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Episodic Impacts from California Wildfires Identified in Las Vegas Near-Road Air Quality Monitoring
Citation:
Kimbrough, Sue, M. Hays, B. Preston, D. Vallero, AND G. Hagler. Episodic Impacts from California Wildfires Identified in Las Vegas Near-Road Air Quality Monitoring. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 50(1):18-24, (2016).
Impact/Purpose:
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 recent year-long near-road monitoring study conducted in Las Vegas, NV, a substantial increase in background air pollution due to distant wildfires was observed that led to apparent additive and synergistic effects on near-road air quality. Several indicators of biomass burning – particularly elevated levoglucosan and ultraviolet-absorbing particulate matter (UVPM) – were apparent in August and September, 2009. Back-trajectory modeling and satellite images confirmed the transport of air pollutants from wildfires burning in southern California. During the time (August 14-22, 2009 and August 29-September 4, 2009) of sustained local impact from the wildfires, an indicator of biomass burning, levoglucosan, had its highest concentration (0.83 µg/m3), as did PM10 (58.42 µg/m3, 24-hour mean), black carbon (1.7 µg/m3, 24-hour mean), NO2 (26.87 ppb, 24-hour mean), UFP20-100 nm (7381.20 #/m3, 24-hour mean) and UVPM (2.68 µg/m3, 24-hour mean). Mass-based particulate measures had notable increases, but total particle number count did not significantly change. In fact, particle number concentration in the ultrafine (<100 nm) size fraction substantially decreased whereas accumulation mode particles (100-200 nm in diameter) dramatically increased. When direction was from the road, the ratio of ultrafine particles to carbon monoxide nearly half that of periods experiencing high UVPM concentrations (“smoke present”) compared to periods of low UVPM concentrations. This indicates that the presence of aged wildfire smoke may decrease near-road ultrafine particle counts by accelerating particle growth, due to condensation or agglomeration.
Description:
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 recent year-long near-road monitoring study conducted in Las Vegas, NV, a substantial increase in background air pollution due to distant wildfires was observed that led to apparent additive and synergistic effects on near-road air quality. Several indicators of biomass burning – particularly elevated levoglucosan and ultraviolet-absorbing particulate matter (UVPM) – were apparent in August and September, 2009. Back-trajectory modeling and satellite images confirmed the transport of air pollutants from wildfires burning in southern California. During the time (August 14-22, 2009 and August 29-September 4, 2009) of sustained local impact from the wildfires, an indicator of biomass burning, levoglucosan, had its highest concentration (0.83 µg/m3), as did PM10 (58.42 µg/m3, 24-hour mean), black carbon (1.7 µg/m3, 24-hour mean), NO2 (26.87 ppb, 24-hour mean), UFP20-100 nm (7381.20 #/m3, 24-hour mean) and UVPM (2.68 µg/m3, 24-hour mean). Mass-based particulate measures had notable increases, but total particle number count did not significantly change. In fact, particle number concentration in the ultrafine (<100 nm) size fraction substantially decreased whereas accumulation mode particles (100-200 nm in diameter) dramatically increased. When direction was from the road, the ratio of ultrafine particles to carbon monoxide nearly half that of periods experiencing high UVPM concentrations (“smoke present”) compared to periods of low UVPM concentrations. This indicates that the presence of aged wildfire smoke may decrease near-road ultrafine particle counts by accelerating particle growth, due to condensation or agglomeration.
