Weather and air quality

Wind carries air contaminants away from their source, causing them to disperse. In general, the higher the wind speed, the more contaminants are dispersed and the lower their concentration. However, high wind can also generate dust – a problem in dry windy rural areas.

As the ground heats during daytime the air becomes more turbulent, especially in the middle of the day. Air turbulence causes polluted air to disperse as it moves away from its source.

In contrast, stable conditions often occur at night when the air is cooler. Air contaminants released in urban areas at night, such as from home fires, are not easily dispersed causing localised air pollution.

Air usually cools with increasing height in the atmosphere. However, sometimes an upper air layer is warmer than a lower one. This is called an inversion. In the Waikato, inversions often form on clear, calm nights when the ground cools rapidly.

The upper layer of warm air acts like a lid. It traps a layer of cold air beneath it, and air contaminants, such as smoke from home fires, get trapped in the bottom, colder layer.  These trapped contaminants can cause health and nuisance effects. Air contaminants build up when inversion layers form close to the ground (mixing depth). 

Inversion layers are usually dispersed by wind or by warm air rising as the ground heats up. But if the inversion layer stays in place for a long time pollutants can build up to high levels.

Some towns in the region, such as Tokoroa and Te Kūiti, are especially prone to inversion layers. 

The weather also often determines people's activities, which in affects air pollution.

For example, in cold weather people more often light fires for home heating and travel to work in motorised forms of transport.

And in warm weather we often tend to use barbecues more often and get in our motor vehicles to head away for weekend trips or holidays.