This report describes a study designed to measure hemispheric infrared downward-directed irradiance at the earth's surface and ambient aerosol concentrations at Research Triangle Park, North Carolina. A Funk-type net radiometer (with a blackened cavity on the underside) was used to measure the incident all-wave energy. From the value obtained, the observed solar radiation was subtracted to determine the infrared component. The expected incident infrared irradiance was calculated from prevailing atmospheric conditions. Six methods were used for these calculations: four empirical equations based on surface conditions, the Yamamoto chart, and a radiative transfer program using vertical profiles of temperature and moisture. The observed-minus-calculated downwelling irradiances were then compared to concurrent measurements of turbidity obtained with a Volz sunphotometer, nephelometer-indicated atmospheric extinction coefficient, and a relative humidity. These measurements were analyzed by least-squares regression to determine the extent to which incident hemispheric infrared radiation is affected by varying amounts of atmospheric aerosols and relative humidity.

"Prepared for Environmental Protection Agency, Office of Research and Development." "Program Element No. lAA009; ROAP No. 26AAS." "May 1975." Includes bibliographical references (pages 32-35).