Preliminary four wavelength nephelometer measurements at Mauna Loa Observatory

Abstract

A 4λ nephelometer has been included as part of the aerosol monitoring program at Mauna Loa Observatory, Hawaii. This instrument is capable of measuring the clean air (nighttime downslope wind conditions) aerosol light scattering coefficient of b_sp ≃ 3 × 10⁻⁷m⁻¹, about 1% of the molecular scattering of air. Typical light scattering values for “dirty” (upslope wind) conditions are of the order of b_sp ≃ 5 × 10⁻⁵m⁻¹. Although rare, vigorous fountaining at Kilauea Volcano occasionally ejects particulate into the upper air and encroaches upon the clean air at Mauna Loa. However, volcanism does not interfere significantly with the background monitoring program. The aerosol size information obtained from the 4λ nephelometer functions as an indicator of the aerosol source and therefore of possible global trends in aerosol size or concentration.