No solution in sight to improve Central Otago's smoggy sky
Frost fighting fans and wind machines are among several hypothetical "novel methods" scientists are exploring to solve Central Otago's winter smog problem.
Scientists from Bodeker Scientific, in Alexandra, have completed a report for the Otago Regional Council, looking at methods to improve air quality in Alexandra.
The use of frost fighting fans and wind machines, emulating a naturally occurring 'low-level jet' wind and drawing air down the Clutha River gorge were among a range of hypothetical schemes that were assessed as possible "interventions" to reduce particulate matter pollution of 10 microns in size or smaller (PM10) concentrations during winter.
Jono Conway, who authored the report, said some Central Otago towns experienced poor air quality in the winter months, primarily due to meteorological conditions that limited the dispersal of smoke from wood burners used for domestic heating.
At present, the Otago Regional Council (ORC) accepted that wood-burners were currently necessary to provide residents with adequate heating during winter months. However, even with a significant portion of wood-burners being upgraded to MfE-compliant models during the past 10 years, non-dispersing smoke still created particulate matter levels that regularly exceeded the standard set in the National Environmental Standard for Air Quality (NESAQ).
The ORC was looking to explore "novel methods" to reduce PM10 concentrations, he said.
Conway examined the effect of several hypothetical schemes to modify the structure or circulation of the atmosphere in various ways, and their effects on PM10 concentrations during high-pollution nights.
One of the novel methods looked at using wind machines to "modify" the inversion and disperse the polluting particles.
A total of 58 machines would need to be installed across the entire area in Alexandra needing intervention, with "moderate" effects, the report says.
"There are several complications to the use of wind machines for PM10 intervention. Wind machines are not able to operate in supercooled fog as there is the potential for severe damage to the machine due to ice buildup on the blades. This could limit operation on cold nights, which typically lead to high PM10 concentrations. In addition, because wind machines have only been investigated for use in agricultural settings, it is uncertain how effective wind machines would be at modifying inversion characteristics in the complex surface environment of an urban area."
The machines were also noisy so could cause a "significant problem" with getting consent.
Each of scheme assessed, would require significant energy inputs (on the order of 10 MW or more) and would need to be run continuously during periods of strong inversions and resultant periods of limited dispersion - conditions typical of Alexandra winter nights, he said.
"With continuous operation, moderate reductions in PM10 concentrations were found for all schemes. To reduce PM10 concentrations to levels needed to meet the NESAQ, it is likely that two or more schemes would need to be run simultaneously.
"No scheme is likely to succeed in reducing PM10 concentrations to consistently meet required NESAQ levels within reasonable energy input limits."