Pollutants get trapped and are not blown away. Its also the same effect which, in white water, makes keepers on the downstream side of a dam. The power plant developers propose to build 300 foot high smokestacks. These will be below the ridge, which is about 800 feet to 1000 feet high. So, under certain weather conditions, hot exhaust gases, moisture and particulants produced by the power plants will build up in the Valley.
Gas turbines produce a lot of moisture.
You see that as contrails on high flying jets. Water vapor in the air is reduced as the air temperature drops. That s why cold winter air is dry and hot summer air can be very humid. If the air temperature drops and moisture content is right, micro water droplets will form. The vapor needs micro-particles of dust or other solid matter in order to condense out while in the air.