asmac

And here's what happens when it's way below freezing: Nunavut tea toss photo at -40 C proves internet gold - North - CBC News

tjspiel

I've done that with just hot water but I don't have the eye for photography that this guy does. It makes a cool sound too.

Bikerdave222

Anyone heard from the OP, TransitBiker lately?

cyccommute 

First, air temperature is just a critical as ground temperature in the formation of ice. Seldom will the ground be cold enough to form ice if the air blanketing it is above the freezing point of water...mostly because the water in the air is above the freezing point of water. Any water deposited on a cold surface is going to give up its heat to the surface warming the very top layers enough that surface where freezing can occur will quickly warm above the freezing point.

Well the "exhaust" from an internal combustion engine is composed of water and carbon dioxide. If the engine is running poorly, it may have a bit of unburned hydrocarbon in it...not likely in the age of catalytic converters...and, if it is starved for air, a bit of carbon monoxide...again not likely in the catalytic converter age. It will also have some oxides of nitrogen in it, although, again, that is handled by modern catalytic converters. Of the possible components of car exhaust...carbon dioxide, carbon monoxide, nitrogen oxides, unburned hydrocarbons and water...only water has any possible chance of condensing at temperatures experienced on the inhabited bits of Earth. Unburned hydrocarbons might condense out of the air if they were there quantities several fold higher than possible with even a poorly tuned IC engine and if the temperature was extremely cold. Even then, it is unlikely that hydrocarbons would form a visible cloud that water vapor does when it condenses.

The only component of a car's exhaust that can condense is the water vapor and, due to the properties of water and hydrogen bonding, form "clouds" that are visible. But, as I pointed out post 156 above, even if every last drop of water could be wrung out of a car's exhaust...which is impossible...there isn't enough water in car's exhaust (or even hundreds of car's exhausts) to cause icing. Yes, the water condenses out of the exhaust and some of it reaches the ground but most of it is going to be mixed with other air. If there is sufficient water in the air over the pavement or ground, it can condense out an form black ice (which is really just clear and colorless) on the road surface but the water vapor in car exhaust is going to be an insignificant contribution to the process.

I have little problem with the formation of "black ice" nor explanations on how it forms (with the exception of the idea that car exhaust contributes much to the issue). However to state that "there's no warning before you're on it" is just wrong. Americans over use the term. "I was just driving along when all of a sudden I hit a patch of black ice! No one could have predicted that it was there," is a very common statement...or I should say a very common excuse. "Black ice" doesn't magically appear. The conditions for its formation are very well known. Fog, drizzle, freezing drizzle, etc. all can form "black ice". People who claim they never saw it just aren't being very observant. Every time I've crashed on ice...and I've crashed on a lot of "black ice", I knew it was there or, at least, should have known it was there. It forms from melt water or from freezing drizzle or from a municipality not fixing a water main leak for around 15 years but it always comes with a warning. If I see water on the ground and the air temperature is below freezing and the ground has been cold for a few days, that's a "warning". Or if I'm driving my car and the temperature is below freezing and the road looks wet, that's a warning. Anything else is just an excuse for being unobservant.

I disagree...big surprise. In many decades of observing weather, I seen "black ice" on roads when the roads are warm (very common for Denver) and the air temperatures drop suddenly during a cold front. I've seen "black ice" during freezing drizzle storms in the spring when the roads are warmer here. I've seen "black ice" form during a snowstorm when the roads are still warm but the snow is melting and freezing. I've seen "black ice" following snow storms when the snow melts and runs across the road and refreezes at night when the air temperature drops. Sometimes it forms when the pavement is cold but, from my experience, it's just a likely to form when the roads are warm but are being cooled by an atmospheric event.

fietsbob

Took a Shuttle van to the PDX VA Hospital the 22nd Rest Area stop on top of US26 , stepped out onto a thin transparent sheet if Ice ..

Promptly fell on my Butt.. the others took note , and got out much more carefully.. this may be my next Purchase .. ICEtrekkers Diamond Grip Traction | Free Shipping at L.L.Bean

Im OK On the bike with Suomi Nokian Finland Made Studded tires , its Off the bike trying to walk that can get sketchy.
when the sidewalks are covered with Ice ..

