Climate and weather
The weather and local climate affect air quality. Find out how sunshine, rain, air temperature and wind speed can affect air quality in the Waikato region.
Air pollution can change hourly – depending on:
- changes in weather patterns
- the pollutants being emitted.
Within the Waikato region, different areas are exposed to different weather patterns and different levels of air quality. For example, coastal areas in the region are exposed to consistent winds, which help disperse any pollutants. In inland areas, air pollutants can build up when there is little or no wind.
Some towns such as Tokoroa and Te Kuiti, are especially prone to inversion layers. Inversion layers occur when a layer of warm air, which acts like a lid - traps a layer of cold air beneath it. Air contaminants, such as smoke from home fires, get trapped in the bottom, colder layer. Find out about how Waikato Regional Council monitors fine particles (PM10) in the air (for example, smoke).
What the weather is doing can have direct effects on air quality at a given location. For example, sunshine, rain, air temperature and wind can affect the amount of air pollution present:
- Sunshine - makes some pollutants undergo chemical reactions, producing smog.
- Rain - washes out water-soluble pollutants and particulate matter.
- Higher air temperatures - speed up chemical reactions in the air.
- Wind speed, atmospheric turbulence/stability, and mixing depth - affect the dispersal and dilution of pollutants.
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 the day 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.
Inversions are important because the upper warmer layer acts like a lid. The inversion layer traps air contaminants underneath.
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.
The diagram below shows an inversion layer trapping smoke from a home fire.
Air contaminants build up when inversion layers form close to the ground (mixing depth). Inversion layers trap air contaminants which can cause health and nuisance effects.
The weather can also affect air pollution by affecting people’s activities.
For example, in cold weather we tend to:
- light more fires - for home heating
- travel to work in motorised forms of transport more often.
In warm weather we tend to:
- use barbecues more often
- go away for weekend trips or holidays - using motor vehicles.