ANALYSIS, MANAGEMENT, AND RESTORATION OF AIR QUALITY IN HARRIS COUNTY
DRAFT TASK 5 REPORT: 2011 MOBILE SOURCE PM2.5 EMISSION INVENTORY
Prepared for:
Houston Advanced Research Center
4800 Research Forest Drive
The Woodlands, TX 77381
HARC Contract No. AQRSCA13
Prepared by:
SC&A, Inc.
1608 Spring Hill Road, Suite 400
Vienna, VA 22182
February 19, 2014
TABLE OF CONTENTS
1.0
Introduction ..................................................................................................................................... 1
2.0
Background ...................................................................................................................................... 1
3.0
General Overview of Harris County PM2.5 Mobile Source Emission Inventory................................ 2
4.0
Mobile Source Categories ................................................................................................................ 3
4.1
Onroad Sources................................................................................................................... 3
4.2
NONROAD Model Sources .................................................................................................. 7
4.3
Commercial Marine Vessels.............................................................................................. 10
4.4
Locomotives ...................................................................................................................... 12
4.5
Airports ............................................................................................................................. 14
5.0
Revised Emission Estimates ........................................................................................................... 16
6.0
References ..................................................................................................................................... 17
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SC&A – February 19, 2014
1.0
INTRODUCTION
Recent ambient air quality monitoring data indicate that the Houston area (effectively Harris County)
may be close to being in nonattainment of the National Ambient Air Quality Standard (NAAQS) for
particulate matter with an aerodynamic diameter of 2.5 microns or less (PM2.5). This project is designed
to compile a base year 2011 PM2.5 emission inventory for Harris County, Texas as the initial step toward
developing an analysis of relative importance of local emission sources in contributing to any potential
or actual NAAQS exceedances.
This report summarizes the development of the Harris County 2011 PM2.5 emission inventory for mobile
sources. Mobile sources include onroad vehicles, off-road equipment and vehicles, aircraft, commercial
marine vessels and railroad locomotives.
2.0
BACKGROUND
The starting point for developing 2011 PM2.5 emission estimates for Harris County was a TCEQ-provided
mobile source emissions data base for that year. This inventory was developed by TCEQ for inclusion in
the mobile source portion of U.S. EPA’s 2011 National Emission Inventory (NEI). This 2011 PM2.5
emission inventory was used as the starting point for this project. Emissions from mobile sources are
typically calculated using a variety of methods and models. Table 1 summarizes the general
methodology or models used to calculate the TCEQ 2011 mobile source inventory and the key
references documenting each of these sectors.
Table 1. Source of TCEQ Emission Estimates for 2011 Harris County Mobile Source Emission Inventory
Non-Point Source Category
Onroad Sources
NONROAD Model Sources
Commercial Marine Vessels
Locomotives
Airports
Drilling Rigs
Draft Task 5 Report
Source of TCEQ 2011 Emission Inventory Estimate
2011 MOVES2010a runs with local Transportation
Demand Model-based activity
2008 Texas Nonroad (TexN) run, grown to reflect 2011
values based on local data
Development of 2011 Statewide Toxics and Actual
Annual and Ozone Season Weekday Emissions
Inventories for Commercial Marine Vessels.
Class I railroad emissions based on 2011 data from
railroad companies; Class II/III emissions based on
growing 2008 fuel consumption data
EDMS model for specific aircraft; generic emission
rates otherwise
Model rig profiles with NONROAD2008a emission
factors
1
References
TTI 2012
ERG 2008
ERG 2012c
ERG 2012a
ERG 2012b
ERG 2011
SC&A – February 19, 2014
3.0
GENERAL OVERVIEW OF HARRIS COUNTY PM2.5 MOBILE SOURCE EMISSION INVENTORY
The Texas Commission on Environmental Quality (TCEQ) provided an initial PM2.5 emission inventory for
mobile sources. Table 2 summarizes the PM2.5 and PM10 emissions by major mobile source category
from this 2011 TCEQ inventory. Based on this table, onroad emissions account for 55 percent of the
Harris County 2011 PM2.5 emissions followed by nonroad engines, which account for an additional 33
percent of the PM2.5 emissions. Commercial marine vessels and locomotives combined account for 12
percent of the inventory, and drilling rigs and aircraft combined account for less than 1 percent of the
county’s PM2.5 emissions.
Table 2 also presents comparable 2008 PM emissions from EPA’s 2008 National Emission Inventory for
Harris County. This table shows significant decreases in PM2.5 emissions from mobile sources over this
period. In general, for mobile sources, newer engines being phased into the vehicle or equipment fleet
often must meet more stringent emission standards than the vehicles or engines being replaced. This
natural turnover can lead to emission reductions over time when the differences in emission rates
between new engines and the replaced engines outpace any increases in activity over the same time
period. Similarly, retrofit emission controls can be used to reduce mobile source emissions from existing
engines. However, the PM2.5 emission reductions shown in Table 2 for airports and commercial marine
vessels (CMVs) of 69 percent and 61 percent, respectively, are both outside of the range that might be
expected over this 3-year period. Thus, our analyses below focused on identifying potential problems in
the TCEQ 2011 emission estimations for these categories. Additionally, at the kickoff meeting for this
project, where emission summaries for Harris County from EPA’s 2008 National Emission Inventory were
presented, several concerns relating to mobile sources were noted. The issues noted at this meeting
include:


The rail locomotive PM-2.5 emissions look low relative to the emissions from other similar
categories. The main railroads operating in the area include BNSF and Union Pacific, so they are
potential information sources.
Port emission studies include a recent Coast guard analysis of activity in the area, as well as a
2007 Starcrest analysis.
These issues are addressed in the corresponding sections for locomotives and commercial marine
vessels.
The sections below summarize how the emissions for the major source categories were developed, as
well as recommendations for revisions, where appropriate.
