Solar radiation: absence of air pollution trends at Mauna Loa.

Measurements of solar radiation made at Mauna Loa, Hawaii, over a period of 13 years give no evidence that human activities affect atmospheric turbidity on a global scale. Short-term fluctuations in insolation appear to be associated with naturally produced tropospheric aerosols. The intrusion of volcanic dust into the stratosphere results in prolonged increases in atmospheric opacity due to the extended residence times of aerosols in the stratosphere.