Last reviewed 8 January 2020

Gordon Tranter considers the nature of ambient air pollution, the risks to health and the precautions that can be taken to protect outdoor workers.

There is a growing concern about the harm to health from exposure to air pollution of outdoor workers. The British Safety Council (BSC), in its current Time to Breathe campaign, is leading the way with its call for air pollution to be treated as an occupational health hazard and for outdoor workers to receive better protection.

Because recognition of the risks from occupational exposure to ambient air pollution is a relatively recent development, many businesses are unaware of the risks to outdoor workers. Within a workplace, the risk of people’s exposure to polluted air can be controlled using well-established methods but this is more difficult for workers outside, particularly those near or on busy roads.

Although employers can do little to improve the quality of the outdoor environment, it is important for them to recognise that exposure to air pollution when working outdoors may be an occupational hazard for their workers. In particular, employers whose workers work outdoors near busy roads, or near combustion engine driven vehicles or machinery, need to assess whether the work exposes employees to harm from ambient air pollution. If so, they need to apply protective measures to ensure any hazardous exposure is adequately controlled.

What is air pollution?

Air pollution is complex as its wide range of sources mean a variable composition. Evidence shows the pollutants with the strongest effect on health are particulate matter (PM), nitrogen dioxide (NO2) and polycyclic aromatic hydrocarbons (PAHs). All result from the incomplete combustion of gasoline and diesel fuel in vehicle engines. Other components include ozone sulphur dioxide, ammonia and carbon monoxide.

Particulate matter: PM10 and PM2.5

Of all ambient air pollutants, it is the fine particulate matter that has the greatest effect on human health. The main sources of PM include combustion engines (both diesel and petrol), solid-fuel (coal, lignite, heavy oil and biomass) combustion for energy production in households, industrial activities (building, mining, manufacture of cement, ceramic and bricks, and smelting) and tyre wear, brake wear and road surface abrasion from all vehicles.

PM is classified according to its size, with the main categories in use being PM10 (particles that are less than or equal to 10 microns (µ) in diameter, where 1µ = 0.001mm), and PM2.5 (particles that are less than or equal to 2.5µ in diameter.

There is growing evidence that it is the particles with a diameter of 2.5µ or less that are the main cause of the harmful effects of particulate matter. While particles with a diameter between 10 and 2.5µ can penetrate and lodge deep inside the lungs, PM2.5, those particles with a diameter of 2.5 microns or less, can penetrate the lung barrier and enter the blood system.

PMs are composed of a variety of components including sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. The available evidence suggests that it is the fine particles of carbon produced by incomplete combustion that is the main cause of the adverse health effects caused by PMs. These carbon particles absorb sulphate, nitrate, ammonium, volatile organics and poly aromatic hydrocarbons on their surfaces.

Who is at most risk from occupational exposure to air pollution?

Many thousands of men and women work outdoors and may be exposed to unhealthy levels of air pollution. This includes street cleaners, refuse workers, telecom engineers, traffic police, drivers, cycle couriers, construction workers, maintenance workers, newspaper sellers, gardeners working in urban areas, teachers, HGV drivers and security guards who work on or near busy roads.

Research by scientists at King’s College London has found that HGV drivers have the highest overall exposure to air pollution. Air pollution levels inside vehicles are frequently higher than those outside as a result of fans and air conditioning units venting exhaust fumes from the exhaust directly into the vehicles.

What are the health risks from ambient air pollution?

In its case for action, the BSC claims there is compelling research pointing to 36,000 early deaths in the UK every year from ambient air pollution.

Outdoor air pollution is associated with a broad spectrum of acute and chronic illness. It can cause asthma, chronic obstructive pulmonary diseases and impaired lung function, lung cancer, heart attacks and stroke. There is evidence that exposure to ambient air pollution can bring about adverse birth outcomes. Children and adults with pre-existing asthmatic and respiratory condition and those with high risk of cardio and cerebrovascular diseases are particularly at risk from increased susceptibility to infection and sensitivity to allergens, and increased risk of arrhythmia, ischemia, cardiac failure, and stroke.

