An Investigation of Wintertime Air Quality in Yakima Washington: Ratios of Primary Pollutants
Abstract
Due to increasing emissions of air pollutants, primarily PM2.5 and its precursors, wintertime air quality is becoming a growing concern in areas with valley like topography and cooler climates due to low wintertime boundary layer conditions. Yakima, Washington is one of those areas, and has been very close to violating the 24 hour standard PM2.5 standard of 35 μg/m3 in recent years. In January of 2013, the Washington State University's Mobile Atmospheric Chemistry Lab was deployed to Yakima to make detailed measurements of trace gases and aerosol size distribution and chemical composition. This included measurements of black carbon mass, which ranged from 0.023 to 3.4 μg/m3. One of the main scientific questions that has arisen as a result of this work surrounds the relative contribution of residential wood burning to VOC mixing ratios and black carbon concentrations. The molar ratio of CO to NOx was 13.1, which is greater than the 10.3 calculated from daily averaged MOVES output. This suggests the presence of a high CO, low NOx source in Yakima, such as residential wood burning. Acetonitrile is known to be a tracer of biomass burning, as it has no other significant terrestrial emission sources. Correlation on a molar basis between acetonitrile and VOCs or black carbon were therefore assumed to be indicative of the relative importance of residential wood burning sources, while correlations to NOx were assumed to be indicative of the importance of mobile sources. In general, R2 values for correlations to NOx were greater, although there were a few exceptions. For example, correlations of aromatics to acetonitrile yielded R2 values of 0.55-0.62, while correlations of aromatics to NOx had R2 values of 0.71-0.78. Additionally, the two measured species that are known to originate almost exclusively from combustion, CO and black carbon, correlated more closely to NOx than to acetonitrile. The R2 values were 0.9 for CO to NOx, 0.54 for CO to acetonitrile, 0.77 for black carbon to NOx, and 0.68 for black carbon to acetonitrile. The exceptions are correlations of acetaldehyde, acetone, and formaldehyde with acetonitrile which have R2 values greater than or equal to their corresponding correlations with NOx. Based on these correlations, mobile sources are a larger source, in the wintertime in Yakima, of common combustion emissions as well as many VOCs. The exception to this would appear to be organic compounds containing aldehyde or ketone groups.Correlations of VOCs and Combustion Products to Acetonitrile and NOx
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A31C0077V
- Keywords:
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- 0345 ATMOSPHERIC COMPOSITION AND STRUCTURE Pollution: urban and regional;
- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE Troposphere: composition and chemistry