EPA-600/3-78-048a
May 1978
Ecological Research Series
HOUSTON URBAN PLUME STUDY • 1974
Description and Summary of Results
Environmental Sciences Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
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This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
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mine the fate of pollutants and their effects. This work provides the technical basis
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This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-78-048a
May 1978
HOUSTON URBAN PLUME STUDY - 1974-
Description and Summary of Results
by
James R. Brock
The University of Texas
Austin, Texas 78712
Grant No. R800871
Project Officer
Jack L. Durham
Atmospheric Chemistry and Physics Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Sciences
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
11
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ABSTRACT
The 1974 Houston Urban Plume Study (HUPS) was undertaken as a prelimi-
nary investigation of some of the unresolved features of Houston's air
pollution problem. HUPS was intended specifically to gain limited informa-
tion on the spatial and temporal distribution of air pollutants—particu-
larly, primary and secondary aerosols—in the Houston area as an aid should
a later intensive investigation of aerosol character and transport be needed.
Aerial measurements were made of the principal pollutants (S02, NO ,
CO, aerosol) of the Houston area. Wind-field measurements were alsS
e. These data were used to estimate pollutant budgets. Values for S02
and NO (14 metric tons/hr and 40 metric tons/hr, respectively) were
reasonably comparable with values derived from emissions inventories of the
Texas Air Control Board (13 and 24 metric tons/hr, respectively). On the
basis of the limited sampling period, the industrial area (east of down-
town Houston) apparently is the major contributor of primary air pollutants
in the Houston area. In the morning hours above the mixed layer, relatively
large ozone concentrations (max. 0.2 ppm)—almost certainly of photochemical
origin—were found that correlated closely with light scattering aerosol,
thus indicating the existence above the mixed layer of strong secondary
aerosol sources.
Appendices containing all the data are not included in this report.
A complete, unabridged report is available from the National Technical
Information Service (NTIS) as EPA-600/3-78-048a, May 1978.
This report was submitted in partial fulfillment of Grant No. R800871
by the University of Texas, Austin, under the sponsorship of the Environ-
mental Protection Agency. This work covers the period May 1974 to March
1976. The work was completed as of March 31, 1976.
m
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CONTENTS
Abstract ill
Figures vi
Table vi
Acknowledgment vii
1. Introduction 1
2. Conclusions and Recommendations 4
3. Procedure 6
Meteorological information and data 6
Airborne air pollution measurements 8
Ground based air pollution measurements 8
4. Results 10
Summary data 10
Meteorological data 13
Aircraft measurement data 13
5. Discussion 16
Pollutant budgets for Houston area 16
Additional observations 17
6. Summary and Conclusions 22
References 23
v
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FIGURES
Number
1 The regions studied by instrumented aircraft and
pibal measurements in 1974 Houston Urban Plume
Study
2 Positions of six pilot balloon stations and TACB
monitoring stations during 1974 Houston Urban
Plume Study .
Locations of traverses and spirals of instrumented
MRI aircraft during 1974 Houston Urban Plume
Study 11
Fluxes in metric tons/hr-krrr calculated from air-
craft data of July 19 and 20, 1974 during 1974
Houston Urban Plume Study 18
TABLE
Pollutant transport through cross sections for
Houston area calculated from aircraft data, 1974
Houston Urban Plume Study, metric tons/hr 19
VI
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ACKNOWLEDGMENTS
This study was made possible through the support of the
Atmospheric Aerosol Research Section, Environmental Sciences
Research Laboratory, U.S. Environmental Protection Agency. The
cooperation of the U.S. Air Force Air Weather Service, Texas Air
Control Board, Meteorological Research Incorporated, National
Weather Service, Federal Aviation Administration, University of
Texas School of Public Health, The University of Texas at Austin,
and Texas ASM University is gratefully acknowledged.
vn
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SECTION 1
INTRODUCTION
The City of Houston is situated on the coastal plains of
Texas close to the western section of the Gulf of Mexico. Large
land masses extend for great distances in every direction from
Houston except toward the southeastern quadrant in which lies
the Gulf of Mexico. The proximity of the city to the Gulf leads
to a local climate with some maritime characteristics, while,
at the same time, the adjacent vast expanse of land gives rise
to some continental characteristics. The meteorology is,
therefore, subject to such variation depending on the large
scale wind pattern prevailing at a given moment.
Typically, in the winter months the climate of the Houston
area takes on a continental character owing to penetration of
polar air masses. In summertime, the area normally experiences
a nearly tropical weather regime with very few frontal
passages, high relative humidities, and convective rain showers.
