Article pubs.acs.org/est
Episodic Impacts from California Wildfires Identified in Las Vegas Near-Road Air Quality Monitoring Sue Kimbrough,*,† Michael Hays,† Bill Preston,‡,∥ Daniel A. Vallero,§ and Gayle S.W. Hagler† †
U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, Durham, North Carolina 27709, United States ‡ ARCADIS-US, Inc., 4915 Prospectus Drive, Suite F, Durham, North Carolina 27713, United States § U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, Durham, North Carolina 27709, United States S Supporting Information *
ABSTRACT: Air pollutant concentrations near major highways are usually attributed to a combination of nearby traffic emissions and regional background, and generally presumed to be additive in nature. During a near-road measurement study conducted in Las Vegas, NV, the effects of distant wildfires on regional air quality were indicated over a several day period in the summer of 2009. Area-wide elevated particulate levoglucosan (maximum of 0.83 μg/m3) and roadside measurements of ultraviolet light-absorbing particulate matter (UVPM) in comparison to black carbon (Delta-C) were apparent over the three-day period. Back-trajectory modeling and satellite images supported the measurement results and indicated the transport of air pollutants from wildfires burning in southern California. Separating roadside measurements under apparent biomass burning event (Delta-C > 1000 ng m−3) and nonevent (Delta-C < 1000 ng m−3) periods, and constraining to specific days of week, wind speed range, wind direction from the road and traffic volume range, roadside carbon monoxide, black carbon, total particle number count (20−200 nm), and accumulation mode particle number count (100−200 nm) increased by 65%, 146%, 58%, and 366%, respectively, when biomass smoke was indicated. Meanwhile, ultrafine particles (20−100 nm) decreased by 35%. This episode indicates that the presence of aged wildfire smoke may interact with freshly emitted ultrafine particles, resulting in a decrease of particles in the ultrafine mode.
1. INTRODUCTION
Air pollution from biomass burning episodes transported into an urban area can cause air quality degradation to the point of causing the urban area to exceed EPA’s National Ambient Air Quality Standards (NAAQS).6,15 Additionally, increased air pollution due to these wildfire events is a health concern and as reported by Laumbach et al. can exacerbate existing respiratory conditions such as asthma and can impair lung function.16 Kang et al. reported significant air quality impacts to the Boston, MA area during July, 2002 and May, 2010 which coincided with wildfires burning in Quebec, Canada.10 For example, as reported by Kang et al. ambient CO concentrations showed significant increases (approximately 33%) over typical rush hour traffic CO concentrations.10 PM2.5 concentrations showed a significant increase as wellapproximately 160%.10 BC measurements taken during the same study (Kang et al.10) showed spikes during the wildfire event. Delta-C (UVBC370 nmUVPM880 nm), an indicator of biomass burning, showed significant spikes over background levels.10 Other studies, such as Bein et al., Debell et al., Sapkota et al., and Sillanpaa et al. reported significant increases in ambient air pollutant concentrations during wildfire events.6−8,12,13 The effect of wildfire
1.1. Wildfire Emissions: Impacts on Air Quality. Urban air pollution is generally considered to be primarily from an area’s mix of anthropogenic sources such as stationary fuel combustion, emissions from manufacturing facilities, light-commercial/ industrial manufacturing and fabrication facilities, and transportation facilities.1 Wildfire emissions nearby or transported to urban areas from distant fires can be a sporadic but substantial component of urban air pollution. While the incidence of wildfires and their resulting emissions are highly variable from year-to-year, emissions from wildfires (i.e., biomass burning) can contribute significant air pollution to an area.2−4 For example, EPA’s 2011 National Emission Inventory (NEI) reports that for the western United States approximately 27% of carbon monoxide (CO) emissions and 17% of fine particulate matter (particles with aerodynamic diameters 200 nm. EC9830T, Ecotech, nondispersive infrared photometer. EC9841T, Ecotech, chemilluminescence model 81000, 3-D sonic anemometer, RM Young. PM10 BC, UVPM UFPs near-road study (along I-15)
