CAPITAL AREA COUNCIL OF
GOVERNMENTS (CAPCOG)
Airborne Air Quality Sample Collection in
Central Texas during the 2006 Ozone Season
Final Report
Prepared by
Maxwell Shauck, Grazia Zanin, Sergio Alvarez, Levi Kauffman, Timothy Compton
Baylor Institute for Air Science
Baylor University
Waco, Texas
And
Martin Buhr
Air Quality Design, Inc., Golden, Colorado
March 2007
Prepared in cooperation with Baylor Institute for Air Science, Baylor University (BIAS), the Capital Area Council of Governments, and the
Texas Commission on Environmental Quality. The contents of this publication reflect the views of BIAS, who is solely responsible for the
opinions and data it contains. The contents do not necessarily reflect the official view or policies of the Capital Area Council of Governments or
of the Texas Commission on Environmental Quality
EXECUTIVE SUMMARY
The Baylor Institute for Air Science (BIAS) conducted an Airborne Air Quality Study during a
portion of the 2006 Ozone Season for the Capital Area Council of Governments (CAPCOG).
The CAPCOG geographic region encompasses Bastrop, Blanco, Burnet, Caldwell, Fayette,
Hays, Lee, Llano, Travis and Williamson counties. The primary objective of the study was to
understand the impact of existing regional power plants, other urban areas (notably Houston and
San Antonio), and highways, on Austin’s regional air quality.
The study focused on the
following technical questions:
1. What are the qualitative and quantitative contributions of ozone, ozone precursors,
particulates, and other pollutants from this geographic area?
2. What is the vertical depth and concentration of pollutants in the atmosphere around
known emission sources under different meteorological conditions?
3. How do meteorological conditions affect the concentration, composition and transport of
pollutants at altitudes above 10 meters?
4. What is the role of regional transport of pollutants in this geographic area, with particular
focus on the impact of local power plants?
The study was conducted using a small aircraft, a Cessna 172, carrying an instrument platform
necessary for this type of investigation. The instrument platform provided a complete set of
measurements to assess ozone formation and address related issues. The study targeted: 1)
meteorological conditions that would lead to transport of pollutants from one of six power plants
in the region towards Austin proper and its surrounding counties; 2) the transport of the urban
plumes from Houston and San Antonio towards Austin, and; 3) the impact of emissions from
regional freeways on the local air quality.
The meteorological conditions during the study
allowed for five separate flights. Four of the five flights were traditional pollutant concentration
plume transect flights. Two of these demonstrated long-distance plume transport (60-95 miles),
and ozone formation directly associated with the target plumes. The fifth flight was conducted to
examine the pollutant emissions from a local section of freeway.
The airborne study conducted during 2006 indicates that the air quality in the Austin
region is directly and adversely affected by the power plants and other urban areas located within
about 95 miles of the city. It is important to note that the data used in this analysis were
collected on a limited number of days. A better understanding of the impact of the regional
power plants and other regional pollution sources on the Austin area air quality could be gained
with additional aircraft-based monitoring performed through a greater part of the ozone season.
ii
TABLE OF CONTENTS
Section
Page
EXECUTIVE SUMMARY ............................................................................................................ ii
1.
INTRODUCTION..................................................................................................................1
1.1 Program Objectives ......................................................................................................1
1.2 Program Design ............................................................................................................1
1.3 Measurement Platform and Instrumentation ................................................................3
2.
FLIGHTS PERFORMED AND SUMMARY OF OBSERVATIONS..................................4
2.1 Summary of Flights Performed ....................................................................................4
2.2 Fayette County Power Plant– September 8, 2006 ........................................................5
2.2.1 Flight Summary................................................................................................5
2.3 Fayette County / Houston Urban Plume – September 14, 2006.................................10
2.3.1 Flight Summary..............................................................................................10
2.4 Alcoa Rockdale – September 19, 2006.......................................................................15
2.4.1 Flight Summary..............................................................................................15
2.5 San Antonio Municipal Power Plant Complex / Balcones Cement / Lehigh
Cement – September 27, 2006 ...................................................................................20
2.5.1 Flight Summary..............................................................................................20
2.6 Highway 290 West Mobile Source – December 14, 2006 .........................................24
2.6.1 Flight Summary..............................................................................................24
2.6.2 Measurements of Volatile Organic Compounds (VOCs)...............................27
2.6.3 QA/QC Procedures for the CAPCOG VOC Sampling System. ....................30
3.
SUMMARY OF DATA CALIBRATIONS AND UNCERTAINTY.................................34
3.1 Trace Gas Calibrations ...............................................................................................34
3.1.1 Ozone..............................................................................................................34
3.1.2 NOy (Reactive Odd Nitrogen) ........................................................................35
3.1.3 Sulfur Dioxide (SO2) ......................................................................................36
3.1.4 CO ..................................................................................................................37
3.2 Meteorological Measurements....................................................................................37
3.3 NOy Conversion Efficiency ........................................................................................39
3.4 Pressure Corrections and Standard of Additions Calibration .....................................39
3.5 Evaluation of Data Uncertainty ..................................................................................40
4.
PROJECT SUMMARY AND CONCLUSIONS.................................................................41
4.1 Airborne Observations Summary ...............................................................................41
4.2 Overall Summary and Recommendations ..................................................................41
5.
APPENDIX ..........................................................................................................................43
5.1 Quality Assurance Project Plan (attached) .................................................................43
5.2 Supporting Documentation (attached)........................................................................43
iii
1. INTRODUCTION
1.1
PROGRAM OBJECTIVES
The primary objective of the 2006 airborne measurement study was to understand the
impact of regional power plants and other pollutant sources located in Central Texas on the
Capital Area Council of Governments (CAPCOG) region. This study provides a better
understanding of the air quality in the CAPCOG region attributable to extra-regional sources.
The technical questions addressed to achieve the program objectives included:
1.2
•
What are the qualitative and quantitative contributions of ozone, ozone precursors, and
other pollutants from this geographic area?
•
What is the vertical depth and concentration of pollutants in the atmosphere around
known emission sources under different meteorological conditions?
•
How do meteorological conditions affect the concentration, composition and transport of
pollutants at altitudes above 10 meters?
•
What is the role of regional transport of pollutants in this geographic area, with particular
focus on the impact of local power plants?
PROGRAM DESIGN
To answer the study objectives, the Baylor Institute of Air Science (BIAS) planned to fly
an instrumented Cessna 172 in the Austin region for a total of 20 hours (about 5 to 6 flights).
Measurements to be collected included continuous O3, NOy, SO2, CO; meteorological parameters
(temperature, pressure, wind speed and direction), and volatile organic compounds (VOC)
canister samples. The study period started September 1, 2006 and was scheduled to conclude on
September 31, 2006. A decision to fly an additional mission kept the study period open until
December 13, 2006. During that period BIAS evaluated atmospheric conditions on a daily basis
meeting the following criteria:
1. Forecasted atmospheric conditions conducive to ozone formation
2. Well defined wind flow (5-10 mph) towards the Austin region from the various target
sources
1
The target sources in the Austin region are shown on the map in Figure 1-1, and include
the following power plants: LCRA’s-Fayette County Power Project, LCRA’s-Sim Gideon Power
Plant, GenTex Power Corporation’s-Lost Pines One Power Park, the City of San Antonio’sMunicipal Power Plant Complex, Austin Energy’s-Decker Lake Power Plant, Alcoa’s SandowRockdale Facilities. The Balcones Cement Plant in San Marcos and the Lehigh Cement Plant in
Buda, both located southwest of Austin, were two of the non-power plant point sources included
in the study. A decrease in the likelihood of successful identification of the Houston urban
plume, due to seasonal variability, led to the re-allocation of flight time and inclusion of an
alternate mission: monitoring the Highway 290 West mobile sources.
