- This topic has 8 replies, 6 voices, and was last updated 11 years ago by
.
-
Posts
-
I was wondering today why the weather in Chengdu is always foggy?
Is it because the geographical location of Chengdu? Climate? Or is it because of the pollution in the city? Provide links if possible.
I lived in Beijing for a couple of weeks though it has a high level of pollution there also but you’re most definitely come by a sunny day with blue skies every 2 days or so.
The geography is the main reason. Chengdu is in a “basin”. Surrounded by mountains so the clouds/fog come in and don’t move out. I’m no meteorologist, but that’s how I understand it.
My understanding is the same – it’s geographic, due to the mountains on each side of Chengdu. Condensation gets trapped in the basin.
Quote:it’s also air pollution.My understanding is that fog contributes to pollution because it gets trapped in the water particles suspended in the air, but the opposite is not necessarily true. I’ve noticed that there isn’t necessarily any connection between the appearance of the sky (fog, haze) and the actual pollution levels. Some days it looks clear and great outside but pollution is high, other days the fog is dense but pollution is low. I’ve noticed this on certain days outside but I’ve especially taken note of this in the Chengdu Air photos which I take daily.
There is no direct correlation to fog and pollution, apart from the fact that fog in and of itself causes particulate matter to remain airborne for longer in the absence of wind. So another words if it happens to be that pollution is being generated above normal levels during foggy conditions, the particulate count will rise exponentially until the fog clears. I’m sure there’s a way you could graph this out under accurate measurement. The only reason this is a common occurrence in Chengdu is indeed that we are both in a basin geographically as already mentioned, and suffering higher pollution counts on a regular basis.
Technically, it’s an inversion layer. The mountains around us, especially the Tibetan plateau, create warm air at high altitude. As the air moves over the higher land and slides over the edge of the plateau, it stays at the same altitude. So we usually have a layer of warm air a few thousand meters above us.
Normally when sunlight (or factories or cars) warms the air at ground level it just rises way up to be carried away by the wind. But in our case the air starts to rise, as expected, and when it hits the layer of unusually warm air above us, it stops. The air from our ground level cools as it rises, so that when it meets the air that came off the plateau, it is actually cooler than the air above it. So, the only way for that dirty air to escape to to go sideways. And since there are mountains on three sides of us, blocking the wind, it just stays here.
Back when agriculture was the main activity here, the trapped air would have just formed clouds, great for growing more crops. But now that we have industrial pollution, things are kinda f-ed.
Quote:Technically, it’s an inversion layer.This is the best description of the atmospheric qualities as they relate to pollution that I’ve read. Thanks Brian.
- The forum ‘General Discussion’ is closed to new topics and replies.