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Alexandra is a small town in Central Otago, known as one of the stillest places in the country. Despite its size, the town has very poor air quality during winter months, which is largely due to the cold, calm weather and unique topography.


Alexandra has an inland, continental climate that contributes to extreme temperatures during winter and summer. It is not unusual for overnight temperatures in winter to reach -10°C for several nights in a row. The main source of PM10 in Alexandra is from domestic heating appliances, such as wood burners.

Strong temperature inversions result during periods of calm, still weather and clear skies, forming overnight and into the morning. An inversion layer occurs as the ground rapidly cools and so does the air close to it. This cold dense air is trapped at the surface below warmer and more buoyant air.

These events can also cause PM10 emissions to become trapped near the ground and become more concentrated.

Town Summary
Air quality in this town

The main source of PM10 in Alexandra is from domestic heating appliances. PM10 concentrations peak during winter mornings and evenings, times of the day when it is coldest, and when there is little to no wind. Daily PM10 concentrations regularly exceed the national guidelines from May through August but are quite low during the rest of the year.

Sources of air pollution

Home heating Industrial Outdoor burning Traffic Indoor sources Natural sources
  • Show Hide
    • Sources of PM10 emissions
    • Sources of PM2.5 emissions
    Source Annual percentage Winter day percentage
    Home heating Home heating {{emissions.annualhome}}% {{emissions.winterhome}}%
    Industrial Industrial {{emissions.annualindustry}}% {{emissions.winterindustry}}%
    Outdoor burning Outdoor burning {{emissions.annualoutdoor}}% {{emissions.winteroutdoor}}%
    Traffic Traffic {{emissions.annualmotor}}% {{emissions.wintermotor}}%
    Relative breakdown
    Winter day

    The table shows the proportions of the main sources of PM in this town from home heating, industrial activities, outdoor burning and traffic.  (Indoor sources and natural sources of air pollutants are not included in this breakdown). 

    These values come from 2013 data sourced from MfE’s data service.  Consistent methodology was used to calculate these estimates of PM emissions, which allows comparison between towns throughout New Zealand.  Some regional council published emissions information might differ if they were prepared in a different year or used another method. Contact your regional council for more information about PM and other emissions.

Seasonal variation

  • Show wind speed
  • Show temperature



Wind speed (km/h)

Air temperature (℃)

What is this graph showing me?

The graph shows the monthly average PM concentrations at one representative site in this town for the year selected. In many towns in New Zealand, PM peaks in the winter when air temperatures and wind speeds are lowest as more people heat their homes during colder weather, and still conditions mean that there is no wind to disperse the air pollutants.

Sites 2
Monitored sites in Alexandra

Monitored sites in this town can be categorised according to location:

  • Residential: Air monitoring site is in a suburban area with a relatively high population density, but not close to a busy road or industry.
  • Traffic: Air monitoring site is very close to a busy road or intersection.
  • Industry: Air monitoring site is close to industry, including heavy commercial and processing factories.
  • Coastal: Air monitoring site is close to the coast where there are high levels of sea salt in the air.
  • NES: A site monitored for compliance with the National Environmental Standards for Air Quality (NES-AQ).

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