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SC&A – February 19, 2014
Table 2. 2011 and 2008 Harris County Mobile Source Emissions by Source Category
Annual Emissions (tpy)
Source Category
2011 PM2.5 2011 PM10
2008 PM2.5
2008 PM10
Onroad
1,795
2,629
2,679
3,866
Nonroad
1,089
1,136
1,202
1,252
Drilling Rigs
1
1
N/A
N/A
Commercial Marine
Vessels
280
304
719
890
Locomotives
99
102
142
158
Airports
22
70
72
126
Mobile Total
3,286
4,242
5,409
6,292
Source: EPA National Emission Inventory for 2008 and TCEQ for 2011
4.0
MOBILE SOURCE CATEGORIES
4.1
Onroad Sources
Percentage Change in
PM2.5 Emissions from
2008 to 2011
-33%
-9%
N/A
-61%
-30%
-69%
-39%
Emissions of PM2.5 from onroad vehicles in Harris County are summarized by vehicle type and emission
process in Table 3. The two right-most columns at the right of this table show the breakdown of these
emissions by fuel type. The development of TCEQ’s 2011 onroad emission inventory is documented in a
contractor report (TTI 2012). An overview of the development of this inventory is provided below.
Table 3. Harris County PM2.5 Emissions from Onroad Sources by Vehicle Type and Emission Process
Extended
Idle
(tpy)
Brakewear
(tpy)
Tirewear
(tpy)
Running
(tpy)
Start
(tpy)
0.9
0.8
0.1
0.0
0.0
Passenger Car
379.5
183.5
53.6
105.6
Passenger Truck
171.7
98.5
27.2
38.0
Light Commercial Truck
75.6
49.9
10.2
Intercity Bus
47.3
45.6
Vehicle Type
Motorcycle
Total
(tpy)
Pct.
Diesel
Pct.
Gas
0.0%
100.0%
36.8
0.6%
99.4%
8.0
25.8%
74.2%
12.8
2.7
45.8%
54.2%
0.0
1.4
0.2
100.0%
0.0%
Transit Bus
9.3
9.1
0.0
0.2
0.0
100.0%
0.0%
School Bus
24.7
23.3
0.1
1.1
0.2
99.9%
0.1%
Refuse Truck
11.3
10.7
0.0
0.5
0.1
97.9%
2.1%
Single Unit Short-haul Truck
189.6
162.7
1.2
22.3
3.4
94.7%
5.3%
Single Unit Long-haul Truck
21.3
18.4
0.1
2.4
0.4
94.8%
5.2%
Motor Home
17.1
15.9
0.0
1.0
0.2
95.5%
4.5%
Combination Short-haul Truck
381.0
366.3
0.4
11.7
2.6
99.6%
0.4%
Combination Long-haul Truck
465.6
429.6
0.3
22.2
11.1
2.5
100.0%
0.0%
1,795.0
1,414.3
93.2
22.2
208.2
57.1
68.8%
31.2%
Total
Draft Task 5 Report
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SC&A – February 19, 2014
Summer Weekday Emissions
Emissions were first calculated for a summer weekday by TTI in developing the TCEQ 2011 onroad
emission inventory. Emissions were calculated using EPA’s Motor Vehicle Emission Simulator (MOVES)
model (version MOVES2010a) to estimate emission rates along with activity estimated from the travel
demand model (TDM) used for the Houston/Galveston nonattainment area for a summer weekday in
2011. Emissions were calculated at the hourly and link level of detail. The MOVES model was used to
generate a look-up table of emission by pollutant, emission process, vehicle speed, hour of day, road
type and source use type. The vehicle speeds modeled were 2.5 mph and 5 mph through 75 mph in 5
mph increments. An emission rate for each pollutant, emission process, hour, and source use type was
then assigned to each road link by interpolating these emission rates to estimate an emission rate to
match the average speed of the road link. For each emission process, the appropriate link-level activity
data were then multiplied by the assigned emission rate to estimate link-level emissions for each
pollutant, emission process, hour, and source use type.
In order to run the MOVES model, a MOVES county database was developed for Harris County. Details
on the specific inputs included in the county database and the data sources used to develop these
inputs are summarized below:





Hourly temperature and humidity data. These inputs were developed by TCEQ and represented
the average hourly temperature and humidity for the period from June 1 through August 31 of
2011 for the Houston-Galveston-Brazoria TxDOT district.
Age distribution data. Harris County-specific data were used to develop the age distributions for
motorcycles, passenger cars, passenger trucks, and light commercial trucks. Texas statewide
registration data were used to develop the age distributions for long-haul trucks while data for
the Houston nonattainment area counties were used in developing the age distributions for
short-haul trucks. All of the registration data within Texas were from a mid-year 2011 vehicle
registration database. MOVES default age distributions were used for refuse trucks, motor
homes, and all bus types.
Engine fuel type distributions by source use type. These fractions, indicating the fraction of
gasoline versus diesel-fueled vehicles by source use type and model year were estimated from
the Texas statewide registration database for short-haul trucks and single unit long-haul trucks.
All other fuel engine fractions used the MOVES defaults.
Fuel properties. Summer 2011 gasoline properties were based on sales-weighted average fuel
data from EPS’s reformulated gas survey from data collected in the Houston area. Diesel fuel
sulfur content data were obtained from TCEQ’s summer 2011 fuel survey.
Inspection/Maintenance (I/M) program parameters. I/M program parameters for Harris County
were based on the program design included in the Texas SIP, with current compliance and
waiver rates.
Additional activity-based inputs used the MOVES defaults. This was done because the MOVES emission
rates option was selected. Therefore, the model outputs emission rates rather than emissions, so the
activity inputs used do not affect the resulting emission rate calculations.
