If the band of showers stretching from the Midwest to New England dampens voter turnout today, we’ll know what to blame.
Cars. Factories, too.
Meteorologists have long known that particles “seed” rainclouds, a process in which water and ice in the clouds grab hold of the particles, forming additional (and larger) droplets that are more likely to fall as rain. That led to the suggestion that particulate pollution emitted by traffic, businesses and factories, all of which are greater during the workweek than on the weekend (traffic to malls notwithstanding), should make for greater rainfall Monday through Friday. A competing theory, however, held that the increased pollution might instead thwart rainfall, by dispersing the water in clouds over more seeds; that would prevent the droplets from growing large enough to fall as rain.
At least for summertime rainfall in the southeastern United States, the verdict is in: weekday pollution is causing more rainfall midweek than on weekends.
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