Armosphmc Enur~~nmenr Vol IO. pp. 813-825. Pergamon Press 1976. Printed in Great Britam



## FREQUENCY AND DIURNAL VARIATION OF DUST STORMS IN THE CONTIGUOUS U.S.A.*

M. M. ORGILL and G. A. SEHMEL Atmospheric Sciences Department, Battelle, Pacific Northwest Laboratories, Richland. WA 99352,U.S.A. (First received 8January 1976and 

### infinal form 19March 1976)
Abstract-Studies ofregional wind erosion and the translocation ofsuspended particles are important for accurate surveys ofair pollution. This category of investigation has nationwide implications for planning and regulatory purposes. However, most regional studies ofwind suspension (airborne dust) havecentered around the Great Plains without much consideration given to other areas ofthecountry. The purpose of this study is to quantitate the wind translocation problem throughout the contiguous United States by using visibility as an index. National Weather Service and military surface observations on dust were analyzed for annual, monthly and diurnal periods. Frequency of dusty periods were based on hourly weather observations from stations recording dust, blowing dust, and blowing sand when visibility was 7 miles or less. Mountainous, forested, and predominantly maritime regions are generally free from major dust storms. The highest dust frequency is in the Southern Great Plains. Secondary dust frequency maxima occur in the Western States, Northern Great Plains, southern coastal Pacific and inland valleys and the Southeast. Maximum dust frequency occurs in early and late spring months for most regions but some regions experience additional dust in summer or fall. Hourly observations show higher dust frequencies occur in the afternoon between 12.00 and 20.00 LST, or during the period of maximum thermal instability. Regional dust frequency patterns are discussed in relation to the principal factors which govern natural wind-caused suspension, i.e. (1) surface properties, (2)particle properties, and (3)meteorological conditions.

INTRODUCTION Studies concerning regional wind translocation of soil particles are important to better understanding of air pollution processes. Selection ofsites for future energy installations and related facilities must include thorough consideration of the location’s potential for wind resuspension of pollutants. There are diverse regions in the United States subject to varying degrees of suspended dust. The regional processes of particulate resuspension should be understood. Planning for the nation’s energy needs should incorporate all possible strategies for control ofenvironmental impacts through competent regulatory and design criteria. Thus it is vital that the frequency, duration and intensity of suspended dust episodes be determined for candidate sites, as well as existing locations of energy-related activity. Most wind translocation dust studies have centered around the Great Plains (Hagen and Woodruff, 1973) with little attention given to other regions of the country. Other regions are generally known to experience significant dust storms (Clements et al., 1963; Orgill et al., 1974) but there are no comprehensive reports concerning the frequency and regional distributions ofsuspended dust for the entire country. Consequently, the major purpose of this research was to quantitate the relative frequency and location ofwind *This paper is based on work performed under U.S. Atomic Energy Commission Contract No. AT(45-l)-1830. translocation regions throughout the contiguous United States. Two methods were considered for analyzing the existing data for regional dust frequency. The first required examination and analysis of actual airborne particulate-concentration data from national and local air pollution monitoring stations during suspended dust episodes. Although this method would probably be best quantitatively, it was not selected for this initial study because of the time and expense ofcollecting and analyzing the vast amounts of data. The second method, which was ultimately used, utilized the National Weather Service and Armed Services summarized surface hourly observations of dust and prevailing visibility to define regional dust frequencies. This method was more qualitative, but the data base for a 15-30 yperiod could be handled more economically and analyzed easily. Consequently, National Weather Service, Air Force, Navy, Army and Marine summarized surface hourly observations on blowing dust and sand were analyzed for annual, monthly, and diurnal periods. In weather observing practice (Huschke, 1969) a dust storm is only reported if blowing dust reduces visibility below 5/8 mile (1km). However, in this study we will use the term “dust storm” to include all dust events that reduced the prevailing visibility below 7miles (11.3km). The frequency and spatial distribution of dusty periods were based on summarized hourly weather 813814 M. M. ORGILLand G.A. SEHMEL



### observations from 343weather observing stations that recorded dust, blowing dust, and sand when the visibility was less than 7 miles (11.3km). This distance is a standard weather observing procedure (NOAA, 1970).The collected and analyzed data showed, with some exceptions, most regions of the continental U.S.A. are susceptible to airborne dust due to wind translocation.