Figure 1-1. Map of the Austin region showing the cement and power plants targeted during the CAPCOG 2006 airborne study
2
1.3
MEASUREMENT PLATFORM AND INSTRUMENTATION
8B
The BIAS measurement platform, instrument systems, and standard operating procedures
(including quality control and assurance procedures) are described in detail in the Quality
Assurance Procedures and Protocol (QAPP) document submitted to the Capital Area Council of
Governments and the Texas Commission on Environmental Quality (TCEQ). The QAPP is
included as an appendix in Section 5. A photograph of the Baylor aircraft used during the study
is shown in Figure 1-2. Table 1-1 lists the measurement systems used aboard the aircraft during
the CAPCOG 2006 study.
Figure 1-2. The BIAS Cessna-172 aircraft used as the sampling platform during the CAPCOG 2006 study.
Table 1-1. Instrumentation used aboard the Baylor C-172 aircraft during the CAPCOG study
Species/Measurement
Ozone (O3)
Analytical Technique
Dual beam UV Photometry
Detection Limit
2 ppbv
Recording
Frequency
1 Hz
Sulfur Dioxide (SO2)
Pulsed Fluorescence
0.2 ppbv
1 Hz
Total Reactive Nitrogen
Chemiluminescence
0.4 ppbv
(NOy)
Carbon Monoxide (CO)
NDIR – gas filter correlation 50 ppbv
Whole Air Samples (WAS) Gas Chromatography (GC) 10 pptv
1 Hz
1 Hz
Upon Request
Position (Lat, Lon, altitude), 2 GPS antennae, transducer, Varies with parameter 1 Hz
RH, temperature, pressure, accelerometers, Platinum
wind direction, wind speed, RTD, RH sensor
turbulence, pitch angle, roll
angle, angle of attack, side
slip
3
2. FLIGHTS PERFORMED AND SUMMARY OF OBSERVATIONS
2B
2.1
SUMMARY OF FLIGHTS PERFORMED
9B
During the study period, BIAS scientists evaluated the meteorological conditions on a
daily basis in search of the criteria outlined in Section 1.2. On five separate occasions, flights
were conducted during appropriate meteorological conditions for a total of 22.6 flight hours.
Table 2-1 lists the flights performed during this study. The data from each of these flights are
presented and discussed in Sections 2.2 through 2.5.
Table 2-1. Summary of flights performed during the 2006 study.
Flight Date
9/8/2006
9/14/2006
9/19/2006
9/27/2006
12/14/2006
Target Power Plant
Fayette County
Fayette County / Houston Urban Plume
Alcoa/Sandow
San Antonio Power Plant / Balcones / Lehigh
Highway 290 - West
Flight Duration
(hours)
3.7
4.1
4.8
6.6
3.5
The typical flight profile for this study included a vertical profile upwind of the target
source to characterize the incoming air mass, followed by constant altitude transects
perpendicular to the target plume at progressively longer distances from the source.
This
procedure allowed characterization of the emissions from the target source and, importantly, the
chemical transformation of those emissions as the plume was advected downwind.
4
2.2
FAYETTE COUNTY POWER PLANT– SEPTEMBER 8, 2006
10B
2.2.1 Flight Summary
24B
The objectives of this flight were: 1. to perform a vertical profile to characterize upwind
vertical distribution of pollutants; 2. to measure the background levels of pollutants; and 3. to
perform multiple transects of the emissions from the LCRA Fayette County power plant and the
LCRA Sim Gideon Power Plant advected into the CAPCOG region under southeast wind flow.
Ozone formation of up to 13 ppbv (average 6 ppbv) above the regional background concentration
was observed downwind of the LCRA Fayette County power plant. The flight path came close to
the TCEQ CAM Station C601 in Round Top, Texas and CAM Station C613 in Pflugerville,
Texas. A comparison of the levels of ozone measured by the aircraft and the CAM station can
be found in Figure 2-1 and a time series plot in Figure 2-3. Note, that the ozone level reported
by the CAM stations 613 and 601 are a one-hour average at near ground level, while the level
measured by the aircraft are two and five minute averages at flight altitude, respectively. During
the transit to and from the Austin area, a broad ozone plume advecting to the north side of Austin
was encountered that can be attributed to the Bryan-College Station urban area and the Gibbons
Creek power plant. Embedded within that plume was another point source plume that is directly
downwind of Sandow-Alcoa plant (see the plumes just before 1:00 PM and after 3:30 PM on the
time series shown in Figure 2-3). Figure 2-2 shows more clearly the plume from the LCRA
Fayette County power plant and the plumes from other sources on the transit flight paths (i.e.,
TNP1, Sandow-Alcoa, Bryan-College Station and Gibbons Creek).
5
Figure 2-1: Map of color-coded ozone concentrations along the aircraft flight path showing an increase of ozone downwind of
the Fayette County power plant. Two caption boxes show averaged ozone data from ground-level CAM stations and the aircraft
at flight altitude. In addition, there are areas of elevated ozone downwind of the TNP1 power plant and Bryan-College Station
on the transit leg (depart Waco), and downwind of the Alcoa-Sandow plant on the next transit leg (return to Waco). The data
points that tend toward red, downwind of the Fayette County power plant, are indicative of ozone formation from the primary
emissions of those sources. The dotted line downwind of the Fayette power plant indicates the approximate plume width and
direction.
6
Figure 2-2: Map of color-coded sulfur dioxide (SO2) concentrations along the aircraft flight track showing an increase of SO2
downwind of the Fayette County power plant. All data points greater than or equal to five parts per billion volume (ppbv) will
show as solid red on flight path. Also shown, are traces of SO2 downwind of the TNP1 and Alcoa/Sandow plants on the transit
flight paths; northeast of the Fayette power plant, and in the Waco, Texas area. The data points that tend toward red, downwind
of the Fayette County power plant are from the primary emissions of that plant. Dotted lines indicate the approximate plume
width and plume direction downwind of the Fayette, Alcoa-Sandow and TNP1 power plants. The black oval near the Fayette
power plant indicates an area of noticeable concentrations of SO2 that are downwind of the Houston urban area.
7
Figure 2-3. Time-series graph of SO2, NOy, O3, and aircraft altitude. This graph shows increases in ozone levels while
transecting the Fayette County plume (FPP). In general, the location of the power plant plume in this time series can be
identified by the sharp increase in the SO2 signal (red trace), and in the NOy signal (blue trace). Time correspondent increases in
the ozone level (green trace) are attributed to FPP. Also shown with arrows and text labels are plumes from other point sources
that the aircraft transected.
The data from this flight are presented in Table 2-2, which highlights the NOy
enhancement and the ozone production that is directly attributable to the Fayette County plume.
In this flight a NOy enhancement of 1-7 ppbv was observed over the average background
concentration, depending on the distance from the source. Ozone production attributable to the
Fayette plume was calculated to be 4-6 ppbv in the downwind transects. Average wind speed
was about 10 miles per hour.