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SC&A – February 19, 2014
Annual Emissions
The emission factors in TCEQ’s 2011 onroad emission inventory for Harris County were calculated using
EPA’s Motor Vehicle Emission Simulator (MOVES) model. The version of the model used was
MOVES2010a. The MOVES emission factors were used to calculate a summer weekday PM2.5 emission
inventory at the hourly, link level of detail. These summer weekday emissions were then converted to
annual emissions by using adjustment factors derived from additional MOVES runs. PM2.5 emissions are
estimated directly in MOVES, so no PM2.5 to PM10 ratios or adjustments were needed for onroad
sources.
The conversion from weekday summer emissions to annual emissions was performed by applying
summer weekday to annual conversion factors to both the activity and emission factors. The emission
factor conversion factors were developed for each combination of source use type, fuel type, roadway
type, pollutant, and emission process. The summer weekday to annual emission factor conversion
factors were developed by executing MOVES for a summer weekday run and an annual run. The annual
run was modeled as January and July monthly runs with January meteorology representing average
winter hourly temperature and humidity and July meteorology representing average summer hourly
temperature and humidity values for 2011. The MonthVMTFraction table in the MOVES county
database for these annual runs included semi-annual VMT fractions allocated to January and July. Fuel
parameters represented seasonal summer and winter fuel formulations and market shares. For the
summer weekday MOVES run, the summer meteorological conditions and fuel parameters modeled in
the summer weekday emissions analysis were applied. These annual and summer MOVES runs were
executed. Using the emissions and activity output from MOVES, annual and summer weekday emission
rates were calculated for each combination of source use type, fuel type, pollutant, process, road type,
and activity type. Next, the ratio of the annual to summer weekday emission factor was calculated for
each of these combinations.
In addition to these emission factor adjustment ratios, summer weekday to annual activity adjustment
factors were also calculated. For activity based on VMT, source hours parked, and source hours idling,
the annual activity adjustment factor for Harris County was 350.422. This factor was calculated based
on the ratio of the estimate of annual VMT for the county in 2011 to the summer weekday VMT
estimate. The annual activity adjustment for vehicle starts are based on MOVES default values for the
number of starts per day and per year and vary by source use type and fuel type with factors ranging
from 279.8 for single unit long-haul trucks to 611.7 for motorcycles.
Once both the emission rate and activity adjustment factors were calculated, emissions were calculated
by multiplying the summer weekday emissions at the source use type/fuel type/emissions process/road
type level of detail by the corresponding emission rate adjustment factor and the activity adjustment
factor.
After review of the procedures and data used to develop the Harris County PM2.5 onroad emission
inventory for 2011, no revisions are recommended. The methods used and data sources all appear
reasonable. The only concern would be in the development of the summer day to annual emission rate
Draft Task 5 Report
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SC&A – February 19, 2014
adjustment factors. Due to the sensitivity of the PM light-duty vehicle emission rates in MOVES to
temperature, it may have been preferable to use an additional season of meteorological data
representing spring/fall temperature conditions in developing this adjustment. In developing these
emission rate adjustment factors, temperature and humidity data from June through August 2011 were
used to represent summer conditions and January, February, and December 2011 temperature and
humidity data were used to represent winter conditions. Thus, the milder spring/fall conditions are not
represented. Sensitivity tests on the effects on the PM2.5 emission rates would be useful to determine
whether using additional temperature data would have significantly impacted the resulting emissions.
Table 4 shows the meteorological data used in the MOVES runs to estimate emissions for Harris County.
Considering that the winter temperatures shown in Table 4 are so mild, the impact of not modeling the
spring/fall conditions is likely to be fairly small, particularly when compared with areas with colder
winter temperatures.
Table 4. Houston-Galveston-Brazoria Area 2011 Hourly Temperature and Humidity Data
Hour Beginning
at:
Midnight
1:00 AM
2:00 AM
3:00 AM
4:00 AM
5:00 AM
6:00 AM
7:00 AM
8:00 AM
9:00 AM
10:00 AM
11:00 AM
Noon
1:00 PM
2:00 PM
3:00 PM
4:00 PM
5:00 PM
6:00 PM
7:00 PM
8:00 PM
9:00 PM
10:00 PM
11:00 PM
Draft Task 5 Report
Summer (June, July, August Average
Data)
Temperature
Relative Humidity
(oF)
(%)
81.78
81.05
80.42
79.88
79.38
78.92
78.66
79.91
82.99
85.64
88.01
90.11
91.82
92.94
93.60
93.82
93.55
92.67
91.15
88.90
86.34
84.64
83.45
82.54
77.92
80.26
82.41
83.82
85.06
86.09
86.78
84.25
76.56
67.93
59.29
52.73
48.13
45.45
43.78
43.29
43.99
45.94
49.19
54.47
61.24
66.62
71.05
74.73
Winter (January, February, December
Average Data)
Temperature
Relative Humidity
(oF)
(%)
51.54
51.23
50.92
50.73
50.46
50.21
49.94
49.80
51.06
53.20
55.28
56.87
58.05
58.86
59.45
59.52
59.02
57.66
56.05
54.86
54.09
53.39
52.76
52.17
6
80.99
82.08
82.98
83.46
83.73
84.05
84.28
84.25
81.65
77.09
72.53
68.96
66.37
64.00
62.08
61.06
61.48
64.32
68.34
71.09
72.97
75.09
77.38
79.29
SC&A – February 19, 2014
4.2
NONROAD Model Sources
SC&A evaluated the underlying population figures and emission factors used in the TCEQ PM2.5 estimate
for the NONROAD model categories. As shown in Table 5 below, the main off-road categories for Harris
County PM2.5 emissions are Construction and Mining, Commercial Equipment, and Lawn and Garden.
These were the source categories that received the most attention in determining potential areas for
inventory improvement.