monitoring location
Table 1. Summary of Measurement Methods
2. METHODS AND MATERIALS 2.1. Project Site Description. The air pollution measurement sites were located along a major interstate (I-15) in Las Vegas, Nevada between the I-15/Russell Road interchange to the north and the I-15/I-215 to the south. The shelters were located 25, 115, and 300 m from I-15 on the east side of the freeway and 135 m west of the freeway.23 Las Vegas is approximately 665 m above sea level but is surrounded by mountains that are approximately 1000 m to 2000 m higher than the city’s elevation. Southwesterly winds predominate although seasonal variations exist. During the winter season, winds are predominately from the north−northeast quadrant.23 2.2. Air Pollution and Meteorology Measurements. The results presented in this study are a subset of extensive gaseous, PM, meteorology, and traffic data collected over a full year, as part of a multisite near-road study that has been described previously and are designated as near-road (“NR”).22−24 In addition, several PM data sets from nearby state-run monitoring sites are incorporated into the analysis, designated as Clark County (“CC”). Specific data in this present analysis include PM smaller than 10 μm (PM10-CC and NR), levoglucosan (Lg-CC), black carbon (BC-NR), ultraviolet-light absorbing particulate matter (UVPM-NR), ultrafine particles (UFPs-NR), carbon monoxide (CO-NR), oxides of nitrogen (NO, NO2-NR), and meteorology (temperature [T], relative humidity [RH], wind speed, and direction-NR). The measurements are further described in Table 1 and quality assurance details are provided in SI. Upon the basis of previous analysis investigating any apparent
measurement
instrument description
sampling interval
emissions on particle number (PN) concentration appears to vary with distancePhuleria and Fine11 observed highest PN levels close to fire areas in California, but lower PN at sites further away, whereas particulate mass measures remained high at distant sites. They speculated that the small particles dominating the PN may be scavenged by larger particle emitted by the wildfires, resulting in lower PN at distant locations. 1.2. Near Road Study. Air pollution in a near-road environment which includes emissions from freeways, airports, and railroads is a major health concern.17−20 This health concern is justified since approximately 15% of the United States population resides within approximately 90 m of a major transportation facility.21 To address this emerging public health concern, the U.S. Environmental Protection Agency (EPA), in collaboration with the Federal Highway Administration (FHWA), conducted a large-scale, year-long monitoring study in Las Vegas, NV beginning in mid-December, 2008 thru midDecember, 2009. The study was designed to characterize the impact and behavior of air pollutant emissions in a near-highway environment.22−24 Air pollutants of interest included: CO, oxides of nitrogen (NO, NO2, NOX), black carbon (BC), and particles with aerodynamic diameters 95 °F) and low humidity (SI). Periods of calm winds kept the smoke from the California wildfires from being transported out of the Las Vegas area for several days.25,36−40 Las Vegas is meteorologically and topographically complex. This complex terrain (i.e., mountains and mountain passes) can result in significant pollutant pooling until there is sufficient change in the meteorology (i.e., wind speed and wind direction) to improve local air quality.41,42 3.2. Impact of Biomass Smoke on Urban and NearRoad Air Quality. Integrated CC PM10 filter measurements and corresponding daily averages at the near-road station indicated elevated area-wide concentrations (Figure 3), particularly on August 30, however NAAQS were not exceeded. While high hourly O3 values were recorded at CC stations during this same time frame, the historical 1-h NAAQS for O3 (0.12 ppm) was not exceeded.43,44 With August 30 identified as the apparent highest regional influence by wildfire smoke, daily average roadside concentrations were normalized to the August 30 average (Figure 4).
