Next, measure out about two thirds of a shot of Tequila and poor it into the tank and stir well. You have just made a Margarita with a Tequila concentration of 1 ppm. The Margarita seems pretty weak, but curiously, the human nose can easily detect SO 2 at a concentration of about half of this, or 0.5 ppm. If, on the other hand, you are 20 km directly downwind, the concentration may be only 1 or 2 parts per million. The answer to this question is literally blowing in the wind.
Wind direction is also critical for determining gas or vog concentrations at a given location.
The prevailing northeasterly trade winds typically transport the constant airborne stream of vog around the southern end of the island and up the Kona coast. This is purely a meteorological phenomenon that causes warm, moist fume and steam from volcanic vents to cool, condense, and become more visible in air that is already completely saturated with water vapor. Our ability to see vog is also affected by humidity. The small particles which comprise vog are sub-micron in diameter and actually absorb excess humidity, causing them to become more visible. Consequently, a voggy day can appear to become more voggy simply by an increase in atmospheric humidity.