REDUCTION OF HIGHLY REACTIVE
VOLATILE ORGANIC COMPOUNDS &
VARIABLE EMISSIONS IN
HOUSTON/GALVESTON:
MONITORING, MODELING, MEASURING,
RULEMAKING
David Allen
Department of Chemical Engineering, and
Center for Energy and Environmental Resources
University of Texas
(512-471-0049; allen@che.utexas.edu)
The Houston-Galveston area is a severe ozone nonattainment area; costs and benefits of controls have been
estimated to be ~$5 billion/yr
The current EPA approved State Implementation Plan (SIP,
approved in 2000) calls for significant NOx emission
reductions (approximately 70% of the 2007 inventory; 90+%
for point sources); SIP also called for some VOC emission
reductions
Proposed new plan adds emission reductions for highly
reactive VOCs from industrial facilities and applies 80%,
rather than 90% industrial NOx emission reductions
Outline


Why focus on Highly Reactive Volatile Organic
Compounds (HRVOCs)? Why are we
considering variability in emissions? This
presentation will provide an overview of the
scientific basis for decision-making
Impact of scientific findings on air quality
policy and current direction of technical
analyses impacting policy decisions
Focus on HRVOCs emerged out of
the Texas Air Quality Study -2000
(TEXAQS - 2000)
(www.utexas.edu/research/ceer/texaqs/)
(www.utexas.edu/research/ceer/texaqsarchive)
TEXAQS - 2000: Study overview
Study conducted from approximately
August 15 - September 15
 Approximately 300 investigators
 5 aircraft
 5 major ground chemistry sites
 Coordinated with Houston fine
particulate matter Supersite sampling
intensive

TexAQS and other research programs
address key areas of uncertainty
Emission inventories
 Chemical and physical processes in the
atmosphere, particularly those leading
to rapid and efficient ozone formation
(a.k.a. ozone “spikes”)
 Regional air quality modeling/air quality
policies

Chemical and physical processes in
the atmosphere: Rapid ozone
formation events
TexAQS data have played a crucial role in
understanding these events:
Physical insights
Hydrocarbon Reactivities
40
150
35
OH Reactivity (s )
100
-1
-1
OH Reactivity (s )
30
50
25
Anthropogenic
Biogenic
CO
Methane
20
15
10
5
0
.01
0
1
5
50
90
99
Bottom 10%
Mean
Top 10%
Percent of Samples
Top 10% of samples exhibit reactivities that are 4x the
mean value. For the most part the highest reactivities are
geographically associated with industries in the Ship
Channel.
Apportionment of reactivity
for high reactivity samples
•For the high reactivity
samples, low molecular
weight alkenes (propene,
ethene and butenes) are a
major source of
hydrocarbon reactivity for
ozone formation.
Twin Otter VOC Samples
Average for 26 samples with k>10 s-1
TexAQS showed us that
HRVOCs are important, but
what is relative importance of
short, episodic releases vs.
continuous, steady emissions?
HRVOC emissions
HRVOCs defined as ethylene,
propylene, butylenes and 1,3-butadiene
 Continuous emissions – to be addressed
with a CAP (and trade?) program
 Emission events to be handled through
a short term cap

Conceptual issue
In most of US, industrial emissions are relatively constant or are small
enough that meteorology is cause of “worst conditions”
In Houston, both meteorology and emissions are cause of “worst conditions”
Conceptual issue
Estimating variability for
continuous emissions
Event Emissions and their impact on ozone
formation in the Houston Galveston Area
Key Questions



Are the magnitudes of emission events, singularly
and collectively, significant relative to routine
emissions?
What are the characteristics of the events in terms
of time, space, and composition?
How do the events influence ozone formation?
Harris, Galveston, Chambers, and Brazoria Counties
NOX Event Emissions
as Reported Jan 31 - Dec 31, 2003
Event Emissions
2001 Annual Avg
25,000
24,083 lbs/hr
Average hourly emissions
of all point sources
15,000
First 11 Months of
reporting:
10,000
7665 lbs/hr
5,000
0
0
Jan 1
730
1460
2190
2920
3650
4380
5110
5840
6570
7300
8030
8760
Dec 31