Figure 2. HYSPLIT model results: August 28, 2009 through September 3, 2009 (24-h backcast).
mass, indicating regional-scale biomass smoke. Overall, the Lg values reported here are well within the range of ambient concentrations collected globally (0.0078 μg m−3) within the 2000−2010 decade.26 Sizeable input from residential wood combustion was not expected due to the late summer time frame under investigation. In addition, 5 min Delta-C measurements provided a higher time resolution indication of regional wildfire impact on near-road air quality (Figure 1b). Reported by the instrument in concentration units as an equivalent amount of BC, UVPM values in excess of the instruments BC readings (Delta-C) can be interpreted as an indication of other light-absorbing carbon (i.e., brown carbon). The Delta-C and Lg data can be seen to similarly indicate biomass smoke contributing to air pollution in the area during August 29 − September 1. It should be noted that the Delta-C values should be interpreted more as binary in nature (“smoke indicated or not”), as numerous particulate chemical compounds may contribute to UV-absorption and have unique mass absorption efficiencies. Satellite imagery and photographic evidence of visibility deterioration confirm wildfire plumes transported from California in late-August, 2009 (SI). Back-trajectory analysis (Figure 2) indicates meteorological conditions conducive to the movement of air masses from southern California, area of the Station fire, to the Las Vegas, NV urban area during the time between August 29 and September 1. Other studies have used backtrajectory modeling to show transport of wildfire plumes over long distances (e.g., Bein et al., Colarco et al., DeBell et al., Kang et al., and Sapkota et al.6,7,9,10,12).
Figure 4. Daily mean concentrations, normalized to the daily mean for August 30 (a), and wind speed averaged at hourly and daily intervals (b).
Continuous roadside measurements indicated a daily average maximum for CO, BC, PM10, and PN100−200 on August 30 (Figure 4a), despite daily average wind speed nearly doubling (Figure 4b). Meanwhile, ultrafine particles (PN20−100) exhibited
Figure 3. CC and NR PM10 observations. D
DOI: 10.1021/acs.est.5b05038 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Figure 5. CO, BC, UFP (20−100 nm), accumulation mode particle (100−200 nm), and total particle number (20−200 nm) concentrations (15 min averages) measured during periods of low and elevated Delta-C during the period of August 1−September 30, 2009, selecting only periods with wind from the road, moderate wind speeds (2−4 m s−1), and matched days of week. The number (N) of 15 min averages ranged 329−335 and 39−41 for low Delta-C and high-Delta-C conditions, respectively.
31 vs 33 °C, traffic speed was 63 vs 62 mph, and traffic volume was 1310 vs 1220 (vehicles per 15 min interval). Comparing these two observation periods, CO, BC, PN100−200, and PN20−200 experienced a statistically significant (nonoverlapping 95% confidence intervals) increase of 65% (+0.17 ppm), 146% (+1.6 ug m−3), 366% (+2370 cm−3), and 58% (+1960 cm−3) during the biomass burning event (indicated by high Delta-C), respectively (Figure 5a,b). Meanwhile, UFPs had a statistically significant decrease of 35% (−1000 cm−3) (Figure 5c). UFPs, BC, and CO are all directly emitted by vehicles and have been observed to covary when measured at a roadside location (e.g., Hagler et al.45). During the biomass episode, a significant shift in the particle size distribution occurred, with a substantial increase in particles >100 nm and also a decrease in ultrafine-mode particles ranging from 20 to 100 nm. The 35% decrease in UFPs occurs despite an ∼7% increase in traffic volume for the two periods compared. These results suggest an interaction between traffic-emitted UFPs and background pollution resulting from the long-range transport of biomass smoke, such as increased agglomeration of particles and condensational growth. The increase in total particle number and accumulation mode under high Delta-C conditions may be due to both the long-distance transport of biomass smoke, as well as local particle emissions and postemissions transformation. Previous research has also indicated the loss of the ultrafine particles during transport of wildfire emissions,11 however this may be the first observation of apparent roadside ultrafine particle loss related to a regional influx of wildfire emissions.
