Dispersion condition categories indicate the ability of the atmosphere to dilute airborne particles (i.e. smoke, pollution, pesticides). Atmospheric dispersion includes both horizontal and vertical dilution of released vapor-like particulates. The higher the dispersion number category the faster atmospheric dilution is likely to occur. When conditions are poor (2) or very poor (1) vapors can stay concentrated for long periods of time. Dispersion categories are: Excellent (Category 6); Good (Category 5); Moderately Good (Category 4); Moderately Poor (Category 3); Poor (Category 2); and Very Poor (Category 1).