TO: Texas Air Research Center
FROM: David Allen (PI; allen@che.utexas.edu), Elena McDonaldBuller (co-PI; ecmb@mail.utexas.edu), and Gary McGaughey
University of Texas at Austin, Center for Energy and
Environmental Resources, Austin, Texas 78758
SUBJECT: Annual Progress Report
PROJECT NUMBER: 413UTA0148A
PROJECT TITLE: Emissions inventory evaluations using DISCOVERAQ aircraft data
PROJECT PERIOD: September 2013 – July 15, 2015
DATE: September 15, 2014
Project Description
The first and second Texas Air Quality Studies documented significant reductions in
ambient concentrations of ozone precursors in the Houston-Galveston-Brazoria (HGB)
region; however, the studies also revealed significant uncertainties in emission
estimates, especially those associated with industrial sources in the Houston Ship
Channel (HSC). This project will use data collected during September 2013 as part of
the DISCOVER-AQ (Deriving Information on Surface Conditions from Column and
Vertically Resolved Observations Relevant to Air Quality) field campaign to characterize
the magnitude and variability in emissions of volatile organic compounds (VOCs), highly
reactive volatile organic compounds (HRVOCs), oxides of nitrogen (NOx), and other key
pollutants in the HSC. One of the primary instrument clusters deployed during
DISCOVER-AQ was onboard a NASA P-3 aircraft; measurements included
meteorological variables (e.g., temperature, humidity, winds), multiple hydrocarbon
species, most reactive nitrogen species, and relatively stable chemical species such as
CO2. P-3 flights were conducted on nine days during September 2013 where each flight
day included late morning, early afternoon, and later afternoon traverses within the HSC
region following a well-defined flight track. Each flight track typically included aircraft
spirals north and south of the HSC in addition to a low altitude, east-west transect of the
HSC. These flights generated a rich dataset to be used for evaluating emission
inventories.
Objectives
The project consists of three major tasks:
(1) For P-3 flight periods, characterize mixing heights, vertical profiles of wind speed
and wind direction within aircraft spirals, and concentrations of key pollutants
within aircraft spirals as well as upwind and downwind of the HSC;
(2) Obtain and analyze photochemical modeling developed specifically for the
DISCOVER-AQ period and conduct comparisons with observations;
(3) Determine the potential impact of emissions variability on ozone production
through sensitivity studies with the photochemical model.
Methodology
The emissions inventory will be based on the most recent available for the Houston
area from the Texas Commission on Environmental Quality (TCEQ) for 2012.
Recognizing that the base year of the TCEQ inventory may not be coincident with the
September 2013 DISCOVER-AQ period, targeted investigation of available data for
2013 (such as a review of emissions upset reports) will be performed to the extent
possible with the resources of the project. The base case photochemical modeling for
DISCOVER-AQ will establish the detailed spatial and temporal distributions of
emissions for the HSC. Data from DISCOVER-AQ aircraft spirals, collected up to three
times daily, will be analyzed and compared to the results from photochemical modeling
for appropriate chemical species; the comparison will be used to scale the base case
inventory for the HSC, while maintaining the spatial and temporal patterns of the
inventory. Both the base case inventory and the inventories based on the modeled to
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measured comparisons will be used in sensitivity studies with the photochemical model
to assess the impacts of daily variations in emissions inventories on ozone production.
The expected benefits of this work include an analysis of airborne observations in the
HSC during DISCOVER-AQ that will inform emissions inventory assessments and an
improved understanding of the role of emissions variability on ozone formation.
Accomplishments/Problems
NASA P-3 flights were performed in Houston on a total on nine days during the
DISCOVER-AQ September 2013 program as summarized in Attachment 1. A
representative flight track (repeated three times throughout the day) is shown in Figure
1a. Spirals at eight different locations along the flight track were typically flown between
the near-surface and 3.5-4 km above the ground surface (AGL). To date, our analyses
have focused on measurements collected in the paired sets of HSC spirals (ref. Figure
1b) flown over Channelview and Deer Park. The routine flight track called for a
downward spiral at Channelview (located immediately north of the HSC) followed by a
southward low-level leg, a touch-and-go at La Porte Airport, and an upward spiral at
Deer Park (immediately south of the HSC) before continuation of the flight.