8
Table 2-2: Ozone generated and NOy enhancement in Fayette plume, September 08, 2006
Ozone (O3)
Transects
Distance
from
Fayette ,
mi
U
1
(Upwind)
Total reactive odd nitrogen (NOy)
(NOy = NOx +HNO3+PAN…)
Avg.
ozone in
plume
(ppbv) (std
dev)
Max.
ozone
in
plume,
(ppbv)
Avg.
background
ozone, 1
(ppbv) (std
dev)
NA
NA
82(±3.1)
Average
Ozone
generated,
ppbv 2
NA
Avg. NOy
in plume
(ppbv) (std
dev)
Max.
NOy
in
plume,
(ppbv)
Avg.
background
NOy, 1 (ppbv)
(std dev)
NOy
enhancement
in plume,
ppbv 2
NA
NA
6.5(±0.5)3
NA
ne 7.3(±0.5)
ne 6
sw 6.1(±0.4)
sw 7.2
ne 80(±2)
T1
4
NA
NA
sw 84(±2)
NA
82
13.3
(±9.0)
37
6.7
ne 81(±1.9)
T2
10
NA
NA
sw 83(±2.2)
NA
82
T3
T4
T5
T6 4
19
28
40
48
86
(±3.8)
84
(±4.1)
86
(±3.7)
93
ne 82(±2.3)
ne +4
sw 81(±1.9)
sw +5
82
91
+5
ne 79(±1.6)
ne +5
sw 77(±2.3)
sw +7
78
94
+6
ne 86(±1.9)
ne 0
sw 81(±2.3)
sw +5
84
87(±2.1) 92
+5
ne: 87(±2.1)
ne 0
sw 81(±2.1)
sw +6
84
+6
10.7
(±2.8)
7.5
(±1.6)
7.9
(±0.9)
7.4
(±0.6)
8.6
(±1.7)
15.1
59
not
detectable
NA
sw 82(±2.1)
82
ne 4.6
sw 7 (±0.4)
sw 3.7
9.2
ne 0.8
sw 6.4(±0.4)
sw 1.1
ne 1.6
sw 6.3(±0.5)
sw 1.6
1.6
ne 7.1(±0.4)
ne 0.3
sw 6.2(±0.3)
sw 1.2
6.7
8.7
1.0
ne 6.3(±0.4)
6.3
8.5
4.2
ne 6.7(±0.4)
6.3
0.3
ne 7.8(±0.4)
ne 0.8
sw 6.4(±0.3)
sw 2.2
7.1
1.3
ne 6.2(±0.3)
ne 83(±2.4)
T7
ne 6.1(±0.2)
6.6
10.4
6.6
NA
not
detectable
NA
sw 6.2(±0.3)
NA
6.2
Note: 1) Average background concentrations (NOy & O3) presented in this table are the average of two values which are averages of concentrations taken on
adjacent sides of the plume on the northeast (ne) and southwest (sw) ends of transect. On transects where background concentrations were not determined, the
average was taken on the spacing segment between transects. Background is defined as the measurements taken in the area adjacent to the targeted plume for each
transect. 2) Average ozone generated and NOy enhancement columns (shaded grey) were computed by subtracting the average background values from average inplume values. 3) On the upwind transect of the Fayette power plant, the sampled air contains elevated traces of SO2 and NOy. 4) On transect 6; there was a
significant NOx enhancement when the aircraft flew over Elgin, Texas and highway 290.
9
2.3
2.3.1
FAYETTE COUNTY / HOUSTON URBAN PLUME – SEPTEMBER 14, 2006
1B
Flight Summary
25B
The objectives of this flight were: 1. to perform a vertical profile to characterize upwind
vertical distribution of pollutants; 2. to measure the background levels of pollutants, and 3. to
perform multiple transects of the emissions from the LCRA Fayette County Power Project
facility advected into the Austin region under southeast wind flow. Ozone formation up to 16
ppbv (average 8-10) above the already elevated background levels were measured downwind of
the LCRA Fayette County Power Project facility. This flight path, similar to the flight path of
the September 8th mission, again came within a close proximity to the CAM Station C601 in
Round Top, Texas and CAM Station C613 in Pflugerville, Texas. A comparison of the levels of
ozone measured by the aircraft and the CAM station can be found as captions in Figure 2-4 and
a time series plot in Figure 2-5. Note that the ozone level reported by the CAM station is a onehour average at near ground level, while the level measured by the aircraft is a thirteen minute
average at flight altitude. Additionally, the strategically long upwind leg was flown in an
attempt to identify the Houston urban plume as it was transported toward the Austin regional
area. The ozone plume observed on the upwind transect is likely attributable to the Houston
urban area. However, the wind speeds were low enough that it is not likely that this plume had
significant impact on the Austin area.
10
Figure 2-4. Map of color-coded ozone concentrations along flight track showing an increase of ozone downwind of the Fayette
County power plant. . All data points greater than or equal to five parts per billion by volume (ppbv) will show as solid red on
flight path. The data points that tend toward red, downwind of the Fayette County power plant are from the primary emissions of
that plant. Also shown is a broad area of ozone (black oval) on the upwind transect (U) that is considered to have been
transported from Houston, Texas (1437 CDT).
11
Figure 2-5. Map of color-coded sulfur dioxide (SO2) concentrations along flight track showing an increase in SO2 downwind of
the Fayette County power plant (FPP) and significant SO2 concentrations downwind of Alcoa-Sandow facility. All data points
greater than or equal to five part per billion by volume (ppbv) will show as solid red on flight path. The data points that tend
toward red, downwind of FPP are from the primary emissions of those power plants.
12
Figure 2-6.
Time-series graph of SO2, NOy, O3, and aircraft altitude. This graph shows increases in ozone levels while
transecting the Fayette County plume. In general, the location of the power plant plume in this time series can be identified by
the sharp increase in the SO2 signal (red trace), and in the NOy signal (blue trace). Time correspondent increases in the ozone
level (green trace) may be attributed to the power plant source.
The data from this flight are presented in Table 2-3, which highlights the NOy
enhancement and the ozone production that is directly attributable to the Fayette County plume.
In this flight, a NOy enhancement of 1-4 ppbv was observed over the average background
concentration, depending on the distance from the source. Ozone production attributable to the
Fayette plume was calculated to be 2-7 ppbv in the downwind transects. On transect 3 and 4, the
Houston urban plume coalesced with the Fayette plume as indicated by the increase in
background concentrations on the northeast end of two transects (T4 and T5). Average wind
speed was about 7 miles per hour.
13
Table 2-3. Aircraft ozone and NOy concentrations in Fayette County / Houston Area plume and background air on September 14, 2006
Total reactive odd nitrogen (NOy)
(NOy = NOx +HNO3+PAN…)
Ozone (O3)
Transects
Distance
from
Fayette,
mi
U
3
(Upwind)
Avg.
background
ozone,
ppbv1
dev)
Max.
ozone
in
plume,
ppbv
NA
NA
91 (±1.8)
Avg.
ozone in
plume,
ppbv (std
(std dev)
ne 91(±1.9)
T1
7
101(±2.9)
106
sw 98(±2.5)
95
ne 92(±2.0)
T2
17
100(±3.6)
111
sw 97(±2.2)
95
ne 101(±1.8)
T3
30
99 (±2.7)
105
sw 97(±2.3)
99
ne 100(±1.7)
T4
41
102(±3.3)
107
sw 93(±2.0)
97
ne 92(±2.0)
T5
57
94(±1.7)
98
sw 93(±2.0)
93
Average
Ozone
generated,
ppbv 2
Avg.
