I would first be looking for pulp paper plants or similar industrials using sulfuric acids within a fifty mile radius. Emissions output combined with stagnant atmospheric conditions, such as would usually result in fog, would put the odor(s) back along the ground.
Exactly what were the atmospheric conditions last night? Low clouds? fog? little to no wind?
Even light rain, at times, causes the paper mill 30 miles to the east of my hometown to make the outside air smell like an open sewer. Sulfur dioxide, I think, is the culprit.
Could be that too.