Limestone Slurry Scrubbing. Stack gas is washed with a recirculating slurry (pH of 5.8-6.4) of limestone and reacted calcium salts in water using a two-stage scrubber system for particulates and SO2 removal. Limestone feed is wet ground prior to addition to the scrubber effluent hold tank. Calcium sulfite and sulfate salts are withdrawn to a disposal area for discard.Lime Slurry Scrubbing. Stack gas is washed with a recirculating slurry (pH of 6.0-8.0) of calcined limestone (lime) and reacted calcium salts in water using a two-stage venturi scrubbing. Lime is purchased from "across the fence" calcination operation, slaked, and added to both circulation streams. Calcium sulfite and sulfate are withdrawn to a disposal area for discard.Magnesia Slurry Scrubbing-Regeneration to H2SO4. Stack gas is washed using a two-stage venturi scrubbing. Water is utilized for removal of particulates, and a recirculating slurry (pH 7.5-8.5) of magnesia (MgO) is utilized for removal of SO2. Makeup magnesia is slaked and added to cover only handling losses since sulfates formed are reduced during regeneration. Slurry from the SO2 scrubber is dewatered, dried, calcined, and recycled, during which concentrated SO2 is evolved to a contact sulfuric acid plant producing 98% acid.Sodium Solution Scrubbing-SO2 Reduction to Sulfur. Stack gas is washed with water in a venturi scrubber for removal of particulates and then washed in a valve tray scrubber with a recirculating solution of sodium salts in water for SO2 removal. Makeup sodium carbonate is added to cover losses due to handling and oxidation of sodium sulfite to sulfate. Sodium sulfate crystals are purged from the system, dried, and sold. Water is evaporated from the scrubbing solution to crystallize and thermally decompose sodium bisulfite, driving off concentrated SO2. The resulting sodium sulfite is recycled to the scrubber, and the SO2 is reacted with methane for reduction to elemental sulfur. Catalytic Oxidation. Stack gas is first cleaned of particulates by a high-temperature electrostatic precipitator. Then the SO2 is catalytically converted to SO3, and available excess heat is recovered. The SO3 reacts with moisture in the stack gas to form H2SO4 mist which is scrubbed in a packed tower using a recirculating acid stream to yield 80% acid. The mist is removed by a Brink mist eliminator, and the clean 254°F gas is exhausted to the stack. Acknowledgment I am indebted to T. Y. Yan of Mobil Research and Development Corp. for his help in constructing the material balance tables and A. M. Chung of Drexel University for his valuable suggestions.

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The data base provided by the collection and analysis of California's aerosols lends itself to research efforts in numerous areas. Future work will concentrate on: Element-element correlations, which lead to characterization of sources Aerosol-to-gas pollutant correlations, which lead to information on gas pollutant sources Aerosol-to-visibility correlations, which lead to information on sources of visibility degradation By means of the «-scattering technique, analysis of very light elements (H-»F) leads to subsequent presentation of total, and size-segreated mass values in the 0.1 -20-µ size domain.As of July 1, 1975, the two-year research phase of the program ended, and the system was incorporated into the Air Resources Board monitoring effort at the level of 10,000 station-days of sampling per year.It is our opinion that the aerosol data generated by this program gain their greatest utility in their combination with data presently collected on gas pollutants, weather, and visibility at the same sites by existing ARB programs. AcknowledgmentSpecial appreciation is extended to the efforts of the late Dale Hutchison, who encouraged this program in its early stages. The support of the National Science Foundation was instrumental in developing the analytical system to a standard necessary to support such an effort. Donation of beam handling equipment to this effort by the U.S. Navy is also gratefully acknowledged. The enthusiastic cooperation of the staff of the Crocker Nuclear Laboratory was essential to the performance of this work.Literature Cited(1) Lundgren, D. A., "An Aerosol Sampler for Determination of Particle Concentration as a Function of Size and Time," J. Air Pollut. Control Assoc. 17 (4), (April 1967). (The Environmental Research Corp. Multiday Impactor is of the Lundgren type.) (