Gas in Atmosphere to Block Out Sun?

Might be instructive to run a Google search on 'atmosphere of venus' as this sounds similar to what you want.

How would they live with no sunlight = no food?

Sammychel said:

For one of the novels I'm writing, one of the key elements is the fact that something has happened to permanently darken the sky. The explanation for this I've come up with is that, in light of the ozone layer's destruction, some scientists created a compound which they believed would replenish it through chemical reactions (essentially, add a little bit and it would continue to react until the layer was re-created). Something backfired on them, however, and essentially created a thick coating that blocks the sun's light. So, in the "day" the sky looks dark red, and at night it's pitch black (stars/moon don't have much chance of coming through either).

Question being, how plausible is this, and what would be a logical scientific explanation for it? Also, what would probable effects in, say, temperature be?

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This sounds extreme - there are ways of doing it, but it's probably not as easy as "something going wrong" unless what's known about the atmosphere is seriously in error.

There's precedence for this, though. There's been a "natural" occurrence that's illustrative:
http://en.wikipedia.org/wiki/Krakatoa
http://en.wikipedia.org/wiki/1883_eruption_of_Krakatoa
There's also several man-made ways of doing it. It would be an indirect consequence of nuclear war:
http://en.wikipedia.org/wiki/Nuclear_winter

There are ways that it can be done directly, as in sending up atmospheric aerosols (the same sulfur dioxide that volcanoes spew out in large volumes) - this is one of the main ideas (other than, of course, reducing greenhouse gases) for battling global warming:
http://www.wired.com/wiredscience/2009/01/georank/
I recall the book "Superfreakonomics" says this would only cost $20 million or so (per year?) to do, so it might be possible that several countries and rich individuals start doing it all about the same time AND with all of them keeping secret what they're doing (never mind how to keep secret a several-miles-high smokestack!), then in a few years time they realize their mistake and that they've gone too far. This may not be permanent, but it could easily last several years. Maybe, after a few years after the event when the effect is lessened, toss in a couple of big nuclear strikes that cause huge city and forest fires over a recently drought-plagued area, to inadvertently pump in even more sun-blocking stuff into the stratosphere. "When it rains, it pours."

ULTRAGOTHA said:

How would they live with no sunlight = no food?

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Not very well, but you can bet Japan, Germany and other would be firing up all the decommissioned nuclear power plants.

ULTRAGOTHA said:

How would they live with no sunlight = no food?

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There are creatures (plants and animals) that live in caves in complete darkness. So, people can theoretically adapt to living without sunlight. Plus if electricity is still functional, then plants can be grown under artificial light.

benbradley said:

There are ways that it can be done directly, as in sending up atmospheric aerosols (the same sulfur dioxide that volcanoes spew out in large volumes) - this is one of the main ideas (other than, of course, reducing greenhouse gases) for battling global warming...

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Being pedantic, they are atmospheric aerosols formed from sulphur dioxide. The difference is important, however, because the process relies on oxidation reactions (which, incidentally, scavenge ozone). I must admit this idea makes me smile because it is so whacky - countering a debatable anthropogenic change in climate by trying to force one.

As for the original question, it is not possible to get a red sky during the day (other than at sunrise or sunset). Rayleigh scattering gives us the blue colour (and red at sunrise/sunset), but it only works for short wavelengths (i.e. blue light).

The most logical explanation for reducing sunlight would be from an attempt to increase cloud cover somehow, although it's hard to see such a change being permanent because clouds are almost entirely restricted to the dynamic part of the atmosphere.

I think your planet would cool down in a hurry, heralding in another Ice Age.

Or so much heat would be trapped, ala Venus, and be unable to escape, the planet would become another Venus.

So many variables, so many things to think about.

Two things crossed my mind: Nuclear winter and out-of-control greenhouse effect.

So what's needed for life to survive:

Consider what is needed to run electricity. One might be able to pull off a wind farm because chances are, winds are going to get a lot worse. Other than that, it's going to be difficult to refine nonrenewable energy sources; solar power is out of the question; tidal and hydroelectric would be either frozen solid or boiled away (and thus leading into other issues, such as water sources and tidal pull, because tidal pull will probably affect the Moon's orbit); geothermal issues might also be a concern, especially if there's no tidal pull. More volcanoes could exacerbate the situation, darkening the sky further.

The compound you speak of is science fiction--probably force field-related. It would probably have to be something done at a molecular level.

This sounds like an extinction level event to me -- I'd be interested to see how you're going to pull this off.