Air-Quality Challenges of Prescribed Fire in the Complex Terrain and Wildland Urban Interface Surrounding Bend, Oregon

Abstract

Prescribed fires in forest ecosystems can negatively impact human health and safety by transporting smoke downwind into nearby communities. Smoke transport to communities is known to occur around Bend, Oregon, United States of America (USA), where burning at the wildland–urban interface in the Deschutes National Forest resulted in smoke intrusions into populated areas. The number of suitable days for prescribed fires is limited due to the necessity for moderate weather conditions, as well as wind directions that do not carry smoke into Bend. To better understand the conditions leading to these intrusions and to assess predictions of smoke dispersion from prescribed fires, we collected data from an array of weather and particulate monitors over the autumn of 2014 and spring of 2015 and historical weather data from nearby remote automated weather stations (RAWS). We characterized the observed winds to compare with meteorological and smoke dispersion models using the BlueSky smoke modeling framework. The results from this study indicated that 1–6 days per month in the spring and 2–4 days per month in the fall met the general meteorological prescription parameters for conducting prescribed fires in the National Forest. Of those, 13% of days in the spring and 5% of days in the fall had “ideal” wind patterns, when north winds occurred during the day and south winds did not occur at night. The analysis of smoke intrusions demonstrated that dispersion modeling can be useful for anticipating the timing and location of smoke impacts, but substantial errors in wind speed and direction of the meteorological models can lead to mischaracterizations of intrusion events. Additionally, for the intrusion event modeled using a higher-resolution 1-km meteorological and dispersion model, we found improved predictions of both the timing and location of smoke delivery to Bend compared with the 4-km meteorological model. The 1-km-resolution model prediction fell within 1 h of the observed event, although with underpredicted concentrations, and demonstrated promise for high-resolution modeling in areas of complex terrain.

Optical properties of biomass burning aerosol during the 2021 Oregon fire season: comparison between wild and prescribed fires

“…MCE typically spans the range of 0.7-1.0, with higher values implying flaming combustion that efficiently converts fuel to CO 2 . 24,25 Smoldering combustion (MCE < 0.9) emits less BC and more OC relative to flaming combustion (MCE > 0.9). 26,27 Secondary chemical transformations have competing effects on BB aerosol absorption following emission.…”

Wildland fire emission factors in North America: synthesis of existing data, measurement needs and management applications

“…Hardy et al (2001) also provided EFs by flaming, shortterm smouldering and long-term residual smouldering phases of combustion. Summarising EFs by combustion phase is generally useful for fire managers to inform smoke reduction techniques, such as finding optimal burn windows that maximise flaming combustion and minimise long-term smouldering (MACTEC Federal Programs 2004), which can contribute to greater overall pollutant emissions of PM and CO and nighttime intrusions into communities (Miller et al 2019).…”

A quantitative wildfire risk assessment using a modular approach of geostatistical clustering and regionally distinct valuations of assets—A case study in Oregon

“…Its population of roughly 98,000 residents, significant infrastructure, and industry make Bend the socio-economical supply center of the otherwise rural region. Bend exhibits a growing wildland urban interface which makes its outskirts particularly susceptible to wildfire threats [ 4 , 83 ].…”