Is Canterbury air quality really improving like ECan say?

By Ian Longley

You may have seen a story in The Press (10^th August 2015), or elsewhere, covering the latest air quality monitoring data from Environment Canterbury (ECan). The Press article states:

“Christchurch's air quality is improving but there are still too many high pollution days, monitoring data shows.

In the first seven months of this year, there have been seven exceedances of the PM10 particulate threshold in the Christchurch airshed.

That is a significant reduction on the 39 breaches recorded in 2005 and an improvement on the 19 recorded last year but still well above the NESAQ target [of one].”

In our experience data like this can often be met with a degree of scepticism by the public. After all, Ecan is the regulator and may have a vested interest, some will say, in telling a good news story. Sometimes an independent expert opinion might come in useful.

So here’s mine.

But before that, you have a right to ask: Am I truly independent?

So I work for NIWA, and NIWA has no role at all in air quality monitoring, regulation or policy. We have no statutory role in saying anything at all about this data. The only reason I am about to give you my opinion is because it is my role to help all New Zealanders have access to the best scientific evidence.

So, firstly, is the data of sufficient quality? Emphatically yes. Ecan spend a lot of time and money on ensuring the data is of the highest quality available.

So, do I believe air quality in Christchurch is definitely getting better then? Yes. And yet….

There are two main limitations to this data, as there are to all air quality monitoring done around this country and others.

Firstly, air quality appears to be improving WHERE IT IS MEASURED. The good news is air quality is generally measured where it is expected to be worst. But that does not eliminate the potential that it may actually be getting worse at other unmonitored locations. Our research has shown how air quality can vary a lot from street to street, even in small towns like Rangiora. This doesn’t necessarily mean Ecan are doing anything wrong, it just exposes the fact that you can’t monitor everywhere. Regulatory monitoring sites are very expensive and most towns have only one monitor (two in Christchurch).

That is one of the things CONA is trying to improve. By having lots more smaller, cheaper monitors in any given town we can better ensure that Ecan’s data accurately represents what’s happening across the whole town.

To understand the second limitation let me ask you – WHY do you think it might be that air quality is improving? Is it due to Ecan’s policy efforts? Or might there be some other explanation?

You may already know that air quality is strongly influenced by the weather. If, one year, there are fewer hours with light winds there will almost certainly be an improvement in air quality. And that is just what happens. Every spring air quality officers at councils around the country start chatting to each other about “what kind of a season did you have?” Meaning, was it windy, wet and warm (air quality will have been better) or calm, dry and cold (and therefore worse)?

Deciding whether the difference between this winter’s air quality and last year’s was due to changes in emissions (and effectiveness of policy) or due to natural changes in the weather is a major and pressing research challenge. Until we crack this problem it is incredibly difficult to evaluate whether any given policy is working.

This, again, is one of the problems CONA is designed to help us solve. The Press article goes on to say…

“In the Rangiora airshed, three exceedances have been recorded, while in the Kaiapoi airshed there have been 12 exceedances, according to Environment Canterbury (ECan) monitoring.

Under the NESAQ, Rangiora will only be permitted one exceedance a year from September 2016, while Kaiapoi will only be permitted three.”

So why is Kaiapoi worse than Rangiora? Will they meet the 2016 target? What if 2016 has the “wrong” kind of weather?

The records show that the air quality of both towns fluctuates quite a bit from year to year. Our research has shown that a lot of this can be explained by differences in the weather. But there is one big puzzle we cannot yet explain.

In Rangiora, as in many NZ towns, poor air quality only occurs in winter when winds are very light. But on some winter nights when the wind drops air quality remains stubbonly good. Why? Are people burning less wood on those nights? And if so, why? Or are they just behaving normally, but something other than the wind is keeping the air clean? Is, for instance, the smoke being lofted up away from ground level?

These things are hard to measure. That’s why CONA is testing new ways of gathering more data to understand what’s going on. The better we understand how many homes are burning wood on any given night (and at any given hour) the better we can explain why air quality is good on one night and poor the next. And then, we’ll be able to understand whether the differences in overall air quality from one year to the next are due to fluctuations in the weather, or mean that our emissions are actually changing. Then we’ll be able to judge what kind of policies or interventions are most effective.

So if you live in Rangiora, but haven’t yet signed up to help us with gathering this kind of data, check out the web page and sign up! The more people that join us, the better informed we’ll all be.