The air pollution potential for the Houston area is low
owing to strong thermal mixing and to almost continuous low
level winds. The ventilating effect of these winds usually
provides good dilution of air pollutants. Long periods of air
stagnation are not too common, although frequent periods of
short duration (one day or so) do occur. Most commonly, these
periods of atmospheric stability are associated with surface-
based, radiation-type inversions, although occasionally this
low-level stability is caused or reinforced by the advection of
cool air from the Gulf of Mexico.
The low air pollution potential for the Houston area is
fortunate in view of the area's large pollutant sources. Along
the Houston Ship Channel, immediately to the east of the down-
town area, lies one of the world's greatest concentration of
petrochemical and related process industries. Along the Gulf
Coast, centered around Houston some 40% of the nation's basic
petrochemicals are produced. In addition, in terms of popula-
tion the Houston area is one of the fastest growing in the
country with a metropolitan population of 1,677,863 in 1970.
The city has more single family homes and fewer apartments than
other cities of comparable size and boasts a high figure for
registered motor vehicles (1,521,245 in 1975 for Harris
County).
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Along with the low air pollution potential, the area has
benefited from the use of natural gas, a clean fuel, as its
principal energy source. As this fuel increases in price,
becomes depleted, or both, substitution of other fuels will
occur and it is possible that this advantage in maintaining air
quality may diminish.
In brief, the low air pollution potential for the Houston
area is offset by relatively large sources of air pollutants.
As a result, Houston usually exceeds (with year to year excep-
tions) the national standards for carbon monoxide (highest
hourly values), total suspended particulate matter (highest
daily values), ozone (highest hourly values), and non-methane
hydrocarbons (highest values for 6-9 a.m.). In addition, the
Houston area is marked by persistent haze conditions caused by
light scattering aerosol and the area may act as a source of
oxidants and other air pollutants which could produce damage
to the peanut, soybean, rice, and other important crops in the
coastal region.
Much of what is known of the air pollution problem in the
Houston area is based on routine surface monitoring stations
operated by the Texas Air Control Board and the City of Houston
and on emissions inventories compiled by the Texas Air Control
Board. As valuable as such information is, it has left un-
resolved a number of questions concerning Houston's air pollu-
tion - notably, the sources of Houston's oxidant problem and
the Houston haze.
The 1974 Houston Urban Plume Study (HUPS) was undertaken
by the Atmospheric Aerosol Research Section, Environmental
Sciences Research Laboratory, USEPA as a preliminary investiga-
tion of some of the unresolved features of Houston's air
pollution problem. HUPS was intended specifically to gain
limited information on the spatial and temporal distribution
of air pollutants - particularly, primary and secondary
aerosols - in the Houston area as an aid should a later
intensive investigation of aerosol character and transport be
needed. The regions studied are indicated in Figure 1.
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AREA OF 1974 HUPS ,
/Houston x^7 I Beaumont x.
Intercontinental, Por| Arfhur
\-5- \\ ^^>i robby \>36*Gi
^ ^^(A^/
Figure 1. The regions studied by instrumented aircraft and
pibal measurements in the 1974 Houston Urban Plume
Study.
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
The 1974 Houston Urban Plume Study (15-24 July, 1974) had
as its objective a preliminary investigation of some of the un-
resolved features of Houston's air pollution problem. The prin-
cipal tool in this investigation was an instrumented fixed wing
aircraft. The following conclusions derived from the study are
based on limited data representing seven days (18-24 July, 1974)
of actual operation.
(1) Pollutant budgets for the Houston area for S02 and NOX
(14 metric tons/hr and 40 metric tons/hr, respectively) were
found to be in reasonable comparison with values derived from
emissions inventories of the Texas Air Control Board (13 and 24
metric tons/hr, respectively).
(2) On the basis of the limited sampling period, it appears
that the industrial area (east of downtown Houston) is the major
contributor of primary air pollutants in the Houston area.
(3) During the period of the study, in the morning hours
above the mixed layer, relatively large ozone concentrations
(max. 0.2 ppm) - almost certainly of photochemical origin -
were found which were correlated closely with light scattering
aerosol. This correlation indicated the existence above the
mixed layer of strong secondary aerosol sources, possibly asso-
ciated with the oxidation of S02-
This preliminary study has served to indicate more clearly
what additional studies are needed to delineate the aerosol
character and transport in the Houston area. The most important
recommendations are:
(1) Future field studies in the Houston area should be
preceded, planned, and carried out adaptively with an adequate
air pollution model for the Houston area.
(2) These studies should integrate ground based and air-
craft measurements, preferably involving two or more aircraft.