a minima on August 30, a factor of ∼2.7−3 reduction compared to August 26−28. The contrasting temporal trends for ultrafine and accumulation mode particles led to a negligible change in total particle number during this time period. 3.3. Ultrafine Particles during Biomass Smoke Episode. Although ultrafine particles appear to have decreased during the biomass episode, this observation could have arguably been due to higher wind speeds or a low frequency of wind direction from the road. Although daily average wind speeds appeared to be higher, at an hourly resolution it can be seen that wind speeds had high variability during the biomass burning time period (Figure 4b). Considering a two month period (Aug 1−Sept 30) of roadside observations, 15 min averages for UFPs, BC, and CO were allocated as either measured during an indicated biomass burning event (Delta-C > 1 μg m−3) or a nonevent period (Delta-C < 1 μg m−3). To isolate the influence of biomass burning smoke compared to other factors that may influence roadside pollution, further constraints applied to the data required wind from the road (210−330 degrees), wind speed within 2−4 m s−1, traffic volume between 500 and 2000 (counts per 15 min increment). In addition, the days of the week used for comparison were isolated to Saturday, Sunday, and Monday, corresponding to the biomass burning event time span detected in Las Vegas. Sampling hours were confirmed to be similar between the two time periodsthe selection for moderate wind speeds and wind from the road resulted in the majority of the observations occurring during evening and early morning hours (SI). Meteorological and traffic factors were similar between the data sets; for the two periods compared (low Delta-C vs high Delta-C), mean wind speeds were 2.6 s−1 vs 2.9 m s−1, relative humidity was 14% vs 10%, temperature was E
DOI: 10.1021/acs.est.5b05038 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
■
(10) Kang, C.-M.; Gold, D.; Koutrakis, P. Downwind O3 and PM2.5 speciation during the wildfires in 2002 and 2010. Atmos. Environ. 2014, 95, 511−519. (11) Phuleria, H. C.; Fine, P. M.; Zhu, Y.; Sioutas, C. Air quality impacts of the October 2003 Southern California wildfires. J. Geophys. Res. 2005, 110.10.1029/2004JD004626 (12) Sapkota, A.; Symons, J. M.; Kleissl, J.; Wang, L.; Parlange, M. B.; Ondov, J.; Breysse, P. N.; Diette, G. B.; Eggleston, P. A.; Buckley, T. J. Impact of the 2002 Canadian forest fires on particulate matter air quality in Baltimore City. Environ. Sci. Technol. 2005, 39 (1), 24−32. (13) Sillanpaa, M.; Saarikoski, S.; Hillamo, R.; Pennanen, A.; Makkonen, U.; Spolnik, Z.; Van Grieken, R.; Koskentalo, T. A.; Salonen, R. O. Chemical composition, mass size distribution and source analysis of long-range transported wildfire smokes in Helsinki. Sci. Total Environ. 2005, 350 (1−3), 119−135. (14) Langmann, B.; Duncan, B.; Textor, C.; Trentmann, J.; van der Werf, G. R. Vegetation fire emissions and their impact on air pollution and climate. Atmos. Environ. 2009, 43 (1), 107−116. (15) Viswanathan, S.; Eria, L.; Diunugala, N.; Johnson, J.; McClean, C. An analysis of effects of San Diego wildfire on ambient air quality. J. Air Waste Manage. Assoc. 2006, 56 (1), 56−67. (16) Laumbach, R. J.; Kipen, H. M. Respiratory health effects of air pollution: Update on biomass smoke and traffic pollution. J. Allergy Clin. Immunol. 2012, 129 (1), 3−11. (17) HEI. Mobile-Source Air Toxics: A Critical Review of the Literature on Exposure and Health Effects; Health Effects Institute: Boston, MA, 2007. (18) HEI. Traffic-related air pollution: A critical review of the literature on emissions, exposure, and health effects; Health Effects Institute: Boston, MA, 2010. (19) Karner, A. A.; Eisinger, D. S.; Niemeier, D. A. Near-roadway air quality: Synthesizing the findings from real-world data. Environ. Sci. Technol. 