1Link-based vs NEIOn-road Emissions ImpactOn Air Quality Model Predictions2008 Emission Inventory ConferenceSession 11- Mobile SourcesPortland, OregonJune 5, 2008Madeleine Strum, Karen Wesson, Sharon Phillips – EPA OAQPSDavid Brzezinski, Harvey Michaels, Rich Cook – EPA OTAQAlison Pollack, Michele Jimenez, Stella Shepard - ENVIRONAllan Beidler, Melanie Wilson, Computer Sciences Corporation2Purpose• Compare AQ Model-ready link-based on-roademissions from CONCEPT MV with NEI– NEI is county-level, used less accurate data– CONCEPT MV is link-based, hourly, gridded• Quantify/understand differences in VMT,emissions, spatially and temporally using Detroitdata• Determine differences in modeled concentrationsand impact of data inputs versus method3Comparison ofEmission Estimation ApproachesLocal data from MPOLink-specific speeds, by hourHour and grid-specifictemperatures from 12km metdata used for AQ modelingDetailed temporal profiles byhour/day/month from trafficclassification monitoring dataLink-level, hour-specific, fromTransportation DemandModel, adjusted usinghour/day/month temporalprofiles from traffic counterdataCONCEPT MVSame as NEIUniform across all hours,days. County database:uses national defaults wheredata not submitted by State.VMT mixLocal data from MPO as inCONCEPT MVCONCEPT speed bindistribution, VMT weightedby roadway type and hourVMT-weighted by county(across gridded met datawithin each county)Uses CONCEPT daily totalsNMIM w/ CONCEPTInputsCounty database: usesnational defaults where datanot submitted by StateCounty database: usesnational defaults where datanot submitted by StateMonthly average 24-hrtemperature by county fromNWS dataCounty-level, monthly, byroad type; either provided byState or allocated to countyfrom MSA-level VMT usingpopulationNEIOther M6inputsSpeedTemperatureVMT4NEI Processing forAQ Modeling• Processed county-level monthly emissions for AQmodeling using SMOKE:– Spatially allocated using miles of roadway (orpopulation for local roads)• 12 km grid cells for CMAQ• 1 km grid cells for AERMOD– Temporally allocated from monthly to day-of-week andhour of day using temporal profiles– Speciated emissions for use in photochemical model5CONCEPT MVLink-Based MethodLink-level VMT and speeds from SEMCOG transportationdemand model (TDM)– VMT and speed on ~15,000 links,by period of daySEMCOG Roadway Network6Link vs NEI Comparisons: Detroit• Link emissions based on CONCEPT MV forcomparison to NEI:– Estimated for seven-county SEMCOGtransportation network– One representative week for each of four seasons3⁄4January, April, July, October 2002– Emissions estimated for 8 MOBILE5 vehicle classes– Results were used to estimate monthly andannualized emissions7County-level VMT Similar –Michigan Provided VMT Inputs to NEI

Annual VMT (millions)NEI05,00010,00015,00020,00025,000 L i vi n gst o n M a c omb Mon ro e O akl a n d St. Clair Wa s htena w W a yn eLINKNEI8Spatial Distribution of VMT for GridModeling is Very Different WhenLink VMT is UsedLink VMT gridded to 1kmVMT distributed across moreroads – more detailed spatialcoverageMax VMT= 301Max VMT= 89NEI County VMT gridded to1kmAllocation based on CensusTIGER roadway surrogates;creates VMT “hot spots”9Hourly Temporal Allocationfor AQ Modeling is DifferentWhen using the NEI,SMOKE temporally allocatesmonthly emissionsto day-ofweek and hour-of-day.Example:Monday Benzene for UrbanInterstates, April-200,000400,000600,000800,0001,000,0001,200,0001,400,0001,600,0000 2 4 6 8 10 12 14 16 18 20 22 24Hour

