Establishing Representative Background
Concentrations for Quantitative Hot-Spot
Analyses for Particulate Matter
Adam N. Pasch1, Ashley R. Russell1, Leo Tidd2, Douglas S. Eisinger1,
Daniel M. Alrick1, Hilary R. Hafner1, and Song Bai1
1Sonoma
Technology, Inc., Petaluma, CA
2The Louis Berger Group, Inc., Morristown, NJ
for
National Cooperative Highway Research Program
AASHTO Standing Committee on the Environment
NCHRP 25-25/Task 89
August 20, 2014
STI-6051
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NCHRP Background PM Study
• Overview
– Project motivation
– Research purpose
• EPA guidance
• NCHRP study (focus of this presentation)
– Ambient data use
• Four-step method
• Phoenix, AZ examples
– CTM use
• Future research needs
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Overview
Project Motivation
• Background concentrations are
required for PM hot-spot analysis
• Determination of representative
background concentrations is
critical (especially when the
project increment is small)
• Current guidance is limited on
how to assess representativeness
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Overview
Research Purpose
• NCHRP 25-25 Task 89
– Support PM hot-spot analyses
– Develop step-by-step methods
– Create illustrative examples and template
• Key technical issues
– Selection of representative monitor(s)
– Identification of exceptional or exceptional-type
events
EPA Guidance
EPA Guidance: Two Methods
1. Estimate background PM concentrations
using ambient data (three years)
– Single representative monitor
– Interpolation among representative monitors
2. Calculate background PM concentrations
using chemical transport modeling (CTM)
outputs (not discussed in this talk)
Interagency consultation is required.
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EPA Guidance
EPA Guidance: Exceptional Events (EEs)
• Exceptional events: unusual or naturally
occurring events that affect air quality but are
not reasonably controllable (NAAQS violation).
– Require a detailed demonstration to be submitted
and approval by EPA to remove data
– Regulatory impact
• Exceptional-type events (no NAAQS violation
or no demonstration packet submitted).
Handled as research only at this time.
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NCHRP Study
Using Ambient Data: Major Steps
1. Select representative PM monitoring site(s).
2. Acquire and process PM concentration data.
3. Assess data quality and representativeness.
4. Calculate background PM concentrations,
following EPA requirements.
Determine data impacted by an exceptional-type or air
transport event and document and remove these data
from consideration (research purposes only).
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NCHRP Study
Step 1: Select Representative Monitor Site
Considerations include
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Distance from project site
Wind patterns (upwind of project preferred)
Land use/density/mix of sources
Monitor height and elevation
Monitor type and purpose
Data availability and completeness
Interagency consultation
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NCHRP Study
Identify Candidate Monitors and Data
Hypothetical
Project Location
Example: PM10 monitor sites and data
acquisition from EPA AirData website.
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NCHRP Study
Assess Meteorology and Land Use
Example below: Map of land use
types based on USGS data.
Example above: wind rose created
using the AirNow-Tech website.
NCHRP Study
Step 2: Acquire and Process PM Data
Sources include
• AirData (replaces AirExplorer – linked to AQS) –
recommended by EPA guidance
• AirNow-Tech (backfilled with AQS data)
• AQS Data Mart
• AQS Web Application
• Local air quality agency
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NCHRP Study
Example of PM Data Acquisition Methods
Example below: data acquisition
from the AirNow-Tech website.
Example above: data
acquisition from the
AirData website.
NCHRP Study
Step 3: Assess Quality, Representativeness
• Identify and remove concurred EEs
• Cautionary notes for AirData users
– AirData flags data as Exceptional, but not
Exceptional and concurred
– Analysts need to manually identify and exclude
concurred EEs within AirData
• Check data completeness (75% by quarter,
over three years minimum)
• Identify exceptional-type events (research)
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NCHRP Study
Screen Anomalous PM Data
Considerations
Temperature (was residential wood burning likely?)
Visibility
Wind (i.e., wind speeds greater than 25 mph)
Smoke or haze reported (or smoke plumes evident
from satellite observations)
• Transport (i.e., trajectories from a source region)
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Research only:
Exceptional-type events
Air transport events
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NCHRP Study
Phoenix PM10 Data: Exceptional Event
Data obtained from AirNow backfilled with AQS data.
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NCHRP Study
Met. Data: Blowing Dust All Quadrants
BLDU ALQDS = Blowing Dust All Quadrants
Haze
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NCHRP Study
Visibility Photos: August 3, 2011
12:00 a.m.
3:00 a.m.
Source of images: Arizona Department of Environmental Quality (ADEQ)
http://www.azdeq.gov/environ/air/plan/download/eed_080311.pdf
NCHRP Study
Step 4: Calculate Background PM
• PM10 design value
– 24-hr maximum over three years
• PM2.5 design value
– Annual average: average for each quarter, then
average for each year over three years
– 24-hr
• Tier 1 – simpler, more conservative design values
• Tier 2 – more complex
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NCHRP Study
Step 4: Calculate Background PM
• Using 2010–2012 data
– Before = 341 µg/m3
• Removing PM10 data
– All exceptional events
• 144 µg/m3
– Exceptional-type events
• 129 µg/m3 (research)
(24-hr PM10 NAAQS = 150 µg/m3)
2010 to 2012 maximum daily PM10 concentrations
for the Central Phoenix Monitor (based on data
obtained from AirData).
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Future Research Needs
• EPA-approvable data exclusion methods to
handle exceptional-type events.
• Help to obtain CTM outputs for use in
forecasting future background PM
concentrations.
• Best practices and lessons learned from realworld PM hot-spot analyses.
• Processes to encourage SIP development to
support background PM estimation.
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Conclusions
• Monitor site selection will be influenced by many
practical considerations; multiple sites may be
needed for large, spatially complex projects.
• Project analysts should budget analyses to cover
complex data processing such as exceptional
event removal and multi-year data assessments.
• Exceptional-type events can substantially impact
background concentrations.