Table 5. 2011 Harris County Major Nonroad PM2.5 Emissions Categories (TPY)
Category
Construction and Mining
Commercial Equipment
Lawn and Garden
Other
Nonroad Total
Emissions
588.4
165.1
139.3
196.0
1,088.9
Emissions from the nonroad sector were estimated by TCEQ using the Texas NONROAD (TexN) model.
The TexN model uses Texas specific data files, including area-specific equipment populations, activity,
growth, and temporal allocation files, as appropriate. Then TCEQ developed and populated baseline and
projected inventory lookup tables, reflecting variations in fuel properties, temperature, and selected
control strategies, at the county and SCC level. The 2011 TCEQ inventory updated 2011 meteorological
data, fuel data and some HAP profiles in the Texas NONROAD (TexN) model. Equipment population
inputs have not been changed from TexN inputs for the 2008 inventory, although they were grown to
reflect 2011 values. Default NONROAD inputs are used for emission factors, model year distributions,
deterioration factors and engine technology phase in schedules.
Emission Factors
Emission factors come from the latest version of the EPA NONROAD model (NONROAD 2008a). The
latest round of engine testing in the NONROAD model was performed in calendar years 1999-2001 on
model years 1996-2001 for nonroad engines. Some nonroad engines can have a median replacement
age of 30 years or more, and the calculation for 100% replacement is two times the median replacement
age (i.e. 60+ years). NONROAD includes the phase-in of Tier 2, 3 and 4 emission standards, which takes
place after the testing was completed. EPA has formulas for how these stricter standards will reduce
emissions.
SC&A consulted with Ed Glover, EPA’s NONROAD expert, to clarify the write-up and discussion of the
NONROAD Model. He indicated the emission factors within the NONROAD model are based on testing
performed on model years 2001 and earlier. These are a combination of Tier 0 and Tier 1 engines. The
emissions reductions from Tier 2/3 and Tier 4 technologies are estimated based on the standards put
into place, rather than based on certification data or other engine testing. There has been some testing
of nonroad engines for high emissions categories, such as construction, but this information has not
Draft Task 5 Report
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SC&A – February 19, 2014
been incorporated into the NONROAD model yet. We also spoke with EPA’s Jason Gumbs, who works
on nonroad engine certification data. He said that nonroad engines are not subject to production line
testing and that all certification data is provided by the manufacturers, and this information is publicly
available.
Given that the emission factors used in the NONROAD model are nearly fifteen years old, and are based
entirely on data provided by the manufacturer, rather than engine testing data or real world emissions
testing, SC&A sought to find any potential emissions factors that might be more recent or accurate. This
analysis focused on engine testing in the construction/mining sector, because these make up more than
half of all nonroad emissions. One possible data source was the 2010 TRB study by Frey, Rasdorf and
Lewis. This includes actual, in-use testing of a wide variety of construction vehicles, including some of
the largest emitting categories in Harris County like skid steer loaders and bulldozers. This emissions
data could be used to update emissions factors for NOx, HC, CO and CO2. Unfortunately, this study did
not include PM directly, and instead presents these emissions as Opacity (g/hr). Opacity is only useful as
a stand-in for PM insofar as it allows “for relative comparisons of PM emission rates for different fuels or
equipment types, but not for characterization of the absolute magnitude of PM emissions” (Frey,
Rasdorf and Lewis, 2010). Therefore, we did not use the PM emission factors in this study to update the
EFs used by TCEQ.
SC&A was not able to locate any other studies to improve or update the emissions factors used by TCEQ
to estimate the Harris county nonroad emissions. Therefore, emissions factors for 2011 remain
unchanged.
Harris County Equipment Population
The equipment population figures that were used to estimate nonroad emissions come primarily from
the TexN model for 2008, and then they were grown to reflect 2011 values. The data sources used by
the TexN model are summarized in Table 6 below.
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SC&A – February 19, 2014
Table 6. Data Sources for TexN Equipment Populations
Equipment Type
Diesel Construction
Equipment
Data Source
Eastern Research Group, Nonroad Ammonia Emissions Inventory
Development, prepared for Texas Commission on Environmental Quality,
November 24, 2006
Commercial Lawn and
Garden
Eastern Research Group, Development of Commercial Lawn and Garden
Emissions Estimates for the State of Texas and Selected Metropolitan
Areas, prepared for Texas Commission on Environmental Quality,
November 24, 2003
Diesel Cranes
Eastern Research Group, Nonroad Mobile Source Emissions Inventory
Development for the Houston- Galveston-Brazoria Area, submitted to the
Houston- Galveston Area Council, July 28, 2006
LPG Forklifts
Eastern Research Group, Data Collection, Sampling and Emissions
Inventory Preparation Plan for Selected Commercial and Industrial
Equipment: Phase II, Final Report, prepared for the Texas Commission on
Environmental Quality, August 31, 2005
Agricultural Equipment
Development of Emissions Inventory of Agricultural Equipment in All
Texas Counties Phase Two
Other Nonroad Equipment
Categories
NONROAD defaults - User’s Guide for the Final NONROAD2005 Model,
EPA420-R-05-013, December 2005
SC&A investigated how these equipment population estimates could be improved. There was a 2007
study of construction equipment populations in Houston (ERG, 2007). This study estimated construction
vehicle population data based on statewide sales data and vehicle scrappage rates. However, this study
is only marginally more recent than the 2006 study used for construction equipment in TexN, and there
were concerns that this sales data approach may not match well with the equipment population data in
other emissions categories. Given the uncertainty that any change would result in an improved
equipment population estimate, SC&A decided against updating the construction vehicle estimates
based on this database.
SC&A obtained a database of cargo handling equipment populations from the Port of Houston. At the
moment, it is not clear to what extent cargo handling equipment at ports has been included in the 2011
inventory, because they were not included as a separate subcategory within the CMV emissions. It is
possible that cargo handling equipment is being included in the larger commercial vehicles category, but
we cannot separate port CHE from what is included in the NONROAD model. No more recent
equipment inventory has been created at the state or county level for either all nonroad equipment, or
Draft Task 5 Report
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SC&A – February 19, 2014
for any of the major categories (such as construction or commercial equipment), and therefore the
equipment population database has not been changed.