NOx emission event
emissions are small
compared to annual
average emissions

At specific times and
locations, VOC and
HRVOC emissions can
be large relative to
annual average
emissions
Yearly Hour
Total Event Emissions = 280,954 lbs
Harris, Galveston, Chambers, and Brazoria Counties
VOC Event Emissions
as Reported Jan 31 - Dec 31, 2003
50,000
45,000
64,860
lbs/hr
53,983
lbs/hr
Event Emissions
2001 Annual Avg
86,557
lbs/hr
64,539
lbs/hr
40,000
Emissions (lbs/hr)
Emissions (lbs/hr)
20,000
TCEQ event database,
established in early
2003
35,000
30,000
25,000
20,000
15,000
10,359 lbs/hr
10,000
5,000
0
0
Jan 1
730
1460
2190
2920
3650
4380
5110
5840
6570
7300
8030
8760
Dec 31
Yearly Hour
Total Event Emissions = 4,035,322 lbs
Harris, Galveston, Chambers, and Brazoria Counties
VOC Event Emissions
as Reported Jan 31 - Dec 31, 2003
50,000
45,000
64,860
lbs/hr
53,983
lbs/hr
2001 Annual Avg
86,557
lbs/hr
40,000
Emissions (lbs/hr)
Event Emissions
64,539
lbs/hr
35,000
VOCs
30,000
4,000,000 lb
25,000
20,000
15,000
10,359 lbs/hr
10,000
5,000
0
0
Jan 1
730
1460
2190
2920
3650
4380
5110
5840
6570
7300
8030
8760
Dec 31
Yearly Hour
Total Event Emissions = 4,035,322 lbs


Total mass of over 4 millions pounds (2000 tons) contributes
4% to the 45,000 tons of VOC emitted over a single year from
point sources in the four counties.
14 times (18 hours) during the eleven-month period, event
emissions exceed the annual average for all facilities in the
region.
Harris, Galveston, Chambers, and Brazoria Counties
all HRVOC Event Emissions
as Reported Jan 31 - Dec 31, 2003
Event Emissions
2000 SpEI Annual Avg
25,000
39,340
lbs/hr
HRVOCs
Emissions (lbs/hr)
20,000
1,650,000 lb
15,000
10,000
5,000
1,552 lbs/hr
0
0
Jan 1
730
1460
2190
2920
3650
4380
5110
5840
6570
7300
8030
8760
Dec 31
Yearly Hour
Total Event Emissions = 1,656,672 lbs


