I did mean like a valley, not like just a dip in the road. But explanation noted and welcomed.
Struggling to make sense of this. If our atmosphere were composed of sulfur hexafluoride, bulk CO2 would not pool in low-lying areas at all. It would immediately and vigorously rise, in much the same way that helium does in our current atmosphere.
Gases don’t engage in bulk flow unless they are driven to do so by density differences (buoyancy-driven convection) or by ambient wind (forced convection). Two bodies of differing gas will diffuse into one another over time, but this is different from bulk flow and is unaffected by gravity.
That’s an example of a large outgassing of CO2 that does its damage before it has had a chance to mix with the rest of the atmosphere.
Unless you live near a volcano, that’s not generally going to be relevant.
The fog that you see is not CO2, but water that is condensed out of the air. It sinks because water droplets are heavier than air.
Agreed. I posted it as an example of buoyancy-driven bulk convection, specifically to point out that it’s not the kind of phenomenon that causes elevated ground-level CO2 concentrations low-lying urban/suburban areas.
There is a minor increase in density that comes from condensing the water vapor into droplets - but I think the bigger factor is the fact that the air containing those water droplets has been cooled by the dry ice, making the air itself more dense. A pool of cool air would still persist around the dry ice even if it were completely dry air. The addition of CO2 to that pool of air will also increase its density - and the sublimation of the dry ice to cool that air definitely will be adding CO2 to it.
The above would actually be an interesting job for the OP’s CO2 monitor. What does the concentration rise to in a sink containing dry ice and warm water?
That was my thought. As a tech, I have found if it doesn’t have a calibration sticker on it, don’t rely on it for absolutes – differentials are another matter.
Last August our heat pump quit. It was replaced with a brand new one and a brand new ecobee smart thermostat. In order to get the heat pump to achieve the same temperature (82-F) on the internal thermometer – which was not replaced – the new thermostat had to be set to 70-degrees. The old Honeywell bimetallic thermostat and thermometer were in agreement.
OTOH, the external thermometer has frequently reaches 123-F when the record high at the airport is 122-F, reached twice in thirty years.
I also misunderstood your question, then. On the city-level, I’m basically on the gentle slope of a hill, about 10 blocks down from one of the highest points in the city. That said, Seattle itself is a sea-level city (abutting Puget Sound), but the sound is relatively small, and we have mountains to both sides - the Olympics to our west and the Cascades to the east - each, say, 50 miles or so. So we’re in a bit of a dip, at that level of scale. We have no major fossil fuel burning power plants, so CO2 production is largely the normal urban stuff - cars, houses (particularly in the winter), etc.
The data is a few years old but this animated map shows the way C02 moves around the globe at varying concentrations:
Similar to Lake Nyos, Lake Kivu in central Africa contains an enormous quantity of dissolved carbon dioxide in its waters. In the local area is evidence of massive local extinctions every thousand years which is assumed to be because of outgassing from the lake. It is thought to contain 65 cubic kilometres of methane and 256 cubic kilometres of carbon dioxide. If a landslide hits the water a very large poisonous cloud would suffocate everything in its path. Nobody understood the risk at Kivu until Nyos happened. And Kivu is a giant compared to Nyos.
That was awesome to see. Thanks, @Fiendish_Astronaut!
No, not what I was meaning. If you’re sea level, then there’s always an outlet.
I was thinking of a depression - where the bottom of the valley is lower than all the surroundings. Like a sink, or a caldera-type situation.
We got sinks where I used to live in Johannesburg because of subsidence. Entire blocks of suburbs in a depression in the landscape. Not full-on sinkholes or anything dramatic like that, just the whole circular area is …lowered. Best seen from the air, the mine geology dept. I worked for at the time had the responsibility of monitoring that kind of thing, and they could be quite dramatic from a helicopter.
Seconded, that is a cool site.
Sure, I know what you mean. We have an outlet, of course - the Puget Sound connects to the Pacific via the Strait of Juan de Fuca - but it’s fairly narrow.
[quote=“k9bfriender, post:23, topic:938192”]
The fog that you see is not CO2, but water that is condensed out of the air. It sinks because water droplets are heavier than air.[/quote]
So pour the gas, no water, out of an erlenmyer onto a candle flame. The sinking CO2 will put out the flame, you just won’t be able to see the bulk gas movement.
Right, because the CO2 is not the fog that you see.