4.3
Commercial Marine Vessels
There are three recent studies that have estimated CMV emissions for Harris County. Two were
sponsored by the TCEQ and the third was sponsored by the Port of Houston (POH). Because all of these
studies examined CMV activity in Harris County, our analysis of the emissions for this source category
focused on adapting the emissions and activity estimates from one or more of these studies to suit our
purpose, rather than developing our own activity estimates (which would have been cost prohibitive).
The three studies considered in this analysis include:
1. A Starcrest analysis for the Port of Houston, which estimates 2007 emissions for the Houston
area (Starcrest 2009);
2. An Environ report which uses the Starcrest information for the Houston area, makes few small
adjustments to that data, and uses other data sources to estimate CMV emissions for other
Texas coastal counties (ENVIRON 2010); and
3. An ERG report for TCEQ, which documents the 2011 CMV emission estimates for the Texas
counties that have CMV emissions (ERG 2012c).
The Port of Houston is a 25 mile long complex of diversified public and private facilities located on the
Gulf of Mexico. It is made up of Port of Houston Authority (PHA) and the 150-plus private industrial
companies along the Houston Ship Channel (HSC). In the Starcrest report, POH is used to mean the
entire HSC area, and PHA means that part of the HSC on PHA property only.
The Starcrest analysis for 2007 included landside operations as well as ships, but our evaluation for this
study focused on: (1) ocean-going vessels (e.g., containerships, bulk cargo ships, tankers), and (2) harbor
vessels (assist tugs and tugboats push or tow barges).
The outer boundary of the study area is located approximately nine nautical miles off the coast at the
outer sea buoy. Emissions associated with vessels that called on private and public facilities along the
Houston ship channel are included; port-specific emissions for the ports of Galveston, Texas City and
Freeport, and the Galveston, Texas City and Freeport Ship Channels are outside the scope of this study.
Starcrest estimates PHA associated CMV emissions for 2007, with PHA associated defined as including
vessels that visit a terminal on PHA property, whether PHA operated (Barbours Cut, Turning Basin, or
Bayport Terminals) or tenant operated. Emissions during dwelling, maneuvering and transiting the
Houston Ship Channel are included.
Because Galveston Bay is part of Galveston County, in order to use the Starcrest emission estimates, we
need to remove the OGV and harbor craft emissions that occur from the Federal/state waters boundary
through the Galveston Bay until the CMV enters Harris County near the entrance to the Houston Ship
Channel. Table 7 summarizes the 2007 Houston Area CMV emissions for PHA associated and non-PHA
associated trips from the Starcrest analysis. Their total PM-2.5 2007 emission estimate for the area was
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SC&A – February 19, 2014
825 tpy. However, as noted above, this includes emissions that occur outside of Harris County (in
Galveston Bay).
Table 7. 2007 Houston Area CMV -Related Emissions (Starcrest 2009)
Owner
PM-10
(tpy)
Vessel Type
PM-2.5
(tpy)
PHA
OGVs
Harbor vessels
Total CMVs
296
3
299
237
3
240
Total CMVs
732
585
1,031
825
Non-PHA
PHA+non-PHA
Starcrest used a fuel sulfur content of 2.7% for the residual oil used in ocean-going vessels during 2007.
Fuel sulfur levels affect both sulfur dioxide and PM emissions.
The ERG 2011 CMV emission estimates for Harris County convert the activity for Category 1 & 2 and the
Category 3 engines into kW-hours and then multiply the activity values by the criteria pollutant emission
factors for CMVs for each engine category. The PM-2.5 emission factor for Category 1&2 engines is 0.50
grams per kilowatt-hour. The PM-2.5 emission factor for Category 3 engines is 0.68 grams per kWh. In
response to a question from SC&A, TCEQ staff indicated that they (ERG) adjusted the load to generate
activity estimates that were more in-line with activity levels they observed outside of the HGA. They said
that the original Starcrest data assumed an 80% load for all vessels, whereas they found a 30% load to
be more realistic when looking at activity levels throughout state waters and by port/underway split.
TCEQ also indicated that because the Houston Ship Channel is a reduced speed zone that a load factor of
30 percent was assumed for underway emissions. It is understood that in the upper reaches of the ship
channel loads may be as low as 6 percent, and that towboat operations may be as high as 65 percent.
EPA guidance says that emission factors are considered to be constant down to about 20 percent load.
Below that threshold, emission factors tend to increase as the load decreases.
Table 8 summarizes ERG’s 2011 CMV emission estimates for Harris County. This table also shows the
emission factors used to estimate PM-2.5 emissions for the two engine categories. SC&A has two
concerns about how ERG estimated 2011 PM-2.5 emissions within Harris County. One is that their base
emission factors are well below the main engine emission factors used by EPA in recent studies, which
are in the range of 1.3 to 1.4 g/kW-hr. Unless there is evidence that CMVs in the Houston area were
using residual oil with a sulfur content below 2.7%, then the low emission factors applied by ERG do not
appear to be justified. The second concern is that ERG does not apply adjustment factors to account for
the lower loads that are typical within the Houston Ship Channel. The Starcrest study for the POH does
a better job of capturing the emissions at low loads that are characteristic of CMV travel within Harris
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County. Lower loads produce higher PM emission rates than are observed when the CMVs are
underway.