PROCEDURES 

### Visibility, as a measure ofatmospheric opacity, is perceived by an observer to be an indicator ofthe quantity ofpollution (in this case, dust) in the air. Prevailing visibility is the greatest visibility equaled orexceeded throughout one-half ofthehorizon circle (NOAA, 1970).It isa subjective measurement which depends upon individual ability to both detect and recognize distant objects seen against thehorizon sky by day or to detect distant lights at night. Prevailing visibility istaken routinely at National Weather Service observation stations and military installations that have observers on duty. Charlson (1969) has shown that prevailing visibility and particulate concentrations are approximately related when the particle size distribution remains constant and the relative humidity is less than 70% or deliquescent particles arenot present in significant numbers. A theoretical visibility-concentration relationship (Hagen and Woodruff, 1973) can be derived by assuming: (1)visibility isreduced only by scattering; (2)airborne particles are ofuniform size; and (3)the scattering area coefficient isconstant. In this case,

C = y 

### (mgme3), 

### (1)
where V

### isprevailing visibility inkm.Anearly identical empirical visibility-concentration relationship at 1.8m above the surface was found by Chepil and Woodruff (Hagen and Woodruff, 1973)

C= $$(mgmm3).

This empirical concentration-visibility relation agrees with the theoretical relation when V 

### is about 1km, but has a smaller concentration than the theoretical one for visibilities greater than 1km. National Weather Service and military surfade observations ofdust are only reported when the prevailing visibility isless than 7 miles (11.3km). Ifthe assumptions are met, substitution of 11.3km into equations (1)and (2)gives a dust concentration from
*The shaded regions ofFigs. 2,5a-d represent regions where no hourly observations were found with visibility ~7 miles due to dust, etc. If dust storms with visibility >7 miles were to be included, the relative dust frequency would be higher but the location of dusty areas should not change significantly. 

### 2.7to 5.1mg mm3.Unfortunately, this criteria eliminates any consideration ofdust storms with visibility greater than 7 miles or with dust concentrations between 75 pgrnw3 (ambient air standard) and 2700 pgme3. If these data could be included they would increase the relative frequency ofdust storms, but it is not known whether the relative frequency distributions ofthe >7mile dust storms are the same as the ~7 mile dust storms. We suspect not, but we don’t have the data on hand to verify it. Therefore, dust frequency data based onprevailing visibility refer only to dust storms when the dust concentration is from 3to 5mgm-’ or greater. Measured dust concentrations in dust storms have been reported from 0.1to 176mgme3 depending on stage ofstorm development (Gillette et al., 1972; Shinn et al., 1974; Viletto and Ohman, 1972). Hourly observations of prevailing visibility and occurrence ofdust have been collected over several years and are available either from tabulated summaries (Part A) or magnetic tapes at the National Climatic Center in Asheville, North Carolina. Tabulated summaries were obtained for 249 weather stations and an additional 94 summaries were specially processed for this research program by the National Climatic Center. Hence, tabulations for 343 weather stations were utilized in this study. Figure 1 shows the distribution ofstations. Thedata forindividual weather stations weretabulated in terms ofpercentage frequency ofoccurrence forvarious weather elements forannual, monthly, and 3-hperiods. Data pertaining to percentage frequency ofdust wereextracted, plotted and analyzed. The country was divided into seven different regions (Fig. 1)depending partially on relative dust frequency, spatial dust frequency patterns and geography.To quantify the dustiness in these seven regions asimple regional average dust frequency was defined asfollows: i=Nc RADF = .x’ ;,

i= 1 

### whereRADF istheannual ormonthly regional average dust frequency;J is the annual or monthly percent frequency ofdust occurrence for the ith station in eachregion, and N isthe total number ofstations for each region.
RESULTS Annual distribution ofsuspended dust and sand 

### The frequency ofoccurrence of suspended dust or sand from major dust storms on an annual basis for the country (excluding AK and HI) is shown in Fig. 2.In this figure, frequency isopleths approximate the regional dust frequency. The isopleths were drawn subjectively with the goal of delineating dust frequency on a broad regional basis. These isopleths range fromN(none)* to3% ofthe total hourly observations.Dust storms in the contiguous U.S.A. 815

North central l

Fig. 1.Distribution of343weather observation stations used in study and seven defined dust regions

ofthe country. Dash lines represent the Appalachian Mountains.

