Simple Chemical modeling of ozone sensitivity to NOx and VOCs in Atlanta

Jin Liao EAS 6410

04/24/2007

Outline

1.Introduction

2. Troposphere ozone production mechanism in urban region

3. Simple Chemical modeling of ozone sensitivity to NOx and VOCs in Atlanta

4. Modeling result and ozone control in Atlanta

5. Conclusion

The importance to control ozone in Atlanta

Tropospheric Ozone :1. Cause photochemical smog, toxic to ecosystem, destroy material such as rubber… Increase ground-level2. A primary source of hydroxyl radicals ozone concentration3. Greenhouse gas

Ozone ---- one of the U.S. EPA’s six criteria pollutants and is regulated by a National Ambient Air Quality Standard.

Atlanta---One of 77 nonattainment areas in former U.S. EPA standardThe new U.S. EPA standard is more stringent.

The budget of ozone in Troposphere

500-1500Dry Deposition

300-4200Chemical loss

3400-5700Sinks

400-1100Transport from Stratosphere

300-4600Chemical Production

3400-5700Sources

Tg O3 yr-1

Global models of tropospheric chemistry in a three-dimensional frame-work to estimate tropopheric O3 budget

Chemical Production = Chemcial LossModel only considerChemical Process

Troposphere O3 Production and Loss Mechanism in Urban Region

The emissions of NO and VOCs from the surface drive this cycle to produce o3.

To control the local ozone concentration, it is necessary to quantify the ozoneconcentration relative to NOx and VOCs concentration.

Emission

HNO3

Emission

Ozone

NO

NO2 OH

HO2 VOCs

hv

hv

Simple Chemical modeling of ozone sensitivity to NOx and VOCs in Atlanta

Basic modeling conception:1. Only consider chemical production and loss reaction processes2. We can determine the maximum ozone concentration with initial NOx ,VOCs concentrations and photolysis rate

Input File(reaction mechanism and reaction rates)

Process(solves differential equations)

MATLAB

Acuchem

Output File(species concentration VS. reaction time)

Peak Ozone concentration Isopleths

This input file includes 37 chemical reactions for ozone formation and loss.

The photolysis rates for Atlanta come from http://cprm.acd.ucar.edu/Models/TUV/Interactive_TUV/.Other reaction rates come from IUPAC : http://www.iupac-kinetic.ch.cam.ac.uk/ (John H. Seinfeld et al.,1998) Atmospheric chemistry and physics

The unit of photolysis rate : min-1 The unit of other reaction rates : ppm-1min-1.

The initial concentration for NOx :0.01ppm~ 0.2ppm The initial concentration for VOCs :0~2ppmC. CH4 concentration : 1.7ppm CO concentration : 0.3ppm.

The Integration Tolerance : 10-8. The reaction time for every cases changes from 5000~106mins.

0.02 0.02

0.0

60.0

6

0.0

8

0.1

NOx(ppm)

VO

Cs(

ppm

C)

Peak Ozone Mixing Ratio Isopleths

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

NOx limited region

VOCs limited region

(ppm)Atlanta

NOx concentration in Atlanta 2003~2005

Cited from Georiga Department of Natural Resources Ambient Monitoring Program 2003~2005 annual reports

0.03290.69381792005

0.03290.79584072004

0.03360.62684832003

Annual Arithmetic Mean (ppm)

1st Max (ppm)Hours measuredYear

Oxides of Nitrigen concentration in Atlanta

(fulton county)

VOCs concentration in Atlanta from 2003 to 2005

VOCs concentration:2003: ~95ppb2004:~110ppb2005:~165ppb

Isoprene is by far the largest contributor to ozone formation at every site.

VOCs(ppmc)=VOCs(ppm) * 5( for isoprene)Georiga Department of Natural Resources Ambient Monitoring Program 2005 report

0.02 0.02

0.0

60.0

6

0.0

8

0.1

NOx(ppm)

VO

Cs(

ppm

C)

Peak Ozone Mixing Ratio Isopleths

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

NOx limited region

VOCs limited region

(ppm)Atlanta

Compare modeling ozone concentration to the measurement

Cited from Georiga Department of Natural Resources Ambient Monitoring Program 2005 annual report

Ozone concentration control in Atlanta

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 0.05 0.1 0.15 0.2 0.25

NOx(ppm)

Ozo

ne(p

pm)

Ozone

Ozone control in Atlanta is in the NOx limited region.

Peak ozone concentration can be reduced to from about 0.09ppm to 0.08ppm by decrease NOx concentration from 0.03ppm to 0.02ppm.

Peak ozone concentrations depend ondifferent NOx levels with VOCs in 0.8ppmC

Conclusion

1.The modeling result of peak ozone isopleths plot of Atlanta makessense for ozone production is suppressed by the relationship between VOCs and NOx concentrations indicated in the chemical mechanism.

2. According to the modeling result and the measurement of NOx,VOCs concentration in Atlanta, ozone control in Atlanta is in the NOx- limited region .

3. There are also some uncertainties in the modeling and result.(1) Software(2) Modeling: only consider chemical process(3) Measurement of NOx, VOCs and photolysis rates(4) Detail VOCs compounds in Atlanta