Part 1: Why monitor NO2 and PM at construction sites?

It is well known that construction sites can generate and emit many different forms of pollution, the most obvious being material waste, visible dust, noise and vibration. However construction and demolition sites also produce less obvious pollutants which are of serious concern for human health and impact on the environment. Two of these pollutants are a gas called nitrogen dioxide (NO₂) and fine dust particles called particulate matter (PM). In this blog series we will discuss:

In the United States alone there are over two million pieces of construction and mining equipment, which consume over 6 billion gallons (23 billion litres) of diesel fuel per year. The main environmental concern from construction equipment is emissions of air pollutants that impact air quality, climate change and cause a major health burden for construction workers. Collectively these vehicles and equipment are known as Non-Road Mobile Machinery or NRMM.

In inner-city areas construction machinery such as diggers, caterpillars and electricity generators make up more than a quarter of the traffic-related particulate matter emissions. In particular locations the pollution caused by them is significantly higher. The London Atmospheric Emissions Inventory estimates current emissions from NRMM used on construction sites are responsible for 7% of NO_x emissions, 14% for PM_2.5 and 8% of PM₁₀ emissions in London. How do these pollutants occur on construction sites and why are they harmful?

Combustion of fossil fuels from vehicles, power plants and industrial activity produces oxides of nitrogen (NO_x). NO_x is primarily made up of nitric oxide (NO) and nitrogen dioxide (NO₂). NO₂ is of most concern due to its impact on health. However NO easily converts to NO₂ in the air – so to reduce concentrations of NO₂ it is essential to control emissions of NO_x. National ambient air quality standards set NO₂ as a criteria pollutant and indicator of the larger group of nitrogen oxides.

Construction and demolition sites generate NO₂ from diesel or gasoline fuelled engines in industrial trucks, excavators, loaders, bulldozers, mobile cranes, off-road machinery and static engines such as pumps and electricity generators. Idling engines are a significant contributor to NRMM emissions and personal exposure to NO₂.

Scientific evidence links short-term NO₂ exposures with adverse respiratory effects including airway inflammation in healthy people and increased respiratory symptoms in people with asthma. Studies also show a connection between short-term exposure and increased hospital admissions for respiratory illnesses. In addition to contributing to ground-level ozone effects on the respiratory system, NO_x reacts with ammonia, moisture, and other compounds to form small particles. These small particles can penetrate deeply into sensitive parts of the lungs.

Particle pollution or particulate matter (PM) covers all particles suspended in the air, and is a complex mixture of extremely small particles and liquid droplets. In the context of construction sites, the two PM-related concerns of key interest are PM_2.5 and PM₁₀ (another way to define particle size is by measuring respirable vs inhalable dust.) The exhaust from diesel-powered construction equipment includes fine particles, virtually all of which are PM_2.5 (2.5 micrometres or smaller in diameter); exhaust particulate is sometimes called primary PM_2.5. Fine particles such as PM_2.5 are also chemically formed in the atmosphere from various pollutants, some of which are emitted by diesel-powered equipment, and these particles are referred to as secondary PM_2.5.

Construction-related dust includes larger size or coarse particles also known as PM₁₀ (between 2.5 and 10 micrometres). PM₁₀ is generated from bulk material operations on construction sites, such as earthworks, demolition, crushing and grinding operations, soil and aggregate stockpiling, and from smaller activities such as cutting building materials. These operations contribute to windblown dust problems—sometimes called fugitive dust—and the movement of dirt from the construction or demolition site onto nearby roadways. Once dirt or dust from a site has been ‘tracked out’ onto a road, passing vehicles can cause the dirt to become suspended in the air as re-entrained road dust. Fugitive and re-entrained dust particles can remain in the air for days or even weeks.

Particle pollution is linked to a number of health problems, including coughing, wheezing, reduced lung function, asthma attacks, heart attacks and strokes. It also is linked to early death. The fine particulate matter (PM_2.5) in diesel engine exhaust is classed as being carcinogenic to humans and in 2004 the World Health Organisation (WHO) advised that there is no evidence of a safe level of PM exposure or a threshold below which no adverse health effects could occur.
Inner-city areas are particularly at risk. For example, air quality in London is in breach of European legal limits for NO₂ and many areas exceed safe limits for particulate matter as set by the World Health Organisation. During 2010 an estimated 9,500 premature deaths in London were attributable to exposure to NO₂ and PM in the air.
In summary, construction sites as hotspots, contribute considerably to high local concentrations of NO₂ and PM pollution. The health impacts can include:

Environmental agencies set air quality standards and monitoring regulations which are typically specified by local authorities in planning applications for construction and development sites. For example, guidance on monitoring dust and emissions from construction and demolition sites is published by environmental agencies in Australia, New Zealand and the United Kingdom.

While road transport is already subject to many measures reducing harmful NO₂ and PM emissions, construction site emissions have not been sufficiently regulated. However, amongst new initiatives the Mayor of London has proposed the world’s first Ultra Low Emission Zone (ULEZ) for non-road mobile machinery which includes standards to reduce emissions of PM₁₀, PM_2.5 and NO₂ from construction and demolition activity and associated equipment. The ULEZ will take effect from 2019 more than a year earlier than originally planned.

In 2014 the Greater London Authority (GLA) published Control of Dust and Emissions during Construction and Demolition Supplementary Planning Guidance (SPG). The SPG combines standards for both nitrogen oxide (NO_x) and particulate matter (PM) and states that, “continuous site monitoring is an important way for developers to manage the generation of dust including PM₁₀ and PM_2.5 and NO_x emissions during construction and demolition.”

In a strong indication of toughening regulations the GLA further directs that, “all demolition and construction sites should be monitored for the generation of air pollution. It is essential to monitor for dust generation, including PM₁₀. The need to monitor PM_2.5 and NO₂ will be determined on a case by case basis by the local planning authority.”

It is foreseeable that as the ULEZ rolls out PM_2.5 and NO₂ monitoring will become mandatory in addition to PM₁₀ at all construction sites. Other cities looking at implementing ULEZ for reducing NO₂ and PM emissions include Paris, Stuttgart, Berlin, Athens, Brussels, Madrid and Singapore.

Air quality monitoring at construction sites fulfils a number of objectives:

Read about the pros and cons of various monitoring methods for construction sites here.

Aeroqual makes advanced sensors and equipment for air quality monitoring. We help developers, consultants, and local authorities make better air quality decisions by providing them with cost effective and reliable instrumentation and information. Our instruments are used for reliable air monitoring on construction and demolition sites around the world. Please Contact Us and tell us about your requirements. We can also direct your inquiry to a local distributor.