Fig.2.Annual %frequency ofdusty hours based on hourly observations from 343weather observation stations that recorded dust, blowing dust and sand when prevailing visibility was less than 7miles (11km). Shaded areas (N) represent no observations of dust. Total period between 1940and 1970, approx.816 M. M. ORGILL and G.A.SEHMEL



### The occurrence ofsuspended dust isrelatively infrequent. For example, themaximum annual percentage frequency for the country is 3.1% at Lubbock, TX. This amounts to a total of5 133 h in a 23-y period (105 580 h ofobservation) or 223dust h y-l on the average. Ageneral description ofthe distribution ofannual dust frequency in the seven general regions of the country as shown in Fig. 2follows: Pacific coast region. 

### Coastal and inland valley regions (westofthe Cascade Mountains) ofWA and OR have very fewoccurrences ofmajor dust storms because of the prevailing onshore winds and frequent precipitation, although, strong winds (>7ms-l) do occur at times. The major areas of relatively highincidence arefound in the San Joaquin Valley (0.24.8x) and Los Angeles basin of CA (0.14.4”/,. In central and Southern CA, dutit frequency gradients are very steep, due in part to the mountain ranges. Rocky Mountain Region. 

### Dust frequency is highest in the broad river valleys, deserts, and leeside areas of mountain ranges, such as the Mojave Desert in southern CA and AZ (0.74.8”/,), Great Salt Lake Desert (0.3%), western NV (0.3%), east’ern WA (0.1-0.2x) Snake River Valley (0.1x), southern Rio Grande Valley (O&> I%),and the higher desert plateaus ofAZ (-0.2%) and WY (-0.05%). Southern central region. 

### The highest annual dust frequency (l-3%) in the country is located along a north-south axis, through west TX, OK, KS, and eastern CO, approx. 300km east from the crest of the Rocky Mountains. Further east, the frequency of dust (- 0.1%) decreases by afactor l&30 in the states of MO, AR and LA. North central region. 

### The north-south axis ofhigh dust frequency from the south central region also extends through central NB and eastern S and ND, but with lower frequencies. A secondary maximum (0.6%)islocated in eastern ND. An eastward extension of high dust frequency extends from this area through MN toward MI. GreatLakes region.

### The northern Great Lakes area has averylowdust frequency (0.05%to N)but areas south ofthe Great Lakes in IL, IN, and OH have anincreased incidence (0.0254.1%) ofdust. Evidently, a major part of the suspended dust that occurs in theGreat Lakes area are due to“dust fronts” moving east from the south central regioli and north central region (Cohen and Pinkerton, 1966). Southeasternregion.

### The southern states, aswell as TN, KY, WV, and VAhave annual dust frequencies (0.1-0.2”/,) comparable to some western mountain regions. Frequencies are low along the Applachian. Mountains, but maximum frequency (0.14.2x) areas occur through TN, KY, GA, and the Carolinas. Again, “dust fronts” from the south central region contribute to the dust frequency in this area. Northeastern region. 

### Dust frequency is very low (O.oO~.Ol%) in the northeastern portion of the Table 1.Annual average regional dust frequency forseven regions ofthe 

### U.S.A.

South central region 0.61 Rocky Mountam region 0.17 North central region 017 Pacific coast region 0.07 South eastern regton 0.06 Great Lakes region 0.04 North eastern region 0.0

### I

country, and especially along the Applachian Mountains. The urban area between Boston and Washington, D.C., indicates a minor high frequency (O.OO%O.lo/,)

area ofdustiness. The authenticity ofthis feature may be questionable and requires further verification. A comparison ofrelative average dustiness of the seven regions was made by computing an annual average regional dust frequency from equation (3) for each region. These are shown in Table 1. Comparison ofthe annual average dust frequency for the seven regions shows that the south central, Rocky Mountains, and north central regions of the country have thehighest relative dust frequency. The northeast and Great Lakes regions the lowest frequency. The relatively high frequency ofdustiness for thePacific coast region isdue solely to the influence ofCentral and Southern CA. The coastal regions of OR, WA, and NC have one ofthe lowest (ifnot the lowest) dust frequency in the nation.

40 m)NrH OF MAXIMUM

FREQUENCY OF AIRBORNE DUST

ia

a JAN FEE AWR APR WY JUN JUL AUC SEP CC1 WV DEC JAN MONTH Fig. 3. The % of observation stations that have a maximum frequency of airborne dust during a particular month.Dust storms in the contiguous U.S.A.

