STI-6051

1. 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

2. 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

3. 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

4. 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

5. EPA Guidance EPA Guidance: Two Methods • Estimate background PM concentrations using ambient data (three years) • Single representative monitor • Interpolation among representative monitors • Calculate background PM concentrations using chemical transport modeling (CTM) outputs (not discussed in this talk) Interagency consultation is required.

6. 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.

7. NCHRP Study Using Ambient Data: Major Steps • Select representative PM monitoring site(s). • Acquire and process PM concentration data. • Assess data quality and representativeness. • Calculate background PM concentrations, following EPA requirements. Determine data impacted by an exceptional-typeor air transport event and document and remove these data from consideration (research purposes only).

8. NCHRP Study Step 1: Select Representative Monitor Site Considerations include • 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

9. NCHRP Study Identify Candidate Monitors and Data Hypothetical Project Location Example: PM10 monitor sites and data acquisition from EPA AirData website.

10. NCHRP Study Assess Meteorology and Land Use Example below: Map of land usetypes based on USGS data. Example above: wind rosecreated using the AirNow-Tech website.

11. 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

12. 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.

13. 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 concurredEEs within AirData • Check data completeness (75% by quarter, over three years minimum) • Identify exceptional-type events (research)

14. 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) Exceptional-type events Air transport events Research only:

15. NCHRP Study Phoenix PM10 Data: Exceptional Event Data obtained from AirNow backfilled with AQS data.

16. NCHRP Study Met. Data: Blowing Dust All Quadrants BLDU ALQDS = Blowing Dust All Quadrants Haze

17. 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

18. 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

19. NCHRP Study Step 4: Calculate Background PM • Using 2010–2012 data • Before = 341µg/m3 • Removing PM10 data • All exceptional events • 144µg/m3 • Exceptional-type events • 129µg/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).

20. 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 real-world PM hot-spot analyses. • Processes to encourage SIP development to support background PM estimation.

21. 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.