Air pollution unexplained

An unseasonal day of high air pollution in Christchurch has authorities scratching their heads to figure out the cause.

The Garden City recorded its seventh high air pollution day of the year on Wednesday.

Timaru also recorded puzzling high pollution readings on Tuesday and Wednesday.

Environment Canterbury air quality science team leader Tim Mallett said it was an unusual time of year for high air pollution. A high air pollution day is one that averages 50 or more micrograms of particulate (bits of pollution smaller than 10 millionths of a metre) per cubic metre of air over the whole day.

That level is a health-based benchmark set by the Ministry for the Environment.

A monitoring site in King Edward Tce in Woolston averaged 51mcg on Wednesday but one in Coles Place in St Albans averaged 20mcg. Mallett said it was not unusual for the two sites to have such different readings.

The main causes of these particulates is the combustion of fuels like wood, coal, petrol or diesel, and is mostly from home heating, industrial activity and vehicles.

Mallett said the particles recorded on Wednesday were relatively coarse, so were unlikely to be from traffic, industrial coal or wood burning.

There were particularly high readings about 3am, 8am and 1pm. He said the 1pm spike was

Tim Mallett Environment Canterbury

near the beginning of a strong norwester, so was likely to have been windblown dust from somewhere nearby.

‘‘There is a possibility that some of the particles are from the Australian dust and fire events but we don’t have any proof of that at this stage, and it is a bit unlikely given concentrations were low at St Albans.’’

Mallett said ECan generally looked for an obvious source when high air pollution days were recorded but there was often limited information it could get after the event.

He said readings at Woolston were ‘‘a lot lower’’ yesterday.

Christchurch’s other high air pollution nights this year were June 28, July 1, 7 and 28, and August 7 and 8.

Parts of the North Island are experiencing a thick haze, expected to stay over the weekend, caused by the 65 bushfires burning in New South Wales and Queensland in Australia.

Raybon Kan’s heart skipped a beat when he met his hero,

Clive James, in 2004.

‘‘There is a possibility that some of the particles are from the Australian dust and fire events but we don’t have any proof of that at this stage.’’