Despite changes to solid-fuel burners, Central Otago town air pollution levels regularly continue to exceed national environmental standards, making the air bad to breathe. Central Otago reporter Lynda van Kempen takes a closer look at the novel methods the Otago Regional Council is exploring to address the problem.
FIifty shades of grey sums up winter mornings in Central Otago towns.
Think smog rather than smut, however.
Freezing temperatures combined with calm conditions means smoke from hundreds of wood burners hovers over the towns for the morning or longer, boosting the air pollution levels.
Technology and the design of wood burners have improved and the heating devices, favoured by many in the towns, now burn more cleanly, providing dry wood is used.
But the smoke still lingers, so options for man-made intervention to disperse it are being explored, to provide the winter winds that Mother Nature is reluctant to dish out.
Alexandra is the focus of the latest studies as it regularly "tops the chart'' of air quality breaches.
Air quality is strongly affected by inversion layers, which trap the cold and smoky air near the ground.
Using masses of wind machines or a giant air blower to reduce the smog, "exporting'' air pollution down the Roxburgh Gorge, has been considered, along with a community heating scheme using the Clutha River as a source of energy to provide central heating for all Alexandra residents.
These ideas and more are being considered by the Otago Regional Council as it develops an air quality strategy for Otago.
Levels of PM10 (particles smaller than 10 microns across) are used to measure air quality.
The particles are so small they can get into lungs, causing serious health problems.
According to the national standard for air quality, by 2020 towns should record more than 50mcg per cubic metre of PM10 particulates in the air on only one day a year.
The council's recent discussion document on air quality said it was hoped upgrades to solid-fuel burners in the past decade would have resulted in a 50% reduction of PM10 emissions but air pollution levels in Alexandra and other Otago towns still regularly exceeded the national standards.
A recent report for the council, prepared by Alexandra-based business Bodeker Scientific, outlines hypothetical ways of reducing those PM10 concentrations.
Although the report's focus is Alexandra, where air pollution levels are the highest within the region, the results are applicable to most Central Otago towns, the report says.
Several hypothetical intervention schemes designed to "modify'' the atmosphere and inversion layer and disperse the air pollution were assessed, including using frost-fighting fans, emulating a naturally occurring "low-level jet'' wind and drawing polluted air down the Roxburgh Gorge.
There were no examples of such schemes in operation anywhere else, the report said.
The council document said improvements in air quality would continue as newly available technology became embedded in communities.
All innovation and progress so far focused on reducing emissions but residential community heating schemes, although untested in New Zealand, might have a place in the future of air quality management, the report said.
"These schemes are technically feasible but they would require a very different kind of utility owner/operation than currently exists. It may be that a small demonstration project involving new development is the best way to prove its applicability in Otago.''
Climate modification techniques to reduce air pollution did not seem feasible as the energy requirements were extraordinarily large.
"The resources needed for these schemes to be successful would be much better spent in improving housing and heating options for households in communities, '' the document said.
Climate-modification options
The latest report looked at "intervention'' methods of dispersing air pollution.
It explored three scenarios:
Wind machines
Machines such as those used in frost-fighting operate by increasing turbulence in the atmosphere close to the ground. For a wind machine concept to be effective over the whole of the Alexandra air zone, it was estimated about 58 fans would be needed.
Drawbacks: The required power consumption, noise and limitation of working in supercooled fog. Usually used in agricultural setting, unsure how effective they would be in an urban setting.
Helicopters could be used but to be effective, they would have to pass over every 30 to 60 minutes, about 25m above the ground. Low-level flying over populated areas would be prohibited under civil aviation rules, so this was not seen as a viable alternative.
Creating low-level jet stream
Some nights when PM10 levels are expected to be high, they are not, because a stream of air is blowing at higher levels - between 50m and 130m above the surface. It is thought this ‘‘jet stream'' brings in cleaner air and encourages the dispersal of ground-level particulate. A low-level jet stream was modelled using a very large blower.
Drawbacks: Energy required to produce enough air movement to achieve even a moderate reduction of particulate would be in the tens of megawatts.
Enhancing airflow down the Roxburgh Gorge
Similar to creation of a low-level jet stream - this scheme would ‘‘export'' polluted air down the gorge. Wind speeds of 40kmh (about 20 knots) would be needed for it to be effective.
Drawback: The power requirements would be extraordinarily large.
Conclusion
The schemes would moderately reduce air pollution levels, if run continuously during typical winter night conditions. However, they require a significant amount of power to run and to reduce PM10 concentrations to the level needed to meet national air quality standards, it was likely two or more schemes would need to be run simultaneously, the report said.
Community heating schemes
Centralising the heating source, and controlling emissions by eliminating hundreds of individually owned and operated solid fuel burners, is one avenue the Otago Regional Council wants further explored.
Bodeker Scientific was already looking at the technical feasibility of using the Clutha River as a potential source of energy for such a system. It would use water-sourced heat pump technology to generate enough heat to supply a small town such as Alexandra.
In community-wide schemes, heat was generated at a central point (boiler or heat pump station) and distributed via a network of pipes to a community or district, providing central heating for homes.
The heat could be conveyed by hot water or steam, fuelled by wood, coal, geothermal, solar or water sources.
Although there were no residential district-heating schemes in this country, such schemes were common in Europe, the council report said. Wood chip, waste geothermal heat and even water could provide fuel for heating. Overseas, the schemes were usually incorporated into new high-density housing areas since they required extensive networks of piping.
In Norway, a water-source district heat pump scheme used sea water to provide 14MW to more than 200 large buildings. In the United Kingdom, a water source heat pump scheme used water from the Thames to heat homes and a hotel. Further investigation into this option was needed, the report to the council said. It might be more suited to new development rather than retrofits in existing housing.