KNOXVILLE.TENNESSEE CHATTANOOGA. TENNESSEE 817

SMYRNA.TENNESSEE BRISTOL. TENNESSEE k a4 NONE

a6 FE6 a4 82

MARa4 a2

APR ;;

a4 MAYa2

a4 SEP a2

a4 OCTa2

NOV

## ,“: NONE 

### I

a DEC NONE

IiIIII a4 a2
@HZ M-L-@ 12-14 18-20 m-6 09-11 15-17 21-23 TIM DATARECORD:

IW-1964 

### Ad4 a2

APR a4 a2
a4 WYa2

a4 ‘UNa2 (16 JuL a4 a2

a4 0CTa2 NONE

a4 NOV a2 NONE

(16 DEC a4 a2 116 DEC a4 (16 OEC a4 a2 a2
OH?2 W-03 12-14 18-20 Go-a? M-c6 12-14 18-20 m-02 06-08 12-14 18-20 m-c5 09-U 15-17 n-n m-05 09-11 15-17 21-D m-c6 lx-11 15-17 21-23 TINE TIME TIME DATARECORD:

lW8-1960 DATARECORD: 1948-1964 DATARECORD: lp12-1%6 a4 JAN a2 NONE 

### I
(16 FEBa4 a2

MARa4 a2

hwa4 a2

(16 JULa4 a2

a4 SEPa2

a4 OCTaz

a4 NOV a2 a4 JAN a2
(16 FE8a4 a2

MARa a2

A,,;:

a4 “uya2

a4 ‘UNa2
L16 JULa4 a2

a4 AUG a2

a4 SEPa2

a4 OCTa2

a4 NOV a2

Fig. 4. Four stations in TN showing a definite dust frequency maxima during the Spring months as well as diurnal variations.
Seasonal andmonthlyvariationofsuspended dustand sand The maximum frequency of suspended dust for the country occurs during the months of March, April and May. Figure 3 shows that during this period around 72% of the stations showed maximum monthly dust frequencies. In March, 41% of the stations indicated monthly maximum dust frequencies. Figure 4 shows four observation stations in TN that illustrate a definite spring maximum in dustiness. This spring maximum in dustiness is largely the result of strong winds (~7 ms- ‘) associated with spring cyclonic and convective storm activity. A definite afternoon maximum in dust frequency is often observed in the spring but this feature will be discussed later. A much smaller secondary maximum in dust frequency (4-5x of the stations) occurs during the months of September and October. This is the result of several stations in the Pacific Coast and Rocky Mountain regions having their monthly maximum dust frequency during the fall months. This is the case in eastern WA and the San Joaquin-Sacramento Valleys of CA. The spatial distiibution of the monthly dust frequency for the country are shown in Fig. 5(a-d). One of the distinguishing characteristics of the monthly dust frequency patterns is the persistence of dust source regions west of Mississippi River. The spatial dust frequency patterns are generally fixed to certain regions of available soil, e.g. Mojave Desert, Great Salt Lake Desert, and South Great Plains. Regions east of the Mississippi River show intermittent and variable regional dust frequency patterns from month to month. During the spring months, when the frequency of dust generally increases over

## a

6 -0 

### 9Dust storms in the contiguous U.S.A. 819

Fig. 5.Monthly % frequency of dusty hours for January (a), March (b), July (c) and October (d) based on hourly observations from 343weather observation stations that recorded dust, blowing dust and sand when prevailing visibility was less than 7 miles (11km). Shaded areas (N) represent no

observations ofdust. Other months available from authors.820 

### M. M.ORGZLL and G.A. SEHMEL

JAN FE8 MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN MONTH Fig. 6. Monthly regional average dust frequencies for seven defined dust regions in the contiguous U.S.A.


### the eastern section of the country, fairly persistent maximum dust frequency areas appear in the southeast region including TN and KY. Another maximum area occurs through the northern Great Lakes area and appears to o~ginate from the north central region. By the month ofJune, these rn~~~ dust frequency areas have reduced in magnitude and become more variable in location, but still have a tendency to persist in the southeast and southern Great Lakes region throughout the year. A monthly regional average dust frequency was computed foreachoftheseven regions ofthecountry foreach month by equation (3).The results are presented in Fig. 6. One of the most distinguishing characteristics ofFig. 6 is the definite maximum in dustiness during the spring months for all areas except the Pacific Coastaf region. In this latter case, the m~imum occurs during the fall and early winter months. Alltheregions show a definite decrease during the summer months. At least three ofthe regions, south central, Great Lakes, and Rocky Mountain, have a seasonal bimodal distribution in dust frequency with a primary maximum in the spring months and a secondary maximum in the fall or early winter months. Also, a number of stations in some of the other regions show bimodal dust frequency distributions. Four selectedstations that show bimodal seasonal dust frequencies are shown in Fig. 7.Each station shows the characteristic dust frequency maxima in the spring months, the decrease during the summer months, another maxima in dustiness during the fall months and then another decrease during the winter months.
Diurnal variation ofdustjPequency 

