Earthquake dust has led to the number of high pollution days in Christchurch almost doubling in the past year.
The Canterbury regional council's director of investigations and monitoring, Ken Taylor, says there were 21 high pollution days in the year to 31 July.
This compares with 12 in the same period in the previous year.
Mr Taylor says only nine of those were typical high pollution days, with the other 12 due to the February and June quakes.
High particulate levels were recorded on several days after those earthquakes, especially in February when there was a large amount of windblown silt and debris, he says.