At least one helicopter would be desirable to permit sampling
below 1000 feet (304.8 m.) owing to frequent low level night-
time inversions in the Houston area.
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(3) The studies should be of sufficient duration to permit
an adequate sampling of meteorological conditions and diurnal
and seasonal variations.
(4) Special attention should be given to characterization
of primary sources and background values for the principal air
pollutants - particularly for particulate matter.
(5) The test of an adequate delineation of the aerosol
transport and character for the Houston area can only be in the
form of predictive success of an air pollution model developed
previously and adapted extensively from field results.
It is safe to say that studies in the Houston area which
proceed without these elements cannot be decisive in resolving
the nature of Houston's air pollution problem.
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SECTION 3
PROCEDURE
The 1974 Houston Urban Plume Study (HUPS) covered the ten
day period 15-24 July. The major elements of the study were a
fixed wing aircraft instrumented to measure concentrations of
the principal air pollutants and six pilot balloon stations to
provide hourly data on wind speed and direction in Houston's
atmosphere. These elements were intended to supply information
on the spatial and temporal distribution and fluxes of the prin-
cipal air pollutants.
The following description gives detail on these major ele-
ments and list as well auxilary elements of HUPS.
METEOROLOGICAL INFORMATION AND DATA
(a) Meteorological forecasting and analysis were provided
to HUPS by Dr. Gale F. Hoffnagle, INTERA Environmental Consul-
tants, Ltd., Houston, Texas.
(b) Six single theodolite pilot balloon stations were
operated by personnel of the U. S. Air Force, Air Weather Ser-
vice, 6th Mobile Weather Squadron, Tinker A.F.B. with the
assistance of students from Texas A&M University, University of
Texas School of Public Health, and North Carolina State Univer-
sity.
The positions of these six pilot balloon (pibal) stations
during much of the study (the position of one was shifted
occasionally) are indicated on the map, Figure 2.
(c) Important meteorological support was furnished by
several agencies. Mr. Ervin Vollbrecht and Mr. William Cope of
the National Weather Service, Houston office, made available
facilities in collection of rawinsonde data and their fore-
casting skills. Forecasting assistance was also provided by
the Texas Air Control Board, Meteorological Section - particu-
larly Mr. Rollie Schroder. Additional surface wind data were
furnished by the Houston Lighting and Power Co. and from a re-
cently installed ambient air quality network made available by
Mr. Tim Oujezdaky of the Environmental Protection Agency.
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30°0'N
29°30'N
Stations for 1974 HUPS
D TACB
(Conrinupus
Monitoring)
Houston
Intercontinental
Airport
a
Interstate 10
San Jacinto
Mon.
w7?bur/yH.S./Airp0rt
Galveston Bay
24
25 26
95°30'W
32 33
Figure 2. Positions of six pilot balloon stations and TACB
monitoring stations during the 1974 Houston Urban
Plume Study.
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AIRBORNE AIR POLLUTION MEASUREMENTS
(a) The principal air pollutants were measured by means of
an instrumented Cessna 206 with Robertson STOL modification and
a belly pod. This aircraft operated out of Hobby Airport indi-
cated in Figure 2. The following measurements were obtained by
the aircraft.
Condensation Nuclei - Environment 1 Condensation Nuclei
Counter
Bscat ~ MRI !ntegrating Nephelometer
Carbon Monoxide - Andros 7000 CO Monitor
Hydrocarbon - TEDLAR Bag samples analyzed with a Loenco gas
chromatograph using flame ionization detection
Nitric Oxide-Nitrogen Dioxide - Monitor Labs N0-N02 Monitor
Ozone - REM Ozone Monitor
Sulfur Dioxide - Theta Sensor
Particle Size~Distribution - Minnesota Aerosol Analyzer
System
Particle Filter Samples - membrane and glass fiber filters
Temperature, Relative Humidity, Air Speed, Altitude,
Turbulence - A.I.P. Sensors
Data from on-board sensors were acquired by magnetic tape data
logger. Calibration of the pollutant gas sensors was provided
by the Texas Air Control Board.
(b) It was determined that for purposes of this prelimi-
nary study, the aircraft would fly a pattern designed to deter-
mine pollutant concentrations at a cross section approximately
normal to wind direction. This mode of operation was designed
to make possible calculation of pollutant fluxes at the cross
section. Flight patterns were to consist of "traverses" and
"spirals" in the cross section. A single "traverse" consists of
flight in the cross section at a fixed altitude between two
specified points on the ground. A single "spiral" consists of
a spiral flight path located in a cross section beginning
(usually) at maximum altitude and descending to lowest altitude
possible around a fixed point on the ground.
