zinc, ZRf = fine zirconiuim, PBf = fine lead, and MNf = fine manganese. Fine 

aerosol is < 2.5 μm (IMPROVE 2013).
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Appendix D. St. Luke’s Meridian NCORE Site Speciation Data 

for February 14, 2011

Table D-1. St. Luke’s NCORE site speciation for February 14, 2011—XRF elements.

Parameter 

Code Parameter

Sample 

Value, 

ug/m3

Alternate 

Method 

Detectable 

Limit

Uncertainty Note

88102 Antimony 0 0.042 0.014

88103 Arsenic 0 0.0017 0.00064

88104 Aluminum 0.138 0.013 0.016

88107 Barium 0 0.01 0.0039

88109 Bromine 0.0023 0.0018 0.0011

88110 Cadmium 0 0.019 0.0062

88111 Calcium 0.147 0.0047 0.011

88112 Chromium 0 0.0022 0.00072

88113 Cobalt 0.00081 0.0011 0.00071

88114 Copper 0.00023 0.0013 0.0017

88115 Chlorine 0.0409 0.005 0.0037

88117 Cerium 0 0.0068 0.003

88118 Cesium 0 0.034 0.011

88126 Iron 0.147 0.0014 0.011

88128 Lead 0 0.0049 0.0016

88131 Indium 0 0.022 0.0073

88132 Manganese 0.00306 0.0018 0.0008

88136 Nickel 0.00001 0.0011 0.00045

88140 Magnesium 0.00671 0.011 0.0044

88152 Phosphorus 0 0.01 0.0041

88154 Selenium 0 0.002 0.00068

88160 Tin 0 0.032 0.011

88161 Titanium 0.0113 0.0043 0.0026

88164 Vanadium 0 0.003 0.0013

88165 Silicon 0.554 0.011 0.046

88166 Silver 0 0.015 0.0049

88167 Zinc 0 0.0035 0.0012

88168 Strontium 0 0.0023 0.00076

88169 Sulfur 0.105 0.0073 0.0082 a

88176 Rubidium 0 0.0018 0.00059

88180 Potassium 0.0803 0.0039 0.006

88184 Sodium 0.0961 0.04 0.014

88185 Zirconium 0 0.0045 0.0069

88301 Ammonium 0.147 0.017 0.01

88302 Sodium 0.0351 0.03 0.064
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Parameter 

Code Parameter

Sample 

Value, 

ug/m3

Alternate 

Method 

Detectable 

Limit

Uncertainty Note

88303 Potassium 0 0.014 0.001

88306 Nitrate 0.27 0.0072 0.021

88403 Sulfate 0.232 0.01 0.019 b

88502 Particulate matter 

2.5u 6.1 0.77 0.41

88355 OC IMPROVE TOT 0.989 c

88357 EC IMPROVE TOT 0.244 d

88370 OC IMPROVE 

TOR 0.975e

88374 O1 IMPROVE 0.0241

88375 O2 IMPROVE 0.204

88376 O3 IMPROVE 0.368

88377 O4 IMPROVE 0.218

88378 OP IMPROVE 

TOR 0.161 f

88380 EC IMPROVE TOR 0.258 g

88383 E1 IMPROVE 0.373

88384 E2 IMPROVE 0.0458

88385 E3 IMPROVE 0

88388 OP IMPROVE TOT 0.175 h

Notes:

a Qualifier-1 = 5

b Qualifier-1 = 5

c OC = Organic Carbon, TOT = by total optical TRANSMITTANCE

d

EC = Elemental Carbon, TOT = by total optical 

TRANSMITTANCE

e OC = Organic Carbon, TOR = by total optical REFLECTANCE

f OP = Pyrolysis Carbon, TOR = by total optical REFLECTANCE

g EC = Elemental Carbon, TOR = by total optical REFLECTANCE

h OP = Pyrolysis Carbon, TOR = by total TRANSMITTANCE
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Appendix E. DEQ Air Quality Alerts and Public Education

Air quality alert and public education sheet for yellow alerts sent out February 15, 2011,

10:23 a.m. MST by DEQ’s Boise Regional Office.
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Air quality alert and public education sheet for orange alerts sent out February 16, 2011,

9:09 a.m. MST by DEQ’s Boise Regional Office.
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Appendix F. News Articles

Idaho Statesman, The (Boise, ID)

February 16, 2011

Section: Local, as provided by the The McClatchy Company

Wind-blown dust leads to orange air quality alert in Treasure Valley, but snow expected to improve 

air quality

Author: Boise - Idaho Statesman

Article Text: 

The Idaho Department of Environmental Quality issued an orange alert for Wednesday due to poor air 

quality. The cause is particulates from dust that has blown in from the desert, said David Luft, airshed 

coordinator for the Boise regional office. 

An orange alert means that members of sensitive groups should limit time outdoors. Indoor wood burning 

is restricted in Ada County when the AQI is 74 or higher. Within unincorporated Ada and Canyon 

counties, only EPA-certified woodstoves are allowed when AQI is above 74. 

"This is pretty high for us," Luft said of the air quality index of 110, the low end of the orange level. 

Luft said dry conditions combined with sustained winds of 10 to 20 miles per hour from the southeast for 

two days impacted air quality. 

Luft expected that precipitation overnight Tuesday would prevent the need for an alert, but that did not 

materialize and the air quality got worse. The cold front moving through the area Wednesday should clear 

the air, Luft said. 

Snow was falling throughout the Boise metro area Wednesday morning. The Valley will get a half inch to 

1 inch of snow today, according to meteorologist Megan Thimmesch. She said Boise hit a high 

temperature for the day of 46, and temperatures will fall through the rest of the day. 

It was about 34 degrees at noon, and the overnight low is expected to be about 30 degrees. There's a 25 

percent chance of precipitation Thursday, and that's likely to be snow. The high Thursday will be about 

41. 

Copyright (c) 2011 The Idaho Statesman, All Rights Reserved.

Record Number: 201102161456KNRIDDERIDSTATES_6f947997a02ef64f079c76f03f11475a
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NBC - 7 KTVB (Boise, ID)

February 16, 2011

Section: Local News

Treasure Valley air quality improves, in moderate range

Article Text: 

BOISE -- The Idaho Department of Environmental Quality reports that air quality in the Treasure Valley 

has improved and is now in the moderate or yellow range. 

As of 2 p.m. Mountain Time, DEQ's website puts the Air Quality Index at 65. 

Idaho's Chief Meteorologist Rick Lantz credits the precipitation we received earlier in the day for the 

improved air quality. He says there was a lot of dust in the air before the storm moved through. 

High winds overnight were responsible for an orange air quality alert in the Treasure Valley. The AQI hit 

110. 

An orange air quality alert means the air quality is unhealthy for sensitive groups, meaning people with 

respiratory or heart disease, the elderly, and children. 

While the alert is in effect, outdoor burning is prohibited. 

Even though the air quality is back in the moderate range, usually sensitive people are encouraged to 

reduce their outdoor activities. 

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