KEY POINTS:
A town-known for its pristine mountain vistas is the most polluted in New Zealand - and its picturesque setting is partly to blame.
Alexandra, in Central Otago, tops a list of pollution hotspots supplied to the Herald on Sunday by the Ministry for the Environment.
The top five
spots are all in the South Island, with Rotorua the North Island's worst offender at number six, followed by Tokoroa and Hastings at nine and 10.
The rankings are based on the number of times a year recorded pollution levels exceeded the national standard over the past three years.
Officials focused on key pollutant PM10 - essentially fine particles in the air. Alexandra exceeded the standard level 46 times in one year but Christchurch recorded the highest single concentration - 172 micrograms per cubic metre of air, more than three times the standard.
About 1000 New Zealanders die prematurely each year from air pollution, with a similar number of hospital admissions for respiratory and cardiac illnesses.
Pollution costs the country an estimated $1.14 billion a year in damage to health and productivity.
Ministry senior adviser Louise Wickham said home fires fuelled by wood and coal were the primary source of PM10, except in Auckland where motor vehicles were the culprit.
Geographical features also played a big part. The centres at the top of the list are in basins or valleys with cold winters and frequent windless days.
Otago Regional Council's John Threlfall said Alexandra sat in the bowl of a valley and experienced extreme temperatures.
"The ground cools quickly at night, leaving a very stable, cold layer of air, and clearly people use solid fuel to heat their homes and the smoke's got nowhere to go," he said.
Auckland came in at 20, but the Auckland Regional Council's Kevin Mahon said that was no cause for complacency. The list concentrated on winter peaks but didn't reflect the health risks of long-term exposure, which were up to 15 times greater than the short-term effects.
In winter, home fires were responsible for two-thirds of Auckland's fine particles and Wickham said air pollution was linked to poor house insulation. "It is important that measures to improve air quality are not at the expense of promoting warm, healthy homes," she said.
The rankings were compiled for Clean Heat, a programme run by the Government's Energy Efficiency and Conservation Authority, which funds retrospective insulation and clean heating for low-income householders.