A HAPEM Update andExposure Efforts in our Current Air Toxic Program
Air Toxics Workshop IIAir Toxics Research: Implications of Research on Policiesto Protect Public Health
Houston, TX
June 12, 2007
Ted Palma,, USEPA, Office of Air Quality Planning and Standards, RTP, NCChad Bailey USEPA, 2Office of Transportation and Air Quality, U.S. EPA, Ann Arbor, MI
Exposure Efforts in our Current Air Toxic Program
Air Toxic Program transition from emission based towards risk based Initial program assessments are focusing on chronic cancer and non-cancer
inhalation exposure We are also now beginning to look at acute & multimedia exposures
Residual Risk Assessment Exposure and risk assessments at facility level to evaluate remaining risk after
technology MACT standards implemented Need to determine both Maximum Individual Risk (MIR) and population exposure
(human and ecological)
Other National Rules MSAT - February 2007
National/Urban/Local Assessments National Air Toxic Assessment (NATA) City/Neighborhood scale exposure and risk assessments Personal monitoring studies
Overview of Exposure Models
Simple HEM3 (Inhalation with no activity patterns) HAPEM6 (Inhalation with activity patterns) HHRAP (Multipathway tool)
Complex APEX (Inhalation with activity patterns) SHEDS (Inhalation – ORD tool) TRIM.Fate TRIM.Expo
Inhalation Ingestion
Human Exposure Model (HEM3)
a tool that combines a dispersion model (ISCST or AERMOD) with 2000 census data to predict population exposure
Model does NOT account for human activity pattern Assumes everyone lives at census block centroid for
entire exposure period Exploring residency times (less than 70 year)
Being utilized in current Residual Risk Assessments Latest version released May 2007 on FERA
What is The Hazardous Air Pollutant
Exposure Model (HAPEM)?
Screening-level exposure model Long-term inhalation exposures General population, or a specific sub-population Urban to national scale Version 5
HAPEM5 - Exposure model component of the 1999 National Air Toxics Assessment (NATA)
Version 6 (release January 2007) HAPEM6 - Mobile Source Air Toxic Rule
includes near roadway effects
Overview of HAPEM
Six primary sources of information Population data (model supplied)
2000 census for 6 demographic groups at the tract level (66,301 tracts) nationwide (also PR and VI)
Activity Data (model supplied) CHAD
Microenvironmental (ME) Data (model supplied)
Tract-to-tract commuting probability data derived from 2000 census commute file (model supplied)
Residence and Workplace relationship to roadway data (model supplied)
Near major roadway residential/business file developed nationally for each census tract – 75m and 200m from 4 lane roadway
Air Quality Data (user supplied)
Plans for HAPEM
Updates Census block and block group resolution Seasonal and monthly air quality Fix random seeds (for sensitivity and
reproduction) Regulatory Uses
NATA Community Scale projects Criteria Reviews?
Air Pollutant Exposure Model (APEX)
Refined inhalation exposure modeling Used to model both criteria and air toxics at urban scale Acute to chronic exposures User selects number and types of microenvironments to be included,
selection of time period of interest, use of either monitored ambient data or values provided from dispersion model
Models individuals (instead of cohorts) that meet population profile Sub-Census tract resolution; accepts point estimates or distributions for
most inputs; includes temperature variation across study area; can build lifetime exposure profile
Can use either a mass balance approach or ME factor based approach to estimate indoor or in-vehicle concentrations
Programmers and Users Guide Case Study available Runs on PC Available on FERA
TRIM.FaTE(Fate, Transport &
Ecological Exposure)
TRIM.Risk (Risk
Characterization)
Farm Food Chain
Quantitative risk & exposure characterization, U/V, assumptions, limitations, …
FaTE LibraryPhysical/chemical properties,algorithms, site-specific data, etc.
Exposure Input Files(e.g., Activity data, population data,microenvironments, etc)
HH Tox Database human health dose-response assessment values (e.g., RfC, URE)
Eco Tox Database Ecological effectsassessment values
EcoHH
----- MULTI-MEDIA IMPACTS -----
IngestionInhalation
TRIM.Expo(Human Exposure Event)
----- AIR-only IMPACTS ----------------
AQ Model (CMAQ, ISC, etc)or
AQ Data
HAPEM
[Inhalation Risk] [Ingestion Risk] [Eco Risk]
HH Criteria Pollutant Database Human health dose-, concentration-, and exposure-response functions
Total Risk Integrated Methodology (TRIM)
{for epi-based assessment}
Comparison Of Inhalation Exposure To Ambient Air Quality Levels
1.0
0.8
0.6
2.0
5th
95th
25th
75th
Median
Metals
Gases
Mixtures
1999 NATA National HAPEM5 to ASPEN Ratios
Summary – HAPEM5 to ASPEN Ratios
HAPEM5 exposure concentrations generally lower then ASPEN ambient concentrations Typically ratio (HAPEM5/ASPEN) :
1.0-0.8 for gaseous pollutants0.6-0.4 for particulate pollutants0.7-0.6 for gas/particles (mixed) pollutants
Can vary across source category because of proximity factor Some ratios greater than 1.0 for on-road sources
Examples of the Effects of Commuting On Exposure Levels
Estimated Reductions in Ambient Benzene Levels
(Year 2020, Without-CAAA Minus With-CAAA Scenario)
Estimated Reductions in Benzene Exposure (HAPEM) (Year 2020, Without-CAAA Minus With-CAAA Scenario)
Summary - Effects of Commuting on Exposure Concentrations
Overall exposure pattern: Commuting increases exposure levels in suburbia
tracts Exposures accounted for in “home” tract
Overall exposure magnitude: Greatest HAPEM to ASPEN ratios in “clean” tracts
Capturing Near-Roadway Exposure Concentration Enhancement with HAPEM6
(after Zhu et al. 2002)
Near-Roadway Concentration Enhancement
Ratio of Near-Roadway-to-Remote Concentration
0.0
0.2
0.4
0.6
0.8
1.0
0 1 2 3 4 5 6 7 8
Ratio
Cu
mu
lativ
e P
rob
ab
ility
0 to 75 meters:median = 2.5
75 to 200 meters:median = 1.6
Near-Roadway Effects on Population Risks
Benzene Risks - Nationwide
1
10
100
1,000
10,000
100,000
1,000,000
10,000,000
100,000,0004.
0E-0
4
3.0E
-04
2.0E
-04
1.0E
-04
9.0E
-05
8.0E
-05
7.0E
-05
6.0E
-05
5.0E
-05
4.0E
-05
3.0E
-05
2.0E
-05
1.0E
-05
9.0E
-06
8.0E
-06
7.0E
-06
6.0E
-06
5.0E
-06
4.0E
-06
3.0E
-06
2.0E
-06
1.0E
-06
9.0E
-07
8.0E
-07
Population > than risk bin
Po
pu
lati
on
HAPEM6
HAPEM5