Therefore, SC&A has requested that Starcrest, via the POH, provide its 2007 CMV emission estimates
for Harris County (which were not available in the original report), and that the 2011 emissions will be
estimated for this study by applying any needed adjustments to account for CMV activity changes from
2007 to 2011 in the Houston area, and any fuel sulfur changes that have occurred between 2007 and
2011. It is expected that the resulting Harris County PM-2.5 emission estimate will be about 550 tpy.
Table 8. 2011 Harris County CMV Emissions (ERG 2012c)
Vessel
Category
SCC
SCC Description
Category 1&2
2280002100
Diesel-Port
Category 1&2
2280002200
Diesel-Underway
Category 3
2280003100
Residual-Port
Category 3
2280003200
Residual-Underway
Total CMVs
4.4
Emission Factor
(g/kWh)
Emissions (tpy)
Activity (kWh)
PM-10
PM-2.5
PM-10
PM-2.5
460,131
0.52
0.5
0.26
0.25
49,554,545
0.52
0.5
28.20
27.36
277,682,625
0.74
0.68
227.87
208.29
58,358,017
0.74
0.68
47.89
43.77
304.22
279.67
386,055,318
Locomotives
Emissions of PM10 and PM2.5 from locomotives in Harris County are summarized by SCC in Table 9. The
development of TCEQ’s 2011 locomotive emission inventory is documented in a contractor report (ERG
2012a). An overview of the development of this inventory is provided below.
Table 9. Harris County PM Emissions from Locomotives by SCC
SCC
2285002006
2285002007
2285002010
2011 Annual Emissions (tpy)
PM10
PM2.5
45.75
44.38
1.75
1.61
54.36
52.73
SCC Description
DIESEL: LINE HAUL LOCOMOTIVES: CLASS I
LINE HAUL LOCOMOTOVES: CLASSII/III
DIESEL: YARD LOCOMOTIVES
Total
101.86
98.72
Class I Line Haul Emissions
TCEQ’s contractor collected data from the two largest Class 1 rail companies operating in Texas in
2011—Union Pacific (UP) and Burlington Northern Santa Fe (BNSF). Both of these railroad companies
provided PM10 emission estimates by county, as well as some related activity data by track segment.
PM2.5 line haul emissions from these major railroad companies were then calculated by multiplying the
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PM10 emission estimates by 0.97. This follows EPA’s guidance for estimating PM2.5 emissions from
locomotives (EPA 2009).
Table 10 summarizes the EPA emission factors converted to grams per gallon for PM10 for locomotives
manufactured in 2011 or earlier. This table also shows the average emission rates used by the two Class
I railroads that provided data for the TCEQ 2011 locomotive inventory. The emission factors shown in
Table 9 for these two railroads were calculated based on the statewide PM10 emissions and fuel
consumed in line haul activities by each of these railroad companies. A comparison of the railroadprovided data with the EPA data by locomotive tier indicates that the average railroad emission factors
are between the expected minimum and maximum, which would likely indicate that they are using data
based on the fleet mix of their locomotives. Based on the provided documentation, however, it is
unknown whether an average emission factor was used statewide, or if the emissions that were
calculated at the track segment or county level were based on the actual fleet mix in those specific
locations. Based on the available information, the PM10 emission rates used are reasonable. In addition,
the activity data used are the actual fuel consumed by track segment or county in 2011. Thus, the
emissions in the 2011 TCEQ inventory for Harris County for SCC 2285002006 Diesel Line Haul
Locomotives: Class I are of good quality and are expected to be reasonably accurate. As a result, no
revisions have been made or recommended for this SCC.
Table 10. Locomotive Line-Haul Emission Factors
Emission Standard Tier/
Railroad
Uncontrolled/Tier 0
Tier 1
Tier 2
UP
BNSF
Year of Original
Manufacture
Through 1992
1993-2004
2005-2011
PM10 Line Haul
g/gal
6.66
6.66
3.74
4.35
4.4
Class II/III Line Haul Emissions
Class II and III railroad companies did not respond to data requests for local line haul data in the
preparation of the TCEQ locomotive inventory. TCEQ’s contractor instead used Class II/III route miles
from a Federal Railroad Administration (FRA) database along with emission profiles for Class II/III
railroads developed by the Eastern Regional Technical Advisory Committee (ERTAC) effort to prepare a
national 2008 locomotive emission inventory (Bergin et. al 2009). This resulted in an estimate of
2,797.74 gallons of fuel consumed per route-mile from Class II/III railroads in 2008, which was multiplied
by the FRA route-mile estimates for 2008 to estimate annual gallons of fuel consumed. These 2008 fuel
consumption estimates were grown to 2011 using data from the Annual Energy Outlook 2012, which
provided a national annual growth rate of 0.8% increase in ton-miles via rail over the period 2010
through 2035. Thus, three years of growth at 0.8% were applied to the estimated 2008 fuel
consumption from Class II/III line haul activity.
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SC&A – February 19, 2014
The PM10 emission rate used with the estimated tons of gallons of fuel consumed in the TCEQ inventory
is 5.824 g/gallons and the PM2.5 emission rate is calculated by multiplying this rate by 0.97. The selected
emission rate follows the ERTAC process guidance and represents the PM10 non-regulated emission rate
of 0.32 grams per brake horsepower-hour (bhp-hr) multiplied by EPA’s recommended conversion factor
for small line haul locomotives of 18.2 bhp-hr/gal (EPA 2009).
The cited version of AEO shows that most of the growth in rail ton-miles occurs in the long term. In the
first 5 to 10 years, there is little growth, and in some years a decline, in rail ton-miles. Thus, this long
term growth rate is not appropriate to apply for the period from 2008 to 2011. However, in Harris
County, as shown in Table 9, PM10 emissions from line haul activities for Class II/III railroads are only
1.75 tpy. An estimate of the effect of correcting this growth rate leads to 1.68 tpy of PM10 or 1.54 tpy of
PM2.5. Thus, the impact on the inventory of this growth assumption is negligible.