NOy in
plume,
ppbv (std
dev)
Max.
Avg.
NOy
background
in
NOy, ppbv
plume
1
(std dev)
ppbv
NA
NA
NA
ne +10
sw +3
ne 8.9(±0.3)
13.2(±3.1)
22.4
ne +8
+6
ne 7.8(±0.3)
10.4(±0.8)
12.5
ne 9.1(±0.4)
9.2(±0.5)
10.2
ne +2
8.9(±0.5)
9.9
+6
+2
8.1
NA
ne 4.3
sw 4.3
4.3
ne 2.6
sw 1.5
2.0
ne 0
sw 0.6
0.3
ne 0
sw 7.5(±0.3
sw 1.4
ne 6.8(±0.3)
7.4(±0.3)
ppbv 2
ne 9.0(±0.3)
8.3)
ne +2
sw +1
sw 8.6 (±0.4
8.9)
+2
sw +9
sw 8.9(±0.4)
8.4
ne 0
sw +2
sw 8.9(±0.4)
8.9
+7
sw +3
8.7(±0.3)
NOy
enhancement
in plume
sw 7.0(±0.3)
6.9
0.6
ne 0.6
sw 0.4
0.5
Notes: 1) ) Average background concentrations (NOy & O3) presented in this table are the average of two values which are averages of concentrations taken on adjacent
sides of the plume on the northeast (ne) and southwest(sw) ends of the transect. On transects where background concentrations were not determined the average was taken
on the spacing segment between transects. Background is defined as the measurements taken outside the targeted plume for each transect. 2) Average ozone generated
and NOy enhancement columns (shaded grey) were computed by subtracting the average background values from average in-plume values.
14
2.4
2.4.1
ALCOA ROCKDALE – SEPTEMBER 19, 2006
12B
Flight Summary
26B
The objectives of this flight were: 1. to perform a vertical profile to characterize vertical
distribution of pollutants; 2. to measure the background levels of pollutants; and 3. to perform
multiple transects of the emissions from the Alcoa - Rockdale facility into the Austin region
under east-northeast wind flow. Ozone production of up to 13 ppbv (average 1-4 ppbv) was
measured (Figure 2-7) downwind of the Alcoa - Rockdale facility, as well as long range
transport of the plume into the Austin area. Figure 2-9 is a time series plot of this flight. The
flight path came close to the TCEQ CAMS Station C614 in Dripping Springs, Texas and CAMS
Station C613 in Pflugerville, Texas. A comparison of the levels of ozone measured by the
aircraft and the CAMS station can be found in Figure 2-7.
Figure 2-7: Map of color-coded ozone concentrations along flight track showing an increase of ozone downwind of the AlcoaSandow facility and two transects downwind of Austin, Texas.
15
Figure 2-8: Map of color-coded sulfur dioxide (SO2) concentrations along flight track showing the Alcoa-Sandow facility plume
advected to the southwest over a portion of the Austin urban area. Also shown, increased SO2 concentration downwind of the
Lehigh point source and traces of SO2 on the vertical profile, north of the Alcoa-Sandow facility. SO2 concentrations greater than
or equal to 5 ppbv are shown as solid red.
16
Figure 2-9: Time-series graph of SO2, NOy, O3, and aircraft altitude. This graph shows increases in ozone levels while transecting
the Alcoa-Sandow plume. In general, the location of the power plant plume in this time series can be identified by the sharp
increase in the SO2 signal (red trace), and in the NOy signal (blue trace). Time correspondent increases in the ozone level (green
trace) may be attributed to the power plant source. Also shown, the Austin urban plume and Lehigh cement kiln plume merging
with the Alcoa-Sandow plume on transects 7 and 8, respectively.
17
Figure 2-10: Vertical profile plots. The plot on the left shows concentrations of NOy , SO2 and air temperature (x-axis). The plot
on the right shows the wind speed and direction. From approximately 800 to 3,000 ft msl, there are considerable traces of SO2.
The data from this flight are presented in Table 2-4, which highlights the NOy
enhancement and the ozone production that is directly attributable to the Alcoa - Sandow plume.
In this flight a NOy enhancement of 1-27 ppbv was observed over the average background
concentration, depending on the distance from the source. Ozone production attributable to the
Alcoa-Sandow plume was calculated to be 2-4 ppbv in the downwind transects. Average winds
for this flight were about 8 miles per hour. The vertical profile presented in Figure 2-10 shows
evidence that the aloft layers were influenced by other, upwind, sources. In particular the SO2
signature suggests that other power plants, possibly TNP1, impacted the observed air
composition.
18
Table 2-4. Ozone generated and NOy enhancement in Alcoa –Sandow plume, September 19, 2006
Transects
U3
(Upwind)
Distance
from
Alcoa /
Rockdale ,
mi
2
Ozone (O3)
Total reactive odd nitrogen (NOy)
+HNO3+PAN…)
Avg. ozone in
plume (ppbv)
(std dev)
Max.
ozone
in
plume,
(ppbv)
Avg.
background
ozone, (ppbv)
(std dev) 1
NA
NA
71 (±1.8)
Average
Ozone
generated,
ppbv 2
NA
Avg. NOy in
plume (ppbv)
(std dev)
NA
Max.
NOy in
plume,
(ppbv)
NA
nw 72(±2.2)
T1
2
62(±11.4) 72
se 71(±2.8)
NA
72
T2
8
71 (±2.2)
78
nw 70(±1.8)
nw +1
se 70(±1.8)
se +1
70
T3
15
72 (±2.5)
72
T43
23
74 (±3.6)
82
nw +2
se 71(±2.3)
se +1
nw +2
se 71(±1.8)
se +3
T5
31
75 (±3.2)
82
nw +4
se 71(±2.5)
se +4
71
T64
38
75 (±3.4)
84
52
77 (±3.1)
83
62
82 (±2.9)
89
nw 6.1(±0.3)
nw 26.1
se 5.3(±0.4)
se 26.9
nw 3.5
se 5.1(±0.3)
se 3.9
nw 3.7
se 5.0(±0.4)
se 3.3
3.5
nw 5.1(±0.4)
nw 3.3
se 4.6(±0.4)
se 3.8
4.9
6.0 (±0.7) 7.5
3.7
nw 4.6(±0.3)
4.8
8.4 (±1.7) 10.8
26.5
nw 5.5(±0.4)
5.3
8.3(±.2.5) 12.1
NA
3.6
nw 4.3(±0.4)
nw 1.7
se 4.8(±0.4)
se 1.2
4.6
1.5
nw 71(±1.7)
nw +4
nw 5.0(±0.4)
nw 1.9
se 71(±2.5)
se +4
se 4.4(±0.3)
se 2.5
+4
nw 80(±1.7)
nw +5
se 72(±1.6)
se +3
76
T86
5.9 (±0.4)
NOy
enhancement in
plume, ppbv 2
+4
71
T75
11.7
+3
nw 71(±2.0)
Avg.
background
NOy, (ppbv)
(std dev) 1
5.7
+2
nw 72(±1.8)
72
9.0(±1.8)
161.9
+1
nw 70(±1.5)
71
32.2
(±45.4)
(NOy = NOx
15.4&
7.8
8.8 (±1.0) 11.8
nw +9
se 73(±1.7)
se +2
+6
4.7
9.2 (±2.5) 17.9
2.2
nw 7.6(±0.5)
nw 4.0
se 4.8(±0.3)
se 1.2
4.7
+4
nw 80(±2.2)
77
6.9 (±1.4)
2.6
nw 6.8(±0.7)
nw 5.2
se 4.8(±0.3)
se 2.4
5.8
3.8
Note: 1) Average background concentrations (NOy & O3) presented in this table are the average of two values which are averages of concentrations taken on
adjacent sides of the plume for each transect. On transects where background concentrations were not determined the average was taken on the spacing segment
between transects. Background is defined as the measurements taken outside the targeted plume for each transect. 2) Average ozone generated and NOy
enhancement columns (shaded grey) were computed by subtracting the average background values from average in-plume values. 3) Plume advected over Elgin,
Texas (approx. 23 mi from Alcoa-Sandow) 4) Downwind of power plant near Walter Elay Lake. 5) Downwind of Austin. 6) Downwind of Austin and Lehigh
cement kiln.