GROUND BASED AIR POLLUTION MEASUREMENTS
The principal sources of ground based measurements of air
pollutants were the two atmospheric monitoring stations of the
Texas Air Control Board (TACB) located in Aldine and Mae Drive
as indicated in Figure 2. These stations provide hourly data
for the pollutants measured by the aircraft and so are useful
for correlation with the aircraft data. A number of gas bubbler
samples and high volume particulate sampling stations are in
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the Houston area, but these data represent relatively long time
averages which are not useful for correlation with the aircraft
data.
During the period of the aircraft flights, a seven-channel
solar radiometer was operated under the direction of Prof.
Richard K. Severs of The University of Texas School of Public
Health. Optical depth per channel calculations were performed
by NASA-JSC.
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SECTION 4
RESULTS
This section presents the data obtained in the 1974 Houston
Urban Plume Study (HUPS). First a summary record is presented
of the daily activities of the study together with rationale
for the measurement program for each day. The section concludes
with a presentation of the principal data components:
meteorological data, aircraft measurement data, and ground
based measurement data.
SUMMARY DATA
Monday, 15 July 1974 - First day of HUPS devoted to instal-
lation of pilot balloon crews, checking out instrumentation on
MRI aircraft and planning procedures for next day. MRI air-
craft had not been fitted with aerosol size distribution measure-
ment system and personnel at University of Minnesota were
contacted. Based on meteorological forecast, an urban plume
study was set for the next day west of Houston.
Tuesday, 16 July 1974 - MRI aircraft took off at 10:18 a.m.
and returned at 12:30 p.m. Plume study to west of Houston
attempted. Winds light and variable with visibility aloft
(above 300 m.) less than 3 km. Isothermal conditions to
200 m. and near neutral above. Visibility degraded drastically
in afternoon to the extent that MRI aircraft could not be
operated. A severe air stagnation was announced by local
authorities. Data of morning flight lost owing to malfunction
of MRI data acquisition system. No plans for aircraft flights
for next day owing to prediction of heavy precipitation.
Wednesday, 17 July 1974 - Heavy precipitation in Houston
area owing to low in Gulf of Mexico. Day devoted to instrument
calibration and maintenance. Afternoon flight tentatively
planned for next day.
Thursday, 18 July 1974 - Morning cloudy with only very
shallow surface inversion. MRI aircraft took off at 1230 hours
CDT for afternoon plume survey. Traverses and spirals flown
for cross sections G-KE and J-*I (see Figure 3) . Winds from
southeast quadrant. Aircraft data successfully acquired.
Morning flight planned for next day.
10
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• End point of traverse
O Location of a spiral
o Other points
Figure 3. Locations of traverses and spirals of instrumented
MRI aircraft during the 1974 Houston Urban Plume
Study.
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Friday/ 19 July 1974 - Winds from southwest to west weaken-
ing in afternoon. MRI aircraft took off at 0900 hours CDT.
Flew cross section I>A (see Figure 3). Afternoon spent setting
up particle size analysis system. Flight planned for next
morning.
Saturday, 20 July 1974 - Westerly winds. MRI aircraft took
off at 0800 hours CDT. Flew cross section I>A, downwind tra-
verse M+Q, cross section Clear Lake - Flying F-> (C1>FF) , and
cross section Hobby-Dyers (»>D). Particle size analysis system
not yet installed. All other data successfully acquired. Air-
craft returned to base at 1200 hours CDT. Aircraft took off for
afternoon run at 1330 hours CDT. Flew cross sections H-*D, CL+FF.
Data successfully acquired.
Sunday, 21 July 1974 - Westerly winds. MRI aircraft took
off at 0600 hours CDT. Flew cross sections H>D, CL+FF. Air-
craft returned to base 0900 hours CDT. Particle size analysis
system still not operational. All other data successfully
acquired. Particle size analysis system installed Sunday after-
noon.
Monday, 22 July 1974 - Westerly winds. MRI aircraft took
off at 0700 hours CDT. Flew cross sections H*D, CL+FF. Air-
craft returned to base at 1000 hours CDT. Particle size distri-
bution data acquired. All other data successfully acquired.
Aircraft took off at 1400 hours CDT. NO-NOX inoperative due to
blown power supply. Aircraft unsuccessfully attempted to fly
"wind drift"* pattern over the Houston Ship Channel. Increasing
southerly wind component. Several pollutant sensors inoperative
and data system inoperative. Only particle size distributions
obtained.
Tuesday, 23 July 1974 - Day spent in repair and calibration
of instruments.
