3 Nitrogen Oxide (NOx) Emissions
Concentrations of nitrogen dioxide have been measured within a number of urban centres in New Zealand. Results of this monitoring are compared to the following ambient air quality guideline values for New Zealand:
- 200 mgm-3 (one-hour average)
- 100 mgm-3 (24-hour average).
The recommended monitoring method for nitrogen dioxide in New Zealand is AS3580.5.1 - 1993. This method specifies ozone chemiluminescence. Unless stated otherwise, all data presented in this section are based on monitoring methods that comply with AS3580.5.1 - 1993, which is the recommended method in the Good Practice Guide for Air Quality Monitoring and Data Management (MfE, 2000) and is the required method in the Ambient Air Quality Guidelines (MfE and MoH, 2002). The former publication also indicates that some measurements of NO2 in New Zealand are made using passive sampling. Wet chemical methods have also been used in some locations.
3.1 Auckland region
Concentrations of NO2 have been measured at seven sites in Auckland. These sites and their respective site classifications are:
- Penrose (Gavin Street) Industrial dense
- Mt Eden Residential neighbourhood
- Musick Point Special (remote) regional
- Dominion Road Traffic peak
- Khyber Pass Road Traffic peak
- Penrose (ACI) Industrial dense.
Summary data for each site is shown in Table 3.1.
Table 3.1: Summary data for NO2 monitoring in Auckland
View summary data for NO2 monitoring in Auckland (large table)
Figure 3.1 and Figure 3.2 show the percentage of measured concentrations of NO2 within air quality categories at these sites. Of all the sites, the highest concentrations were recorded at Khyber Pass Road where a large proportion of the data were within the 'alert' category for 24-our average concentrations. Guideline value exceedences occurred frequently for both the 24-our average and one-hour averaging periods at this site. The one-hour average guideline value has also been exceeded at Dominion Road in 1994 and at the Penrose monitoring site in 2001.
Figure 3.1: Percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories at Dominion Road, Khyber Pass Road, One Tree Hill and Penrose (ACI site) in Auckland
See figure 3.1 at its full size (including text description).
Figure 3.2: Percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories at Penrose, Mt Eden and Musick Point in Auckland
See figure 3.2 at its full size (including text description).
3.2 Wellington region
Concentrations of NO2 have been measured in the Wellington region since 1998. Initially, monitoring was carried out at the Civic Centre and Huia Pool monitoring sites. Data from these sites indicates NO2 concentrations are well within the guideline values, with 24-hour average concentrations at the Civic Centre typically being between 10 and 33% of the guideline value (Figure 3.3). Monitoring for NO2 in Upper Hutt, Lower Hutt and Masterton indicates concentrations are typically within the 'excellent' or 'good' air quality categories. No guideline value exceedences for NO2 have been measured in the Wellington region.
Table 3.2: Summary data for NO2 monitoring in the Wellington region
View summary of NO2 monitoring in the Wellington region (large table)
Figure 3.3: Percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories in the Wellington region
See figure 3.3 at its full size (including text description).
3.3 Hamilton
Air quality monitoring for NO2 was carried out in Hamilton during 1998 and 1999. Summary data form this site is shown in Table 3.3. Results indicate that while one-hour average concentrations are within the 'excellent' or 'good' air quality categories, a large proportion of the 24-hour average concentrations is greater than 33% of the guideline value (Figure 3.4).
Table 3.3: Summary data for NO2 monitoring in Hamilton
View summary data for NO2 monitoring in Hamilton (large table)
Figure 3.4: Percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories in Hamilton
See figure 3.4 at its full size (including text description).
3.4 Taranaki region
Monitoring for NO2 in Taranaki includes source monitoring of concentrations downwind of major industry from 1996-1998 as well as ambient air quality monitoring during 1997-1998. Additional ambient air quality monitoring for NO2 was carried out during August 2001. All monitoring was carried out using passive samplers. Results are shown in Figure 3.5. It was not possible to graph the percentage of the measured concentrations within the air quality categories because of the limited number of samples. However, with the exception of the New Plymouth data, which were in the 'good' category, concentrations of NO2 were within the 'excellent' category (less than 10% of the guideline value).
