Average winter PM10 levels in Carterton have remained fairly static over the 2010, 2013 and 2016 monitoring periods. Daily PM2.5 levels, measured using a reference method for the first time in 2016, failed to meet the World Health Organization guideline. During 2016, there were also two exceedances of the National Environmental Standard for PM10. These exceedances were associated with the strong and unusually persistent anticyclone situated over central New Zealand in the first week of June 2016. This type of synoptic condition is atypical and would be expected to occur about once every 10 years.