The Royal College of Physicians in its report Every Breath We Take: the lifelong impact of air pollution (2016), identified one of the most vulnerable groups as people who work near busy roads. The World Health Organization (WHO), in its 2013 review of evidence, points to many studies that have shown links between proximity to roads and excess risks for such outcomes as cardiovascular and respiratory mortality. Studies on traffic police indicate that air pollution is linked to abnormal sperm count, mobility and morphology and a significantly higher percentage of spermatozoa with damaged DNA.

In 2013, the International Agency for Research on Cancer (IARC) concluded that outdoor air pollution is carcinogenic to humans. IARC say that people who are more exposed to outdoor air pollution because of their jobs (eg traffic police, drivers, street sellers, etc) are also at increased risk. Diesel engine exhaust emissions (DEEEs), a significant component of outdoor air pollution, has unsurprisingly been classified by IRAC classified as carcinogenic to humans (Group 1).

What is the law on air pollution?

Air Quality Standards Regulations 2010

The EU Ambient Air Quality Directive (2008/50/EC) sets legally binding limits and target values for concentrations of major air pollutants. It was transposed into law across the UK through the Air Quality Standards Regulations 2010. The directive includes limit values for NO2, PM10 and PM2.5, sulphur dioxide (SO2), polycyclic aromatic hydrocarbons and ozone. A number of zones in the UK exceed some of the limit values particularly the limit for NO2. In fact, in October 2019, the UK Government published its latest figures on air pollution data for across the country, which revealed that 83% of reporting zones had illegal levels of air pollution.

The WHO has guidelines for limit values for NO2, SO2, and ozone and also has guidelines for PM10 and PM2.5 using gravimetric measurement.

Control of Substances Hazardous to Health Regulations 2002

The Control of Substances Hazardous to Health Regulations 2002 (COSHH) do not state a specific exposure limit for ambient air pollution as a whole. There are workplace exposure limits (WELs) outlined in EH40/2005 for the individual chemicals (including NO2, SO2 and ozone and black carbon) that are components of ambient air pollution. There is not a WEL for PMs although there is a WEL for black carbon, a component of the PMs.

The COSHH WELs are significantly higher than the Air Quality Standards Limit Values. This means that workers whose work has the potential to expose them to ambient air pollution will not, in all likelihood, experience exposures that exceed limits set by COSHH. Consequently, WELs do not effectively operate in the ambient environment. Instead the Air Quality Standards or the more stringent values in the WHO guidelines should be used to assess the risk.

How to undertake a risk assessment for air pollution

Defra’s UK AIR: Air Information Resource website hosts an air pollution forecast map ( giving advanced information on the expected levels of air pollution for the UK. Information is updated daily early in the morning and provides forecasts for that day, the following day and the following three days. UK Forecast maps can be searched by place name or postcode to give a more detailed local view. The information is in the form of an air quality index which is numbered 1–10 and divided into four bands, low (1–3), moderate (4–6), high (7–9) and very high (10). Recommended actions and health advice are provided for each band.

In addition, air pollution alerts are issued when any of the thresholds in Directive 2008/50/EC on ambient air quality for ozone, NO2 and SO2 are exceeded.

The assessment of the risks from exposure to ambient air pollution while working should take into account the following issues.

  • The air quality index.

  • Whether vulnerable workers could be exposed. Vulnerable individuals include those with heart disease, coronary artery disease, congestive heart failure, lung diseases such as asthma, emphysema or chronic obstructive pulmonary disease (COPD), pregnant women and the elderly.

  • The nature of the environment:

    • is it near to a busy road?

    • is the work going to take place at peak traffic times?

    • is the nature of the site such that pollution could accumulate (eg narrow streets lined with tall buildings can trap pollutants)?

    • what will be the weather do? During wet or windy conditions pollution concentrations remain low, either blown away or removed from the air by rain. During hot weather, pollution is able to build up to harmful amounts. Concentrations also increase in winter when low winds lead to a build-up of traffic pollution.

  • Whether the nature of the task is likely to increase exposure:

    • do the workers have to kneel on or near busy roads as they do their jobs where they might be subjected to higher concentrations of air pollution than if they were standing up?

    • does the task involve working close to fuel, particularly diesel, driven heavy machinery?

Control measures for occupational exposure to air pollution

Examples of measures to protect workers from ambient air pollution include the following.

