1. 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

2. 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

3. Type of Data Monitoring Site Selected Data Traffic Counts
Interstate I-77
Jun-Aug,
South Blvd, Wilkinson Blvd, Graham St.
May-Sep,
(8-9 AM, 6-7 PM, daily)
Mecklenburg County Ambient Air Monitors
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
Power Plant Emission Monitors (CEM)
Riverbend, Allen
Marshall, Buck
NOx: May-Sep, ’96-00

4. Traffic Locations, Monitoring Sites, & Power Plants

5. Regional NOx Sources 1996 Mecklenburg County Emissions
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)

6. Traffic Sites

7. I-77 Traffic Volume vs. Time of Day
5000
4000
3000
Hourly Volume
2000
1000
Time of Day (Hour)
Sun
Mon
Tues
Wed
Thu
Fri
Sat

8. May-Sep ‘95-‘98 Plaza Average Hourly NOy40 y 35 30 25
Avg Hourly NO
Concentration (ppb) 20 15 10 5 1 3 5 7 9 11 13 15 17 19 21 23
Time of Day
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday

9. May-Sep ‘93-‘98 Plaza Average Hourly CO
1000
900
800
700
Avg. Hourly CO
Reading (ppb)
600
500
400
300
200 1 3 5 7 9 11 13 15 17 19 21 23
Time of Day (Hour)
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday

10. 1990-1998 May-Sep Diurnal Charlotte Ozone Averages
By Day of Week (weekend days-lines, weekdays-markers

11. Day of Week NOx Emissions from Four Coal-fired Plants near Charlotte20 15 10 5
Allen
% Difference from
7-Day Average -5
Riverbend
-10
Marshall
-15
Buck
-20
-25
Sun
Mon
Tue
Wed
Thu
Fri
Sat
Day of Week

12. Coal-fired Power Plant Hourly NOx Emissions by Day of Week for a Recent Season
55.00
50.00
Emissions
Sun
45.00
Mon x
40.00
Tue
Wed
35.00
Daily Tons NO
Thu
Fri
30.00
Sat
25.00 5 10 15 20
Hour of Day

13. Day of Week Variation in Average Noon to Noon BTEX Levels in Charlotte Aug-Sep ’96 and May-Aug ’97
Day of Week Variation at Dilworth Urban BTEX
Day of Week Variation at Fontana Urban BTEX
Sampling Site
0.15
Sampling Site
0.1
0.15
0.05
0.1
Benzene
0.05
Benzene
Toluene
-0.05
Toluene
m/p-Xylene
-0.05
I-77 Traffic Cts
-0.1
m/p-Xylene
-0.1
-0.15
I-77 Traffic
-0.15
Sun-Thu
Thu-Sat
Sat-Sun
Cts
Sun-Thu
Thu-Sat
Sat-Sun
Day of Week Variation at Kennedy Urban BTEX
Sampling Site
0.2
Benzene
0.1
Toluene
Fraction of Diff from 7-Day Avg
m/p-Xylene
-0.1
I-77 Traffic
Cts
-0.2
-0.3
Sun-Thu
Thu-Sat
Sat-Sun

14. Traffic Growth for I-77 and South Blvd Locations
6000
5000
4000
3000
2000
1000
4000
1990
1991
1992
1993
1994
1995
1996
1997
3500
Year
3000
2500
2000
1500
1000
500
1990
1991
1992
1993
1994
1995
1996
1997
1998
Year
Average Hour Traffic
8:00 Traffic
18:00 Traffic

15. 7-9 AM Yearly NOy and CO Trends at County Line and Plaza (Gar ’00) Sites

16. May-Sep Mecklenburg County Ozone Trends
1990
1992
1994
1996
1998
2000
Year
County Line
Arrowwood
Plaza

17. NOx Emission Trends from the two Coal-fired Power Plants, Allen and Riverbend, near Charlotte
80.00
70.00
60.00
/ Day
1996
50.00 x
1997
40.00
1998
Avg Tons NO
1999
30.00
2000
20.00
10.00
0.00
June
July
Aug
Jun-Aug
May-Sep

18. Long-term Trends for Allen & RB NOx Emissions, Power, and Emissions per Unit of Power
5.50
5.00
4.50
/ Megawatt-hr
emissions + GigaWatt-Hours
4.00
3.50 x
3.00
Lbs NO
2.50 x NO
2.00
1996
1997
1998
1999
2000
Tons NOx emissions
GigaWatt-Hours
Lbs NOx/Mwt-hr

19. ’95-’99 AM Hydrocarbon Reactivity-weighted Concentration Trends for the Plaza Site

20. ’95-’99 AM NMOC/NOy Ratios for the Plaza Monitoring Site20 NO
Limited x 15 y
NMOC/NO 10
VOC Limited 5
1994
1995
1996
1997
1998
1999
2000

21. 7-8 AM Within Week Fluctuations for NOy, CO and Traffic Data
1.4
1.2 1
0.8
Reading / 7 Day Average
0.6
0.4
0.2
Sun
Mon
Tue-Fri
Sat
NOy CO
Traffic

22. May-Sep 1990-1998 Within Week Ozone Averages for the three Mecklenburg County Monitors
1.05
1.03
1.01
Reading / 7 Day Average
0.99
0.97
0.95
Sun
Mon
Tue-Fri
Sat
County Line
Arrowwood
Plaza

23. 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
0.3373
Mo/Tu-Fr
0.7488
0.9473
0.0381
0.3484
0.0023
Sa/Tu-Fr
0.0012
0.4683
0.0025

24. 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

25. Conclusions
Total Power Plant NOx emissions from Allen and Riverbend Power Plants are stable
From , power generated during May-Sep by the two Gaston Co. plants increased 27%.
From , NOx emissions per unit of power decreased 20%.
From , total NOX emissions from Allen and Riverbend increased 4%.

26. Conclusions Hydrocarbon Trends Ozone within week variation:
From , average AM Hydrocarbons levels at Plaza decreased
The Charlotte metropolitan region appears to be a VOC-limited area
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

27. 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

28. 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)