Measurement of the background atmospheric aerosol

Abstract

INTRODUCTION IN THE last 10 years there has been a growing realization of the importance of determining the concentration, size distribution and nature of the atmospheric aerosol and of measuring the changes of these properties with time. The determination of the global background aerosol trend is necessary because of the influence of aerosols in inducing climatological changes, both because of the capacity of the larger particles for initiating the condensation of water and of the properties of the total aerosol population in radiation scattering. There have always been natural atmospheric phenomena associated with the presence of particles, for example the fogs off the Grand Banks of Newfoundland and the spectacular world-wide optical effects associated with single volcanic eruptions, but the cause for present concern is the continual escalation of man's particle-forming activities which has already produced more than local climatological effects in industrialized societies. To establish long-term trends it is necessary to make measurements in an area free from the rapid periodicity, both in sources and in concentration, which occurs in most 'civilized' areas of the world due to man's activities, and this implies working in remote areas where the aerosol level is relatively constant. For this reason the recent United Nations Conference (STRONG, 1972) has recommended the routine measurement of background aerosols and JUNGE (1971), for example, has made aerosol measurements in the air over the South Atlantic Ocean in latitudes from 0 to 40°N. Junge's work is of very great value especially because he was able to distinguish between marine aerosols and air loaded with Saharan desert dusts, but this very fact shows that measurements over the South Atlantic cannot be considered entirely satisfactory as global background determinations since temporal variations do occur in the short term. What is primarily required is an area where the atmospheric aerosol is stored for a considerable time with minimal perturbations. As will be seen this requirement appears to be met by the atmosphere over Greenland in summer.