Wednesday, 24 July 1974 - Westerly winds. Aircraft took
off at 0900 hours CDT. Morning spent in obtaining particle
filter samples, particle size distributions, and hydrocarbon
bag samples over Houston Ship Channel. Aircraft took off for
afternoon run at 1500 hours CDT. Flew to Galveston Island and
performed spiral over the Gulf of Mexico from 10,000' to 200'.
Then flew East to West heading north of Texas City to obtain
cross section measurements I-II. Aircraft returned to base at
1730 hours CDT. All data successfully acquired. Final meeting
of participants terminating HUPS held in evening.
A "wind drift" pattern refers to a mode of flight in which
the only component of the velocity of the aircraft in the direc-
tion of the wind is that due to the wind.
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METEOROLOGICAL DATA
All measured meteorological data for the 1974 Houston Ur-
ban Plume Study have been presented in a separate report by
Dr. Gale F. Hoffnagle (1). These data will not be reproduced
in this report. Data obtained include surface anemometer data,
pilot balloon soundings up to approximately 4000 feet altitude,
rawinsonde soundings from the National Weather Service, and
National Weather Service national weather plots.
From the conclusions of Dr. Hoffnagle's report (1), the
following are some of the important features of the meteorolog-
ical data as they apply to HUPS.
(a) The period of HUPS represents an unusual meteorologi-
cal situation. A strong and persistent high over Arkansas
prevented normal weather systems from penetrating to the
Houston area.
(b) This high allowed a mesoscale pattern of consistent
and strong westerly to southwesterly flow on each successive
morning. The mixing layer was, therefore, well ventilated.
(c) Because of opposing flow.for low-level (westerly) and
upper-level (easterly) winds, most of the mornings experienced
a very calm transition zone between 3000 and 5000 feet. Flows
in this zone were weak and variable in direction.
As will be evident in the discussion which follows, the
persistent westerly lower-level flows which existed for 19, 20,
21, 22 July were extremely fortunate and made possible day-to-
day comparisons of pollutant fluxes and separation of the urban
and industrial (Houston Ship Channel) contributions to the air
pollutant fluxes. Without this persistence, it would not have
been possible to obtain pollutant fluxes at comparable cross
sections as was done in this study.
AIRCRAFT MEASUREMENT DATA
Table A-l in Appendix A summarizes all the traverses and
spirals flown by the instrumented MRI aircraft during the 1974
Houston Urban Plume Study (HUPS). The first column in Table
A-l is the identification number (4 or 5 digits) which appears
on the computer plots for each pollutant concentration (or other
measure). The second column gives date of the run and the
third and fourth columns give the times, respectively, for
beginning and ending a particular traverse or spiral. The fifth
column identifies the beginning and ending surface points for a
traverse or, in the case of spirals, the location of the surface
point for the spiral. The sixth column gives for a particular
13
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traverse the altitude in feet of the aircraft. The locations
of all the surface points are indicated in Figure 3.
In Appendix A are assembled, according to the code in
Table A-l, computer plots of all the real time data acquired by
the instrumented MRI aircraft during HUPS. The information in
Table A-l is reproduced for each plot sequence which comprises
the data for bscat, condensation nuclei concentration, CO, 03,
NO, NOX, S02i temperature, and relative humidity.
Airborne Hydrocarbon Bag Samples
In Appendix B are found the data for ambient hydrocarbon
concentrations. Hydrocarbon samples were collected in Tedlar
bags, the usual procedure being to fill a bag during a given
traverse or spiral. Subsequently, the bag samples were analyzed
by means of a Loenco gas chromatograph.
Airborne Particulate Filter Data
Two types of particulate filter samples were collected in
the air: glass fiber filter samples for subsequent sulfate
analysis and membrane filters for subsequent microscopic exami-
nation.
The glass fiber filter samples were obtained in the usual
manner,when sampling for particulate sulfate - namely, two
filters, suitably treated to reduce their effect in oxidizing
gaseous S02/ are employed in series. The first filter is
designed to collect particulate sulfate; the second filter
similarly treated serves as a reference for the extent of con-
version of S02 to sulfate on the first filter. Unfortunately,
ambient conditions were such that in all samples, sulfate on
the first filter was found to be only 7-35% higher than the
second, backup, filter. Thus, the reliability of the data are
questionable. These data are, therefore, omitted from this
report.
Aerosol samples were collected on 0.8 ym Millipore filters
on 19, 20, 21 July 1974, using the MRI aircraft sampling
systems. The prevailing westerly winds were the same on all
the sampling days and during all sampling runs. These samples
were analyzed by optical and electron microscopy by Drs. R.
