Charlotte-Rock Hill-Gastonia MSA Summertime Ozone Formation

Photos from 2001 Mecklenburg Country State of the Environment Report

2

Arizona’s Valley of the Sun “Brown Cloud”

• Observed since early 1990’s; contains C Particles and NO2

(brown) gas

• From burning fossil fuels: cars, construction equipment, power plants, lawn mowers, leaf blowers contribute to this brown cloud

• Weather also a key factor

Phoenix photo from http://phoenix.about.com/library/weekly/uc051601a.htm, accessed Mar 2004

3Image take from http://www.al.noaa.gov/WWWHD/Pubdocs/TropoRural.html, accessed Mar 2004

4

Presence of NO2 (brown gas) results in inevitable formation of ozone

NO2 (brown) + sunlite NO• + O•

O• + O2 O3 (Ozone)

•Control measures to effectively address ground-level ozone must focus on minimizing NO2 formation

5

Ozone precursorsNitrogen Oxides

•Dry Air is 78% Nitrogen (N2), 21% Oxygen (O2)

•Heating air to high temperatures forms NO• (motor vehicles, fossil-fuel power plants, lightning)

• NO• is an ozone precursor and also reacts directly with ozone to destroy it

Volatile Organic Compounds (VOC’s)•VOC’s continuously emitted by fuel spills, motor vehicles, trees, air fresheners, paints, and countless other sources

•OH• hydroxyl radical is the atmosphere’s “natural detergent” that cleans VOC’s from the air by initiating the process that converts them into carbon dioxide and water

6

Volatile Organic Compound (VOC) RemovalAir’s natural VOC cleanser produced from ozone and

water

•Ozone (O3) + UV-B -> O2+ *O•

*O• + H2O 2OH•

•OH• works by transforming stable VOC molecules (R-H) into reactive radicals (R•)

OH• + R-H R• + H2O

•Reactive organic radicals immediately combine with oxygen to form peroxide radicals

R• + O2 (R-O-O•)

7

Formation of Nitrogen Dioxide

NO• + R-O-O• NO2• + RO•

Formation of NO2 (and O3) driven primarily by:

•Concentration of VOC’s (near emission sources)

•Concentration of NO• (rural & downwind areas)

•Concentrations of both NO• and VOC’s

***Summertime ozone pollution results from an overload in our air of NO•, VOC’s, or both

8

NO and VOC Effects on Ozone Production

NO•

Sensitive

Region

VOC

Sensitive

Region

Both NO• + VOC Sensitive

Both NO• + VOC Sensitive

Figure from : http://www-personal.engin.umich.edu/~sillman/ozone.htm, accessed Mar 2004

9

’95-’99 AM NMOC/NOy Ratios for the Plaza Monitoring Site

0

5

10

15

20

1994 1995 1996 1997 1998 1999 2000

NM

OC

/NO

y

NOx Limited

VOC Limited

From Perry, JL and Owens, PM, “Weekday/Weekend Variability and Long-Term Trends in Traffic, CO,

NOy, and Ozone for the Charlotte Metropolitan Area during the 1990's, AWMA, June 2001

10

I-77 Traffic Volume vs. Time of Day

0

1000

2000

3000

4000

5000

Time of Day (Hour)

Ho

url

y V

olu

me

Sun Mon Tues Wed

Thu Fri Sat

From Perry and Owens, AWMA, 2001

11

5

10

15

20

25

30

35

40

1 3 5 7 9 11 13 15 17 19 21 23

Time of Day

Avg

Ho

url

y N

O y

Co

nce

ntr

atio

n (

pp

b)

Sunday Monday Tuesday Wednesday

Thursday Friday Saturday

May-Sep ‘95-‘98 Plaza Average Hourly NOy

From Perry and Owens, AWMA, 2001

12

1990-1998 May-Sep Diurnal Charlotte Ozone Averages

By Day of Week (weekend days-lines, weekdays-markers County Line

0

0. 01

0. 02

0. 03

0. 04

0. 05

0. 06

0. 07

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 2122 23

Arrowwood

0

0. 01

0. 02

0. 03

0. 04

0. 05

0. 06

0. 07

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 2122 23

Plaza

0

0. 01

0. 02

0. 03

0. 04

0. 05

0. 06

0. 07

1 2 3 4 5 6 7 8 9 10 11 12 13 1415 16 17 18 19 2021 22 23

From Perry and Owens, AWMA, 2001

13Obtained from John White, NC DAQ

14From: http://www.epa.gov/airnow/showmaps.html?/airnow/2000/20000601/8p-ncsc.gif, accessed Mar 2004

15From: http://www.epa.gov/airnow/showmaps.html?/airnow/2000/20000601/8p-ncsc.gif, accessed Mar 2004