I have beaten it to death, but smog-free days are a pleasant rarity in Santiago. Today Neil and I took a quick run up Cerro Manquehue, a common destination for a 2-hour hike due to its proximity to town. Neil picked me up shortly after 0800 and we were on the trail around 0915. The parking lot was reasonably occupied and we encountered a few people on the trail. But the great surprise was the lack of smog in town.
We spent a little over an hour making our way up to the summit and were rewarded with excellent views of the Andes and the city of Santiago. There was some evidence of smog/smoke in the valleys to the north of town, but the downtown was imminently visible.
After thirty minutes on the summit we re-traced our steps, weaving our way through the ascending crowds. The packing lot was incredibly full by that point; lower down on the road an manned traffic control station had been set up to keep the upper lot from being overwhelmed with cars. Good thing we had gotten up early!