Benzene levels in air

Methods - how we monitored benzene levels in air

• Where and how we collected the data

  Waikato Regional Council monitored concentrations of benzene in Hamilton and Tokoroa. 

  Waikato Regional Council monitored benzene in Hamilton because this is the area where the greatest number of people are exposed and is the area where concentrations are likely to be the highest. 

  Monitoring sites

  There were eight benzene monitoring sites in Hamilton. The monitoring sites are marked in blue on the map below.

  The Peachgrove Road monitoring site was originally used to determine average exposure to benzene, whereas the high-density traffic site on ANZAC Parade (formerly Bridge St) was selected to investigate likely peak concentrations. 

  

  Monitoring frequency

  The monitoring frequency was consecutive sampling of three-month passive absorption badges.

  Monitoring history

  Benzene concentrations were first monitored in Hamilton in 1995/96 as part of a national benzene monitoring programme carried out by the Ministry of Health. Results of that study indicated benzene concentrations in Hamilton met national air quality guidelines of the time. 

  Waikato Regional Council started monitoring benzene in Hamilton at two sites in Hamilton (Peachgrove Road and ANZAC Parade (formerly Bridge Street) in February 2003 and continued through until January 2021.   Another site near Claudelands Bridge was added in 2004 and three further sites (Hamilton Intermediate, Greenwood St, and Tristram St) were added in 2006. In 2019, the Hamilton Intermediate site was removed and two additional sites were added, namely Clyde Street/Wairere Road and Lorne Street (Close to the Ohaupo Road intersection). In Tokoroa monitoring commenced in May 2003 and concluded in February 2004.

  Measurement technique

  Passive sampling for benzene was carried out using BTEX passive absorption badges. The method used is as described in the survey carried out by Stevenson et al.,(1999) with duplicate badges being deployed for periods of three months. The analysis was carried out by Hill's Laboratories in Hamilton.
• How this indicator was compiled

  Monitoring results were reported in relation to the National Ambient Air Quality Guideline for benzene, which is the same as the Regional Ambient Air Quality Guideline (section 6.3 of the Waikato Regional Plan). 
• Guidelines and standards

  National and Regional ambient air guidelines for benzene (specified as annual averages) were 10 µg/m³ until 2010 and 3.6 µg/m³ from 2010.
• Limitations

  The passive sampling technique used to monitor benzene concentrations in the Waikato region does not comply with the monitoring method specifications outlined in the Ministry for the Environment’s ambient air quality guidelines.  While this type of passive sampling is recommended as a screening method only, it is the most common approach to benzene monitoring in New Zealand and is significantly more cost effective than compliant methods.

  Another minor limitation was the duration of monitoring carried out in Tokoroa (May 2003 to February 2004), which was less than the annual monitoring requirement by the guideline.  Notwithstanding this, results from this monitoring were of value in assessing a likely annual average concentration.
• Quality control procedures

  Waikato Regional Council, 1999: Environmental Monitoring Technical Manual. Waikato Regional Council, Hamilton. (unpublished)

  Waikato Regional Council, 2003: Quality Assurance Procedures Manual for Ambient Air Quality Monitoring at Environment Waikato. Waikato Regional Council, Hamilton. (unpublished)