– Cloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen, to make them acidic.

– changes in temperature caused by the expansion (cooling) or compression (warming) of a body of air as it rises or descends in the atmosphere.

– Additionally

– The horizontal transport of air or atmospheric properties. Commonly used with temperatures, i.e., “warm air advection”, or moisture, i.e., “moisture advection”.

Issued for weather situations that cause significant inconveniences but do not meet warning criteria and, if caution is not exercised,

– above ground level.

A large body of air having similar horizontal temperature and moisture characteristics.