### Three-hour dust frequency data wereexamined for anumber ofstations. The diurnal dust frequency was generally classified into four types. These are: (1)the afternoon maximum; (2)random; (3)mixed; and (4) late afternoon and evening. Examples of these four diurnal dust fr~uency types are presented in Fig. 8. The afternoon maximum in dust frequency is very common and occurs atmany locations. Lubbock, TX, aswellasthe stations in Fig. 7illustrate this diurnal variation. The highest dust frequencies occur during afternoon hours when the atmospheric boundary layer isnormally deep and turbulent mixing is more pronounced. The random diurnal dust pattern is illustrated by Lufkin, TX. The dust frequency variation is devoid ofany significant peaksin dust frequency. In thiscase the dust distribution is probably due to the random occurrence of strong winds (>7 ms- ‘) associated with frontal or thunderstorm activity. The mixed diurnal dust pattern is illustrated by Hanford, WA, and Fig. 4. In this case, the random occurrence of storm activity is superimposed on an afternoon maximum resulting in peak dust frequencies at different local times depending on the month. Thelate afternoon and evening diurnal dust pattern is not very common. It appears best developed at Bakersfield, CA, between April and August. Apparently, during these warm months a strong sea-breeze front invades the Bakersfield area and, at times, produces late evening dust storms of varying degrees (U.S.Dept. ofCommerce, 19711.

DISCUSSiON
The 

### suspended dust potential ofa region depends on several closely interrelated factors. Factors which may influence soilparticle translocation are generally divided into particle properties, surface properties, and meteorological factors (Hilst and Nickola, 1959). These factors and their components have been the subject of extensive research by soil scientists and others for several years. Past studies (Viletto and Ohman, 1972; Ohman er al., 1972) have attempted to evaluate the potential dustiness ofan area by examining the particle distribution and physical characteristics ofsoil.Itwasconcluded that soilswith potential dust particles are very common on a world basis so other factors such as surface cover properties and meteorological factors must befactored in topredict dust suspension. Techniques have been developed by soil scientists for estimating soil loss by wind erosion (Woodruff and Siddoway, 1965;Skidmore and Woodruff, 1968),but the problem ofparticle suspension under various surface and met~rological conditions has not been completely solved.Dust storms in the contiguous U.S.A.

JAN

APR

JUN

JULY

LPT

NOV s E~AR~AFE, CALIF.
r 1

MB &ca u-14 w2D DM? a-L.8 u-14 Is-20 awK o&63 u-14 i&20 aI-@ 06-m u-14 18-2D B-5 D?iI IS-17 a-23 D3-16 OF11 L5-17 21-23 @3-i?J OF11 B-17 a-z? m-m Dwl 15-17 a-t3 Tlbtt TIKL TIME TIM DATA RECORD: 1962-1965 DA~h~CORD: l~Z-1~ OATAR~COff~ l%U-15'70 DATA RECORD: 1992-1967 Fig. 7. Monthly and 3 MAR21

2 APR 1

JUN 1

2 JULY, 2 JAN 1-

APR z1-I

2- JUN l2 - JUU'1 -

AU0

SEPl

NOV 

### % SIOUXCITY. IOWA

lJ 2 - NOV lkd 2 APR 1

2 JUN 1

2 JUL 1

SEP 21 3 h5AR2 1

diurnal dust frequency variations at 

### fourlocationsthathaveaseasonalbimodal

distribution ofdustfrequency.

