What is nitrogen dioxide?
Nitrogen dioxide (NO2) is a gas in the air. In New Zealand, most human-made NO2 comes from motor vehicles.
When people breathe in NO2, it can cause a range of health impacts, including increasing their susceptibility to infections and asthma. Health impacts from NO2 include premature death, hospitalisations (for cardiovascular and respiratory diseases), and childhood asthma.
Over 2,000 deaths from human-made NO₂ in 2016
In 2016, human-made (anthropogenic) NO2 air pollution in New Zealand caused an estimated:
- 2,025 premature deaths (in people aged 30+ years)
- 8,531 hospitalisations for cardiovascular and respiratory disease, including 845 hospitalisations for childhood asthma
- 13,229 cases of childhood asthma.
If there was no NO2 from human-made sources in New Zealand, then over 2,000 deaths would have been avoided in 2016.
Motor vehicles were the main contributor to health impacts from NO₂
In New Zealand, nitrogen dioxide (NO2) comes mainly from motor vehicles – with most of that (~77%) from diesel-fuelled vehicles. In 2016, the social costs of NO2 air pollution from motor vehicles was $9.4 billion (Figure 1). This was larger than the social costs of human-made PM2.5 (an overall social cost of $6.2 billion in 2016). These social costs reflect the cost of all air pollution impacts to New Zealand - not only in terms of direct costs incurred in the health system but also due to loss of life, lost quality of life and lost productivity.
Overall, the social costs from NO2 were about 61% of the social costs from all human-made air pollution in New Zealand in 2016.
Figure 1: Social costs from human-made air pollution (NO₂ and PM₂.₅) in New Zealand, by air pollutant and source of air pollution, 2016 ($millions)
The largest health impacts of NO₂ were in Auckland and Christchurch
In 2016, the territorial authorities (TAs) with the highest number of premature deaths due to human-made NO2 were Auckland City (685 deaths) and Christchurch City (287 deaths) (Figure 2).
Other TAs with higher numbers of premature deaths from NO2 air pollution included Dunedin City (79 deaths), Tauranga City (74 deaths) and Hamilton City (70 deaths).
Figure 2: Number of premature deaths due to NO2 air pollution (among people aged 30+ years), by territorial authority (TA), 2016
Christchurch had the highest rate of premature deaths from NO₂
Accounting for population size, Christchurch City had the highest rate of premature deaths from human-made NO2 in 2016 (128 deaths per 100,000 people aged 30+ years) (Figure 3).
Other TAs with high rates of premature deaths from NO2 included Dunedin City (108 per 100,000), Napier City (106 per 100,000) and Nelson City (100 per 100,000).
Figure 3: Premature deaths due to NO2 air pollution, rate per 100,000 people aged 30+ years, by territorial authority (TA), 2016
Auckland children experienced the bulk of asthma burden from NO₂
Children in the Auckland region experienced the highest number of asthma hospitalisations due to exposure to NO2, in terms of absolute numbers, in 2016 (Figure 4). This reflects the proximity to busy roads of many children's homes.
Figure 4: Asthma hospitalisations due to NO₂ exposure, among children aged 0–18 years, by region, 2016
Health impacts from NO₂ have increased since 2006
The health impacts from NO2 increased from 2006 to 2016, including premature deaths, hospitalisations and social costs (Table 1). In particular, the number of deaths due to NO2 increased from 1,580 in 2006 to 2,205 in 2016. The increases in these health impacts all remained even after accounting for population size.
These increases are consistent with the increase in the number of diesel vehicles over this time.
Table 1: Changes in health impacts from human-made NO2 air pollution in New Zealand, 2006 to 2016 (numbers and rates)
About one in three New Zealanders are exposed to NO₂ above recommended levels
Higher levels of annual average NO2 concentrations can impact on people’s health. The World Health Organization (WHO) recommends that annual average NO2 levels do not exceed 10µg/m3, in their 2021 air quality guidelines.
In 2016, 31.4% of New Zealanders lived in areas with NO2 levels exceeding the WHO 2021 guideline level (Figure 5). The proportion was lower among Māori (23.1%), but much higher among Pacific peoples (54.5%), reflecting differences in where they live.
Figure 5: Percentage of population living in areas with NO₂ higher than the WHO 2021 guideline (10µg/m3), total population and by ethnic group, 2006 and 2016
For more information on exposure to NO2, see Exposure to poor air quality.