EXAMINATION OF THE EFFECTS OF SULFATE ACIDITY AND RELATIVE-HUMIDITY ON LIGHT-SCATTERING AT SHENANDOAH-NATIONAL-PARK

Sulfate aerosols in the eastern United States of America are known to be acidic, at least on an episodic basis. Intensive particle and optic al measurements made during a special study at Shenandoah National Par k in the summer of 1991 are used to examine the acidity and how it inf luences light scattering. Reconstructed fine mass, calculated by summi ng the constituents, matches measured mass quite well if water associa ted with sulfates is included. However, reconstructed scattering is mu ch lower than measured even when acidity-dependent mass and scattering efficiencies are used for sulfates. It is hypothesized that the mass of organic particles may be underestimated and/or organics may be hygr oscopic. Uncertainty in relative humidity is also fairly large. Reduct ion of this uncertainty may allow closer agreement between reconstruct ed and measured scattering in future studies. Sulfates were found to b e about 1/2 neutralized on average during this study.