John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Grainy clouds wafting their way north have contributed to pollution woes in London.
Folks waking up in Eastern Europe with weird, rust-colored coatings on their cars can blame the Sahara Desert, which recently belched up immense dust clouds that have floated as far north as Sweden.
The above image from NASA’s OMPS blog shows dense concentrations of airborne aerosols swirling over northern Africa on Monday, with sandy tongues extending into Italy, France, and elsewhere. The dust was thick enough to trigger health alerts in London this week, as it was expected to form a cap that traps toxic chemicals from farming operations at low levels.
And at least one person in Austria is blaming the desert grime on hazy sunsets:
Scientists have known about the atmospheric wanderings of the Sahara for three or four decades. Depending on the strength of winds, the dust can travel for thousands of miles, winding up as far west as Brazil and the United States. Last summer, a Saharan dust storm raised pollution fears in Houston. And here’s a NASA animation of dust making its way to the Amazon, where it helps fertilize plants with phosphorous.
The space agency writes:
The data show that wind and weather pick up on average 182 million tons of dust each year and carry it past the western edge of the Sahara at longitude 15W. This volume is the equivalent of 689,290 semi trucks filled with dust. The dust then travels 1,600 miles across the Atlantic Ocean, though some drops to the surface or is flushed from the sky by rain. Near the eastern coast of South America, at longitude 35W, 132 million tons remain in the air, and 27.7 million tons — enough to fill 104,908 semi trucks — fall to the surface over the Amazon basin. About 43 million tons of dust travel farther to settle out over the Caribbean Sea, past longitude 75W.