When you say, 'How often are we monitoring', as Ian mentioned there, we're monitoring, theoretically, 24/7. We have continuous sites across Wales, and they're all available on the Welsh air quality forum website. So, a continuous analyser for nitrogen oxides, for example, will give us a nitrogen dioxide concentration every 15 minutes, which is logged and pushed via the websites, and you can see the real-time data, the live data. A lot of the diffusion tube stuff that I mentioned before, for nitrogen dioxide, which we and all the local authorities use, is a cheaper method, because they're at completely opposite ends of the scale of cost. It's a way for us then to target much larger areas across our authorities, to get a handle on and to quantify the actual concentrations—what are we experiencing at this intersection, this road section. Because a lot of the issues, certainly with nitrogen dioxide, are traffic based, but we also need to know the background concentrations as well.
There's lots of evidence out there to show that nitrogen dioxide will drop off quickly, reducing concentration quickly from the kerbside. So, whilst you might think the exposure is high at the street, by the time you get to the facade of the property 20m away, it has actually dropped. But then there's a different threshold there; there are different metrics on an annual mean or an hourly exposure, which are set now within the regulations. So, that's what we're looking to assess against. Because we know that what's on the route to school is different to what you're experiencing at your actual place of residence. We're constantly looking at that, but we are always in the resource mindframe—we can't monitor everywhere, as much as we'd like to, so we move the easy, cheaper diffusion tube kit around. The real-time monitoring is fixed locations. They're expensive to run, they do cost, but the analysers that we use then are fully EU certified, they are referenced, they are passing the mark, we know the data is robust.
At the moment, with the Welsh air quality forum, there is an audit capacity for the sites, and, also, a ratification process of the data, so that what comes from the website you know is correct. That then can be used by developers and applicants for planning applications. Because in certain areas we will ask for a report on the potential for this development, this site, to impact upon current air quality, and, if you're increasing traffic, what will happen in the future. We will ask that, and lots of discussions have gone on about that. So, it's a day-to-day operation. Resource wise, if we're being asked to do more, yes, there will be an impact upon the local authority, not only in officer time, but actually in purchasing kit. But then, the continuous kit is an upfront loaded cost, once you put the site in, in the right area. And—sorry to go back—there are requirements that we have to meet when you want to site a bit of kit, to be in the right place, so that it's getting a correct measurement—it's not interfered with by buildings or trees or anything affecting how the wind will bring the pollutant through—so that you're getting a robust measurement, and it needs to be in an area that's relevant.