VMTHDDVHDGVLDGTLDGVLDDTLDDVMCCONCEPT temporally allocatesVMTfor different time blocks ofthe day to hourly based onanalysis of traffic counter dataExample:Monday VMT for Urban Interstates, April0.0000.0200.0400.0600.0800.1000.1200.1400 2 4 6 8 10 12 14 16 18 20 22Hour

Tons Benzene10In CONCEPT VMTMix Varies by HourHDDV VMT fraction is lower during am and pm peak traffic hoursSEMCOG Freeway VMT Mix by Hour of Day - Weekdays0%10%20%30%40%50%60%70%80%90%100%1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28Hour of Day

Percent of Total VMTMCHDDVHDGVLDDTLDGT 3&4LDGT 1&2LDDVLDGVNEI Average11NEI Benzene EmissionsHigher Than Link0100200300400JANUARY APRIL JULY OCTOBER

Benzene (Tons)LinkNEISum across 7 Counties17%29%26%50%Differences most likely dominated by differences in the MOBILE6inputs. Differences due to methodology appear to be small.Much closer when NMIMis run with Local InputsOne day/month05101520January April July OctoberLINKNMIM-w/local inputs12Other Pollutants Emissions –NEI Greater Than Link0%5%10%15%20%25%30%35%40%45% Acet a ldehyde Benzene Butadiene Forma l dehyde Tol uen e PM2.5

Percent difference from link13Reasons for Higher Emissions• Other than VMT, inputs to NEI were nationaldefaults and didn’t match the local inputs used inthe link based approach• Speeds – speed values and spatial distribution• Temperatures – County/monthly average profilesversus day-hour and grid cell-specific• These and further differences (e.g., agedistribution) are currently being investigated14Link Based Emissions Have LittleImpact on 12 km Model Evaluation8 hr Ozone: Macombcounty site - 260990009observed8 hr Ozone Macomb county site - 260990009Daily PM2.5 Wayne county site – 261630001observed15Total Benzene Gridded to 1 km(On-road Sector is 66% of Total Emissions)using NEI on-road using link-based on-road26tons5tonsNEI on-road emissionsgridded using Census TIGERroadways surrogatesOn-road emissionsfrom CONCEPT MV(gridded link-based)16CMAQ results Benzene12 km Annual Average.398.329.26.191.121.052-.017-.086-.1552.0480.121.8071.5661.3251.0840.8430.6020.361NEI Benzene ug/m3(NEI – Link) Benzene ug/m3LargestNegativeDifference relates to theNEI underestimating risk by 1 in a million(NEI 16; Link 15)LargestPositiveDifference relates to the NEIoverestimating risk by 3 in a million (NEI 14;Link 11)Orange/RedCells:Risk is 12-16 in a millionRisk computed based onconcentration * Unit Risk Estimate(URE)Benzene URE =0.0000078(1/[ug/m3])Differences vary across grid cells17Benzenerisk differences:NEI – link-1.2 to -.255-.255 to -.17-.17 to .529.529 to 1.261.26 to 3.1Link ConcentrationsAre Higher Than NEI for Cellswith Few Major Roads18Conclusions• Compared NEI to CONCEPT/TDM (link) for Detroit Area:– VMT: totals are similar– Emissions: NEI benzene roughly 20% higher (across 7-countyarea)– Concentrations: vary over geographic regions, maximumbenzene differences caused 1-3 ina million change in risk (fromNEI base of roughly 12-16 in a million)• Differences in aggregate emissions are primarily due toinputs, not methods• Use of NEI could result in inaccurate representation ofspatial distribution of certain pollutants due to the spatialallocation approach for the emissions• No significant differences inmodel performance betweenno link and link methods at 12 km resolution for ozone,PM2.5, toxics. Expect to see differences at finerresolution.19Next Steps• Perform analyses for more pollutants• Isolate MOBILE6 input parameters of importance• Run AERMOD at1 km resolution and comparefine scale modeling results• Run 1 km resolution through exposure andbenefits models and compare results to 12 km