The first blog in this series addressed two critical air pollutants, nitrogen dioxide (NO₂) and fine particulate matter (PM), how they occur on construction sites, impact on health and environment, and what monitoring regulations apply.

In this post we discuss the principal methods used to measure NO₂ and PM and their relevance to monitoring in the construction industry for compliance purposes, for managing pollution events, and measuring effectiveness of mitigation measures.

The next blog considers when, where and how many air quality monitors to install around a site.

There are a wide variety of monitoring techniques available to measure NO₂ and particulate matter. These include “active” (powered) samplers that continuously measure gaseous pollutants (e.g. NO₂ and NO_x) and specific dust fractions (e.g. PM₁₀ and PM_2.5), to simpler “passive” (unpowered) samplers like diffusion tubes which absorb NO₂, and gauges that collect dust deposition for post-analysis.

Active samplers include expensive and sophisticated, automatic analysers that provide real-time, high-resolution measurements of NO₂ and PM concentrations. Such instruments are usually operated according to strict QA/QC guidelines and the readings can be directly compared to mandated air quality objectives/limit values Then there are other lower cost automatic analysers that measure real-time concentrations of NO₂ and PM which are indicative in comparison to the objectives/limit values. Each technique has advantages and disadvantages, and varying applicability to air quality monitoring at construction sites.

Construction site emissions monitoring present unique objectives and challenges for air quality professionals. Some factors to take into account in choosing an appropriate method include:

The table below is based on technical advice published by the Department for Environment Food & Rural Affairs and the Institute of Air Quality Management.

Nitrogen Dioxide NO₂

Particulate matter (PM)

In the United Kingdom, the Environment Agency DEFRA provides technical guidance for Local Air Quality Management which approves the use of optical particle monitors for identifying short-term pollution events at construction, demolition or waste transfer sites, and for short term, local campaigns. Many of these instruments have been certified using the Environment Agency’s Indicative instrument certification scheme MCERTS.

The Greater London Authority requires that all major development sites should have continuous air pollution monitoring carried out, along with noise and vibration. PM₁₀ dust monitoring in real-time is required so in the event that higher concentrations are recorded on these monitors the cause is investigated, recorded and mitigation actions taken immediately. The requirement to monitor PM_2.5 and NO₂ is determined on a case by case basis by the local planning authority depending on the existing air quality in the area and air pollution risks from the development to local receptors.

Environmental agencies in Australia and New Zealand have also identified light scattering instruments as Other Approved Methods for air quality monitoring at construction and demolition sites. The Ministry for the Environment’s Good Practice Guide for Assessing and Managing Dust states that optical instruments can be used for compliance monitoring where their limitations are understood and acknowledged.

Optical and sensor-based instruments offer significant advantages on construction and demolition sites. They can be easily deployed at the site boundary. Remote real-time monitoring can provide SMS/email trigger alerts and information on effectiveness of mitigation measures. Their minimal requirement for routine service and maintenance is beneficial in construction site environments, and they can be used to identify any periods of unexpectedly high levels of dust. Some analysers offer the capability to combine simultaneous real-time NO₂ and PM₁₀ and PM_2.5 measurement with wind speed and direction data into a compact integrated system for total source apportionment.

Read the next blog to learn about siting these monitors around a construction environment.