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oEPA
Office of Environmental
Engineering & Technology
a siil fa te
episode:
1976
August 16 to
August 29,1976
EPA
600/
1976.3
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astdfote
episode: 1976
Widespread turbid air masses, sometimes referred
to as "hazy blobs," are the most obvious
characteristics of prolonged elevated pollution
episodes. By using photographs taken from
satellites, these large-scale pollution events, which
may occur several times during a normal summer
season, can be detected and tracked as they cross
over land and ocean.
A major episode occurred from August 16-29, 1976,
over substantial portions of the North American
continent and contiguous north Atlantic Ocean. As
the blob developed and dissipated over a twelve-
day period, it extended as far westward as Kansas,
southward through much of the Mississippi River
Valley out over the Gulf, northward to James Bay,
Newfoundland and beyond, and eastward, far out
over the ocean.
The following pages document the development of
this prolonged elevated pollution episode. The
satellite photos taken at an altitude of about 25,000
miles show clouds and hazy air masses
superimposed over the geographical features of the
North American continent. Bright areas on the
photographs indicate dense cloud cover, while
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bright streaks and fine-grained patterns are other
cloud structures. Pollution-laden hazy air masses
appear as amorphous milky areas on the
photographs, such as the one extending from Ohio
eastward past New Jersey out over the Atlantic on
August 22. Care must be taken in interpreting these
photographs to distinguish clouds from haze, as
they are frequently intermingled—while over
extended water areas the contrast is more
pronounced.
Standard weather map symbols are used to show
the locations of high and low pressure systems and
frontal systems on the SURFACE WEATHER &
VISIBILITY display. Grey areas on this map delineate
the area covered by haze as observed from the
satellite. Colored areas indicate the regional extent
of significantly degraded visibility as determined by
airport observations.
The PRIOR 3-DAY AIR PARCEL TRAJECTORIES
display shows the paths followed by individual air
parcels. The arrows can be thought of as the tracks
of balloons simultaneously released into the air
mass. The arrow shows the position of the air parcel
at noon of the day indicated and its prior seventy-
two hour track. Arrow length represents the distance
covered, and therefore the average speed of the air
parcel (wind speed). All trajectories are computed
from upper air wind measurements at 600 meters
(2,000 ft.) elevation above the local terrain.
The SULFATE display shows 24-hour sulfate
concentrations for those areas where monitoring
data was available. Note that for August 22, no data
was available for the majority of the region under the
hazy blob—due to the twelve day cycle of most
sulfate monitors. The OZONE display shows those
areas where the maximum hourly value for ozone
was above 80 parts per billion. Determining the full
regional extent of elevated ozone concentrations is
hampered by insufficient monitoring sites.
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The twelve day episode began on August 16, as
relatively clean air from the north moved in behind a
frontal system that swept southward across the
eastern United States. This air stagnated as a strong
high pressure system developed over the central
Mississippi and Ohio Valleys. Emissions from the
many industrial and transportation sources
(particularly, large power plants) were trapped in the
stagnant air and were slowly transformed into
harmful oxidants and sulfates. These formed the
aerosols which were observed as haze from the
satellite and were responsible for substantially
reduced ground level visibility. After twelve days of
"cooking" this polluted air mass moved off to the
northeast as a new frontal system swept eastward
over the continent.
Measurements of sulfate concentrations within the
turbid air mass were found to correspond closely
with observations of areas of visibility reduction.
Particulate sulfate 24-hour concentrations inside the
blob were over 60 ug/m3, while in relatively
unaffected "clear air" areas they ranged from 1.3 to
14 ug/m3. Maximum hourly ozone concentrations
measured over 250 parts per billion. As observed
from the satellite, the hazy air mass extended well
beyond the maximum areas of ground level air
quality degradation.
The ability to perform analyses of these major
prolonged elevated pollution episodes on a sub-
continental scale is severely hampered by a lack of
daily sulfate data. However, the use of satellite
photographs enables us to interpret the available
data in order to determine the full geographical
extent and severity of these episodes which result
from long range pollution transport.
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16 August 1976
• A fresh Canadian polar air mass has entered the
United States... The first phases of stagnation
are in progress.
• Slight visibility degradation at ground level...
Little evidence of hazy blob on the satellite
images.
• Moderately elevated sulfate and maximum ozone
concentrations are found at the southern and
western fringes of the high.
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16 August 1976 I
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surface weather & visibility
haze 5-mile visibility •< 3-mile visibility
sulfate
L- 1
10-20 pgm/M3
20-30
30-40
40-50
I > 50
single point observation/
j v
NO OTHER \
DATA AVAILABLE/
prior three-day air parcel
trajectories (at 600 Meters)
ozone
LJ> 80 PPB (areas where ozone
peaked above 80 PPB,
maximum hourly average)
• 80 PPB
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I 22 August 1976
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• The high has been stagnant for eight days... Air
parcel trajectories indicate recirculation of the air
mass over high SOa emission areas.
• The hazy area on the satellite image stretches
from Kansas to the east, far into the Atlantic... A
sharp discontinuity in turbidity has formed aiong
the front through the Great Lakes region.
• Incomplete sulfate data shows very high values in
Ohio and Pennsylvania (over 50 micrograms/
cubic meter)... This is coincident with a region of
nearly stagnant air. Most ozone monitors within
the hazy blob record greater than 80 PPB.
Ground-level visibility drops below three miles
over an extensive area.
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'SlKa^«^i
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surface weather & visibility
LLJhaze •< 5-mile visibility •< 3-mile visibility
sulfate
D10-20 fjigmlM3 fl 30-40 /tgm/M3
EH 20-30 j*gm/M3 | 40-50 pgm/M3
single point observation I ^
NO OTHEH \
DATA AVAILABLE/
prior three-dqy air parcel
trajectories (at 600Meters)
ozone
I | > 80 PPB (areas where ozone
peaked above 80 PPB,
maximum hourly average)
K80PPB
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27 August 1976
• After twelve days, air parcel trajectories indicate
the air mass is streaming northeast... A strong
Pacific cold front begins to push the stagnant air
mass eastward. A large-scale ducting situation is
created, which transports the polluted air mass
into Canada.
• Haze now extends more than 700 miles into the
Atlantic.
• High sulfate and high ozone values continue to
be recorded in the hazy area ahead of the front
,., There are still extensive areas of less than
three-mile ground visibility.
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surface weather & visibility
iH haze EH < 5-mile visibility I< 3-mile visibility
sulfate
n 10-20 pgm/M3
D 20-30 /igm/M3
u.8) single point observation (
^~"M* ^
l30-40pgm/M3
Uo-5QMgm/M3
NO OTHER \
DATA AVAILABLE/
prior three-d^y air parcel
trajectories (at 600Meters)
ozone
I—I > 80 PPB (areas where ozone
peaked above 80 PPB,
maximum hourly average)
• < 80 PPB
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view from
Whiteface
Mountain
New York
State
with clean air mass from
the north
two days later,
after winds from Ohio
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