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 optical measurements made during a special study at Shenandoah National Park in the summer of 1991 are used to examine the acidity and how it influences light scattering. Reconstructed fine mass, calculated by summing the constituents, matches measured mass quite well if water associated with sulfates is included. However, reconstructed scattering is much 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 hygroscopic. Uncertainty in relative humidity is also fairly large. Reduction of this uncertainty may allow closer agreement between reconstructed and measured scattering in future studies. Sulfates were found to be about 1/2 neutralized on average during this study.