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Estimating On-Road Vehicle Emissions Using CONCEPT

Alison K. Pollack

Ralph Morris

ENVIRON International Corporation

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Overview

• WRAP On-Road Emissions Estimates for Regional Haze Modeling

• CONCEPT Overview • CONCEPT MV Inputs Required• CONCEPT MV Emissions Approach & Steps • Summary of Key Differences Between SMOKE

and CONCEPT MV• Denver Example Application and comparison of

SMOKE vs CONCEPT approaches

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On-Road Mobile Emissions Estimates -General Approach

Local Travel Data

Vehicle Miles Traveled (VMT)

and Speed by Roadway Type

VMT Growth Rates

Local ParametersLocal Parameters

TemperatureTemperature

Fuel SpecificationsFuel Specifications

Control ProgramsControl Programs

Vehicle RegistrationVehicle Registration

MOBILE6.2

Generates g/miEmission Factors

X = Emissions

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WRAP On-Road Emissions Estimates(2002, 2008, 2013, 2018)

• Regionally consistent estimation methods• Surveyed State/Local Agencies for Most Up-to-Date

Detailed Inputs– 2002 Base year inputs and VMT– Future year inputs, VMT growth– Unpaved road VMT– Responses were received from all state agencies and key local

agencies

• Estimated County-level Emissions • Emissions Were Processed Using SMOKE

– Spatial allocation using Census TIGER roadway mileage– Temporal allocation of emissions using temporal profiles for activity data

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CONCEPT vs. SMOKE for On-Road Mobile

• SMOKE – Emissions are estimated using county-level activity data– Can use day/hour-specific county average – Useful for areas where detailed link data are not available

• CONCEPT MV – Estimates emissions based on detailed link-based activity

data (VMT and speed) from a Traffic Demand Model – Uses day-specific, grid cell-specific meteorological data– Highly resolved temporal and spatial variation of VMT and

fleet mix

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CONCEPT Overview• Consolidated Community Emissions Processing Tool

– Open Source– Freely Available– Database Management System– Community Support & Enhancements– Balances Transparency/QA and Performance/Integration

with GIS/Spatial Tools– Quality Assurance – Intermediate Tables Output

• Includes all Emissions Source Categories– Point, Area, On/Off-Road Mobile, Biogenics

• Performs same emissions processing as SMOKE– Temporal and Spatial Allocation, CEM Emissions

Processing, Speciation, Growth & Control • Motor Vehicle (MV) Module Estimates Highly Detailed On-

Road Vehicle Emissions

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CONCEPT MV

• Uses output from transportation demand models (TDM)

• Generates gridded, hourly link-level emissions by vehicle class

• Uses 8 MOBILE5 vehicle classes• Detailed temporal resolution of traffic

volume, speeds, and VMT mix • Uses day/hour-specific gridded met data• Stores many intermediate emissions

tables for QA and data review

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TDM Link Inputs to CONCEPT MV

• Endpoint coordinates and projection definition• Volume and capacity

– Typically provided for multi-hour periods for typical weekday, e.g. am peak, midday, pm peak, overnight

• Speeds – Generally free flow speeds are provided– Congested speed is calculated from free flow speed

and volume/capacity ratio for each hour• Roadway type

– MOBILE6 has different emission factors by roadway type

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CONCEPT Temporal Allocation

• CONCEPT disaggregates link data (volume, capacities) for multi-hour periods into hourly volumes and capacities

• Requires hourly total volume profiles by roadway type, month, day of week

• Total volume temporal profiles are developed from analysis of local area automated traffic recorder (ATR) data (available from State DOTs)

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Denver Example Total Volume Temporal ProfilesDenver Hourly Profiles for Urban Interstates

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Denver Hourly Profiles for Urban Principal Arterials

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Denver Day of Week Profiles for Urban Interstates

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Denver Day of Week Profiles for Urban Principal Arterials

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CONCEPT Vehicle Mix Disaggregation

• TDM link volumes are generally total across all vehicle classes

• CONCEPT disaggregates total volume into eight MOBILE5 vehicle classes

• Requires hourly VMT mix profiles by roadway type, month, day of week, hour of day

• VMT mix temporal profiles are developed from analysis of local area vehicle classification recorder data

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Denver Example Vehicle Mix Temporal Profile  Denver Hourly Class Fractions (Sun-Sat) for Interstates, July

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HDDV HDGV LDDT LDDV LDGT1 LDGT2 LDGV MC

HDDV VMT fraction is lower during am and pm peak traffic hours

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CONCEPT MV Steps in Estimation of On-Road Motor Vehicle Emissions

• Temporally allocate VMT to hours• Adjust free flow speeds for congestion• Spatially allocate links to grid cells• Allocate total VMT to 8 MOBILE5 vehicle classes• Run MOBILE6 with grid-specific meteorology• Apply MOBILE6 emission factors using county

inputs for fuel parameters and control programs• Speciate emissions for air quality modeling

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Summary of CONCEPT vs. SMOKE Methods for On-Road Mobile Emissions

SMOKE CONCEPT MV

VMT County-level, by roadway type, by season Link-level, hour-specific, from Transportation Demand Model (TDM), adjusted using hour/day/month temporal profiles from traffic counter data

Speeds EPA national defaults by roadway type and vehicle class if data not submitted by States

Link-specific speeds from TDM, adjusted for congestion using hourly volume/capacity ratio

VMT mix Uniform across all hours, days. Uses EPA national defaults where data not submitted by States

Detailed temporal profiles by hour/day/month from traffic classification monitoring data

Temperature and humidity

Calculates hourly average across all grid cells in each county

Hour- and grid cell-specific temperatures

Temporal allocation Emissions are temporally allocated using EPA default national-level profiles based on activity data

Link-level hourly VMT estimated from link-specific inputs and hour/day/month temporal profiles from local traffic counter data

Spatial allocation County-level emissions are allocated to grid cells using Census TIGER files, smaller roads not included

Link-based emissions are allocated to grid cells based on link coordinates

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Spatial Distribution of VMT for Grid Modeling is Very Different When Link VMT is Used

Link VMT gridded to 1km

VMT distributed across more roads – more detailed spatial coverage

Max VMT = 301

Max VMT = 89

County-level VMT gridded to km

Allocation based on Census TIGER roadway surrogates; creates VMT “hot spots”

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Denver O3 SIP CONCEPT MV Application

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Improved Denver Ozone Performance using CONCEPT MV Link-Based Emissions

• Denver 8-hour ozone Early Action Compact (EAC) SIP (2002-2003) allocated county-level mobile emissions using Census TIGER roadways surrogates– Ozone suppressed in Denver metropolitan area every

day of the episode leading to underprediction bias• New Denver 8-hour ozone SIP modeling using

CONCEPT MV to generate spatially and temporally highly resolved inventory does not exhibit such a large ozone hole– Better distinguishes weekend effect when high ozone

occurs in metropolitan Denver

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• Example 8-h ozone model performance from Denver 8-h ozone EAC SIP modeling

• Ozone “hole” occurs every day

• Modeled ozone “hole” in metropolitan Denver of 55-60 ppb ozone where some observed values > 70 ppb

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• Example 8-h ozone model performance for new Denver SIP modeling using CONCEPT MV (Saturday)

• Model now able to reproduce high ozone in metropolitan Denver

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CONCEPT MV Regional Application: 22 State and Local Networks in LADCO Domain