An important factor in assessing the dust potential ofa region is the presence or absence of protective vegetation cover. Dense vegetation which is often found inthehigh mountains and inregions ofmoderatetohigh precipitation provides excellent protection from strong wind movement. Thus, a large share of thecoastal Pacific northwest, Rocky and App~achi~ Mountains, the Great Lakes region, and the northeast region have very lowdust frequencies. However, dust may be transported from other regions. Table 2 shows monthly dust frequencies in mountainous regions for the available stations. Table 2 generally indicates dust frequencies are quite low in mountainous terrain, but dust isnot totally absent. Apparently, alarge share ofthe reported airborne dust originates and is transported from local surrounding dust source regions. When thevegetative cover isdisturbed bymechanical means, such as construction, plowing, strip-mining,etc.theregional dust potential isexpected to increase.Sincetheearly spring and fallmonths arenormally the time period in which farmland isprepared for future crops, vast areas ofdisturbed soil become available forwind translocation. Appar~tly, agricultural activity is a factor that may explain the high frequency ofdustiness for the whole country during the spring months and possibly again during the fall months asindicated in Figs. 3and 6. The ground surface characteristics also changes during the winter. In the northern states and in the mountanous areas the ground may freezeor become covered with snow at times. Dustiness is nearly nonexistent during thistime, but the snow cover itself will be subjected to wind translocation. Blowing822 M. M. ORGILL and G. A. SEHMET

* a LUEBDCK.TEKAS
6 MN b 2 0 

# IJAN 

### * BAKERSFIELD, CALIF. 

### * LUFKIN. TEXAS I 1 I2 JAN 1 JAN

### 2t

6 FEB b 2 0 10 a MAR 6 MR



# I

APR 4 

### * HANFDRD. WASH. .6 .b .2 .D .b .2 .O .b .2 .O .6 .b .2 .O APR 2 1 2 APR 1
2 0 12 10 8 APR 6
4 2
8 6 My 4 WAY

JUN .b .2
.o .b .2 .O 2 JUN 1 2 JUN 1

JULY 1 .2 .O .b .2 .O .6 .b .2 .O 2 JULY1

2 0 AU0

### ’ 1

4 JUN 2 I SEPTl 0 JULY o AIn? 0 2 2 SEP7 D OCT .2 DCT 1 OCT , mD .O NW 2 2 2 i NW NW .2 1 No” 1

D (8-Q 09-11 I%17 21-23 ws wn u-17 21-23 ows o)-11 ls-17 21-23

TIM TIhE TIME DATARECOW lW-1%7 DATARECORD: 398-1970 DATARECORD:lW8-I%4 

### NONE 

# E

NM

(B-05 Dell E-17 21-23

TIM DATARECORR 1@9-15W Fig. 8. Four types of diurnal dust frequency variations; afternoon maximum: Lubbock, TX; random: Lufkin, TX; mixed: Hanford, WA; late afternoon and evening maximum (warm season): Bakersfield, CA.

Table 2. Monthly dust frequency for stations in mountainous areas (% of total monthly or annual hourly observations) station Jan. Feb. Mar. Apr. May Jlllle July Aug. Sept. Oct. NOV. Dec. Year Montague. CA NOIX N0Ile Blue Canyon, CA NOIX NolIe Donna Summit. CA NOIX O.l(“) O.Ol(?) Baker, OR 0.008 0.016 0.049 0.016 0.007 Ely, NV 0.036 0 038 0.053 0.254 0.018 0.018 0.053 0.019 0.055 0.019 0.081 0.056 Bryce Canyon. UT 0.126 0.008 0.011 FlagshIT, AZ 0.068 0.030 0.008 Ft. Huacbuca, AZ 0.1 0.2 0.1 0.01 0.

### I 0.035 Dillon, MT O.GQ9 O.OOR 0016 0.003 Kalispell, MT 0.016 0.015 0.015 0.031 0.006 Eanle. CO 0.065 0.063 0.008 0008 0.012 Asheville, NC 0.035 0.166 0.008 0 024 0.019 Roanoke. VA 0.026 0.079 0.047 0.013 Elkins, WV 0104 0.040 0.008 0.012 Plattsburgh, NY NolIe NolIe Burlington, VT 0.015 0.001Dust storms in the contiguous U.S.A. 823

snow, during the winter, is more common than dust. Winter monthly frequencies of blowing snow may vary between 1and 12% of the total hourly observations. These frequencies are substantially higher than dust frequencies. However, the role of blowing snow in the translocation of radioactive particles or other potentially hazardous materials has not been investigated. Meteorological systems or events that can cause major dust suspension throughout the country are:
1. Convective weather systems, i.e. squall lines, thunderstorms, tornadoes. 2. Warm and cold frontal passage. 3. Cyclogenesis. 4. Low-level winds associated with upper-level jet streams. 5. Diurnal winds. 6. Mountain katabatic winds, e.g. Chinook and Santa Ana.

