Note that London smog requires humid/foggy air while LA. smog requires clear, sunny skies (since L.A. photochemical smog requires sunlight for at one of the key chemical reactions).

A reactive organic gas (ROG) is a volatile organic compound (VOC) that, in gaseous form, tends to promote certain oxidizing reactions in the photochemical smog. They are key to formation of the ozone found in our smog.

Oxides of nitrogen, or nitrogen oxide (NOx) is a family of nitrogen + oxygen compounds, with x =1 (nitric oxide, NO) and x = 2 (nitrogen dioxide, NO_2), being the most prominent ones.

Temperature inversions seem to be common for L.A. and London smogs, since high concentrations for any local pollution depend on the inverstion strength and mixing height.

L.A. smog does not have the soot and ash of coal smoke, so the air looks clearer; however, small particles do exist either as emissions or stuff produced from compounds in the smog to cause a haziness to the air. Frequently, in L.A. the air is hazy, but not necessarily from smog---it can come from ocean salt particles growing into small haze droplets from the relatively high levels of humidity that we have along the coast.