Similar to last fall, a foul smell has blown into the Twin Cities this week, prompting some to ask on social media where the smell came from and wondering how long it will last.

The unpleasant odor is caused by fertilizer and manure on farms surrounding the metro area, and it is a common occurrence in the fall. According to David Brown, an air quality meteorologist for the state, the manure smell has arrived early this year.

Typically, the smell becomes noticeable in November after crops are harvested and new fertilizer is put down. But Brown said the historically dry weather in recent weeks may have dried out last year's fertilizer to the point that the wind can carry the manure particles from rural areas into the Twin Cities.

"It does seem a little bit early this fall, and that may be because of the drought conditions. The drier soils, dust and those soils are more easily lifted into the atmosphere by gusty wind," Brown said.

He noted that the fertilizer smell does not decrease air quality or make it harmful to participate in outdoor activities.

"It's more of just a nuisance," Brown said, adding that the smell is likely to linger until below-freezing temperatures set in.

The air quality has been listed as "moderate" in recent days in the southern half of Minnesota, Brown said, slightly worsened by wildfire smoke coming from Wyoming and Idaho.

Mike Griesinger, a meteorologist with the National Weather Service in Chanhassen, said the manure smell in the Twin Cities is very common because of how many farms surround the region.