Air quality in New Zealand has continued to improve over the past decade, but winter smoke from wood and coal burners is still seeing safety guidelines breached in some parts of the country.
The 2014 Air domain report, released today by the Ministry for the Environment and Statistics New Zealand, looks at three key indicators - vehicle emissions, PM10 particulates, and health impacts from PM10.
PM10 is a collective term for very small airborne particles, 10 micrometres or less in diameter, which are associated with health problems, ranging from respiratory irritation to cancer.
The report showed that at a national level, annual PM10 concentrations had declined between 2006 and 2012, falling by 8 per cent.
New Zealand's average national PM10 concentration was the seventh lowest of 32 developed countries in 2011, and in 2012, 87 per cent of monitoring sites in the country - or 48 out of 55 - met the World Health Organisation's long-term guideline.
Over the period, PM10 concentrations fell by 8 per cent in cities, 11 per cent in medium sized towns and 19 per cent in small towns.
But a number of locations still breached PM10 health guidelines, particularly in winter due to wood and coal burners.
On average, guidelines were exceeded more in medium-sized towns, while rural areas had the lowest concentrations of PM 10.
A range of other pollutants are covered in the report, such as carbon monoxide, lead, sulphur dioxide, and nitrogen dioxide.
These mostly met short- and long-term health guidelines, although occasional breaches of guidelines occurred at some sites close to roads or major industry.
The number of homes using wood and coal had declined since 1996, while on-road transport emissions had also declined since 2001, even though vehicle usage had increased.
Key pollutants from vehicles had decreased between 25 and 50 percent, brought about by improvements in New Zealand's vehicle fleet and cleaner fuels.
The report follows the release last week of new air quality data from the World Health Organisation, which featured 17 New Zealand centres among 1600 worldwide cities.
It showed that in New Zealand, PM10 levels were 11.7 micrograms per cubic metre, much lower than the OECD average of 20.9 micrograms per cu m and also much lower than the annual guideline limit of 20 micrograms per cu m set by the World Health Organisation.
Timaru was shown to have the highest PM10 value of 28 micrograms per cubic metre, while Christchurch had the second highest, with 23, although both were based on 2011 records.
Other centres listed, with records based on 2012 levels, were Rotorua (20) Blenheim (19) and Dunedin (18), Auckland (15) Hastings (15) Whangarei (15) Napier (14) Masterton (14) Wellington (13) Hamilton (13) Taupo (13) and Porirua, (12).