Merging Low-Cost and Conventional Air Monitoring Methods to Investigate Biomass Burning in a Highly Impacted, Multi-Cultural Rural Setting

Abstract

The lower Yakima Valley of Washington State is a rural area home to communities including Latinx farmworker families, the Confederated Tribes and Bands of the Yakama Nation, and Native Americans of other tribes. Episodic poor air quality impacts this region, partly due to a mixture of different particulate matter (PM) sources, including residential wood smoke, agricultural biomass burning, and diesel emissions. We investigated air quality using low-cost and conventional approaches. University of Washington partnered with Yakama Nation Environmental Management Program and Heritage University to collect data at a tribal air monitoring site from 1/29/18-3/12/18 using a laser based, low-cost, 5-bin particle counter and a 5-wavelength aethalometer (MA200 Aethlabs). We used an established indicator for biomass burning and wood smoke: Delta-C, the difference in absorbance of the aethalometer at 375nm-880nm. We estimated an indicator for soot and aged diesel using the ratio of the mass at 375 vs. 880, where a ratio closer to 1 indicated more soot and aged diesel. A co-located tribal beta-attenuation monitor measured hourly PM2.5 mass. Over 43 days, the daily PM2.5 mean was 7.5 μg/m3 (SD 4.7 μg/m3, range 1.3-20.7 μg/m3). Hourly Delta-C mean was 0.27 μg/m3 (IQR 0.34 μg/m3). For 11 instances, the hourly ratio of Delta-C to PM2.5 mean was >1/7.5, indicating episodes of high biomass burning. The hourly ratio of the mass at 375 vs. 880 mean was 1.5 (IQR 0.95). Nighttime mean PM2.5 (8.8 μg/m3) and Delta-C (0.39 μg/m3) were greater than daytime PM2.5 (5.9 μg/m3) and Delta-C (0.16 μg/m3). The mean ratio of Delta-C to PM2.5 mass was greater at night (0.038) than daytime (0.027). Daytime correlations varied between Delta-C and PM1 (0.33), PM2.5 (0.28), and PM10 (0.21) and nighttime correlations were all 0.79. This study shows a promising example of merging data from novel low-cost instruments with existing technology that can inform a community about their exposure to biomass burning.