Within-Week Variability and Long-Term
Trends in Traffic, Power Plant Emissions,
and Ambient CO, NOy and Ozone for the
Charlotte Metropolitan Area
Jennifer L. Perry* and Patrick M. Owens
Department of Chemistry
Winthrop University, Rock Hill, SC 29733
*Current address:
Department of Chemistry, Duke University, Durham, NC 27708
Objectives
Show Charlotte regional growth by traffic
volumes and power plant emissions
Characterize trends in NOy, CO, Hydrocarbon,
and Ozone monitoring data
Understand how traffic and power plant
emission fluctuations within each week affect
pollutant levels
2
Type of Data
Monitoring Site
Interstate I-77
Selected Data
Jun-Aug, 1990-1997
Traffic Counts
South Blvd,
Wilkinson Blvd,
Graham St.
Mecklenburg
County Ambient
Air Monitors
Power Plant
Emission Monitors
(CEM)
May-Sep, 1990-1997
(8-9 AM, 6-7 PM, daily)
Plaza, County Line
O3 : May-Sep, ’90-00
CO: May-Sep, ’93-00
NOy: May-Sep, ’95-00
Hydrocarbons, ’95-99
Arrowwood
O3: May-Sep, ’90-00
Riverbend, Allen
Marshall, Buck
NOx: May-Sep, ’96-00
3
Traffic Locations, Monitoring Sites, & Power Plants
4
Regional NOx Sources
1997 Gaston County Power Plant Emissions
 12,930 tons (Allen)
 3,780 tons (Riverbend)
1996 Mecklenburg County Emissions


17,295 tons (mobile sources)
687 tons (stationary sources)
5
Traffic Sites
Roadway
Tachograph Loc.
Data Available
Interstate 77
SC Welcome Center
Between Exits 88 & 90
June-August 1990-1997
(Hourly data)
South Blvd (Hwy
521)
Between Poindexter &
Marsh @ Pepsi Plant
May-Sept 1990-1998,
(7-8AM, 5-6PM, Daily)
Wilkinson Blvd
(Hwy 29&74)
Remount Rd
Intersection
May-Sept 1990-1998,
(7-8AM, 5-6PM, Daily)
Graham St.
Past Railroad Tracks
@ 12th St.
May-Sept 1990-1998,
(7-8AM, 5-6PM, Daily)
6
I-77 Traffic Volume vs. Time of Day
Hourly Volume
5000
4000
3000
2000
1000
0
Time of Day (Hour)
Sun
Mon
Tues
Thu
Fri
Sat
Wed
7
Avg Hourly NOy
Concentration (ppb)
May-Sep ‘95-‘98 Plaza Average Hourly NOy
40
35
30
25
20
15
10
5
1
3
5
7
9
11
13 15 17
19 21
23
Time of Day
Sunday
Monday
Tuesday
Thursday
Friday
Saturday
Wednesday
8
May-Sep ‘93-‘98 Plaza Average Hourly CO
Avg. Hourly CO
Reading (ppb)
1000
900
800
700
600
500
400
300
200
1
3
5
7
9
11
13
15 17
19 21 23
Time of Day (Hour)
Sunday
Monday
Tuesday
Thursday
Friday
Saturday
Wednesday
9
1990-1998 May-Sep Diurnal Charlotte Ozone Averages
By Day of Week (weekend days-lines, weekdays-markers
10
Day of Week NOx Emissions from Four
% Difference from
7-Day Average
Coal-fired Plants near Charlotte
20
15
10
5
0
-5
-10
-15
-20
-25
Allen
Riverbend
Marshall
Buck
Sun Mon Tue Wed Thu
Fri
Sat
Day of Week
11
Daily Tons NO x Emissions
Coal-fired Power Plant Hourly NOx Emissions
by Day of Week for a Recent Season
55.00
50.00
Sun
45.00
Mon
40.00
Tue
Wed
35.00
Thu
Fri
30.00
Sat
25.00
0
5
10
15
20
Hour of Day
12
Day of Week Variation in Average Noon to Noon BTEX
Levels in Charlotte Aug-Sep ’96 and May-Aug ’97
0.15
Day of Week Variation at Dilworth Urban BTEX
Sampling Site
Day of Week Variation at Fontana Urban BTEX
Sampling Site
0.1
0.15
0.05
0.1
Benzene
0
Toluene
-0.05
Benzene
0.05
Toluene
0
m/p-Xylene
-0.05
-0.1
m/p-Xylene
-0.15
I-77 Traffic
Cts
I-77 Traffic Cts
-0.1
Thu-Sat
Sat-Sun
-0.15
Sun-Thu
Thu-Sat
Sat-Sun
Day of Week Variation at Kennedy Urban BTEX
Sampling Site
Fraction of Diff from 7-Day Avg
Sun-Thu
0.2
Benzene
0.1
Toluene
0
m/p-Xylene
-0.1
I-77 Traffic
Cts
-0.2
-0.3
Sun-Thu
Thu-Sat
Sat-Sun
13
Traffic Growth for I-77 and South
Blvd Locations
6000
5000
4000
3000
2000
1000
0
1990
1991
1992
1993
1994
Year
1995
4000
1996
3500
1997
3000
2500
2000
1500
1000
500
0
1990
1991
1992
1993
1994
1995
1996
1997
1998
Year
Average Hour Traffic
8:00 Traffic
18:00 Traffic
14
32
CO Concentration (ppb)
NOy Concentration (ppb)
7-9 AM Yearly NOy and CO Trends at
County Line and Plaza (Gar ’00) Sites
30
28
26
24
22
20
700
600
500
400
300
1993 1994 1995 1996 1997 1998 1999 2000
1995
1996
1997
1998
1999
2000
Year
Year
County
Plaza
County
Plaza
15
May-Sep Mecklenburg County Ozone Trends
0.07500
0.07000
0.06500
0.06000
0.05500
0.05000
0.04500
1990
1992
1994
1996
1998
2000
Year
County Line
Arrowwood
Plaza
16
NOx Emission Trends from the two Coal-fired
Power Plants, Allen and Riverbend, near Charlotte
80.00
Avg Tons NO x / Day
70.00
60.00
1996
50.00
1997
40.00
1998
1999
30.00
2000
20.00
10.00
0.00
June
July
Aug
Jun-Aug May-Sep
17
9000.00
5.50
8000.00
5.00
4.50
7000.00
4.00
6000.00
3.50
5000.00
3.00
4000.00
2.50
3000.00
2.00
1996
Tons NOx emissions
1997
1998
1999
GigaWatt-Hours
Lbs NOx / Megawatt-hr
NOx emissions + GigaWatt-Hours
Long-term Trends for Allen & RB NOx Emissions,
Power, and Emissions per Unit of Power
2000
Lbs NOx/Mwt-hr
18
’95-’99 AM Hydrocarbon Reactivity-weighted
Concentration Trends for the Plaza Site
135
MIR * Concentration (ppbC)
120
105
90
75
60
45
30
15
0
PAMS Tot.
Paraffins
1995
1996
Olefins
1997*
1998
Aromatics
1999
19
’95-’99 AM NMOC/NOy Ratios for the
Plaza Monitoring Site
20
NOx Limited
NMOC/NOy
15
10
VOC Limited
5
0
1994
1995
1996
1997
1998
1999
2000
20
Reading / 7 Day Average
7-8 AM Within Week Fluctuations for NOy,
CO and Traffic Data
1.4
1.2
1
0.8
0.6
0.4
0.2
Sun
Mon
NOy
CO
Tue-Fri
Sat
Traffic
21
Reading / 7 Day Average
May-Sep 1990-1998 Within Week Ozone Averages for
the three Mecklenburg County Monitors
1.05
1.03
1.01
0.99
0.97
0.95
Sun
County Line
Mon
Tue-Fri
Arrowwood
Sat
Plaza
22
P-Values for Day of Week Comparisons of Traffic,
Ambient Pollutants, and Power Plant NOx Emissions
Days
Traffic
CO
NOy
Ozone
Power
NOx
Su/Tu-Fr
0
0
0
0.3373
0
Mo/Tu-Fr
0.7488
0.9473
0.0381
0.3484
0.0023
Sa/Tu-Fr
0
0.0012
0
0.4683
0.0025
23
Conclusions
AM CO and NOy ambient concentrations
correlate well with observed traffic patterns



