Our first air quality map
One of the main things we wanted to show with CONA is that air quality is not the same everywhere - even across a small town like Rangiora. Until now information about Rangiora's air quality came from only one monitoring site - the one run by regulator Environment Canterbury (ECan) in the centre of town. It reports levels of particulate matter (PM) every hour. You can find this data at www.lawa.org.nz, or download it from ECan (data.ecan.govt.nz).
Now, however, for the first time we can combine data from the 16 ODINs we had installed at various locations around the town to produce a map of average particle levels during the month of August 2016.
Now you've seen the map, here comes the disclaimers, how we did it and what it means.
Firstly, this map should be treated as preliminary. With further analysis it might change slightly. It is created by firstly averaging up all of the ODIN measurements for the whole month. We then use a process called 'interpolation' in which computer software estimates values in the spaces between our ODINs (ordinary kriging in ArcMap for those in the know). The map is then coloured green for low levels and red for high levels. I have not provided a legend for you to find out what those levels are on purpose. This is because the ODINs are not 'authorised' instruments and should not be used to make comparisons with guidelines or standards. What I will say is that the red areas have PM levels more than 3 times higher than the green areas.
However, what the map does show very clearly is that there is a wide range of values across the town. The ECan monitor is in the red area. That means it over-represents PM levels in the yellow and green areas ON AVERAGE. This is not a problem for ECan. In fact, it is good news, as the air quality regulations actually require ECan (and all Regional Councils) to monitor where it is expected that air quality will be worst. It is just that, until now, identifying where that location would be has relied on rather uncertain dispersion modelling, or guesswork. In Rangiora, then, ECan got it right.
Now, however, for the first time we can combine data from the 16 ODINs we had installed at various locations around the town to produce a map of average particle levels during the month of August 2016.
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| Map of average PM2.5 levels across Rangiora in August 2016, based on interpolation of ODIN data (green = low, red = high) |
Firstly, this map should be treated as preliminary. With further analysis it might change slightly. It is created by firstly averaging up all of the ODIN measurements for the whole month. We then use a process called 'interpolation' in which computer software estimates values in the spaces between our ODINs (ordinary kriging in ArcMap for those in the know). The map is then coloured green for low levels and red for high levels. I have not provided a legend for you to find out what those levels are on purpose. This is because the ODINs are not 'authorised' instruments and should not be used to make comparisons with guidelines or standards. What I will say is that the red areas have PM levels more than 3 times higher than the green areas.
However, what the map does show very clearly is that there is a wide range of values across the town. The ECan monitor is in the red area. That means it over-represents PM levels in the yellow and green areas ON AVERAGE. This is not a problem for ECan. In fact, it is good news, as the air quality regulations actually require ECan (and all Regional Councils) to monitor where it is expected that air quality will be worst. It is just that, until now, identifying where that location would be has relied on rather uncertain dispersion modelling, or guesswork. In Rangiora, then, ECan got it right.
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