Characterization of a Year of Near-Road NO 2 Measurements in Las Vegas, Nevada

1. Characterization of a Year of Near-Road NO2 Measurements in Las Vegas, Nevada Prepared by Paul T. Roberts, Jennifer L. DeWinter, and Steven G. Brown Sonoma Technology, Inc. Petaluma, CA Presented at the 2010 National Air Quality Conferences Raleigh, NC March 15-18, 2010 3814

2. Outline • Summary of near-road NO2 NAAQS monitoring requirements • NO2 monitoring during U.S. 95 MSAT study • General characteristics of one year of NO2 data • Characteristics on days with highest daily maximum NO2 concentrations • Comparisons of NO2 characteristics to other urban sites • Relationships of NO2 with BC and with CO • Lessons learned and recommendations

3. Summary of Near-Road NO2 NAAQS Monitoring Requirements • One monitor near a major road in any urban area with > 500,000 population • Second near-road monitor if > 2.5 million or road segment with AADT > 250,000 • Where peak NO2 concentrations are expected • Nearby road must have high AADT rank • Consider fleet mix, congestion, terrain, geographic location, and meteorology • Must begin monitoring by January 1, 2013 Reference: http://www.epa.gov/air/nitrogenoxides/pdfs/20100122fs.pdf

4. Near-Road NO2 Monitoring Plan Reference: http://www.epa.gov/air/nitrogenoxides/pdfs/NO2MonitoringSiteMaps.pdf

5. NO2 Monitoring During U.S. 95 MSAT Study (1 of 2) • Thermal Scientific 42i NO-NO2-NOx analyzer (FRM) • Collected data at Fyfe from 9/15/2007 to 9/14/2008 • Daily zero and span checks • Multipoint calibrations at beginning, midpoint, and end of monitoring period

6. NO2 Monitoring During U.S. 95 MSAT Study (2 of 2) Ambient site is 20 m from sound wall, 35 m from on-ramp, 50 m from nearest lane. (Ambient site is indicated by symbol)

7. Locations in Las Vegas, Nevada Distances to nearest lane of major roadway: Fyfe, 50 m; East Tonopah, 1660 m; West Azure, 1890 and 260 m Map showing 3 sites in LV (to come)

8. General Characteristics of One Year of NO2 Data at Fyfe School - All Hours NO2 • Small fraction of all hours over 45 ppb NO2 • Diurnal NO2 peaks during morning and evening rush hours

9. General Characteristics of One Year of NO2 Data at Fyfe School - Daily Maximum NO2 • Peak of daily maximum hour NO2 about 40-50 ppb • Little variation in monthly median daily max NO2 concentrations (35-45 ppb; not shown) • Daily maximum NO2 concentrations occur mostly during morning and evening rush hours at all three sites: Fyfe (shown), East Tonopah (not shown), and West Azure (not shown)

10. Cumulative Distribution of One Year of NO2 Data at Fyfe School - Daily Maximum NO2 Wind speed ○ High X Low All data • Higher daily maximum NO2 concentrations when wind speeds are low • 98th percentile point for one year of data is about 59 ppb

11. Cumulative Distribution of One Year of NO2 Data at Three Sites - Daily Maximum NO2 East Tonopah 11/1/07-10/31/08 Fyfe 9/15/07-9/14/08 West Azure 1/1/08-12/31/08 • 98th percentile point for one year of data at Fyfe is about 59 ppb • 98th percentile point for one year of data at other urban sites is about 60 ppb (East Tonopah) and 47 ppb (West Azure)

12. Characteristics on Days with Highest Daily Maximum NO2 Concentrations • Typical diurnal pattern with morning and evening NO2 peak on five of seven days • 4/21/2008 with earlier NO2 peak; sharp wind shift with Fyfe now upwind caused NO2 to decrease • 11/08/2007 with late morning peak NO2; corresponding to the arrival of aged urban air

13. Relationships of NO2 with BC and with CO • NO2 correlates with black carbon (BC) and CO up to about 30 ppb • BC and CO are correlated

14. Lessons Learned and Recommendations • Both morning and evening rush hours are important for daily maximum 1-hr NO2 concentrations. • Distance to the edge of the nearest traffic lane is not the only factor influencing NO2 concentrations. • Sound walls and other mitigating objects may influence pollutant concentrations. • The logistics of near-road siting may be difficult.