Railyard Emissions
As shown in Table 9, switchyard activities account for the greatest portion of PM emissions from
locomotives in Harris County. Emissions in this SCC (2285002010) include both Class I and Class II/III
railroads. In the TCEQ 2011 inventory, activity (in terms of gallons consumed in rail yards) was provided
by UP, while emissions from rail yards were provided by BNSF.
Railyards that were included in the 2008 inventory that were not represented in the UP or BNSF
datasets were used as the basis for the Class II/III railyard emission estimates. The activity from the
ERTAC 2008 inventory was grown by 0.8%, as the Class II/III line haul activity was grown. The PM10
emission factor used to calculate the UP and Class II/III railyard emissions was 6.688 g/gal, which
represent the switchyard emission rate for uncontrolled locomotives of 0.44 g/bhp-hr multiplied by a
fuel conversion factor for switching of 15.2 bhp-hr/gal (EPA 2009). Again, PM2.5 emission rates were
estimated by multiplying the PM10 emission rates by 0.97.
Similar to the effect of using the 0.8% annual growth rate for the Class II/III line haul emissions, applying
this growth rate to the switchyard emissions will also cause an overestimate in these emissions.
However, because a portion of the activity in Harris County from the Class I railroads is not separated
from the switchyard activity for the Class II/III, an appropriate adjustment cannot be made. If 100% of
the switchyard activity had been from Class II/III railroads, the estimated overestimation of the 2011
emissions is about 2 tpy for both PM10 and PM2.5. Thus, the impact on the overall PM2.5 inventory for
Harris County of the overestimation of growth assumption is minimal.
4.5
Airports
TCEQ’s 2011 emissions of PM10 and PM2.5 from airports in Harris County are summarized by SCC in Table
11. The airport emission inventory includes emissions from aircraft as well as from ground support
equipment (GSE) and auxiliary power units (APUs). The development of TCEQ’s 2011 airport emission
inventory is documented in a contractor report (ERG 2012b). An overview of the development of this
inventory is provided below.
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SC&A – February 19, 2014
Table 11. 2011 Airport PM Emissions in Harris County by SCC
Annual
Emissions (tpy)
SCC
2265008005
SCC Short Description
GASOLINE (4 STROKE) AIRPORT GSE
1.8
0
2267008005
LPG: AIRPORT GSE
0.18
0
2268008005
CNG: AIRPORT GSE
0.14
0
2270008005
DIESEL: AIRPORT GSE
8.57
0
2275001000
MILITARY AIRCRAFT
0.5
0.48
2275020000
COMMERCIAL AIRCRAFT
24.89
0
2275050011
GENERAL AVIATION PISTON ENGINES
19.02
13.12
2275050012
GENERAL AVIATION TURBINE ENGINES
9.45
8.05
2275060011
AIRCRAFT /AIR TAXI /PISTON
0.18
0.13
2275060012
AIRCRAFT /AIR TAXI /TURBINE
4.19
0.65
2275070000
AUXILIARY POWER UNITS
0.64
0
69.56
22.44
Total
PM10
PM2.5
TCEQ and their contractor obtained landing and take-off (LTO) data by engine type from the Bush,
Hobby, and Ellington Airports. This accounts for all of the major airports in Harris County. The Federal
Aviation Administration (FAA) has developed the Emissions and Dispersion Modeling System (EDMS) to
be used in estimating emissions from activities at airports. This model (EDMS version 5.1.3) was used to
estimate emissions from aircraft at the major Harris County airports using LTO data by engine make and
model at each airport, along with information on taxiing time. APUs provide power to the aircraft when
the main engine is shut down and also provides startup power for the main engine. APU emissions were
also estimated using EDMS, which estimates emissions based on the amount of time an APU is operating
per LTO cycle. Both Bush and Hobby airports employ emission reduction strategies to reduce APU
emissions. A 90 percent reduction was therefore applied to these emissions in the TCEQ inventory,
based on EPA guidance. Airports use GSE to perform a number of functions, including loading and
unloading baggage and towing aircraft. Emissions from GSE are estimated within EDMS, using EPA’s
NONROAD2005 model, based on equipment type and time of operation performing services.
For the remaining smaller airports in Harris County, the TCEQ inventory was estimated using EDMS to
calculate emissions from these smaller airports based on LTOs by aircraft and engine type. LTO data for
these airports for 2011 were obtained from FAA’s TAF database. EPA’s default mix of aircraft engine
types within these fleets were used to allocate the LTOs by aircraft and engine type.
The ERG report (ERG2012b) provides a summary of the resulting airport emissions for Harris County for
2011. While the emissions of PM10, CO, NOx, SO2, and VOC reported there are about the same as the
sum of the Harris County airport emissions for Harris County from the SCC-level inventory provided by
TCEQ, there is a significant difference in the PM2.5 emissions reported by these two sources. As can be
seen in Table 11, a number of the SCCs had zero PM2.5 emissions reported in the TCEQ inventory. The
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PM2.5 to PM10 ratio for nonroad engines is fairly standard by fuel engine type. Therefore, a revised
estimate of the PM2.5 emissions was made by applying the PM2.5 to PM10 ratio presented in the ERG
report summarizing state level emissions by the categories shown in Table 11. These ratios were
applied to the Table 11 PM10 emissions and resulted in a revised estimate of PM2.5 emissions from
airports in Harris County in 2011 of 50 tpy. Referring back to Table 2, this revises the percentage change
in airport PM2.5 emissions from a 69 percent decrease to a more reasonable 31 percent decrease.
However, comparisons of aircraft activity from Bush, Hobby, and Ellington airports between 2008 and
2011 (FAA 2014) show about a 12 percent decrease in LTO activity from 2008 to 2011, as shown in Table
12. The documentation of the 2011 TCEQ airport inventory (ERG2012b) summarizes total county-level
LTOs and emissions from Harris County. This shows a total of 714,324 LTOs in Harris County in 2011,
and includes all airports in Harris County, not just the three for which detailed LTO data were obtained.