Figure 1. NASA P-3 flight track on September 25, 2013 for (a) entire flight day and (b)
HSC region during the late afternoon.
(a)
(b)
In late spring 2014, our team downloaded selected trace gas and VOC measurements
from the NASA Tropospheric Integrated Data Center DISCOVER-AQ website
(http://www-air.larc.nasa.gov/missions/discover-aq/discover-aq.html). This website
provides a publicly-available data repository for DISCOVER-AQ measurements as
archived and made available by the individual PIs. The data are typically provided in
ASCII-text (comma-delimited) format in individual files that contain data for each flight
day and instrument(s) and/or PI. The data files incorporate a standardized header that
includes alphabetic revision numbers that track the dataset version and level of quality
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assurance and quality control measures. PIs may continue to periodically provide
updated versions of their datasets to this website.
Attachment 2 presents a table summarizing the NOAA P-3 datasets that were retrieved
and analyzed in support of our project to-date. All retrieved datasets provided
measurements at one-second time resolution. The measurements include:
Geographic: altitude, latitude, longitude
Meteorological: mixing ratio, relative humidity, static temperature, potential
temperature, wind speed, wind direction
Trace gases: Carbon Dioxide (CO2), Ozone (O3), Total Reactive Nitrogen (NOy),
Nitrogen Oxide (NO), Nitrogen Dioxide (NO2), Sulfur Dioxide (SO2)
Biogenic VOCs: Monoterpenes, Isoprene and its oxidation products
MVK_MACR_Crotonaldehyde
Oxygenated VOCs: acetaldehyde, MEK_butanal, aceticacid_glycoaldehyde,
acetone_propanal
Aromatics: benzene, toluene, C8-alkylbenzenes, C9-alkylbenzenes
Alkenes: propene (ethylene was not measured)
Other: acetonitrile, formaldehyde
In order to provide a preliminary analysis of the magnitude of concentrations collected in
the HSC spirals, a subset of the measurement data were extracted by filtering for data
collected only between 350-1000 meters AGL in the HSC region during all nine flights.
This data extraction limits the dataset to lower portions of the boundary layer mostly
within the Channelview and Deer Park spirals. Figure 2 shows the average of all
available one-second measurement data from the dataset extraction. The average
concentration for ozone (not shown) is 60.2 ppbv; average concentrations for the trace
gases range from 1.0 ppbv for NO to 6.7 ppbv for NOy and for VOC species 0.02 ppbv
for monoterpenes to 3.8 ppbv for formaldehyde.
Wind measurements at Deer Park, Channelview, and Moody Tower (ref. Figure 1b for
locations) were used to identify days with predominantly north/south-oriented nearsurface winds so that the Deer Park and Channelview spirals were located immediately
upwind and downwind of the HSC region. Preliminary results show that the flights on
Sept 24th, 25th, and 26th hold particular promise for our work. Late September was
characterized by a series of cold fronts that moved into or through HGB; near-surface
winds on Sept 24th and 25th were generally northerly while return flow from the Gulf of
Mexico was associated with southerly winds on Sept 26th.
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Figure 2. Average concentrations for selected NASA P-3 species measured in the
Channelview and Deer Park spirals.
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Average Concentration (ppbv)
7
6.68
6
5
4
3.57
3
2.56
2
1
0
3.81
3.01 3.06
1.38
0.47
0.21 0.28 0.33 0.35
0.02 0.05 0.13 0.14 0.19
0.74
1.01
Figure 3 compares the 350-1000 meter vertically averaged upwind to downwind
concentrations for the three individual pairs of HSC spirals on Sept 25 th for ozone, NOy,
SO2, propene, and benzene. With the exception of ozone, the average concentrations
are consistently greater in the downwind spiral compared to the upwind spiral. This
relative difference in concentrations is likely due, in part, to downwind enhancements
associated with emissions from HSC industrial sources. In particular, note the morning
measurements that show much higher concentrations in the upwind area; for example,
the Channelview (upwind) and Deer Park (downwind) NOy concentrations are 3.3 ppb
and 28.5 ppb, respectively. Figure 4 presents the median downwind to upwind ratios
across the eight pairs of Sept 24th-26th HSC spirals for all analyzed compounds. Median
ratios less than one are limited to three compound species typically associated with
biogenic emissions; otherwise, the median ratios (excluding ozone) vary from 1.11 for
methanol to 4.05 for benzene.
