Intake fraction assessment of the air pollutant exposure implications of a shift toward distributed electricity generation

Abstract

Small-scale, distributed electricity generation (DG) technologies have been promoted for their many benefits as compared to the traditional paradigm of large, centralized power plants. To evaluate the implications for human inhalation exposure resulting from a shift toward DG, we combined Gaussian plume modeling and a GIS-based inhalation exposure assessment of existing and hypothetical power-generation facilities in California. Twenty-five existing central stations (CSs) were analyzed and compared with hypothetical DG technologies deployed in the downtown areas of the 11 most populous cities in California. The intake fraction (iF) for primary pollutants was computed for populations living within 100 km of each source, using meteorological conditions typical of the long-term observational record and population, lifetime-average breathing rates. The iF (a dimensionless term representing the proportion of pollutant mass emitted by a source that is eventually inhaled) concisely expresses the source-to-intake relationship, is independent of the emissions characteristics of the plants assessed, and normalizes for the large scale differences between the two paradigms of electricity generation. The median iF for nonreactive primary pollutants emitted from the 25 CSs is 0.8 per million compared to 16 per million for the 11 DG units. The difference is partly attributable to the closer proximity of DG sources to densely populated areas as compared to typical CS facilities. In addition, the short stacks of DG sources emphasize near-source population exposure more than traditional CSs, and increase exposures during periods of low wind speed, low mixing height and stable atmospheric conditions. Strategies that could reduce the potential increase in air pollutant intake from DG include maximally utilizing waste heat in combined heat and power operations, increasing the release height of DG effluents and deploying DG technologies that do not emit air pollutants.