Air quality and dust on construction sites: monitoring protocol

Dust raised by earthworks, material transport, crusher operation, compaction and traffic on unpaved tracks constitutes one of the most significant atmospheric emissions from an infrastructure construction site. To this are added combustion gases from machinery (NOx, CO, SO2 depending on fuel quality) and possible emissions of volatile chemical products for certain specific operations.

IFC Performance Standard 3 frames these emissions under pollution prevention, and PS4 under community health. The IFC Environmental, Health and Safety Guidelines (General EHS Guidelines, section 1.1 Air Emissions) provide the reference thresholds for ambient air quality, aligned with the World Health Organisation guidelines (WHO Global Air Quality Guidelines).

This article presents the applicable thresholds for the main pollutants, the monitoring protocol that produces usable results, the hierarchy of mitigation measures for dust, and the communication framework with affected communities.

Reference thresholds for ambient air quality

The WHO Global Air Quality Guidelines, revised in 2021, are the international scientific reference. They set guideline values, stricter than those in force in many national regulations, which the IFC EHS Guidelines adopt as targets.

For fine particles PM2.5 (particles with a diameter less than 2.5 micrometres), the 2021 WHO guideline is 15 microgrammes per cubic metre averaged over 24 hours, and 5 microgrammes per cubic metre as an annual average.

For PM10 particles (diameter less than 10 micrometres), the guideline is 45 microgrammes per cubic metre over 24 hours and 15 microgrammes per cubic metre as an annual average.

For nitrogen dioxide (NO2), the guideline is 25 microgrammes per cubic metre over 24 hours and 10 microgrammes per cubic metre as an annual average.

For sulphur dioxide (SO2), the guideline is 40 microgrammes per cubic metre over 24 hours.

For ozone (O3), the guideline is 100 microgrammes per cubic metre over 8 hours on average, and 60 microgrammes per cubic metre as a seasonal peak over 6 months.

These values are health guidelines. The IFC, in its guidelines, specifies that a project must either comply with national standards (if they are stricter), or aim for WHO values, and must in all cases assess its contribution to the degradation of pre-existing ambient air quality.

The monitoring protocol that produces usable results

Air quality monitoring on construction sites is only usable in audit if it respects four methodological rules.

First, the equipment. PM10 and PM2.5 measurements are carried out with sensors certified according to a reference or equivalent method (gravimetric for reference, optical for continuous monitoring). Low-cost sensors, increasingly widespread, can be used for internal operational indications but are not admissible as evidence of compliance.

Second, positioning. Sensors are placed at the boundary of identified sensitive receptors (residential areas, schools, health centres), at a height of 2 to 4 metres above ground, at a distance from local sources unrelated to the construction site (high-traffic road, domestic hearth).

Third, duration and frequency. Initial characterisation before start-up typically covers one month with continuous measurement. Monitoring during construction combines continuous monitoring on priority areas and broader periodic campaigns (monthly to quarterly depending on activity level).

Fourth, documentation. Each campaign provides a report that specifies meteorological conditions, concurrent construction site operations, parasitic events, and calculation of averages in accordance with the rules of applicable guidelines.

For projects presenting a high risk to air quality, an atmospheric dispersion model may be required during the study phase. This model makes it possible to anticipate foreseeable concentrations at sensitive points and to size mitigation measures before start-up.

The hierarchy of mitigation measures for dust

Construction site dust is combated according to a hierarchy imposed by PS3: avoid first, minimise next, compensate as a last resort.

Avoidance is achieved through the choice of construction methods. Favour wet cladding over dry crushing. Continuously moisten stocks of friable materials. Cover transport lorries. Limit speeds on unpaved tracks.

Source minimisation covers active technical measures. Regular watering of tracks and storage areas (frequency defined by meteorological conditions, several times daily in dry season). Dust screen between construction areas and sensitive areas. Misting system on crushers and storage areas.

Distancing sources. Facilities generating the heaviest dust (crushers, concrete plants) are placed at a distance from sensitive receptors, ideally downwind of prevailing winds. This basic rule is often transgressed for logistical convenience, with foreseeable consequences.

Temporal limitation. Particularly emissive operations are scheduled outside sensitive periods for residents (outside school leaving times, outside community ceremony periods). This coordination with the community calendar falls under the stakeholder engagement plan.

Compensation through information. When exceedances cannot be avoided during limited periods (critical operations, unfavourable season), prior information to communities reduces acceptance of nuisances without suppressing them.

Complementary monitoring of gases and other pollutants

Beyond dust, certain construction sites require complementary monitoring.

Combustion gases from machinery (NO2, CO, SO2, fine particles) are significant when the machinery fleet is large or when the quality of locally available fuel is low. Monitoring focuses on high-traffic areas (construction site entrances, main tracks) and on nearby sensitive receptors.

Volatile organic compounds (VOCs) are emitted during painting operations, wood treatment, solvent application. Their monitoring targets work areas and worker exposures.

Odours, little regulated but strongly generating complaints, are subject to qualitative monitoring via visual records and tracking of community complaints.

Classic errors

Four errors recur regularly.

Economies on initial characterisation. Without baseline, it becomes impossible to distinguish the construction site's contribution from pre-existing ambient background. This gap complicates complaint handling and weakens the project's defence in case of litigation.

Under-sizing of watering. Track watering is the simplest and most effective measure against dust, but it is often under-sized. A single tanker for a construction site of several hectares in dry season is not enough. Watering frequency must be calibrated to actual conditions, not to a theoretical protocol.

Neglect of inter-seasons. Measures are often adapted to the dry season (high emission) but forgotten in inter-season or short rainy season, where sporadic emissive episodes can still be significant.

Dissociation between monitoring and action. Measurement reports reach the E&S manager but do not trigger operational adjustment. A recorded exceedance must trigger action within 48 hours, not wait for the next monthly committee.

Air quality monitoring on a construction site is neither an abstract laboratory exercise nor simple tick-box reporting. It is the operational link between the productive activity of the construction site and the communities that experience its direct effects. The quality of this monitoring determines at once regulatory compliance, the relationship with lenders, and the social acceptability of the project.

A construction site that treats its dust seriously, that documents its measures, that adjusts its methods according to results, that explains its actions to communities, gives itself a strategic asset. It transforms a potentially conflictual subject into a demonstration of operational rigour. It is a modest investment for an important return.