What percentage of sunlight isn't scattered by the atmosphere? What percentage of sunlight isn't scattered by the atmosphere and instead will arrive at your eyes directly from the sun.
It's been aksed here before but a proper answer hasn't been given.
I was thinking about the effects looking directly at the sun would have for someone on the ground relative to someone in space.
 A: It very much depends on the wavelength, the elevation of the Sun, the altitude of the observer and what pollution is in the atmosphere.
A simple example. At zenith, the extinction in the V band (about 550 nm) is about 0.12 astronomical magnitudes at a pristine observatory site, high on a mountain. This means a fraction $1-10^{-0.12/2.5}=0.105$ is scattered or absorbed.
If you observe the Sun at lower altitudes you multiply the extinction at zenith in magnitudes (roughly) by $\sec z$, where $z$ is the angle from zenith, to account for the number of air masses the light travels through. (NB a better approximation is needed as $z$ approaches 90 degrees.)
At bluer wavelengths the extinction is higher - maybe 0.3 magnitudes/airmass at 400 nm and becomes very large of course as you head towards the UV. This wavelength dependence is largely attributable to Rayleigh scattering. At redder wavelengths it is lower maybe 0.06 magnitudes/airmass.
The presence of aerosols, dust and pollutants all can increase the extinction. At sea level in a city, there could easily be 1 magnitude of extinction meaning 60% of the direct light is absorbed or scattered.
A: A good approach to the question is the Air Mass Coefficient, widely used in solar/photovoltaic context.
It deals with the scattering and extinction of the solar radiation in visible and near-visible spectrum.
This may or may not be a good measure for you, depending on what use you have for your sunlight. E.g. human eyes have different sensitivity at different wavelengths and the AM coefficient does not deal with the spectral distribution at all.
From the linked article:
Above the atmosphere, Sun gives off some 1350 watt per square meter.
The best one can hope for at the surface is like 1100W/m2 (noon, summer, clear sky, high in the mountains)
Depending on the particular elevation, time of the day, weather conditions, etc... it can go as low as less than a single watt (e.g. under a violent thunderstorm where you see more scattered than direct light).