19
2.5
SAN ANTONIO MUNICIPAL POWER PLANT COMPLEX / BALCONES
CEMENT / LEHIGH CEMENT – SEPTEMBER 27, 2006
13B
2.5.1 Flight Summary
27B
The objectives of this flight were: 1. to perform a vertical profile to characterize vertical
distribution of pollutants; 2. to measure the background levels of pollutants; and 3. to perform
multiple transects of the emissions from the San Antonio Municipal Power Plant Complex
through the San Antonio urban area into the Austin region under south-west wind flow. Ozone
production of up to 23 ppbv (average 4-19 ppbv) were measured (Figure 2-11) downwind of the
San Antonio urban area. Figure 2-13 is a time series plot of this flight. The flight path came
close to the TCEQ CAMS Station C614 in Dripping Springs, CAMS Station C613 in
Pflugerville, and CAMS Stations C58 and C59 near the San Antonio metro area. A comparison
of the levels of ozone measured by the aircraft and the CAMS station can be found in Figure 211 and a time series plot in Figure 2-13. In general, the observed aloft ozone concentrations
were higher than those observed at the surface.
The gradient towards lower surface
concentrations may be explained by both a transport layer aloft from the surface and deposition
at the surface.
Figure 2-11. Map of color-coded ozone concentrations along flight track showing a significant increase of ozone concentration
downwind of San Antonio and Austin urban areas. The dotted lines are to show the approximate width and transport direction of
the plumes from San Antonio and the power plants located southeast of San Antonio (San Antonio Municipal Complex).
20
Figure 2-12: Map of color-coded sulfur dioxide (SO2) concentrations along flight track showing sources of SO2 emissions and
the increase of sulfur dioxide downwind of San Antonio and the San Antonio Municipal Power Plant Complex.
Figure 2-12 shows the spatial plot for the measured SO2 concentrations during this flight.
It is interesting that the plume from the San Antonio municipal power plant was transported
along the edge of the San Antonio urban plume to and past the Austin urban area. This can be
observed in the time series plot (Figure 2-13) as well, evidenced as the sharp SO2 spike on the
edge of the broader SO2 plume on each traverse.
21
Figure 2-12. Time-series graph of SO2, NOy, O3, and aircraft altitude. This graph shows a decrease in ozone due to the reaction
of NO and ozone in close proximity to the plant. However, as the plume is transported, ozone is gradually generated as shown in
the 4th and 5th transects. In general, the location of the combined urban and power plant plumes in this time series can be
identified by the sharp increase in the SO2 signal (red trace), and in the NOy signal (blue trace). Time correspondent increases in
the ozone level (green trace) may be attributed to the power plant source.
The data from this flight are presented in Table 2-5, which highlights the NOy
enhancement and the ozone production that is directly attributable to a combination of urban
areas and point sources. In this flight, a NOy enhancement of 2-6 ppbv was observed over the
average background concentration, depending on the distance. Ozone production was calculated
to be 4-19 ppbv in the downwind transects.
22
Table 2-5. Aircraft ozone and NOy concentrations of the San Antonio and Austin urban plumes merged together and background air on September 27, 2006
Total reactive odd nitrogen (NOy)
(NOy = NOx +HNO3+PAN…)
Ozone (O3)
Transects
U (Upwind)3
T1
Distance
from JK
Spruce
plant, mi
6
4
(downwind of
San Antonio
and JK Spruce
power plants)
Avg.
ozone in
plume,
ppbv
(std dev)
Max.
ozone in
plume,
ppbv
Avg.
background
ozone, ppbv1
(std dev)
Average
Ozone
generated,
ppbv 2
Avg.
NOy in
plume,
ppbv (std
dev)
Max.
NOy in
plume
ppbv
Avg.
background
NOy, ppbv
(std dev)1
NA
NA
69 (±1.5)
NA
NA
NA
5.3 (±1.5)
nw (ss1) 70(±2.1)
urban nw+4/ se
+3
urban
(±3.3)
74
21
jk spruce
73 (±2.5)
urban 80
jk spruce
78
T2 (downwind
of San Antonio
and upwind of
Austin)
36
76 (±4.4)
87
59
77 (±6.5)
88
79 (±6.2)
91
T6 (partial)
71
nw (ss2)
se (ss3)
(±2.1)
60
se (ss3)
+16
89
81 (±8)
93
7.4 (±1.7)
se (ss4)
(±3.0)
69
se (ss4)
+08
6.6 (±1.7)
17.2
5.5
se (not s4)
+10
4.6 (±0.3)
14.2
5.5
se (ss3)
(±0.3)
3.9
nw (ss5) +21
se (not ss)5 71
(±1.7)
se (not ss) +10
66
3.9
se (ss4)
(±0.3)
2.0
nw (ss2)
1.9
se (ss3)
3.5
nw (ss5)
2.7
se (ss4)
4.6
3.7
3.7
2.0
nw (ss5)
0.9
se (ss4)
2.6
1.8
2.9
nw (ss5)
(±0.3)
jk spruce nw
2.9/ se 2.6
2.7
nw (ss3)
(±0.3)
se (ss4)
(±0.3)
urban nw 4.2/
se 3.9
3.4
nw (ss2)
(±0.3)
nw (ss5)
(±0.3)
+15
60
se (ss2)
(±0.5)
3.0
nw (ss5) +19
60
nw (ss5)
(±2.3)
14.6
+13
69
5.2
4.7
nw (ss3) +17
nw (ss5)
(±2.3)
jk spruce
14.6
+05
60
60
nw (ss1)
(±0.4)
5.4
nw (ss3)
(±2.1)
se (ss4)
(±3.0)
jk spruce 8.1
(±2.9)
ppbv 2
NA
urban
35.7
+11
65
T5
(downwind of
San Antonio
and Austin)
nw (ss2)
(±2.2)
nw (ss5)
(±2.3)
67
jk spruce
nw+3/ se +7
9.4
+4
65
T4 (downwind
of San Antonio
and upwind of
Austin)
71
66
T3 (downwind
of San Antonio
and upwind of
Austin)
se (ss2) 71(±2.2)
urban
(±3.4)
NOy
enhanceme
nt in plume
3.7
nw (ss5)
3.8
se (not ss)5 6.1
(±0.3)
se5
3.0
+16
4.9
3.4
nw (ss5) +24
nw (ss5)
(±0.3)
9.1 (±3.2)
23.6
3.7
nw (ss5)
7.2
se (not ss) +13
se5
4.8
se (not ss)5 6.1
se (not ss)5 71
10.9(±2.9)
17.3
95
84 (±7.3)
96
(downwind of
(±1.7)
(±0.3)
San Antonio
+19
6.0
and Austin)
66
4.9
Note: 1) “Average background” columns (NOy & O3) presented in this table contains values that are averages of an interval on spacing segments (ss1 – ss5) between transects.
