DRAFT Mobile sensitivity How sensitive is the air quality model to changes in VMT? Mike Abraczinskas, Laura Boothe, George Bridgers, Phyllis Jones, Vicki Chandler, Ming Xie, Wyat Appel NC Division of Air Quality Attainment Planning Branch September 30, 2004

Objective Show how the air quality model (ozone) responds to changes in VMT –Changes relative to current emissions –Changes relative to future emissions –In this study Current = 2000 Future = 2007 Modeling System and Episode –MM5, SMOKE, CMAQ modeling system –June 12-15, 1997 (4 day episode)

Background 2002 VMT were submitted to VISTAS for base case modeling In select counties where no TDM VMT was provided, but where TDM data will be available in the future… a factored universe file VMT number was used The factor – a 30% increase – was based on past differences showing that TDM VMT is usually about 30% higher than VMT from the NCDOT universe file.

Domain Reductions/increases were applied to counties in Red

Current year sensitivities 2 sensitivity runs were completed to provide some indication on how predicted ozone concentrations would change if current year VMT estimates were off by 10%. 1.Current year (w/ a 10% reduction in VMT) 2.Current year (w/ a 10% increase in VMT)

Test 1 10 % reduction in VMT relative to current year (2000)

Ozone

10 % reduction in VMT relative to current year (2000) Ozone

10 % reduction in VMT relative to current year (2000) Ozone

10 % reduction in VMT relative to current year (2000) Ozone

10 % reduction in VMT relative to current year (2000) Impacts on ozone DVFs 6 of 36 NCDAQ monitoring sites experienced changes in DVFs (a rigorous application of the USEPA attainment test across the 4-days modeled, 4 km domain only) Recall: DVF = RRF*DVC RRF = future/current –In this sensitivity, only the denominator of the RRF changes MonitorCountyDelta DVF (ppb) –RockwellRowan 1 ppb –Duke StDurham 1 ppb –SophiaRandolph 1 ppb –FarmvillePitt 1 ppb –WadeCumberland 1 ppb –TaylorsvilleAlexander 1 ppb

10 % reduction in VMT relative to current year (2000) DVF Change < 1 ppb

Test 2 10 % increase in VMT relative to current year (2000)

Ozone

10 % increase in VMT relative to current year (2000) Ozone

10 % increase in VMT relative to current year (2000) Ozone

10 % increase in VMT relative to current year (2000) Ozone

10 % increase in VMT relative to current year (2000) Impacts on ozone DVFs 10 of 36 NCDAQ monitoring sites experienced changes in DVFs (a rigorous application of the USEPA attainment test across the 4-days modeled, 4 km domain only) DVF Change < 1 ppb DVF Change > 1 ppb

Future year sensitivities 2 sensitivity runs were completed to provide some indication on how predicted ozone concentrations would change if future year VMT estimates were off by 20%. 1.Future year (w/ a 20% reduction in VMT) 2.Future year (w/ a 20% increase in VMT)

Test 3 20 % decrease in VMT relative to future year (2007)

Ozone

20 % decrease in VMT relative to future year (2007) Ozone

20 % decrease in VMT relative to future year (2007) Ozone

20 % decrease in VMT relative to future year (2007) Ozone

20 % decrease in VMT relative to future year (2007) Impacts on ozone DVFs 16 of 36 NCDAQ monitoring sites experienced changes in DVFs (a rigorous application of the USEPA attainment test across the 4-days modeled, 4 km domain only) Recall: DVF = RRF*DVC RRF = future/current –In this sensitivity, only the numerator of the RRF changes 2 locations showed an ozone DVF change of 2 ppb 14 locations showed an ozone DVF change of 1 ppb

Test 4 20 % increase in VMT relative to future year (2007)

20 % increase in VMT relative to future year (2007) Impacts on ozone DVFs 16 of 36 NCDAQ monitoring sites experienced changes in DVFs (a rigorous application of the USEPA attainment test across the 4-days modeled, 4 km domain only) Recall: DVF = RRF*DVC RRF = future/current –In this sensitivity, only the numerator of the RRF changes 5 locations showed an ozone DVF change of 2 ppb 11 locations showed an ozone DVF change of 1 ppb

Caveats Thorough QA is not complete Only 4 days were analyzed –Additional days may alter the preliminary conclusions Significance of impact will depend on predicted future ozone Additional analysis is needed

Preliminary Conclusions VMT changes of +/- 10% in the current year modeling will have a minor impact on ozone future design values VMT changes of +/- 20% in the future year modeling will have more of an impact on ozone future design values

Preliminary Conclusions Additional investigations could include: –Generation of additional metrics frequency of changes daily RRF changes –Additional episodes to include a greater variety of meteorological conditions Additional days may alter the conclusions Additional analysis is needed.

Questions/Comments