Draftz and J. Graf of I.I.T.R.I. The results of their investi-
gation are discussed in the next section and are presented in
Appendix C.
Airborne Particle Size Distribution Measurements
Particle size distributions were determined using the air-
borne particle size analysis system which consists of a Royco
optical particle counter and a TSI Aerosol Mobility Analyzer.
14
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Calibration values for converting the field readings to particle
size distributions were provided by Dr. Bruce Cantrell of the
University of Minnesota. It must be pointed out that the
measurement of the particle size distribution by this system is
not in real time; a bag is filled over some period of time,
typically of the order of a minute and the bag sample requires
of the order of two minutes to be run by the system. The mea-
surements are, therefore, averages over some unspecified volume
and are subject to inaccuracies owing to those introduced by
bag sampling and to those inherent in the system itself. The
errors introduced thereby, will generally serve to give values
for particle concentrations which are lower than the ambient
values. The data for particle size distribution are presented
in Appendix D as plots of particle volume density, dV/dlogD, in
units of ym-Vcc as a function of particle diameter in ym. The
signals from particle size analysis system were fed into the MRI
data logging system. In some cases, flags were missing so that
some measurements corresponded to samples collected at locations
not precisely known. An index at the front of Appendix D is
given for all the subsequent figures.
15
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SECTION 5
DISCUSSION
During the period of HUPS a strong and persistent high over
Arkansas allowed a mesoscale pattern of consistent and strong
westerly to southwesterly flow on each successive morning ex-
tending up to approximately 1300 meters. These persistent
lower level flows which existed for 19-22 July 1974 made possible
day-to-day comparisons of pollutant fluxes and the separation of
the urban and industrial (Houston Ship Channel) contributions to
the air pollution fluxes.
Also an important qualitative observation was derived from
the real time aircraft data. This was the occurrence above
300 meters altitude during the morning hours of closely corre-
lated layers of light scattering aerosol and ozone approximately
500 meters thick. Maximum ozone concentration in these layers
was of the order of 0.2 ppm. These layers appeared to exist on
each morning during HUPS and apparently extended over the entire
Houston area.
POLLUTANT BUDGETS FOR HOUSTON AREA
In addition to information on the evolution of the Houston
haze aerosol, the principal result of HUPS is the calculation of
pollutant budgets for the Houston area from the aircraft data.
These calculations were performed for three cross sections which
were approximately perpendicular to the lower westerly flows
during the period 19-22 July 1974. Starting from west of down-
town Houston these cross sections were as follows (please refer
to Figure 3) : (a) L->A, a plane perpendicular to the surface
extending from Sugar Land on the south to a point immediately
west of the Flying Acres Ranch on the north up to an altitude of
approximately 1200 meters. (b) H-»-D, a plane perpendicular to
the surface extending from Hobby Airport on the south to Dyers-
dale on the north up to an altitude of approximately 1200 meters.
(c) CL+FF, a plane perpendicular to the surface extending from
Clear Lake on the south up to Flying F Ranch on the north (a
distance of 47 km) up to an altitude of approximately 1200
meters. Pollutant fluxes were calculated in each of these cross
sections.
16
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These fluxes are shown in metric tons/hr-km2 in Figure 4
in a pictorial fashion. The westerly winds are indicated as
being perpendicular to the three cross sections; actually, the
winds deviated from a direction of 270°. The wind velocity
component normal to the cross sections was always employed in
the flux calculations. Pibal data for the study period are
given in Ref. (1) In Tables 1-47 of Ref. (1), the last row
entry of CONROE for Pibal launch site should read San Jacinto
Monument.
These pollutant fluxes were used to estimate pollutant
budgets for the areas between cross sections 1>A to H+D and H+D
to C1>FF. It was determined from the aircraft measurements that
the plane CIv-FF included the pollutant plumes of Houston and the
industrial area along the Houston Ship Channel. Total pollutant
transport rates for the Houston area are presented in Table 1.
Also budget values for the Houston area were calculated by sub-
tracting the background values for L+A from the CL-»-FF values.
These values for SC>2 (14 metric tons/hr) and NOX (40 metric
tons/hr) are found to compare reasonably well with the values
derived from emissions inventories of the Texas Air Control
Board for 1974 (13 and 24 metric tons/hr, respectively).
Suspended particulate matter fluxes and budgets were esti-
mated using an empirical correlation (2) between light scatter-
ing coefficient bscat and particle mass concentration:
Particulate mass concentration (yg/m3) = 38 bscat (lO"^"1) ,
It is not possible to assess the accuracy of this correlation
for the conditions of HUPS.