Weekend AM levels much lower than weekdays
Monday AM CO comparable to other weekdays
Monday AM NOy lower than other weekdays
Within week power plant NOx emissions




Tues-Fri 10% above 7-day average
Mon & Sat 7.5% below 7-day average
Sun 19% below 7-day average
Monday AM NOx lowest in week; low Monday AM
NOy ambient levels may be due to this
24
Conclusions
Total Power Plant NOx emissions from Allen
and Riverbend Power Plants are stable



From 1996-2000, power generated during May-Sep
by the two Gaston Co. plants increased 27%.
From 1996-2000, NOx emissions per unit of power
decreased 20%.
From 1996-2000, total NOX emissions from Allen
and Riverbend increased 4%.
25
Conclusions
Hydrocarbon Trends


From 1997-1999, average AM Hydrocarbons
levels at Plaza decreased
The Charlotte metropolitan region appears
to be a VOC-limited area

1995-1999 Plaza AM VOC/NOy ratios are
primarily between four and eight.
Ozone within week variation:

Weekend ozone levels in Mecklenburg
County are equivalent to weekday levels
26
Recommendations
For the city of Charlotte, implement ozone control
measures that reduce ambient VOC levels
Replace the use of ozone action days with
practices to be implemented throughout ozone
season
Evaluate the use of total NOx emissions budgets
for all power plants in the Charlotte region
27
Acknowledgements
North Carolina Division of Air Quality (Steve Few, Brian
Timin)
Winthrop University students (Gentry Ridgeway and Steve
Hudson)
City of Charlotte Department of Transportation (Charles
Able)
South Carolina Department of Transportation (Joe Boozer)
Duke Energy (Buddy Davis and Kris Knudsen)
28