Spacing segments were also categorized and labeled as northwest (nw) or southeast (nw) sides. Background is defined as measurements taken outside the targeted plume(s) for
each transect. 2) Average ozone generated and NOy enhancement columns (shaded grey) were computed by subtracting the average background values from average in-plume
values. 3) Upwind transect has NOy enhancements from urban emission sources (i.e. mobile and airport) 4) The San Antonio urban plume and JK power plant plumes were not
merged in this transect therefore data is presented for both sources. Two values for ozone generated and NOy enhancement are presented using spacing segment background
concentrations averaged from northwest side and southeast side for comparison. 5) Average background concentration value (O3 and NOy) is from an average of data points on
the southeast side of transect five and six.
23
2.6
2.6.1
HIGHWAY 290 WEST MOBILE SOURCE – DECEMBER 14, 2006
14B
Flight Summary
28B
The objective of this flight was to estimate amount of emissions due directly to an Austin
regional highway segment by measurement of the background and downwind levels of pollutants
parallel to Highway 290 West. A counter-clockwise, 10 mile circuit, centered near the Highway
290W traffic counter (4.2 miles West of FM 1826), served as the study’s flight path. This
highway segment was selected because the Texas Department of Transportation was operating
traffic counters on the study day. The goal was to relate the pollutant concentrations observed to
the number of cars operating on the highway during the measurement period. A map of the
highway segment and the planned flight track is shown in Figure 2-14.
Figure 2-13: Geographical representation of the Highway 290 West flight path. Flight track was flown counterclockwise with
an up-wind lateral separation averaging 0.5 miles and a lateral separation averaging 1.0 mile on the downwind flight tracks.
Actual downwind flight track lateral separations varied slightly to account for changing meteorological conditions during the
flight. Aircraft altitude varied from 300 feet AGL to 800 feet AGL to optimize sampling opportunities.
24
Figure 2-14. Map of color-coded NOy concentrations along the Highway 290 West flight track.
The NOy spatial plot for the flight is shown in Figure 2-15. The time series plot is shown
in Figure 2-16. It is evident from the time series plot that there were no significant differences
between the upwind and downwind traverses. This may be due in part to sources of pollution
upwind of the highway segment.
25
Figure 2-15. Time series plot of NOy and ozone concentrations with indications where the hydrocarbon samples were taken.
26
2.6.2
Measurements of Volatile Organic Compounds (VOCs)
29B
During the Highway 290 flight, hydrocarbon canisters samples were taken on both the
upwind and downwind transects. A summary of the canisters collected is shown in Table 2-6.
A summary of the methods used and results collected is presented in the following sections. The
University of Houston Lab analyzed the hydrocarbon data and, with the continuous gas
measurements obtained, sought a possible link between emission information and flight data.
Table 2-6. Summary of Hydrocarbon canisters collected during the highway emissions flight
Hydrocarbon
Upwind/Downwind
Time
Altitude
(pm)
(ft.)
Can #
UH Can ID
1
047
Upwind
5:08
600
2
026
Upwind
5:23
600
3
019
Downwind
5:28
500
4
006
Downwind
5:41
400
5
015
Downwind
5:59
300
6
027
Downwind
6:05
800
27
Ambient Air Measurements
35B
In this study electro-polished stainless steel canisters (Fäth, Eschau-Hobbach, Germany)
were used to sample ambient air during the flight. These 1L volume canisters are equipped with
two valves. During the mobile source emission objective, on December 14, 2006 between 5 – 6
pm CST, altogether 6 canisters were sampled in the vicinity of Highway 290 W. After
completing airborne sampling, canisters were returned to the UH laboratory and analyzed for C2C9 VOCs using GC-FID (Perkin Elmer Clarus 500 & Turbo Matrix 650 ATD).
Results of the VOC measurements are listed in Table 2-7. All samples were taken at about 2,000
ft A.G.L. (Above Ground Level) under elevated NOy regimes. During the same flight section O3
levels were relatively low. Both observations indicate the impact of mobile sources. The VOC
results show relatively modest variations. Total VOC usually range between 34.0 and 39.7 ppbC;
only two samples indicate higher values around 60 ppbC. Acetylene, a typical indicator of traffic
exhaust, varies between 387 and 528 pptv with maximum values coinciding with higher NOy
values. The toluene/benzene ratio usually varies between 3.3 and 3.5, a ratio which is also typical
for traffic-related sources in the US. As can be expected, isoprene mixing ratios are almost
negligible during this time of year and are mostly below the detection limit of 10 pptv.
As mentioned earlier, two canister samples (ID047 and ID026) showed total VOC values around
60 ppbC. Also, these two samples exhibited unusually high toluene/benzene ratios between 8.9
and 14.4. While benzene did not vary much among the samples, the high toluene/benzene ratio is
basically due to high toluene levels around 1.4 -1.7 ppbv, which is about a factor of 3 higher than
in the other samples. Also, a few other selected compounds are found at higher levels. In
particular this is true for 2,2,4-trimethylpentane (i-octane) which is also about a factor of 3
higher than in the other samples. Both compounds significantly contribute to the overall higher
total VOC levels. In ID047 and ID026 also ethylene is enhanced (by a factor of 2), whereas ipentane and n-pentane are only found in higher amounts in ID026 (factor of 2).
28
Table 2-7. Ambient air canister samples taken December 14, 2006
29
2.6.3
QA/QC Procedures for the CAPCOG VOC Sampling System
30B
The GC-system has been previously calibrated with two certified VOC calibration
gases, one calibration gas cylinder provided by the National Physical Laboratory [NPL],
Teddington/UK (30 component EU Directive ozone precursor mixture at about 4 ppbv for each
VOC) and calibrations standard provided by the National Center for Atmospheric Research
[NCAR], Boulder/CO (70 VOCs in the pptv-ppbv range).
Within the CAPCOG project the CAPCOG VOC sampling system used aboard the C-172
was subject to QA/QC procedures. These procedures included the following tests:
36B
Zero test:
Samples for the zero test were generated using a “Dry Air” gas cylinder provided by
Matheson-Trigas equipped with a Supelco Supelcarb HC Hydrocarbon Trap (volume 120 cc).
The C-172 hydrocarbon sampling system was operated in the same manner as with ambient
sampling (including system flush and fill sequences) while the inlet was attached to the zero air
source. The zero air was presented to the sampling inlet at atmospheric pressure with an
overflow tee. Five canisters were used for this test to check consistency among different
canisters. In addition to this, canister #5 was analyzed twice in order to check for consistency for
one canister. The results for the zero tests are shown in Table 2-8. For a large majority of
VOCs no memory effects are observed. For a few species, however, some consistent memory
effects are visible. These compounds include propylene, i-butane, t-2-butene, 1-butene, i-butene,
c-2-butene, 1,3-butadiene, t-2-pentene, c-2-hexene, 2,4-dimethylpentane, benzene, and 2,2,4trimethylpentane. The same memory effects also occur if zero air tests are applied directly to the
GC-system, i.e,. these memory effects are GC specific. These blank values were subtracted from
the findings in ambient air samples.
