The Changing Global Environment

pp 235-269

The Upward Trend in Airborne Particulates That Isn’t

  • Hugh W. EllsaesserAffiliated withLawrence Liver more Laboratory, University of California

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Diverse data relating to natural and anthropogenic particulate emissions and trends in atmospheric turbidity are reviewed. It is estimated that man now contributes 13.6% of the 3.5 × 109 tons of primary and secondary particulates presently emitted to the atmosphere annually.

Values derived for the anthropogenic effect on the trend in total airborne particulates (if assumed monotonic) range from 0.06 to 0.4% increase per year. Since such an effect would be only marginally detectable in the available record, the much larger rates of increase which have been published as proof of an upward trend must be due to local or temporary effects and cannot be representative of a global trend. On the other hand almost all urban areas plagued by dirty skies prior to 1950 have shown in recent years measurable improvement in terms of visibility, dust fall, suspended particulates, or the ratio of sunshine in the central city to that at an outlying station. This leads to the conclusion that while an anthropogenic upward trend in airborne particulates existed in the past, it was halted and may even have been reversed over the past few decades.