Fly ash, dust, fumes, vapors, gases and other forms of air pollution. No emission shall be permitted which can cause any damage to health, animals, vegetation or other forms of property or which can cause any excessive soiling at any point on the property of others and, in no event, any emission, from any chimney or otherwise, of any solid or liquid particles in concentrations exceeding three-tenths (0.3) grain per cubic foot of the conveying gas. For measurement of the amount of particles in gases resulting from combustion, standard corrections shall be applied to a stack temperature of 500° F. and 50% excess air.