Total mass of over 1.6 millions pounds (830 tons) is ~12% of
the 6800 tons of HRVOC emitted over a single year from
point sources in the four counties.
29 times (115 hours) during the eleven-month period, event
emissions exceed the annual average.
Harris, Galveston, Chambers, and Brazoria Counties
all 1,3-Butadiene Event Emissions
as Reported Jan 31 - Dec 31, 2003
Harris, Galveston, Chambers, and Brazoria Counties
all Propene Event Emissions
as Reported Jan 31 - Dec 31, 2003
Event Emissions
2000 SpEI Annual Avg
1,3-Butadiene
~50,000 lb
Emissions (lbs/hr)
1600
1400
1200
38,734
lbs/hr
9000
8000
Emissions (lbs/hr)
1800
1000
800
600
97
lbs/hr
16,338
lbs/hr
7000
6000
Propene
~500,000 lb
5000
4000
3000
2000
551
lbs/hr
1000
200
0
0
0
Jan 1
730
1460
2190
2920
3650
4380
5110
5840
6570
7300
8030
0
Jan 1
8760
Dec 31
730
1460
2190
2920
3650
4380
5110
Harris, Galveston, Chambers, and Brazoria Counties
all Ethene Event Emissions
as Reported Jan 31 - Dec 31, 2003
Event Emissions
2000 SpEI Annual Avg
7300
8030
8760
Dec 31
Event Emissions
2000 SpEI Annual Avg
10000
2000
Butenes
~100,000 lb
1600
1400
1200
9000
1000
800
600
237
lbs/hr
Ethene
~1,000,000 lb
7000
6000
5000
4000
3000
2000
586
lbs/hr
1000
200
0
0
0
Jan 1
12,239 lbs/hr
8000
Emissions (lbs/hr)
1800
Emissions (lbs/hr)
6570
Total Event Emissions = 543,783 lbs
Total Event Emissions = 53,383 lbs
Harris, Galveston, Chambers, and Brazoria Counties
all Butene Event Emissions
as Reported Jan 31 - Dec 31, 2003
5840
Yearly Hour
Yearly Hour
400
2000 SpEI Annual Avg
10000
2000
400
Event Emissions
730
1460
2190
2920
3650
4380
5110
5840
6570
7300
8030
8760
Dec 31
0
Jan 1
730
1460
2190
2920
3650
4380
5110
5840
6570
7300
8030
8760
Dec 31
Yearly Hour
Yearly Hour
Total Event Emissions = 105,089 lbs
Total Event Emissions = 954,418 lbs
What are the characteristics of the events
in terms of time, space, and composition?
All HRVOC Events
as Reported Jan 31 - Dec 31, 2003
Unscheduled
Frequency of HRVOC events by HRVOC mass
Scheduled
As Reported Jan 31 - Dec 31, 2003
600
500
375
400
Less than 24 hours
Number of Events
Number of Reported Events
500
400
300
200
Daily
300
200
160
142
2-3 times per
week
100
100
33
1
0
0
0-24
24-48
48-72
72-96
96-120
Event Duration (Hours)
120-144
144-168
>168
0-100
100-1000
1,000-10,000
10,000-100,000
>100,000
Mass of HRVOC per Event (lbs)
Most HRVOC events last less than a day, many last less than an hour
Largest number of events is from events of 100-1000 lb, but most of
the mass is associated with events greater than 1000 lb, which occur,
on average, several times per week
Conceptual model




Events with emissions of more than 1000
pounds of HRVOCs occur several times per
week, on average; events with emissions of
more than 10,000 pounds of HRVOCs occur
several times per month, on average
Many are relatively short (well under one
hour in duration)
Among the HRVOCs, ethene and propene
dominate
Events occur primarily in Harris and Brazoria
counties at chemical manufacturing facilities
What are the consequences for
ozone formation?

Example of worst case scenario:
Monitoring data from a 6700 lb, 30
minute ethylene release at LaPorte
10,000+ lb ethylene release at
LaPorte, (6700 lb between 11 and
11:25 AM) 3/27/2002
Short term ozone enhancements
of up to 100 ppb
Add Event to Air Quality Model
(most recent version with 1-km resolution)
Without Event
With Event
Layer One
149.9 ppb
vs
203.0 ppb
Outline


Why Highly Reactive Volatile Organic
Compounds (HRVOCs)? Why are we
considering variability in emissions? An
overview of the scientific basis for decisionmaking
Impact of scientific findings on air quality
policy and current direction of technical
analyses impacting policy decisions
Actions taken by the TCEQ
and current technical analyses


Based on the data from TexAQS, which indicate
that VOC emissions from industrial facilities are
responsible for rapid and efficient ozone formation,
new rules have been proposed for emissions of
highly reactive volatile organic compounds
(HRVOCs) from flares, cooling towers and fugitive
sources
Balance between NOx and HRVOC emission
controls reevaluated, balance between short term
and annual HRVOC emissions being evaluated;
focus of work at UT is on short term releases and
on characterizing scientific uncertainties
Summary
Overview of major findings from
TexAQS Shift in focus to reactive hydrocarbons
 Impact of findings on air quality policy

Shift in focus to reactive hydrocarbons with a focus
on most reactive hydrocarbons – caps on HRVOC
emissions

Current direction of technical analyses
impacting policy decisions (Highly
Reactive Volatile Organic Compounds,
HRVOCs) Relative importance of annual and short
term limits on HRVOC emissions