2010, 44 (14), 5334−5344. (20) Mejía, J. F.; Choy, S. L.; Mengersen, K.; Morawska, L. Methodology for assessing exposure and impacts of air pollutants in school children: Data collection, analysis and health effects - A literature review. Atmos. Environ. 2011, 45 (4), 813−823. (21) U.S. EPA, Primary National Ambient Air Quality Standards for Nitrogen Dioxide (75 FR 6474, February 9, 2010) codified in 40 CFR parts 50 and 58. (22) Kimbrough, E. S.; Baldauf, R. W.; Watkins, N. Seasonal and diurnal analysis of NO2concentrations from a long-duration study conducted in Las Vegas, Nevada. J. Air Waste Manage. Assoc. 2013, 63 (8), 934−942. (23) Kimbrough, S.; Baldauf, R.; Hagler, G.; Shores, R. C.; Mitchell, W.; Whitaker, D. A.; Croghan, C. W.; Vallero, D. A. Long-term continuous measurement of near-road air pollution in Las Vegas: Seasonal variability in traffic emissions impact on local air quality. Air Qual., Atmos. Health 2013, 6 (1), 295−305. (24) Kimbrough, S.; Palma, T.; Baldauf, R. W. Analysis of mobile source air toxics (MSATs)Near-road VOC and carbonyl concentrations. J. Air Waste Manage. Assoc. 2014, 64 (3), 349−359. (25) Toplikar, D. Smokey skies to continue across Las Vegas tonight. Las Vegas Sun August 31, 2009. (26) Ma, Y.; Hays, M. D.; Geron, C. D.; Walker, J. T.; Gichuru, M. J. G. Technical Note: Fast two-dimensional GC-MS with thermal extraction for anhydro-sugars in fine aerosols. Atmos. Chem. Phys. 2010, 10 (9), 4331−4341. (27) Engling, G.; Carrico, C. M.; Kreidenweis, S. M.; Collett, J. L., Jr.; Day, D. E.; Malm, W. C.; Lincoln, E.; Min Hao, W.; Iinuma, Y.; Herrmann, H. Determination of levoglucosan in biomass combustion aerosol by high-performance anion-exchange chromatography with pulsed amperometric detection. Atmos. Environ. 2006, 40, 299−311. (28) Engling, G.; Herckes, P.; Kreidenweis, S. M.; Malm, W. C.; Collett, J. L., Jr Composition of the fine organic aerosol in Yosemite National Park during the 2002 Yosemite Aerosol Characterization Study. Atmos. Environ. 2006, 40 (16), 2959−2972. (29) Fraser, M. P.; Lakshmanan, K. Using Levoglucosan as a Molecular Marker for the Long-Range Transport of Biomass
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.5b05038. Description of wildfires; levoglucosan sample preparation and analysis; and description of quality assurance measures (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*Phone: 919-541-2616; email:
[email protected] (S.K.). Present Address ∥
CSS-Dynamac, 1910 Sedwick Road, Durham, NC 27713.
Notes
This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. The views expressed in this journal article are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency. The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We thank members of the EPA Near-Road team for their contributions to this project. We also acknowledge the contributions of ARCADIS-US, Inc. staff, Clark County Department of Air Quality staff to the success of the near-road monitoring project.
■
REFERENCES
(1) U.S. EPA Our Nation’s AirStatus and Trends through 2010; 2010. (2) Liu, Y. Variability of wildland fire emissions across the contiguous United States. Atmos. Environ. 2004, 38 (21), 3489−3499. (3) Wiedinmyer, C.; Quayle, B.; Geron, C.; Belote, A.; McKenzie, D.; Zhang, X. Y.; O’Neill, S.; Wynne, K. K. Estimating emissions from fires in North America for air quality modeling. Atmos. Environ. 2006, 40 (19), 3419−3432. (4) Hu, Y.; Odman, M. T.; Chang, M. E.; Jackson, W.; Lee, S.; Edgerton, E. S.; Baumann, K.; Russell, A. G. Simulation of Air Quality Impacts from Prescribed Fires on an Urban Area. Environ. Sci. Technol. 