1. Characterization of a Year of Near-Road NO 2 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. 2 Outline Summary of near-road NO 2 NAAQS monitoring requirements NO 2 monitoring during U.S. 95 MSAT study General characteristics of one year of NO 2 data Characteristics on days with highest daily maximum NO 2 concentrations Comparisons of NO 2 characteristics to other urban sites Relationships of NO 2 with BC and with CO Lessons learned and recommendations

3. 3 Summary of Near-Road NO 2 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 NO 2 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.pdfhttp://www.epa.gov/air/nitrogenoxides/pdfs/20100122fs.pdf

4. 4 Reference: http://www.epa.gov/air/nitrogenoxides/pdfs/NO2MonitoringSiteMaps.pdfhttp://www.epa.gov/air/nitrogenoxides/pdfs/NO2MonitoringSiteMaps.pdf Near-Road NO 2 Monitoring Plan

5. 5 NO 2 Monitoring During U.S. 95 MSAT Study (1 of 2) Thermal Scientific 42i NO-NO 2 -NO x 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. 6 (Ambient site is indicated by symbol) Ambient site is 20 m from sound wall, 35 m from on-ramp, 50 m from nearest lane. NO 2 Monitoring During U.S. 95 MSAT Study (2 of 2)

7. 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. 8 General Characteristics of One Year of NO 2 Data at Fyfe School - All Hours NO 2 Small fraction of all hours over 45 ppb NO 2 Diurnal NO 2 peaks during morning and evening rush hours

9. 9 General Characteristics of One Year of NO 2 Data at Fyfe School - Daily Maximum NO 2 Peak of daily maximum hour NO 2 about 40-50 ppb Little variation in monthly median daily max NO 2 concentrations (35-45 ppb; not shown) Daily maximum NO 2 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. 10 Higher daily maximum NO 2 concentrations when wind speeds are low 98 th percentile point for one year of data is about 59 ppb Cumulative Distribution of One Year of NO 2 Data at Fyfe School - Daily Maximum NO 2 Wind speed ○ High X Low All data

11. 11 98 th percentile point for one year of data at Fyfe is about 59 ppb 98 th percentile point for one year of data at other urban sites is about 60 ppb (East Tonopah) and 47 ppb (West Azure) Cumulative Distribution of One Year of NO 2 Data at Three Sites - Daily Maximum NO 2 Fyfe 9/15/07-9/14/08 East Tonopah 11/1/07-10/31/08 West Azure 1/1/08-12/31/08

12. 12 Characteristics on Days with Highest Daily Maximum NO 2 Concentrations Typical diurnal pattern with morning and evening NO 2 peak on five of seven days 4/21/2008 with earlier NO 2 peak; sharp wind shift with Fyfe now upwind caused NO 2 to decrease 11/08/2007 with late morning peak NO 2 ; corresponding to the arrival of aged urban air

13. 13 Relationships of NO 2 with BC and with CO NO 2 correlates with black carbon (BC) and CO up to about 30 ppb BC and CO are correlated

14. 14 Lessons Learned and Recommendations Both morning and evening rush hours are important for daily maximum 1-hr NO 2 concentrations. Distance to the edge of the nearest traffic lane is not the only factor influencing NO 2 concentrations. Sound walls and other mitigating objects may influence pollutant concentrations. The logistics of near-road siting may be difficult.