At Sealevel , near the Ocean Its not as regular an occurrence as the Upper Mid west ..

unterhausen

this is an old 8 page thread, so I'm not reading back through it. Anyone post Key and Peele in it yet?

dscheidt

The ground being cold enough to freeze water while the air temperature is above (sometimes well above) freezing is a regular occurrence in the midwest, the upper great plains, and the northeast. Maybe that's not how the weather is where you are, but it happens a lot elsewhere. Condensation isn't an issue, because the dew point can stay well below freezing even when the air temperature is 50F.

tjspiel

But you made some assumptions in that post that weren't true. The black ice you get from exhaust in extreme cold isn't anywhere near 3 mm thick. It's extremely thin. It also doesn't form on horizontal surfaces, it's on the streets, typically in patches around intersections and not on the sidewalks nearby even. So the amount of water required is much much much less than what you're imagining. It doesn't happen at 20° or 30°, it happens at -20° or -30°, - temps you probably don't see often in Denver. Boiling water will freeze instantly when thrown in the air under those conditions.

It's not that hard to believe when you think about it. At those temps the exhaust from my own face will produce quite a bit of ice on the stuff around it, often including (unfortunately) the inside surface of the lenses of my goggles.

cyccommute 

I'm not sure you understand dew point. The dew point can be well below freezing when the air temperature is warm if the relative humidity (RH) is low. For example, Denver experiences 12% relative humidity (often far less) and 50°F temperatures quite frequently. The dew point under those conditions is -1°F. That means that the temperature of the air has to drop to -1°F without a change in the barometric pressure before dew (or frost at that temperature) will start to form. At 100% RH, dew will start to form at 50°F.

Condensation, by the way, is entirely the issue. You can't form ice if you don't "condense" it from the water in the air. My point during all of this discussion is that the conditions for the formation of ice on the roads are well known and aren't magical. Even if the ground is cold enough to form ice, the air above the ground has to contain water and is usually visible in the form of fog or drizzle or some other form of moisture. To say "I hit a patch of black ice unexpectedly" is simply an excuse for not paying attention to the conditions. Look at the video in post 68, for example. Can you really say that Hypnotoad hit the ice "unexpectedly"? The road is looks wet. He has just ridden through a patch of snow pack and the surrounding ground is covered in snow. What is "unexpected" about finding the roads covered with ice?

How thick do you think 3mm is? It is "extremely" thin. It is 0.11". In my book that is "extremely thin".

We've also been through this "black ice forming from car exhaust" before. To recap: Well, see post 138. Simply put, the science just isn't on your side.

I'm amazed that people find throwing a cup of hot water (sorry but it isn't "boiling" by the time the reporters throw it) into very cold air is "surprising". The water has a lot of heat in it and it is suddenly dispersed and the droplets freeze. Big whoop.

When I think about it, it is that hard to believe...that's my point. Think about the ice formation around your face. I get ice forming on my mustache and maybe a bit on my balaclava when I wear one. That's about all. There's no ice on my handlebars or frame from my breath. On a per minute basis (resting), a human breaths out 0.27 g of water. That's more than a car puts out on the same basis. If, like you propose, a car's exhaust can be responsible for "black ice", you should see ice all over your bicycle from your breath. There's more of it and there is less mixing. Bicyclists aren't terribly aerodynamic but we are also moving slower and have less volume so we are stirring the air around us less.

As for the fogging of you goggles, that's just dew point. You raised the dew point in inside the goggles and lowered the temperature of the goggles to the point where the air can't hold the water anymore. It condenses out and deposits on the cold surface. If you remove the goggles, the air inside mixes with drier air outside and the fog goes away.

Edit: Today is kind of cold here and I was observing something that should dispel the "car exhaust condensing and causing black ice" thing. Take a look at the chimney of a house. The house isn't moving so any exhaust from the chimney doesn't mix as well as a car's exhaust does. The chimney of a house is also more insulated than a car's exhaust so the bricks or metal around the chimney will be closer to the outside temperature. Do you see ice forming on house chimneys? I can't say that I ever have even in the coldest of temperatures. If "black ice" can form from car exhaust, you should see vast deposits of ice around the tops of chimneys or on the roofs of houses. They are a stationary, and nearly constant, source of water vapor.