Figure 3.5: Concentrations of NO2 measured in Taranaki
See figure 3.5 at its full size (including text description).
3.5 Hawkes Bay region
Some monitoring of NO2 concentrations was carried out in Napier and Hastings during 1998 (Table 3.4). Figure 3.6 shows concentrations of NO2 in these areas are generally 'excellent' or 'good', although the one-hour average NO2 concentrations in Napier show some slightly elevated levels with about 12% of the data between 33% and 66% of the guideline value.
Table 3.4: Summary data for NO2 monitoring in Hawkes Bay
| One-hour average |
Hastings 1998 |
Napier 1998 |
24-hour average |
Hastings 1998 |
Napier 1998 |
|
|---|---|---|---|---|---|---|
|
% valid data |
18% |
12% |
% valid data |
18% |
11% |
|
|
Hours>200 µgm-3 |
0 |
0 |
Days>100 µgm-3 |
0 |
0 |
|
|
99.9 %ile µgm-3 |
34 |
63 |
99.9 %ile µgm-3 |
13 |
28 |
|
|
Maximum µgm-3 |
36 |
66 |
Maximum µgm-3 |
13 |
28 |
Figure 3.6: Percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories in Napier and Hastings, 1998
See figure 3.6 at its full size (including text description).
3.6 Canterbury region
Concentrations of NO2 in Canterbury are limited to measurements in central Christchurch at the Packe Street and Coles Place monitoring sites (Table 3.5). Concentrations of NO2 at these sites are generally within the 'excellent' or 'good' air quality categories, although some one-hour average concentrations during 1992 and 1993 were within the 'acceptable' category (Figure 3.7).
Table 3.5: Summary data for NO2 monitoring in Christchurch
View summary data for NO2 monitoring in Christchurch (large table)
Figure 3.7: Percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories at Packe Street and Coles Place, Christchurch
See figure 3.7 at its full size (including text description).
3.7 Otago region
Air quality monitoring of NO2 concentrations in the Otago region are limited to a small number of 24-hour samples measured using wet chemical methods. Table 3.6 shows the results of this monitoring, which was carried out from 1997 to 1999. No graphical analysis was applied to the data owing to the limited number of samples. Results suggest that on the days monitored, NO2 concentrations were much less than the 24-hour average NO2 guideline value. Note, however, that the measurement method used does not comply with existing recommended monitoring methods and is likely to be indicative only.
Table 3.6: Concentrations of NO2 measured in Otago (wet chemical)
View concentrations of NO2 measured in Otago (wet chemical) (large table)
3.8 Nelson
Air quality monitoring for NO2 in Nelson was carried out at the hospital and fire station air quality monitoring sites during 2001 and at the Victory School site during 2002. Summary data from this monitoring is shown in Table 3.7. Figure 3.8 shows the results of monitoring at the hospital and fire station air quality monitoring sites. Although no guideline value exceedences were measured, a small proportion of both the one-hour and 24-hour average NO2 concentrations were within the 'alert' air quality category at the fire station site. In 2002, the NO2 monitoring carried out at the Victory School site showed concentrations were generally within the 'excellent' or 'good' air quality categories (Figure 3.9).
Table 3.7: Summary data for NO2 monitoring in Nelson
View summary data for NO2 monitoring in Nelson (large table)
Figure 3.8: Percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories at the hospital and fire station sites in Nelson, 2001
See figure 3.8 at its full size (including text description).
Figure 3.9: The percentage of measured one-hour and 24-hour average NO2 concentrations within air quality categories at the Victory School site in Nelson, 2002
See figure 3.9 at its full size (including text description).
3.9 Summary of NO2 concentrations
Concentrations of NO2 are typically 'excellent' or 'good' the majority of the time at most air quality monitoring sites in New Zealand. Several guideline value exceedences of the one-hour and 24-hour guideline values have occurred each year at the Khyber Pass Road site. This site is classified as 'traffic peak'.