The flux and budget values for CO appear to be unreasonable,
Examination of the CO data for aircraft measurements in the
spiral mode indicate that the CO sensor was probably malfunc-
tioning during all the aircraft measurements; the reason for
this malfunction is unknown.
ADDITIONAL OBSERVATIONS
A number of important qualitative observations were derived
from the real time aircraft data.
One of these was the occurrence above 300 meters altitude
during the morning hours of closely correlated layers of light
scattering aerosol and ozone. These layers were approximately
500 m. thick and were found over the entire region of the HUPS
study. Maximum ozone concentration in these layers was of the
order of 0.2 ppm.
17
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ESTIMATED POLLUTANT
FLUXES
00
&
Figure 4. Fluxes of pollutants in metric tons/hr-km^ calculated from aircraft data of
July 19 and 20, 1974 during the 1974 Houston Urban Plume Study.
1 foot = 0.3048 meters.
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TABLE 1. POLLUTANT TRANSPORT THROUGH CROSS SECTIONS FOR HOUSTON
AREA CALCULATED FROM AIRCRAFT DATA, 1974 HOUSTON URBAN
PLUME STUDY, METRIC TONS/HR
Cross Section
Suspended
Particulate
Matter*
CQ SO,
O.
NO
Area:
L A
(5.5 km south of Sugar Land
to 5.5 km north of Flying
Acres Ranch X 1200 meters
altitude)
Date and Time: 7/19/74, 0927-1024
CDT
22
950
32
26
Area:
H D
(10 km south of Hobby Airport
to 10 km north of Dyersdale X
1200 meters altitude)
Date and Time: 7/20/74, 1341-1419
CDT
21
960
22
54
15
CL FF
42
1500
46
88
45
Area: (Clear Lake to Flying F Ranch
X 1200 meters altitude)
Date and Time: 7/20/74, 1025-1039
CDT
Calculated from light scattering coefficient.
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The relatively large ozone concentrations observed most
probably are the result of photochemical reactions; no primary
ozone .sources of sufficient magnitude to account for these con-
centrations are known.
The concentration ratios (NO) (03)/ (NC>2) exceed the steady
state value of 0.0209 ppm expected in the presence of only
sunlight, 03, NO, N02, and air . In fact, values of this
ratio ranged from around 0.04 ppm to 0.15 ppm in the ozone
layers. This suggests the presence of hydrocarbons and the
absence of any primary source input of NO into these layers
during the course of the reactions leading to formation of 03.
In addition, the close correlation of bscat and 03 concen-
trations indicates the existence of secondary aerosol sources in
these layers. A possible secondary aerosol source would be that
arising from the accelerated oxidation of S02 which occurs in
the presence of photochemical reactions and involves 03 and
olefinic hydrocarbons. Unfortunately the analysis of particu-
late filter samples for sulfate was not successful so that there
is no direct confirmation of this hypothesis.
Analysis of aerosol samples collected on 0.8 ym Millipore
filters by Drs. Draftz and Graf of I.I.T.R.I, showed that feld-
spars and clay minerals were the predominant types of particles
on all the samples. According to Drs. Draftz and Graf, little
or no urban (auto exhaust, combustion products) aerosol parti-
cles were found in the samples, even in the downwind samples.
Samples downwind of maximum industrial activity in the ship
channel area were believed to contain very few particles indi-
cative of primary sources of fine particles. In fact, the
mineral particle concentrations appeared slightly greater in
these samples than in those collected at the west side of
Houston.
A few samples contained several clusters of fluffy, carbo-
naceous deposits. These have not been identified but are not
believed to be oil soot, auto emissions, or from coal burning.
The extensive industrial activity in the Houston area and
the absence of significant quantities of combustion derived
particles suggests possible malfunction of the filter sampling
system on the MRI aircraft or sample loss in the process of
microscopic analysis. There is ample photographic evidence and
evidence from bscat and condensation nuclei counts from the
instruments aboard the aircraft showing substantial quantities
of fine particles associated with combustion processes. For
completeness, the report of the microscopical analyses of the
filter samples by Drs. Draftz and Graf of I.I.T.R.I, are given
in Appendix C.
20
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Particle size distributions were obtained from data
supplied by a system consisting of a TSI Model 3030 electrical
aerosol size analyzer and a Royco Optical Particle Counter.
The calibrations for converting the raw data were furnished by
Dr. B. Cantrell of the University of Minnesota. In a number of
cases it is observed that there is a substantial mismatch
between the T.S.I, analyzer and the Royco counter in the region
of particle size overlap. In addition to these occurrences,
there are also questions concerning the biasing and sample loss
attributable to the sampling procedure. Added to the suspected
difficulties cited for the filter samples, the operation of the
airborne aerosol size analysis system required filling a
plastic bag with sample which was then retained in the bag for
the 2-3 minutes required for acquisition of the data. No
satisfactory assessment can be given of the possible inaccura-
cies introduced through these deficiencies. At best the data
may be viewed as providing a qualitative measure of the
particle concentration.