30
Table 2-8. Results from blank canisters
31
Table 2-9. Results for the standard recovery test
32
Standard recovery test:
37B
Samples for the standard recovery test were generated using a humidified NPL standard.
The C-172 hydrocarbon sampling system was operated in the same manner as with ambient
sampling (including system flush and fill sequences) while the inlet was attached to the NPL gas
cylinder. The standard hydrocarbon mixture was presented to the sampling inlet at atmospheric
pressure with an overflow tee. Three canisters were sampled and analyzed. The results are shown
in Table 2-9 and include average values, standard deviation, and coefficient of variation for the
carbon responses. The results among the canisters are consistent (coefficient of variation of less
than 8% for all compounds). In addition to the canister checks, the NPL standard gas cylinder
was also attached directly to the sample inlet of the online GC system in order to assess any
possible VOC sample losses for the canister sampling procedure. As shown in Table 2-9 in most
cases the carbon responses of the offline method and their deviations are within 10% of the C
responses of the online method. In rare cases (ethylene, acetylene, 1-pentene, 2-me-pentane) they
are between 15-20%. As demonstrated in Table 2-9 the offline system is capable of recovering
quantitatively VOCs up to C9.
33
3.
3.1
3.1.1
SUMMARY OF DATA CALIBRATIONS AND UNCERTAINTY
3B
TRACE GAS CALIBRATIONS
15B
Ozone
31B
The result of the quality control procedures of the ozone measurement during the study
demonstrate that the instrument was operating consistent with the requirements of the QAPP.
Figure 3-1 illustrates instrument stability as a result of the preflight operational checks and
Figure 3-2 shows the linearity of the instrument with an r2 of .99996. The ozone data was
applied a response factor of 243.6 and an offset. The offset value is an average of an interval of
data points during the zero air level off the preflight calibration sequence.
Figure 3-1. Graph of ozone instrument showing stability of instrument response during project period.
Figure 3-2. Graph of a multipoint calibration of the ozone instrument used on the C172 with a NIST traceable and EPA certified
instrument (y-axis). The r2 of .99996 from the linear regression fit shows the linearity of the instrument response.
34
3.1.2
NOy (Reactive odd nitrogen)
32B
The result of the quality control procedures of the ozone measurement during the study
demonstrates that the instrument was operating consistent with the requirements of the QAPP.
Figure 3-3 demonstrates instrument stability after September 14, 2006. There is a definite step
change in the instrument response. This change is attributed to equilibration of the calibration
system. The response factor applied was 1.08, the average of the calibrations. The baseline
corrections are applied automatically in the processing using data from the periodic in-flight
zeroing of the instrument.
Figure 3-3. NOy instrument slope (y-axis) versus Calibration date (x-axis) .
35
3.1.3
Sulfur dioxide (SO2)
3B
The result of the quality control procedures of the ozone measurement during the study
demonstrates that the instrument was operating consistent with the requirements of the QAPP.
Figure 3-4 shows instrument stability. The response factor applied was 1.93, an average of all
the calibrations. The automatic zeroing of this instrument occurred every twenty minutes due to
the slower response relative to the other instrumentation. The data from the automatic zeros
were used to correct for baseline drift during the flight.
Figure 3-4. SO2 instrument slope (y-axis) versus calibration date (x-axis)
36
3.1.4
CO
34B
The response factor for the CO instrument is shown in Figure 3-5. The step function
from about 5000 to about 4000 near the beginning of the study resulted from an adjustment made
to the sensitivity of the instrument to keep the signals on-scale during normal measurements.
The data collected up to that time were calculated using the higher response factor, whereas the
data after the adjustment were calculated using the average of all ensuing calibrations.
Figure 3-5. Response factor for the CO instrument over the course of the study.
3.2
METEOROLOGICAL MEASUREMENTS
16B
The data shown in Figure 3-6 show a comparison between the aircraft-based and surfacebased meteorological observations collected during take-off from several of the airports visited.
In general the temperature, dew point, and pressure measurements show good agreement. There
are substantial differences in wind speed and direction. These differences may be attributed in
part to the fact that aircraft attitude is pitched higher than usual during take-off and that typically
the AIMMS instrument was just turned on prior to take-off and may have still been locating
satellites during takeoff. This process is almost complete within a minute after the AIMMS is
powered up.
37
2006 CAPCOG Ozone Season
Platform: C-172
Data from AWOS/ATIS preflight and postflight ground checks
##########
NA is used when data is not available.
Note: Aircraft data comes from the AIMMS-20 unit and is intended to measure correctly in flight, not during ground operations.
Surface-based data points are hourly averages taken from ATIS/AWOS stations. Aircraft wind data presented in table are an average value of 50 seconds interval. Temperature, dewpoint and pressure are an average value of a 25 second interval.
QAPP accuracy requirements
Dew Point
±1°C
Temperature
±1°C
Pressure
±2 mb
steady before t/off
Date
Surface Observation Location
9/8/2006
9/8/2006
9/14/2006
9/14/2006
9/19/2006
9/19/2006
9/27/2006
9/27/2006
12/14/2006
12/14/2006
Waco, TX
Waco, TX
Waco, TX
Waco, TX
Waco, TX
San Marcos, TX
Stinson, TX
Georgetown, TX
Waco, TX
Waco, TX (data not available)
Notes
Aircraft raw data
information corresponds
to time in ASOS/AWOS
broadcast, or shortly
before take-off when
using ATIS recording.
KACT ATIS
KACT ATIS
KACT ATIS
KACT ATIS
KACT ATIS
KHYI AWOS
KSSF ATIS
KGTU AWOS
KACT ATIS
KACT ATIS
Time (Local)
Temperature (Deg C)
Pressure (mb)
Wind Direction (°)
Wind Speed (mph)
Data points not available
for comparison.
zulu
16:51
20:51
18:51
21:51
18:51
22:23
18:53
22:35
21:51
Aircraft
29.23
30.2
32.44
30.72
30.32
29.55
32.51
31.57
24.47
Surface
Difference
29
0.23
32
1.8
33
0.56
34
3.28
30
0.32
30
0.45
31
1.51
33
1.43
23
1.47
Max
Min
Avg
Std Dev
NA
Dew Point (Deg C)
3.28
0.23
1.2278
0.9740
Aircraft
17.3
15.12
10.99
9.65
6.87
8.54
17.34
15.14
9.7
Surface
Difference
Aircraft
17
0.3
995.32
13
2.12
995.23
8
2.99
994.26
8
1.65 refer to note
5
1.87
998.77
7
1.54
994.81
17
0.34
993.43
13
2.14
974.39
8
1.7
996.22
Max
Min
Avg
Std Dev
2.99
0.3
1.6278
0.8554
Surface
Difference
1001.01
5.69
997.96
2.73
997.63
3.37
995.59
na
1003.72
4.95
999.32
4.51
996.03
2.6
984.76
10.37
998.30
2.08
Max
Min
Avg
Std Dev
10.37
2.08
4.5375
2.6710
Aircraft
148.07
190.34
186.79
144.36
49.7
32.04
189.21
220.3
196.74
Surface Difference
120
28.07
140
50.34
200
13.21
0
na
0
na
80
47.96
190
0.79
210
10.3
170
26.74
Max
Min
Avg
Std Dev
Aircraft
13.55
7.2
6.97
7.59
6.78
8.92
7.21
19.14
11.07
50.34
0.79
25.3443
18.8066
Surface
6
5.75
9.2
0
5.75
5.75
11.5
13.8
6
Difference
7.55
1.45
2.23
7.59
1.03
3.17
4.29
5.34
5.07
Max
Min
Avg
Std Dev
7.59
1.03
4.1911
2.4324
Data points Not Available
wind Direction - Variable
Wind Direction - Variable
Large ∆ Pressure is due to aircraft pressure data at field elevation non existent. Data used came from altitude 700AGL.
