Wind

Wind directions and speeds are measured by the Sarnia-Lambton Environmental Association

• Wind Directions are predominantly northwesterly and southwesterly.
• Wind Speed influences the dispersion of contaminants.

Records of wind directions and speeds aid in determining the sources of contaminants.

Climate

– temperature, precipitation, solar radiation

Temperature and precipitation are recorded by Environment Canada at the Sarnia Airport.

Solar radiation that is received from the whole hemisphere (i.e. global sun plus sky radiation) is measured by the Sarnia-Lambton Environmental Association.

The radiation sensor utilizes a silicon photovoltaic detector.

Atmospheric Stability

Wind speed data are used in conjunction with solar radiation to calculate atmospheric stability. The stability of the atmosphere determines the degree of dilution or mixing of contaminant- emissions with the surrounding air. When conditions occur that cause air movements (winds) to cease, temperature inversions may form. During these times, atmospheric pollutants can build up in localized regions.

Formation of an Inversion

Night Inversion

At night

• as the earth cools, the air next to it is cooled
• this cooled and therefore denser air, with whatever pollutants it contains, is trapped close to the earth’s surface.

Day Dispersion

During the Day

• the sun’s rays warm the earth
• air next to the earth then is warmed
• the warm air rises, cools and descends