By world standards urban air pollution in New Zealand is comparatively low. This is because of the country's geographical location in the South Pacific Ocean, the constantly-blowing westerly winds, the coastal location of most large cities, and the limited amount of heavy industry.
Air quality monitoring in New Zealand has often been limited, sporadic, and in response to specific perceived problems. As a result, insufficient data makes it difficult to assess many aspects of New Zealand air quality.
Recent monitoring has uncovered air pollution levels in some urban locations that occasionally exceed New Zealand's air quality guidelines. These pollution events occur most often in inner city 'traffic corridors' but can occur over wider 'ambient areas' in winter or during temperature inversions.
Urban air pollution is caused by the cumulative impacts of wintertime open fires and wood burners, motor vehicle emissions and, in some locations, industrial emissions. Household fires are the main contributors to 'ambient' air pollution while motor vehicles are the main contributors to 'traffic corridor' air pollution. Emissions from industry are more easily managed than the diffuse and dispersed emissions from homes and vehicles.
Carbon monoxide (CO) in heavily-used traffic corridors often exceeds the air quality guidelines, particularly when vehicle density is high and wind speed is low or when winter-time fires add to the emissions from vehicles. CO pollution events also occur in some 'ambient' areas where they are caused by wintertime fires. Monitoring has been sporadic and centred mainly on Auckland and Christchurch, but recent results from Gisborne and Whangarei show the problem also occurs in smaller cities.
Lead levels in the air have been dropping since 1986 when the lead content in petrol was reduced. With the banning of leaded petrol in 1996, airborne lead has become a negligible problem, except for people exposed to uncontrolled lead-based paint removal.
The amount of particulate matter (such as dust and smoke and exhaust emissions from diesel vehicles) in the air has decreased in the past decade and is generally low. The exception is in Christchurch where temperature inversion frequently contributes to high wintertime smoke levels caused principally by domestic fuel burning. Particulate levels may be a concern in any town where wood and coal fires burn on calm winter nights.
Sulphur dioxide levels have been dropping over the past 20 years and are generally low when compared with the Ambient Air Quality Guidelines. The most publicised specific source causing concern is the oil refinery at Marsden Point, near Whangarei; but as with particulates, sulphur dioxide from domestic coal fires can be a problem on still winter nights, even in small towns.
Spraydrift from agricultural chemicals, such as 2,4-D butyl ester, is a cause of frequent complaints in some regions.
There is no evidence at present that acid rain, a serious problem in some Northern Hemisphere countries, is a problem in New Zealand. Rainfall chemistry monitoring by the National Institute of Water and Atmosphere Research (NIWA) has now been terminated because of limited resources and other research priorities.
The development of a national set of air quality indicators, coordinated by the Ministry for the Environment, is expected to improve the consistency and coverage of air quality data in the near future.