NEWYORU. NEWY0RKIJ.F.K. AIRPORT WESTHAMPTON. LONGISLAND

JAN

FEE

MAR

APR

JUN

JUL

AUG

SEP

# a:
a2

a4

(18 a6 a4 a2

a4 a2

a4 a2

a4 a2

art a2
(16

t NONE a4 a2 a4 JPda2

a4 MAR a2
I18 (16 APR a4 a2

a4 MAya 

## Jet WNE

a4 JULa2

a4 AUG a2 NONE

a4 SEPa2

OCTa4 a2

(16 DECa4 a2
m-a? M-m u-14 l8-20 m-G5 w-11 15-17 21-23

TIME DATARECORD: lW-l%S DATARECORD: lW-1%7 An interesting climatological feature this study has revealed is that many relatively high-dust frequency areas in the Rocky Mountain region are located in the lee of mountain ranges where katabatic winds often occur. The phenomenon is well known east of the Rocky Mountains and Sierra Nevadas, and also occurs in varying degrees in other locations, such as eastern WA, western NV, western and eastern UT, the WY desert and the southern Rio Grande Valley. This climatic feature is not so apparent east of the Mississippi River unless the dust frequency maximum which occurs during the spring months in eastern S and NC is the result, in part, to the leeside effects of the Appalachian Mountains. The Los Angeles Basin and southern San Joaquin Valley is also another region where katabatic winds cause dusty conditions. Warm, dry and dusty Santa Ana winds blow from the Mojave Desert westward into this region, causing severe dust conditions at times. The maximum dust frequency during the late

CHICOPEEFALLS. MASSACHUSETTS FALAWUTH. MASSACHUSETTSlOTlSA

NO?“,

a6 DEC a4 a2
Ln-@%-!ze 12-Y 18-2il m-a G9-11 1.517 21-a

TIME DATA RECORD: lpll-1%7 

# a: JAN a2

04 FEB a2

a4 MARa2 (18 06 APRa4 a2

a4 mAYa

JUNG4 a2
a4 JULa2

a4 AUGa2

a4 SEPa2

(16 DECa4 a2 OI-LQ t-6-13 12-14 18-20 m-m w-1, u-17 21-B

TINY DATA RECORD: 1pb2-1970 Fig. 9. Monthly and diurnal dust frequency at selected east coast locations824 

### M. M.ORGILLand G.A. SEHMEL

DOVER,DEtAWARE

a6 a4 APRa2

a4 MAYa2

JUN i”,

a6 JUL a4 a2

a4 AUCa2

a4 SEP a2 

# DEc 

# t&LLJ

IX-CQ M-OB 12-14 18-20 m-G5 09-11 15-17 21-23

TIME DATARECORD:

lp12-1965 WRIGHTSTOWN,hEWJERSEY

a2

a4 FEE a2

a4 MARa
a6 a4 APRa2

a4 MAY a2

JUNa4 a2
a6 JUL a4 a2

a4 SEP a2

NO”;“2

(16 DEC a4

m-m lx-11 l5-17 21-23

TIME DATARECORD:

Ip12-1970 LAKEHURST, NfWJERSEY

JANa4 a2

a4 MARa
a6adAPR

a4- MAY azr

JUNa4 a2 NONE

116 JUt a4 a2

a4 AUG a2

a4 SEP a2

a4 OCTa2

13-m M-t3 12-14 18-20 MIDDLETOWN, PENNSYLVANIA

JAN

# ”

a2

a4 :EB a2

a4 MARa
Q6 a4 APRQ2

a4 MAY a2

JUNa4 a2
a6 JULa4 a2

AUG a4 rJ.2

SEPa4 a2

a4 CCT a2

NOV;;

OS-t6 W-11 15-17 21-23 LB-05 09-n 15-17 21-o

TIME TIME DATARECORD:

1945-1972 DATARECORD: 1935-1%7 Fig. 10.Same as Fig. 9,but for 4different locations.



