Contribution of bioaerosols to airborne particulate matter

Fine and coarse particulate matter (PM), as measured, for example, in regulatory air pollution monitoring networks, contains biological entities such as fungal spores, pollen, animal dander, leaf wax, and human skin cells, to mention but a few types. Although these bioaerosols come in a wide range of particle size, of 14 common types nine fall into the 0– 10 µm range and four are in the 0– 2.5 µm range. These bioaerosols contribute to the concentrations of particulates determined by both filter-based and continuous instruments. This paper reviews bioaerosol research conducted worldwide in the last twenty years. Such studies have been conducted in Toronto, Canada, central Germany, Phoenix, Arizona, Davis, California, Dallas, Texas, and at many other sites worldwide. Notwithstanding the wide variety of climates, ecological systems, and urban and rural environments in which these measurements have been made, a reasonable, first-order estimate of the overall bioaerosol contribution to particles 2.5 microns and smaller (PM_2.5) is 16.5% and to particles 10 microns and smaller (PM₁₀) is 16.3%. A percentage contribution of this magnitude from unregulated emissions means that achieving PM standards will require greater reductions in the better understood anthropogenic and natural emissions of geological and combustion particles. In one such case the emission reductions necessary to achieve the standard increase from 25% (with bioaerosols ignored) to 36% (with bioaerosols accounted for). Although to the uninitiated this difference may not appear to be substantial, it can only be considered vast and nearly regulatorily impossible to those policy makers and regulators responsible for enacting emission-reduction regulations. Emissions of airborne biological materials are unregulated. Ignoring this natural component in attempting to achieve national ambient air quality standards for particulates can lead to overly optimistic predictions of attainment. Implications: For those officials still striving to meet federal air quality standards for particulate matter, either PM₁₀ or PM_2.5, it would be prudent to acknowledge the presence of unregulated bioaerosols. Ignoring this portion of PM may lead to over-optimistic projections of attainment.