Figure 3-6. Comparison of aircraft and surface meteorological observations collected during take-off from various airports.
38
3.3
NOY CONVERSION EFFICIENCY
17B
Nitric acid (HNO3) calibrations were performed as part of the pre-flight calibration and
off-day calibration sequences. During the pre-flight calibrations, a single dilution was run;
during the off-day calibrations, five different dilutions were run.
These calibrations were designed to gauge the conversion efficiency of nitric acid by the
molybdenum NOy converter. The NOy converter was maintained at 320°C while in use. The
converter is designed to reduce the NOy components to NO, which is detected by a TEI NO
instrument downstream of the converter. A certified Kintek® nitric acid permeation tube was
used to generate the nitric acid. Using the documented permeation rate of the calibrated tube, the
concentration of nitric acid was calculated with approximately 10 liters per minute of zero air.
While the conversion efficiency measured during the single-point daily calibration tests indicated
relatively low conversion efficiency (average value was 40%), the multi-point off-day calibration
indicated a conversion efficiency that was about 85%. The explanation for this disparity is that a
greater amount of time was allowed for equilibration of the HNO3 standard delivery system
during the off-day calibration. We expect that the airborne measurements were more reflective
of the higher conversion efficiency.
3.4
PRESSURE CORRECTIONS AND STANDARD OF ADDITIONS
CALIBRATION
18B
The NOy and SO2 instruments exhibit a dependence on pressure that is accounted for
through the use of the in-flight calibrations.
The data reported here were corrected using
equations determined from previous years calibrations since we experienced operational
difficulties with our in-flight calibration system this year and were not able to collect an adequate
amount of data to develop current correction curves. That said, the previous years correction
curves are adequate to provide the necessary correction since the pressure dependencies are a
function of the measurement method and should not vary with time. The correction equations
are listed below.
SO2 correction:
so2_cal_zcor=so2_calibrated*((prs_mb_int*-0.013751)+14.93)
NOy correction:
noy_cal_zcor=noy_calibrated*((prs_mb_int*-0.0076954)+8.7958)
39
3.5
EVALUATION OF DATA UNCERTAINTY
19B
The guidelines used for determining the uncertainty of the measurements for this airborne
sampling program were based on the evaluation described in NIST Technical Note 1297. Type A
(A) uncertainty components are those which are evaluated by statistical methods. Type B (B)
components are those which are evaluated by other means. Table 3-1 contains the standard
uncertainties that were used to determine the combined standard uncertainty of each
measurement.
The uncertainties reported serve two purposes. First, they provide an assessment of
whether a given measurement has achieved the accuracy objectives and specifications. Also, and
more importantly, the uncertainty estimates can be used to quantitatively bound the certainty of
any analysis made using the data. It is incumbent on the analyst to evaluate conclusions using
the data collected from the perspective of the uncertainty estimates provided.
Table 3-1. Uncertainty budget for trace gas measurements on the C172.
Sources of uncertainty (standard uncertainty)
Parameter
Baseline4
Combined
standard
uncertainty5
Calibration
standard1
Conversion
efficiency2
Repeatability3
O3
1 % (B)
n/a
1.9% (A)
1 ppbv
±2% +1 ppbv
NOy
5.1 % (B)
85%
10.6% (A)
0.2 ppbv
±12% +0.2 ppbv
SO2
5.1 % (B)
n/a
4.8% (A)
0.1 ppbv
±7% +0.1 ppbv
2 % (B)
n/a
6.5% (A)
20 ppbv
±7% +20 ppbv
CO
1.
2.
3.
4.
5.
Calibration standard. The calibration uncertainty includes the uncertainty on the NIST traceable calibration gas mixture (± 1%) and
the uncertainty of the mass flow controllers (i.e., +/- 5%) used for dilution. For O3, the uncertainty was estimated from an off-day
calibration using a TEI 49C PS photometer that was calibrated to the EPA Reference Photometer (SRP #5) at Region 6. The SRP #5 is
classified as a NIST Standard Reference Material (SRM) which NIST manufactured and certified.
Conversion efficiency. This source of uncertainty applies only to NOy. The NOy Molybdenum converter ce (conversion efficiency)
for NO2 was greater than 95% for all calibrations. (refer to supporting documentation) and 85% for HNO3
Repeatability. This source of uncertainty was estimated from the standard deviation of the slopes from pre flight calibrations for
NOy, O3, SO2 and CO conducted during the study.
Baseline. The baseline for O3, CO, NOy, and SO2 was estimated from the standard deviation of the zero level determinations
(synthetic air) conducted during the study. Although the measurements were corrected from the zero level, this number reflects the
expected variability of that level during ambient measurements.
Combined standard uncertainty. The combined uncertainty was estimated through propagation of the above uncertainties as ((d1)2
+ (d2)2 +(dn)2)1/2. dn is defined as any “component” of the uncertainties (e.g., calibration standard).
40
4. PROJECT SUMMARY AND CONCLUSIONS
4B
4.1
AIRBORNE OBSERVATIONS SUMMARY
20B
During the 2006 study, considering the late start of the monitoring program, the
atmospheric conditions allowed for four flights that followed a target plume toward the
Austin region with one additional flight focusing on mobile source transmissions. A
summary of the 2006 observations include:
• Plumes from the Fayette, Alcoa, and San Antonio urban area and power plants
were tracked into the Austin region.
• Ozone formation of 5-19 ppb above the regional background was observed in
the various plumes.
• Results for examination of emissions from a local highway segment have been
collected and were found to be inconclusive due to the unexpected strength of
upwind sources. In addition the higher than expected wind speeds observed on the
sampling day impacted the aircraft ability to directly sample the highway segment
emissions.
In all cases, the power plant and urban plumes exhibited expected activities in that
the concentrations of the primary pollutants (SO and NO ) was highest near the source
2
y
and the concentration of the secondary pollutant (ozone) was highest downwind of the
source power plant. In regard to tropospheric ozone chemistry, it is important to note that
the influence of these power plant plumes observed was greatest in the range 20-95 miles
downwind. Under atmospheric conditions more conducive to ozone formation than
observed during this limited study period, up to 30 ppb ozone enhancement has been
observed by Baylor aircraft in power plant plumes.
41
4.2
OVERALL SUMMARY AND RECOMMENDATIONS
21B
The 2006 airborne study results show that the air quality in the Austin region is directly
and adversely affected by the power plants and urban sources located within about 95 miles of
the city. It is important to note that the data used in this analysis were collected on a limited
number of days. A greater understanding of the impact of the regional power plants and other
regional pollution sources on air quality associated with the regions defined by CAPCOG could
be achieved with additional aircraft-based monitoring to be performed during the entire duration
of the high ozone season.
42
5. APPENDIX
5B
QUALITY ASSURANCE PROJECT PLAN (ATTACHED)
5.1
5.2
2B
SUPPORTING DOCUMENTATION (ATTACHED)
23B
43