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-level 2. A primary source of hydroxyl radicals ozone concentration 3. 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 standard The new U.S. EPA standard is more stringent.

The budget of ozone in Troposphere Global models of tropospheric chemistry in a three-dimensional frame-work to estimate tropopheric O3 budget 500-1500 Dry Deposition 300-4200 Chemical loss 3400-5700 Sinks 400-1100 Transport from Stratosphere 300-4600 Chemical Production Sources Tg O3 yr-1 Chemical Production = Chemcial Loss Model only consider Chemical Process

Troposphere O3 Production and Loss Mechanism in Urban Region Emission HNO3 Ozone NO NO2 OH HO2 VOCs hv 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 ozone concentration relative to NOx and VOCs concentration.

Simple Chemical modeling of ozone sensitivity to NOx and VOCs in Atlanta Basic modeling conception: Only consider chemical production and loss reaction processes We can determine the maximum ozone concentration with initial NOx ,VOCs concentrations and photolysis rate Acuchem Input File(reaction mechanism and reaction rates) Process(solves differential equations) Output File(species concentration VS. reaction time) MATLAB 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.

Atlanta (ppm) NOx limited region VOCs limited region

NOx concentration in Atlanta 2003~2005 0.0329 0.693 8179 2005 0.795 8407 2004 0.0336 0.626 8483 2003 Annual Arithmetic Mean (ppm) 1st Max (ppm) Hours measured Year Oxides of Nitrigen concentration in Atlanta (fulton county) Cited from Georiga Department of Natural Resources Ambient Monitoring Program 2003~2005 annual reports

VOCs concentration in Atlanta from 2003 to 2005 2003: ~95ppb 2004:~110ppb 2005:~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

Atlanta (ppm) NOx limited region VOCs limited region

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 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 on different NOx levels with VOCs in 0.8ppmC

Conclusion 1.The modeling result of peak ozone isopleths plot of Atlanta makes sense 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. Software Modeling: only consider chemical process Measurement of NOx, VOCs and photolysis rates (4) Detail VOCs compounds in Atlanta