TOTAL SUSPENDED PARTICLES (TSP)

Total suspended particles (TSP) is an archaic regulatory measure of the mass concentration of particulate matter (PM) in community air. It was defined by the (unintended) size-selectivity of the inlet to the filter that collected the particles. Unfortunately, the size cut varied with wind speed and direction and was from 20 to 50 µm (microns) in aerodynamic diameter. Under windy conditions the mass tended to be dominated by large wind-blown soil particles of relatively low toxicity.

In 1987 the EPA revised the National Ambient Air Quality Standard (NAAQS) for PM, and changed the PM pollution index to PM10, an index of the PM that can enter the thorax and cause or exacerbate lower respiratory tract diseases, such as chronic bronchitis, asthma, pneumonia, lung cancer, and emphysema. This switch to a more health-related index stimulated studies of the associations between ambient air PM and mortality, morbidity, and cardiopulmonary function indices. Some of the studies also used measures of the fine PM concentrations in the air, as indexed by PM2.5 and/or sulfate, and were able to show that annual mortality rates were more closely associated with fine particles than with the larger PM10.

In 1997, in its next revision of the PM NAAQS, the EPA supplemented its regulations on PM10 with new regulations on PM2.5. The cut points are not perfectly sharp for any of these PM size indicators; some particles larger than the cut-point are collected and some particles smaller than the cut point are not retained.

The terms "fine" and "coarse" were originally intended to apply to the two major atmospheric particle distributions which overlap in the size range between 1 and 3 microns. Now, "fine" has been defined by EPA as PM2.5 and "coarse" as PM10–2.5. However, PM2.5 may contain, in addition to the fine-particle mode, some of the smaller sized "coarse" particles. Conversely, under high relative humidity conditions, the larger particles in the accumulation mode extend into the 1 to 3 micron range.

The chemical complexity of airborne particles requires that the composition and sources of a large number of primary and secondary components be considered. Major components of fine particles are SO4 = H+, NO3−, NH4+, organic compounds, trace elements (including metals that volatize at combustion temperatures), elemental carbon, and water. Major sources of these fine mode substances are fossil fuel combustion by electric utilities, industry, and motor vehicles; vegetation burning; and the smelting or other processing of metals.

Background emission sources (geogenic and biogenic) include: (1) windblown dust from erosion and reentrainment; (2) long-range transport of dust (including Sahara desert dust over Florida); (3) sea salt; (4) particles formed from the oxidation of sulfur compounds emitted from oceans and wetlands; and the oxidation of NOx from natural forest fires and lightning; and (5) the oxidation of hydrocarbons (such as terpenes) emitted by vegetation.

Major components of coarse particles are aluminosilicates and other oxides of crustal elements (e.g., Fe, Ca, etc.) in soil dust; fugitive dust from roads, industry, agriculture, construction and demolition; fly ash from combustion of oil and coal; and additional contributions from plant and animal material.

Since fine and coarse particles have distinctly different sources, both natural and anthropogenic, different control strategies are needed.

Morton Lippmann

(see also: Airborne Particles; Ambient Air Quality [Air Pollution]; Environmental Protection Agency; Hazardous Air Pollutants; Inhalable Particles [Sulfates]; National Ambient Air Quality Standards; Smog [Air Pollution] )

Bibliography

Lippmann, M., ed. (2000). Environmental Toxicants, 2nd edition. New York: Wiley.

U.S. Environmental Protection Agency (2001). Air Quality Criteria for Particulate Matter. EPA 600/p.99/002. Washington, DC: Author.