Air Monitoring & ResearchTe aroturukinga hau takiwā me te rangahau

Air Monitoring Reports

We monitor air pollution levels, the sources of pollutants and trends in air pollution for Hawke’s Bay.The government has identified a number of air pollutants that are considered important nationally and have set National Environmental Standards (NES) for them. Locally, the main pollutant of concern is PM10 because it is known to exceed acceptable levels in the region’s urban areas, mainly during late autumn and winter. This is mostly due to fires being used to heat homes on chilly, calm nights when smoke from the fires is prevented from dispersing by an inversion layer in the atmosphere.

The Hawke’s Bay Regional Council’s air quality monitoring network includes three stations with automatic beta attenuation PM10 and PM2.5 monitors which continuously record PM10. These are located in Napier, Hastings and Awatoto. The monioring of PM10 in Napier and Hastings sites has been operating since 2006, while the Awatoto monitor has been at its present location since February 2012 after being moved from Meeanee where it was used for a traffic impact monitoring project.   We have been monitoring PM2.5 at St Johns and Awatoto since 2016 and at Marewa Park since 2019.

The objective at these sites is to monitor ambient PM10 and PM 2.5 levels rather than focus on a particular single source. The Marewa Park and St John’s College sites reflect typical residential areas, have average traffic levels and are not dominated by any particular industrial source. The site at Waitangi Road reflects an area dominated by industrial activity. Measurements from these sites are used to monitor the State of the Environment (SOE) and to report on compliance with the new NES for air quality. 

In October 2021 two new Fidas aerosol spectrometers were installed at the Marewa Park and St Johns air quality sites in Napier and Hastings. These instruments simultaneously measure PM10 and PM2.5 (as well as other particle size fractions and particle count) by means of optical light scattering. These instruments will be operating along with our existing beta attenuation monitors for at least a year to ensure continuity of our PM monitoring records.

Screening monitoring

In addition to continuous monitoring, the Council conducts fixed period monitoring (typically one year) at different locations in Hawke’s Bay using low cost monitoring equipment. The purpose of this type of monitoring, called screening monitoring, is to target areas in Hawke’s Bay where no monitoring data exists, to assess whether PM10 or PM2.5 is likely to be a problem or not. Sampling of either PM10 or PM2.5 with a Microvol occurs every 3 days and sample filters are processed the following month in a laboratory. New low-cost monitoring technology allows measurements of PM10 and PM2.5 to be taken continuously and simultaneously.

In recent  years, screening monitoring has been carried out in Wairoa,  and Waipukurau.  The results suggest that the two centres might meet current NES PM₁₀ standards but it’s unsure they could meet a PM_2.5 standard if one is introduced.  A review of particulate standards in the NES is currently underway.

Trends in air quality

The National Environmental Standards (NES) require that PM₁₀ concentrations must not exceed 50µg/m³ (24 hour average) on any more than one day per year in the region’s airsheds. . Since 2006, when continuous monitoring was established in Napier and Hastings, the number of times PM₁₀ concentrations have exceeded 50µg/m³ has varied in Napier between 0 to 5 occasions per year and between 1 and 27 in Hastings.  

Weather conditions during winter influence PM10 concentrations in the air. On windy days the PM10 emitted into the air will be dispersed but on cold, still days a temperature inversion can form in the atmosphere which effectively traps particulates near the earth’s surface. Variations in weather from year to year make it difficult to determine trends in PM10 concentrations over time.

One way of removing the influence of meteorological conditions is to analyse concentrations on days with similar weather. An analysis was undertaken by Dr Emily Wilton of Environet Ltd which looked at PM10 levels only on days when high levels might be expected – on cold days with light winds – referred to as “normalised” PM10 concentrations. The results indicate that concentrations in both Hastings and Napier have been trending downwards over time (Figure 1).

Air Emission Inventories

We use air emission inventories as one tool to identify sources of contaminants within the region and to quantify the contaminants being emitted over a period of time. Quantities are estimated using average emission rates for an activity based on the amount of material used, and, where available, actual emission data, such as from stack monitoring. Inventories undertaken on a regular basis can help to determine the effectiveness of measures undertaken by the Council to reduce emissions.

In June 2005 an Air Emission Inventory was completed for the Hawke’s Bay region. This report quantified sources of PM10 and other contaminants in the air, and was carried out for Hawke's Bay Regional Council by Environet Ltd.

The report provides details of emissions in: Napier, Hastings, Flaxmere and Havelock North; the three areas of Wairoa, Waipawa and Waipukurau jointly; and the rest of the region. It assessed PM10 sources such as domestic heating, motor vehicles, industrial and commercial activities, outdoor burning, orchard heaters, shipping and aviation.

The report’s main finding was that domestic heating (mostly from woodburners) is the largest source of PM10 in Napier and Hastings in winter, which is when concentrations of PM10 exceed the NES for air quality.

In 2010, 2015 and 2020 the inventory was subsequently updated for Napier, Hastings and Havelock North.

The results from each study confirmed that domestic heating was the main source of PM10 in the cities, but that emissions had decreased significantly over time, though in the most recent report the pace of decline had very much slowed. The amount of emissions from domestic, industrial and traffic sources were not measured directly for these studies but estimated from information provided by participants in a telephone survey, discharge consents and traffic modelling.

Source Apportionment Investigations

Compared to emission inventories, source apportionment studies provide a more direct measure of the nature and sources of particles in the air through analytical techniques. It requires the collection and analysis of air samples and because of this is limited to identifying contributions to air quality at specific locations.

