The passage of a thick plume of Saharan dust this weekend led to various internet queries of “dirty rain.”
The term, likely referring to rain falling through this layer of dust, is a colloquial phrase.
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“Dirty rain” is simply rain falling through suspended dust, stemming from Africa, in the atmosphere.
Rain falling through the Saharan air layer may make for dirty cars, but more importantly, these outbreaks, rain or not, typically produce minor air quality issues.
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People with respiratory issues may be impacted in the most prolific occurrences.
Generally, periods of dense Saharan air have a tendency to suppress widespread afternoon thunderstorm development, as well as place a cap on development in the tropics.
The most recent outbreak is proving to do just that.
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June and July provide the peak of these Saharan air episodes for South Florida.
This weekend, Saturday and Sunday yielded milky sunshine in the afternoon with very little in the way of shower and thunderstorm activity.
Unlike acid rain, which contains pH levels nearly 10 times higher than normal raindrops, “dirty rain” is simply rain falling through the layer of dust.
The Environmental Protection Agency studied acid rain in the 1980s, helping achieve major reductions in sulfur dioxide and nitrogen oxide emissions that had effects on vegetation, soils, buildings and other external structures.
While these passing periods of dust with occasional showers may prove “dirty” or inconvenient, it does not prove to be a societal health hazard.