Included in the particle size distribution data given in
Appendix D is an interesting set of measurements taken during
spirals over Hobby Airport. These data represent particle size
distributions from ground level to approximately 3000 m. They
correlated qualitatively with the seven-channel solar radiometer
measurements to be discussed in a separate report.
Unfortunately no filter or bag samples were obtained in
the ozone and particulate-rich layers observed in the morning
above 300 m. This is one of many instances in which immediate
access to data would have been invaluable. In the HUPS study,
the aircraft data were not available for study until six to
twelve months after the completion of HUPS.
21
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SECTION 6
SUMMARY AND CONCLUSIONS
The 1974 Houston Urban Plume Study was intended specifi-
cally to gain limited information on the spatial and temporal
distribution of air pollutants - particularly primary and
secondary sources of aerosols - in the Houston area as an aid
should a later intensive investigation of aerosol character and
transport be needed. To this extent the study was successful.
The principal results and conclusions of the study were:
(1) Pollutant budgets were established for the urban and
industrial (east of downtown Houston) areas of the Houston area.
The budget values for S02 and NOX found by aircraft measurement
(14 metric tons/hr and 40 metric tons/hr, respectively) compared
reasonably well with values derived from emissions inventories
of the Texas Air Control Board (13 and 24 metric tons/hr,
respectively).
(2) On the basis of the limited sampling period, it
appears that the industrial area (east of downtown Houston) is
the major contribution of primary air pollutants in the Houston
area (please see Table 1).
(3) During the period of the study, in the morning hours
above the mixed layer, relatively large ozone concentrations -
almost certainly of photochemical origin - were found which
were correlated closely with light scattering aerosol. This
correlation indicated the existence above the mixed layer of
strong secondary aerosol sources, possibly associated with the
oxidation of SO2-
Additional work as outlined in the recommendations of
Section 2 of this report will be needed to gain an understanding
of aerosol character and transport in the Houston area.
22
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REFERENCES
1. Hoffnagle, Gale F. Air Pollution Meteorology During the
Houston Urban Plume Study, July 1974. EPA-600/3-77-073,
U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina, 1977. 59 pp.
2. Charlson, R. J., Ahlquist, N. C., Selvidge, H., and MacCrea-
dy, P. B. "Monitoring of Atmospheric Aerosol Parameters
with the Integrating Nephelometer". Journal of the Air
Pollution Control Association 19:937-942 (1969).
23
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-78-048a
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
HOUSTON URBAN PLUME STUDY - 1974
Description and Summary of Results
5. REPORT DATE
May 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
James R. Brock
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORGANIZATION NAME AND ADDRESS
The University of Texas
Department of Chemical Engineering
Austin, Texas 78712
10. PROGRAM ELEMENT NO.
1AA008
11. CONTRACT/GRANT NO.
R800871
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTF, NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The 1974 Houston Urban Plume Study (HUPS) was undertaken as a preliminary
investigation of some of the unresolved features of Houston's air pollution problem.
HUPS was intended specifically to gain limited information on the spatial and tempo-
ral distribution of air pollutants—particularly, primary and secondary aerosols—
in the Houston area as an aid should a later intensive investigation of aerosol
character and transport be needed.
Aerial measurements were made of the principal pollutants (SO-, NO , 0_, CO,
aerosol) of the Houston area. Wind-field measurements were also made. These data
were used to estimate pollutant budgets. Values for SO- and NO (14 metric tons/hr
and 40 metric tons/hr, respectively) were reasonably comparable with values derived
from emissions inventories of the Texas Air Control Board (13 and 24 metric tons/hr,
respectively). On the basis of the limited sampling period, the industrial area
(east of downtown Houston) apparently is the major contributor of primary air
pollutants in the Houston area. In the morning hours above the mixed layer,
relatively large ozone concentrations (max. 0.2 ppm)—almost certainly of photo-
chemical—origin were found that correlated closely with light scattering aerosol,
thus indicating the existence above the mixed layer of strong secondary aerosol
sources.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Air pollution
*Aerosols
*Sulfur dioxide
*Nitrogen oxides
*0zone
Plumes
*Measurement
*Wind (meteorology)
Airplanes
*Light scattering
Houston, TX
13B
07D
07B
21B
QIC
20F
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
32
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
24
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