### fall and early winter months (Fig. 6)within the Los Angeles Basin is the result, in part, to these dusty Santa Ana events. A surprising aspect ofthis study was the presence ofdust events in the eastern section ofthe country, especially between Washington, D.C. and Maine. Figures 9 and 10 are a selection of observation stations in this region that indicated dust episodes but at infrequent periods. The origin ofthe airborne dust, ifit is actually dust (possibly observers could confuse haze and smoke with dust in these relatively highpolluted regions), isnot known atthistime.Even though eastern dust events arenot particularly significant, further confirmation ofthese episodes may be ofinterest, but would require a detail examination ofthe hourly observation records of several eastern stations and thesynoptic charts during suspected dust episodes. CONCLUSIONS


### This study has shown that many diverse regions ofthecountry, suchasurban, agricultural, desert, valley,plain and forested areas are subject to suspended dust in varying degrees. Regions ofthe country that are mountainous, forested and predominantly maritimearegenerally freefrommajor “dust storms” (visibility lessthan 11km).The highest frequency ofdust isobserved in the southern Great Plains. Secondary dust frequency maxima are observed in the western states,northern Great Plains, southern coastal Pacific and inland valleys and the southeast. Maximum dust frequency occurs in the early and late spring months for most regions of the country, but someareas experience additional dust in the summer or fall. Observations show that the higher frequencies of airborne dust occur in the afternoonDust storms in the contiguous U.S.A. 825

period between 12:00 and 20:00 LST or during the period of maximum thermal instability. Details on the different regional patterns of dust frequency would require additional studies on the principal factors which govern natural wind-caused suspension, i.e. (1) soil particle properties, (2) surface properties, and (3)meteorological conditions.

REFERENCES Charlson R. J. (1969) Atmospheric visibility related to aerosol mass concentration: A Review. Environ. Sci. Technol.3,913-918. Clements T.,Mann J. F., Stone R. 0. and Eymann J. L. (1963)A study of windborne sand and dust in desert areas. Technical Report ES-& Earth Sciences Div., I/S, Army National Laboratories. Cohen J.M. and Pinkerton C. (1966)Widesnread translo

### . , cation of pesticides by air transport and rain-out. Organic Pesticides intheEnvironment, Advances inChemistrySeries 60,pp. 167-168.American Chemical Society. Gillette D.A.,Blifford J. H.,Jr. and Fenster C. R. (1972) Measurements ofaerosol size distributions and vertical fluxes of aerosols on land subject to wind erosion. J. appl. met. 11, 977-987. Hagen L.J.and Woodruff N.P.(1973)Air pollution from dust storms in the Great Plains. Atmospheric Enuironment 7, 323-332. Hilst G.R.and Nickola P.W.(1959)On the wind erosion ofsmall particles. Bull.AMS 40, 73-77. Huschke R.E.(Editor) (1959)Glossaryof Meteorology, pp. 1833184.American Meteorological Society, Boston, MA. NOAA-National Weather Service (1970)Federal Meteorological Handbook No. 1.Government Printing Office, Washington, D.C. Ohman H. L.,Viletto J.,Jr., Ackerson K. T. and Miller L. L.(1972)Potential sand and dust source areas. Report ETL-SR-72-1, U.S. Army Engineers Topographic Labs., Ft. Belvoir, VA. Orgill M. M., Sehmel G. A. and Bander T. J. (1974) Regional wind resuspension of dust. BNWL-1850, Pt. 3,UC-11,Pacific Northwest Laboratory Annual Report for 1973,to the USAEC Div. of Biomedical and Environment Research, Atmospheric Sciences, 214219. Shinn J.H., Kennedy N. C., Koval J. S.,Clegg B. R. and Porch W. H. (1974) Observations of dust flux in the surface boundary layer for steady and non-steady cases. Atmosphere-Surface Exchange of Particulate and Gaseous Pollutants Symposium, CONF-740921, Richland, WA. Skidmore E. L.and Woodruff N. P. (1968)Wind erosion forces in the United States and their Use in predicting soil loss. Agriculture Handbook No. 346, U.S. Dept. of Agriculture, Manhattan. KS. U.S. Dept. ofCommerce (1971)Narrative Climatologicaf Summary. Bakersfield, CA, Local Climatological Data, NOAA. Viletto J.and Ohman H.L.(1972)Particulate matter considerations in the design of V/STOL Aircraft. Special Report ETL-SR-72-2, U.S.Army Engineers Topographic Laboratories, Ft. Belvoir, VA. Woodruff N.P.and Siddoway F.H.(1965)Awind erosion equation. Soil Sci. Sot. 29, 602-608.

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