In comparison, the 2011 LTO total reported in the FAA TAF database for just Bush, Hobby, and Ellington
airports is 878,232, or about 23 percent more LTOs in 2011 than reported in the TCEQ 2011 inventory
documentation from all of Harris County. Thus, there appears to be an underestimation of activity data
in 2011 for the Harris County airports, which would lead to an underestimation of PM emissions as well.
A summary of the LTO data and emissions by SCC and airport within Harris County from the TCEQ
analysis would be needed for further evaluation.
Table 12. Comparison of FAA LTOs for Airports in Harris County and TCEQ Harris County Total LTOs
Percent Change
Airport
2008 LTOs
2011 LTOs
from 2008 to 2011
George Bush Intercontinental Airport (IAH)
594,126
532,121
-10%
William P Hobby Airport (HOU)
223,612
201,409
-10%
Ellington Field (EFD)
176,756
144,702
-18%
Subtotal of 3 Airports
994,494
878,232
-12%
Harris County Total (ERG 2012b)
714,324
Source: FAA 2014 for airport-specific data, ERG2012b for Harris County total. Note that there are
additional airports located in Harris County besides the three included in this table.
5.0
REVISED EMISSION ESTIMATES
Table 13 summarizes the changes made to the Harris County PM2.5 mobile source emission inventory.
These changes increase the PM2.5 emissions by almost 300 tpy, or about a 9 percent over the original
TCEQ estimate. Further revisions may be warranted, as described in the sections above, for airports and
nonroad cargo handling equipment if additional data can be obtained.
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SC&A – February 19, 2014
Table 13. 2011 Revised Harris County Mobile Source PM2.5 Emissions by Source Category
Source Category
Onroad
Nonroad
Drilling Rigs
Commercial Marine Vessels
Locomotives
Airports
Mobile Total
6.0
Original 2011
PM2.5 Estimate
(tpy)
1,795
1,089
1
280
99
22
3,286
Revised 2011
PM2.5 Estimate
(tpy)
1,795
1,089
1
550
97
50
3,582
REFERENCES
Bergin et. al 2009. M. Bergin, M. Harrell, J. McDill, M. Janssen, L. Driver, R. Fronczak, R. Nath, and D.
Seep. “ERTAC Rail: A Collaborative Effort in Building a Railroad-Related Emissions Inventory Between
Eastern States Air Protection Agencies and Participation with the Railroad Industry.” Presented at the
18th Annual International Emission Inventory Conference, Baltimore, MD, April 14-17, 2009.
EIA 2012. U.S. Energy Information Administration. Annual Energy Outlook 2012 Early Release, Report
Number DOE/EIA-0383ER(2012). Table A7. Transportation sector key indicators and delivered energy
consumption. Released January 23, 2012.
ENVIRON 2010. “Implement Port of Houston’s Current Inventory and Harmonize the Remaining 8county Shipping Inventory for TCEQ Modeling.” Final Report. Prepared by ENVIRON International
Corporation for Texas Commission on Environmental Quality, July 30, 2010.
EPA 2009. “Emission Factors for Locomotives.” US Environmental Protection Agency Office of
Transportation and Air Quality, EPA-420-F-09-025, April 2009. Available online at
http://www.epa.gov/otaq/regs/nonroad/locomotv/420f09025.pdf.
ERG, 2007. “Diesel Construction Equipment Database and NOx Control Technology Evaluation for
Houston.” Prepared for Texas Environmental Research Consortium. Available online at:
http://files.harc.edu/Sites/TERC/NTRD/Projects/DieselDatabaseFinalReport.pdf
ERG, 2008. Texas NONROAD (TexN) Model Version 1.0 User's Guide. Prepared by Eastern Research
Group for Texas Commission for Environmental Quality. August 2008.
ERG 2011. “Development of Texas Statewide Drilling Rigs Emission Inventories for the Years 1990, 1993,
1996, and 1999 through 2040.” Final Report. Prepared by Eastern Research Group, Inc. for Texas
Commission on Environmental Quality Air Quality Division, August 15, 2011.
ERG 2012a. “2011 Texas Railroad Emission Inventory Report.” Final Report. Prepared by Eastern
Research Group, Inc. for Texas Commission on Environmental Quality Air Quality Division, August 17,
2012.
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ERG 2012b. “Development of Statewide Annual Emissions Inventory and Activity Data for Airports.”
Final Report. Prepared by Eastern Research Group, Inc. for Texas Commission on Environmental Quality
Air Quality Division, August 17, 2012.
ERG 2012c. “Development of 2011 Statewide Toxics and Actual Annual and Ozone Season Weekday
Emissions Inventories for Commercial Marine Vessels.” Final Report. Prepared by Eastern Research
Group, Inc. for Texas Commission on Environmental Quality Air Quality Division, August 17, 2012.
FAA 2014. Federal Aviation Administration. Terminal Area Forecast (TAF). http://tafapo.itworkssoftware.com/apotaf/taf.asp. Accessed February 18, 2014.
Frey, Christopher; Rasdorf, William and Lewis, Phil, 2010. Results of a Comprehensive Field Study of
Fuel Use and Emissions and Nonroad Diesel Construction Equipment. Submitted for Consideration for
Presentation at the 89th Annual Meeting of the Transportation Research Board and Publication in
Transportation Research Record.
Starcrest 2009. “2007 Goods Movement Air Emissions Inventory at the Port of Houston.” Final Draft.
Prepared by Starcrest Consulting Group, LLC for Port of Houston Authority, January 2009.
TTI 2012. “2011 On-Road Mobile Source Actual Annual and Weekday Emissions Inventories: Houston
Area.” Final Technical Report. Prepared by the Texas Transportation Institute Transportation Modeling
Program for Texas Commission on Environmental Quality Air Quality Planning and Implementation
Division, August 2012.
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