Investigations of the vertical distributions of pollutants have also been performed. For
example, the distributions with respect to height AGL of temperature and specific
humidity for the late afternoon spirals on Sept 25th are shown in Figure 5. On this day,
the mixed layer height is estimated at ~2.2 km (note the temperature inversion near this
height as well as the rapid decrease in atmospheric moisture). Vertical profiles of ozone
(Figure 6 left) indicate that the average boundary layer ozone concentrations are
approximately 107 ppbv and 121 ppbv in the upwind and downwind locations,
respectively; above the mixed layer, ozone concentrations remain high at 65-75 ppbv.
For SO2 (Figure 6 right), concentrations are near zero above the mixed layer at both
spiral locations; in the boundary layer, downwind concentrations are greater than those
measured upwind and show substantially larger increases and decreases with respect
to height AGL.
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Figure 3. Average 350-1000 meter upwind and downwind concentrations for selected
compounds on Sept 25th within the HSC paired spirals.
Figure 4. For the eight paired sets of HSC spirals flown Sept 24th-26th, the median
downwind to upwind ratios based on the 350-1000 meter averaged concentrations.
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Figure 5. Vertical profiles of temperature (left) and specific humidity (right) during the
paired set of HSC spirals flown on the late afternoon of Sept 25 th.
Figure 6. Vertical profiles of Ozone (left) and SO2 (right) during the paired set of HSC
spirals flown on the late afternoon of Sept 25th.
Ozone (ppbv)
SO2 (ppbv)
3.5
3.5
Channelview
Channelview
3.0
2.5
Height (km)
2.5
Height (km)
Deer Park
3.0
Deer Park
2.0
1.5
2.0
1.5
1.0
1.0
0.5
0.5
0.0
0.0
0
50
100
-5
150
0
5
10
15
Parameter Value
Parameter Value
Figure 7 shows that the highest SO2 concentrations (>5 ppb) are found within the
northern portions of the Deer Park spiral. This result suggests that the relatively large
spiral diameters (~10 km) captures both horizontal and vertical variations associated
with nearby and spatially heterogeneous industrial HSC emissions sources. Limited
analysis indicates that the aircraft is sampling distinct emissions plumes that may or
may not be well-mixed within the mixed layer and cover only portions of the spirals.
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Figure 7. Locations of SO2 concentration >5 ppbv (in red) during the Sept 25th late
afternoon spiral flown at Deer Park.
Future Work
During fall 2014, two additional datasets beneficial to the objectives of our project will
become available. Measurements collected at the La Porte Radar Wind Profiler (RWP)
during DISCOVER-AQ Houston are currently being analyzed to diagnose hourly mixing
heights and vertical profiles of wind speed and wind direction. The processing of the
RWP dataset is being funded, in part, by TCEQ through an Air Quality Research
Program (AQRP) project entitled “Characterization of Boundary-Layer Meteorology
During DISCOVER-AQ Using Radar Wind Profiler and Balloon Sounding
Measurements”. The schedule for this effort is on-track and the environmental data
collected at the La Porte location are representative of overall boundary layer conditions
within the local HSC region. Our project will use the RWP-derived estimates to assess
local transport conditions during each of the paired sets of HSC spirals flown by the
NASA P-3.