  • Reducing exposure: consider reducing the working time outdoors, rotation of workers, restricting work during episodes of severe air pollution and using indoor locations for lunch and rest breaks.

  • Avoiding outdoor workers working too close to machines. Also, ensure idle engines are switched off.

  • Providing respiratory protection: arrange for appropriate respirators, fit testing and training of workers. Respirators should only be provided as a last resort when other means of control are not suitable.

  • Avoiding exposure for vulnerable workers: those with underlying health conditions, pregnant women and older workers.

  • Providing medical surveillance: it is worth undertaking medical checks for underlying health conditions that can worsen with exposure to air pollution, eg asthma, COPD and cardiovascular diseases.

  • Reducing exertion and the pace of work and avoiding long periods of strenuous work. The greater the exertion, the faster the breathing and the more pollutants will be delivered to the lung.

  • Using pollution barriers for roadside work. These can cut exposure by up to 20% and are a relatively cheap option.

  • Encouraging workers to help protect themselves from air pollutants. Make them aware that:

    • a good diet containing antioxidants such as vitamin C (oranges, vegetables) can help protect against some of the effects of pollution

    • exercise will help protect their health, particularly their heart and respiratory systems.

The Canairy app

The BSC’s new mobile app “Canairy” has been developed to enable employers and employees to work together to improve personal health throughout the workplace by minimising the risks posed by ambient air pollution.

“Canairy” helps monitor and control outdoor workers’ exposure to ambient air pollution in London within the M25. The app was developed in collaboration with King’s College London and runs on both Apple and Android platforms. It is based on data produced by the London Air Quality Network (LAQN) ( and draws on the LAQN pollution map and the worker’s GPS to calculate a user’s exposure to pollution on an hourly basis.

By mapping an individual’s exposure and linking the values to WHO limits for the major noxious gases (NO2, ozone, PM10 and PM2.5), the app notifies the user if and when their exposure exceeds WHO limits for these substances. As well as notifications, the app provides links to videos with information and advice to help the user reduce their risk.

The app will collect information to enable the mapping of where and to what degree exposure is happening across London. Using this anonymised exposure data relating to their workers, employers will be able to schedule work to avoid exposure to the worst levels of polluted air.

Time to Breathe: the British Safety Council’s campaign

The BSC is advocating a number of recommendations to establish long-term benefits for outdoor workers. It would like:

  • the UK to recognise and adopt the WHO exposure limits for NO2, ozone, PM10 and PM2.5 rather than the current use of the higher values in the EU Ambient Air Quality Directive for threshold limit values on ambient air

  • the Government to establish ring-fenced funding for local authorities to safeguard resources designed to address air pollution

  • the introduction of charging Clean Air Zones in all local authorities identified as in breach of targets, as a means of providing a population level change in road use in the UK’s urban centres

  • improvements in the monitoring of air pollution levels throughout the UK, with every town and city having the same standard of information and data as the LAQN

  • the Health and Safety Executive (HSE) to recognise exposure to ambient air pollution as an occupational health issue, to recognise outdoor workers as a vulnerable group and to undertake the research needed to assess the scale of the problem — this would enable the necessary actions be taken to protect workers who are exposed to its harmful effects on a regular basis

  • the HSE to establish a WEL related to diesel engine exhaust emissions, with aim of reducing the use of diesel engines in the workplace and consequently reducing exhaust emissions, thereby significantly reducing the risks to workers’ health.


In January 2019, Andy Slaughter MP, on behalf of the BSC, asked a Parliamentary Question about how the HSE regulates the exposure of outdoor workers to ambient air pollution. Sarah Newton MP answered that the HSE does not regulate ambient air pollution and has no plans to research its links to workers’ health.

In May 2019, Paul Farrelly, Labour MP, asked the Secretary of State for Environment, Food and Rural Affairs, whether he planned to ensure that ambient air pollution is treated as an occupational health issue and adopt a workplace exposure limit for diesel engine exhaust emissions. The answers were negative.

At present it seems that the HSE continues to demonstrate a lack of interest and it is unlikely that the HSE will become involved in regulating the exposure of outdoor workers to ambient air pollution. This means that it is even more vital that employers actively work to monitor and protect their workers from the dangers of air pollution.