A GENT sampler has been located at St John’s College, Marewa Park and near the beach at Awatoto for limited periods, to enable us to identify which sources contribute to fine particulates in those areas.

The contribution of different sources to PM10 concentrations in Hastings was examined as part of a national study. PM2.5 (particles less than 2.5 microns in diameter) was also examined.

In Hastings, five sources were found to contribute to the PM10 concentrations. These were identified as domestic home heating, marine aerosol, motor vehicles, sulphate and soil. For this report, domestic heating sources also included outdoor burning of domestic waste. The main contributor to PM10 concentrations in Hastings was domestic heating, which was responsible for most of the annual concentrations and especially the winter concentrations. This is consistent with the findings of the emission inventories.

The total background or “natural” contribution for Hastings during winter is estimated to be 13-15% of total PM10 (soil and sea spray). The background component of the PM10 needs to be accounted for when developing strategies for reducing PM10 concentrations in order to achieve the NES.

Contribution of sources to particulate concentrations in Napier and Awatoto

A similar type of study was conducted in Marewa, Napier in 2010 and again in 2018. The main sources of particulates in the 2010 study were divided into domestic heating; soil, sea spray and a combination of domestic heating and sea spray. Conclusions from this study were that domestic heating was the main source of total PM10 but that the contribution from natural sources was higher than observed in the Hastings study - as much as 23% on high pollution days. In the 2018 study, biomass combustion was the largest source of PM2.5 (56%) on an annual basis and marine aerosol was the largest component of PM10 (35%). However, biomass combustion was the dominant component of PM10 in winter months. A zinc source was also identified, contributing 6% to annual PM10, and attributed to galvanising activities in the nearby Onekawa industrial area.

Source apportionment studies have also been undertaken twice at Awatoto. The first was conducted over a very short time period (February to May 2010) and focussed on trialling a methodology for estimating sea spray and soil contributions to PM10. The instrument taking samples was located very close to the beach and at that location the amount of sea spray and soil was found to be quite high during the period of the study, comprising on average around 58% of total PM10. The second study, conducted from April 2016 to May 2017 at the air quality site in Waitangi Road, found the PM2.5 and PM10 collected over the year comprised 36% and 56% marine aerosol on average respectively. On peak PM10 concentration days, the contribution increased to 80%. Other sources of PM2.5 on an annual basis included secondary sulphate (25%), biomass combustion (20%) and fertiliser (10%).

Airshed Modelling

An airshed modelling study in Hawke’s Bay was carried out by NIWA for the Regional Council in 2006 at a time when continuous monitoring data was limited. An airshed is an area where air quality is likely, or known, to exceed the NES.

The model simulated the National Environment Standard breaches for a typical year in Napier and Hastings.

The findings at the time indicated that breaches of the NES were likely in Hastings and Napier but that Wairoa, Waipukurau, Waipawa and Otane were most likely to meet the NES.

To attain the NES, the model estimated that emissions of PM10 needed to decrease by 79% in Hastings and 55% in Napier.

The modelling study of PM10 concentrations in Napier and Hastings was updated in 2011/12 by Golder Associates, using monitoring data up to 2010. The purpose was to provide an estimate of the spatial distribution of PM10, to quantify transport of the pollutant between and within airsheds and to update projected reductions in emissions required to meet the NES.

The main findings from this exercise were:

• The peak modelled PM₁₀ (24 hour average) was relatively high in Marewa (the site of monitoring) but so too were concentrations around Tamatea and Pirimai.
• The St John’s site in Hastings was relatively well placed to measure peak concentrations, being within a ring of peak PM₁₀ levels around central Hastings.
• Very little of the PM₁₀ in Napier’s Airzone 1 originated in Hastings and vice versa. Nearly all exceedances of the NES in Napier would still occur if there were no emissions in Hastings and vice versa.
• Dispersion within airsheds was significant. Approximately 30-40% of modelled PM₁₀ at Marewa Park originated within the Marewa Census Area Unit (CAU), with the largest contributions from other CAUs coming from those lying to the west and south. Approximately 30-60% of modelled PM₁₀ at St John’s College originated from the Mayfair CAU, with the largest contribution from other CAUs coming from Parkvale to the south.
• The overall reduction in emissions, from 2010 levels, required to meet the NES was 44% in Napier and 48% in Hastings.  This includes an “unmanageable” contribution from natural sources so the estimated reduction in emissions from domestic heating is 47% and 50% for Napier and Hastings respectively. 

A modelling study was undertaken in 2016 to examine potential effects of outdoor burning from orchard redevelopment activities on the Heretaunga Plains. An inventory was undertaken to determine the scale of orchard redevelopment and it was found that 100 hectares was scheduled for that year. The estimated PM10 emissions from orchard burning averaged to 106 kg per day assuming it was undertaken between May and August inclusive, which equated to approximately 20% of emissions generated from within Airzone 1.

‘Typical fires’ were modelled to assess their impact on the wider area. The results suggested the main impacts were local to the fires themselves. Depending on a fire’s location and the weather conditions, the contribution to airshed PM10 concentrations potentially exceeded 2.5 µg/m3 per fire, which is the 24-hour significance criterion applied to new industrial discharges in polluted airsheds. Discharges above the criterion requires the industry to offset its emissions. Variations in burning conditions and a lack of specific information about the temperature and velocity of the plumes were some of the study’s limitations.