What's causing NZ's air pollution problems?

Scientists will attempt to map the main drivers of air pollution in New Zealand centres. Photo / Brett Phibbs

One of the worst towns in the country for air pollution will be the focus of a new study aiming to pin-point the problems.

While New Zealand's air was generally clean, many cities and towns were still blighted by poor quality each winter as households turned to wood-burners to keep warm.

The latest data showed burning coal and wood made the biggest contribution to annual levels of what are called particulate matter (PM).

As these pollution-borne particles were small enough to hang in the air, they could be inhaled and increase the risk of heart-related illnesses and lung-related diseases.

But it wasn't just households to blame, but factory fumes and smog from traffic-crammed streets and highways.

Other nasties lingering amid our urban centres included carbon monoxide, nitrogen oxides and volatile organic compounds – all of which could mix to form a troubling greenhouse gas called tropospheric ozone.

The best way we could drive down urban pollution, scientists say, was first finding precisely where it was coming from.

Air quality experts have previously done this through time-consuming, bottom-up accounting exercises.

"There are a range of air pollution computer models that can take a prescribed emissions map for a city and simulate what the resultant pollution levels around the city would be as a result of those emissions," explained Dr Greg Bodeker, of Alexandra-based firm Bodeker Scientific.

"While knowing the level of pollution is useful, knowing where that pollution came from is far more valuable since city officials can then act to close down, or mitigate, those sources."

His team aimed to develop a new way to create maps of pollution sources as a service to town and city officials.

"The method uses measurements of particulate matter in the air around a town or city, a state-of-the-art computer model that can simulate the distribution of air pollution for given emissions, and a smart mathematical technique to infer emissions from measured concentrations."

Specifically, they'd use an approach called inverse modelling – which effectively ran current models backwards.

This took real-world measurements of pollution and then inferred what the pollution map must have looked like, while building in the uncertainties on the maps.

The goal of the two-year project, supported with a million-dollar grant from the Ministry of Business, Innovation and Employment's Endeavour Fund, would figure out precisely how to do this – but it wouldn't be straight-forward.

"Small uncertainties in transport pathways of air parcels from their sources to where they are measured can result in large uncertainties in the inferred pollution emissions fields," Bodeker said.

"Figuring how to mitigate those so-called non-linear effects, will be a huge challenge.

"This is the first time that this inverse modelling approach has been applied at a city scale and the first time that the goal has been to develop an operational capability."

Timaru currently records some of the highest winter-time levels of pollution in Australasia. Photo / File

Their testing ground would be Timaru, which currently recorded some of the highest winter-time levels of pollution in Australasia.

Last year, the south Canterbury town had 48 nights where PM levels crossed the threshold set by the World Health Organisation (WHO).

"After testing and proving our new technology in New Zealand through this project, we will export it globally through a newly established commercial entity as a service to megacities around the world that are hampered by poor air quality," Bodeker said.

"In this way, in addition to tackling a domestic problem of winter-time particulate matter pollution in local towns and cities, New Zealand ingenuity will be exported globally to address an increasingly urgent global problem."

According to the WHO, air pollution causes 1.8 million deaths due to lung disease and cancer every year.

Unless the world tackled climate change, figures would rise by 60,000 globally by 2030, and by 260,000 by 2100.

Other groups working in the project included Niwa, Environment Canterbury, Canterbury University, Otago University, Germany's Karlsruher Institute of Technology and Washington DC-based company Sigma Space.