Measuring long-term trends in air quality
NIWA scientists are working to develop techniques for the analysis of long-term air quality data.
Many of New Zealand's airsheds fail to meet the National Environmental Standard for PM10 (the mass of particulate matter smaller than 10 µm per cubic metre of air) and one role of regional authorities is to develop and implement policies to improve on this. Once new policies to improve air quality have been introduced, regional authorities need to evaluate their effectiveness over time. Good long-term air quality data are needed; so too are ways of analysing the data so they become meaningful."What happens to emissions in the airshed can vary every night," explains NIWA scientist Jeff Bluett. "This is because of varying weather conditions. For example, the night-time temperature, wind speed and direction, and relative humidity, can all vary significantly from one night to the next. Also, we might have a relatively warm winter one year, and a harsh one the next. This makes it very difficult to compare pollutant concentrations, not just over different nights but also between years."
NIWA's challenge has been to develop statistical analyses that tease out key meteorology variables from concentration variables, enabling year-on-year comparisons of air quality. The team is well on the way to achieving this. Four case studies have been carried out in different South Island locations, allowing the team to enhance and refine their analysis techniques.
The first objective has been to develop robust analysis techniques, and in-house expertise in analysing air quality trends. The team is also working on simpler spreadsheet-based tools that can be used by regional authority staff.
The graph on the right is an example of our project's outputs. It shows the year-to-year variation in 24-hour average PM10 concentration for the 198 'high pollution' days, Nelson, from 2001 to 2008.
Air Quality scientist, NIWA