Air Quality Data from the Pittsburgh Supersite

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Hotline, Winter 2004

by Beth Toor, GASP Board Member

On September 17, 2003, Professor Spyros Pandis gave an Engineering & Public Policy seminar at CMU entitled “Atmospheric Aerosol – From Source to Receptor,” a report on some of the Supersite results (the trailer-like lab, now dismantled, which sat on the hillside near Schenley Drive). The EPA supported this work which Professor Pandis directed with Cliff Davidson, Allen Robinson and about 20 graduate students. Here are some of the results he reported. More information will be available in the future as data analysis is continued.

Particulate Concentration: The number of small particles below 0.01 micrometers (or microns) is very high, with a secondary peak between 0.01 and 0.1 microns. However, the volume of small particles reaches a peak around 2.5 microns. A PM2.5 concentration of 4 micrograms/cubic meter is considered clean; concentrations above the annual standard of 15 micrograms/cubic meter is considered by some people as dirty. For the year June 30, 2001 to June 30, 2002, the average concentration here was 17 micrograms/cubic meter.

Fine Particle Composition: Sulfate is the largest component, especially in summer. Organics are the next largest component and are fairly constant year round. Ammonia is a smaller component, and the concentrations parallel sulfate over time.

Sulfate Reduction: Since sulfate is the largest component, it would appear that lowering sulfate could improve health most rapidly. However, when sulfate is reduced, the resulting free ammonium ions form ammonium nitrate particles, partially replacing the former sulfate particles. Free ammonia must be decreased to prevent this happening. Ammonia is not a harmful pollutant at concentrations typically found in ambient air, but it combines with the gases SO2 and NOx to form particles more harmful than the gases. So sulfate reduction alone does not reduce health effects as much as one would expect, though it does reduce acid rain.

Sulfate Concentrations: Comparing sulfate concentrations from the Supersite to various satellite stations in Steubenville and Athens, Ohio, in Greensburg and other sites in western Pennsylvania, including three in Pittsburgh, the sulfate concentrations are very similar. Therefore, the sulfate particles are not just a local Pittsburgh phenomenon, but come from regions upwind of Pittsburgh, from power plants, industries and other stationary sources and from motor vehicles in Ohio, Indiana and even farther away. The free ammonia is coming from the midwest as well, from farms and especially from cattle and pig waste lagoons. (It turns out that there is a relatively cheap way to cut airborne ammonia by putting straw over the lagoons. This puts the ammonia into the water and makes a different problem, but it cleans the air.)

Organics: Recently, the Pittsburgh region was ranked very high in the U.S. for particulates, but driving that ranking is really the subregion of the Clairton area. The researchers sat on a hill above Clairton and measured particulates with a single particle mass spectrometer. A significant fraction of the particles measured at Clairton are alkyl amines, which are indicative of coke making. Additionally, a small fraction of the particles at the Oakland Supersite can be identified as coming from Clairton.

Steel plants also emit particles containing iron and cerium which are quite recognizable as to source, and make up a small fraction of the particles at the Supersite when the wind is blowing in the right direction (i.e., you can pinpoint the source by the wind direction).

Biogenic organics are about 30% of the organics in summer (terpenes released by Reagan’s killer trees).

Very Fine Particulates: On dirty days when we can see the haze, ammonium sulfates and nitrates condense on already existing particles in the air, so that they are in the 2.5 micron range. But on clear days with blue skies there are peak numbers of very small particles in the 30 nanometer (or 0.03 microns) range. These peaks occur in the spring and fall on clear days, and nucleation is similar over hundreds of miles. This, then, is a widespread phenomenon. Ammonia appears to be the controlling reactant. A modest reduction of ammonia can turn off this nucleation pretty well. Fine ammonium nitrate particles (less than 0.1 microns) are believed to cause health effects. These very small particles get caught in the nose and throat, while larger ones land in the lungs. Particles can get into the bloodstream through inhalation and can pass the blood-brain barrier, since autopsies of small animals exposed to carbon-13 tagged very small organic particulates show the carbon-13 in the brain.