2008, 42 (10), 3676−3682. (5) U.S. EPA National Emissions Inventory. http://www3.epa.gov/ ttn/chief/net/2011inventory.html (last accessed: September 25, 2015). (6) Bein, K. J.; Zhao, Y. J.; Johnston, M. V.; Wexler, A. S. Interactions between boreal wildfire and urban emissions. J. Geophys. Res. 2008, 113, (D7).10.1029/2007JD008910 (7) DeBell, L. J.; Talbot, R. W.; Dibb, J. E.; Munger, J. W.; Fischer, E. V.; Frolking, S. E., A major regional air pollution event in the northeastern United States caused by extensive forest fires in Quebec, Canada. J. Geophys. Res. 2004, 109, (D19).10.1029/2004JD004840 (8) Wu, J.; Winer, A. M.; Delfino, R. J. Exposure assessment of particulate matter air pollution before, during, and after the 2003 Southern California wildfires. Atmos. Environ. 2006, 40 (18), 3333− 3348. (9) Colarco, P. R.; Schoeberl, M. R.; Doddridge, B. G.; Marufu, L. T.; Torres, O.; Welton, E. J. Transport of smoke from Canadian forest fires to the surface near Washington, D. C.: Injection height, entrainment, and optical properties. J. Geophys. Res. 2004, 109, (D6).10.1029/2003JD004248 F
DOI: 10.1021/acs.est.5b05038 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology Combustion Aerosols. Environ. Sci. Technol. 2000, 34 (21), 4560− 4564. (30) Simoneit, B. R. T.; Schauer, J. J.; Nolte, C. G.; Oros, D. R.; Elias, V. O.; Fraser, M. P.; Rogge, W. F.; Cass, G. R. Levoglucosan, a tracer for cellulose in biomass burning and atmospheric particles. Atmos. Environ. 1999, 33 (2), 173−182. (31) Wang, Y.; Hopke, P. K.; Rattigan, O. V.; Zhu, Y. Characterization of ambient black carbon and wood burning particles in two urban areas. J. Environ. Monit. 2011, 13 (7), 1919−1926. (32) Allen, G. A.; Babich, P.; Poirot, R. L. In Evaluation of a new approach for real time assessment of wood smoke PM, Proceedings of the Regional and Global Perspectives on Haze: Causes, Consequences and ControversiesVisibility Specialty Conference, Asheville, NC, USA, 2004; Asheville, NC, USA, 2004. (33) Wang, Y.; Hopke, P. K.; Rattigan, O. V.; Xia, X.; Chalupa, D. C.; Utell, M. J. Characterization of Residential Wood Combustion Particles Using the Two-Wavelength Aethalometer. Environ. Sci. Technol. 2011, 45 (17), 7387−7393. (34) Draxler, R. R.; Rolph, G. D. HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory); NOAA Air Resources Laboratory: Silver Spring, MD, 2012. (35) ESRI. ArcGIS, 10.3.1; Environmental Systems Research Institute, Inc.: Redlands, 2015. (36) Buhler, B. California’s Fire, Our Smoke. Las Vegas Sun September 2, 2009. (37) Manning, M. Wildfire smoke a factor in poor air quality through Wednesday. Las Vegas Sun August 31, 2009. (38) Manning, M. Smoke, dust particles on the rise in Las Vegas. Las Vegas Sun September 1, 2009. (39) Toplikar, D. Hot and smokey conditions today in Las Vegas. Las Vegas Sun August 30, 2009. (40) Topliker, D. Skies still smoky, but slight chance for rain comes to Las Vegas. Las Vegas Sun September 1, 2009. (41) Banta, R. M. Atmospheric Processes Over Complex Terrain; American Meteorological Society: 1990; Vol. 45, p 323. (42) Chow, F. K.; De Wekker, S. F.; Snyder, B. J. Mountain Weather Research and Forecasting: Recent Progress and Current Challenges; Springer Science & Business Media: 2012. (43) Clark County DAQEM Clark County Air Quality Data. http:// ccaqapps5m.co.clark.nv.us/cgi-bin/select_summary.pl (last accessed: September 21, 2012). (44) U.S. EPA Ozone Standards - Table of Historical Ozone NAAQS. http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_ history.html (last accessed: September 11, 2015). (45) Hagler, G. S. W.; Baldauf, R. W.; Thoma, E. D.; Long, T. R.; Snow, R. F.; Kinsey, J. S.; Oudejans, L.; Gullett, B. K. Ultrafine particles near a major roadway in Raleigh, North Carolina: Downwind attenuation and correlation with traffic-related pollutants. Atmos. Environ. 2009, 43 (6), 1229−1234.
G
DOI: 10.1021/acs.est.5b05038 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