A second dataset that we plan to leverage for the project is the DISCOVER-AQ
photochemical model being generated specifically for the September 2012 DISCOVERQA period and led by NASA’s Kenneth Pickering. The Community Multi-scale Air
Quality (CMAQ) version 5.2.2 photochemical model has been employed using three
nested grid domains with horizontal spatial resolutions of 36, 12, and 4 km; the 4 km
grid domain covers the eastern two-thirds of Texas as well Oklahoma, Arkansas, and
Louisiana. Meteorological inputs for CMAQ were generated using Weather Research
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and Forecast (WRF) Version 3.6; anthropogenic emissions use data provided by TCEQ
representative of year 2012. In support of an AQRP program entitled “Analysis of
Airborne Formaldehyde Data Over Houston Texas Acquired During the 2013
DISCOVER-AQ and SEAC4RS Campaigns”, Alan Fried (University of Colorado) has
proposed to develop a fourth grid domain at 1.33 km resolution over southeast Texas.
In support of our work, we plan to leverage the full set of inputs, outputs, and run files so
that the CMAQ base case simulation can be replicated on the UT modeling system.
(Our group utilizes computing resources provided by the Texas Advanced Computing
Center, TACC). If the 1.33 km resolution results are available in time for our project
(e.g., by the end of 2014), we will utilize those outputs in addition to or in lieu of the
soon-to-be-available 4-km resolution outputs.
The CMAQ predictions (either at 4km or 1.33 km horizontal resolution) for the
appropriate chemical species from the base case simulation will be compared to the
results from the aircraft measurements for compounds such as NOy, HRVOCs, and
selected VOCs. This comparison will initially focus on data collected within the HSC
spirals when boundary layer winds are generally oriented parallel to a north/south
direction such that upwind and downwind spirals can be defined. The observed to
modeled comparison of chemical species will likely will be performed using
concentrations (ppbv) as well as by using ratios of selected compounds (e.g.,
NOx/propene).
Complementary analyses will likely be performed to assess the robustness of results.
For example, the impact of our results to uncertainties associated with model
performance (e.g., meteorology and chemistry) as well as potential uncertainties
associated with non-routine emissions such as upset events will need to be assessed.
There are also inherent uncertainties associated with differences in spatial and temporal
averaging between the grid predictions and aircraft measurements that may need to be
considered. The predicted-to-observed comparisons will be targeted towards guiding a
set of sensitivity runs that modify the base case emissions inventory in an appropriate
spatial and temporal manner to reflect any differences in modeled to observed chemical
species; modifications will be limited to HSC industrial sources located upwind of the
downwind spiral location. The goal of the sensitivity tests will be to quantify the impact
of diagnosed and representative uncertainties in the 2012 HSC emissions inventory to
predicted ozone concentrations throughout the HGB area.
List of Publications and Presentations
McGaughey, G., E.C. McDonald-Buller, D.T. Allen, August 8, 2014. Presentation
entitled “Emissions inventory evaluations using DISCOVER-AQ aircraft data”, presented
at the TARC meeting held at Lamar University, Beaumont, Texas.
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Attachment 1: NASA P-3 flight dates during DISCOVER-AQ Houston. The red numbers
indicate the HGB maximum 8-hour ozone concentration in ppbv as provided by TCEQ
(http://www.tceq.state.tx.us/cgi-bin/compliance/monops/8hr_monthly.pl).
62
51
45
51
66
124
89
66
64
Attachment 2: NASA P3 datasets utilized in our project to-date.
Instrumentation
P-3B
NASA LaRC P3B Data System (PDS)
Non-dispersive IR Spectrometer
(NASA/LaRC)
NCAR Difference Frequency Generation
Absorption Spectrometer (DFGAS)
NCAR 4-Channel Chemiluminescence
Proton Transfer Reaction Mass
Spectrometer (PTR-MS; Universität
Innsbruck)
Observations
Meteorological (temperature, pressure, wind speed, wind
direction) and navigational (GPS) data
CO2
CH2O
O3, NO2, NO, NOy
NMHCs
(Routinely measured species: methanol, acetonitrile,
acetaldehyde, acetone, isoprene, MVK, MACR, benzene,
toluene, sum of isomers of C8-aromatics, C9-aromatics,
C10-aromatics, monoterpenes; Others: CH2O; propene,
methyl ethyl ketone, PAN, DMS)
Pulsed UV Fluorescence (CIRES/NOAA)
SO2
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