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Air Control

The potential health effects from ambient air pollution highlight the importance of control measures to reduce exposure.

When John Saunders arrived in Beijing, one of the first things he noticed was the number of people wearing personal respiratory protection. Having said that, the particular day on which John, a ventilation scientist, arrived was not one of the worst. He recalls that the air quality was rated as moderate.

 "Even so we could still see a mist. But we were told that the week before it had been really bad. People who were there said it was difficult to see between buildings." 

In common with many countries, China has serious problems with ambient air pollution. So much so that companies with a base there are becoming concerned about its effects on their workforces. Interestingly, they are almost beginning to regard ambient air pollution as an occupational hazard. In fact, earlier on this year, Panasonic became the first international company to openly state that it is to pay employees it sends to China a premium to compensate for dangerous levels of air pollution1. And when one large company with a base in China wanted advice on how best to tackle the ambient air pollution problem, it turned to a UK organisation focusing mainly on occupational safety and health - the Health and Safety Laboratory (HSL) based in Buxton, Derbyshire. Thus it was that John and an occupational hygienist colleague from HSL found themselves in Beijing. 

"The company was worried about the long term effects of ambient air pollution on its employees," explains John. "They wanted to know how to minimise their exposure." The employees in question were located in Beijing and other Chinese cities and worked in a range of sites from manufacturing facilities to open plan offices. John and his colleague visited all these sites but their assessment was not confined solely to the workplace.

''We were asked to take an holistic approach, to consider exposure on the journey to work and exposure in the home. Therefore we focused on how to reduce 24-hour exposure," states John.

 To help them, John and his colleague in Beijing were able to tap into the wide range of scientific disciplines back at HSL's site in Buxton. This included HSL's chief medical officer and a respiratory protective specialist.

 Investigations like the one carried out in China by John and his colleagues are ultimately driven by measurement. In this instance, a major driver was an air quality index. Governments rely heavily on air quality indexes in order to report air quality to the general population. Most ambient air quality indexes are based on the measured concentrations of the six main ambient air pollutants.

These are:

Particles <2.5ìm (PM2.5) & Particles <10ìm (PM10)

Sources of particulate matter (PM2.5 and PM10) include diesel-powered vehicles (especially older vehicles) and power plants. The smaller the particles the greater their ability to penetrate the respiratory system. Health concerns centre on breathing and respiratory effects, damage to lung tissue and premature death.

Ground Level Ozone (O3)

Ground level ozone is not directly emitted into the air from a man-made source. It is created by the action of sunlight on other airborne pollutants such as nitrogen oxides and volatile organic compounds. Common sources include petrol vapours and the combustion products of fuels. Ground level ozone particularly affects those with impaired respiratory systems (eg. asthmatics) but healthy adults and children can also be affected. Symptoms can include coughing, nausea, chest pain and pulmonary congestion.

Sulphur Dioxide (SO2)

Sulphur dioxide is a gas produced when fuel containing sulphur is burned. Metal smelting is another source. Exposure affects breathing and can cause respiratory illness, alterations in pulmonary defences and aggravation of existing cardiovascular disease.

Nitrogen Dioxide (NO2)

This is generated when fuel is burned at high temperatures. Major sources include motor vehicle exhaust, electrical utilities and industrial boilers. Exposure can irritate the lungs and lower resistance to respiratory infections such as influenza.

Carbon Monoxide (CO2)

Carbon monoxide results from the incomplete combustion of fuel. Motor vehicle exhaust is the major source. Exposure reduces the blood's ability to deliver oxygen to the body's organs and tissues. Those already suffering cardiovascular disease are most at risk. Air quality indexes take into account not only the concentrations of these pollutants but also their health effects.



The Chinese Government monitors levels of ambient air pollution in its major cities and the general public have ready access to this data via an online pollution index. The relevant index in the UK is the Daily Air Quality Index (DAQI). This uses the highest concentration of five pollutants (nitrogen dioxide, sulphur dioxide, ozone, PM2.5 and PM10) to determine the overall air pollution index for a site or region.

 The reported DAQI is expressed on a scale of 1-10 with level 10 posing the greatest hazard. The scale is split into four bands: level 1, 2, 3 - low; 4, 5, 6 - moderate; 7, 8, 9 - high; and 10 - very high. Each banding is associated with two sets of advice, each aimed at a specific group. One set advises "at risk individuals" (eg. adults or children with heart or lung problems). The other targets the general population. For example, for levels 1, 2 and 3 (low) the advice for both groups is to "enjoy your usual outdoor activities". For level 10, however, the advice for "at risk" individuals is "adults and children with lung problems, adults with heart problems, and older people, should avoid strenuous physical activity. People with asthma may find they need to use their reliever inhaler more often" and the advice for the general population is "reduce physical exertion, particularly outdoors, especially if you experience symptoms such as a cough or sore throat".

 All the different air quality index scales used by different countries are similar to the DAQI and all work on the same principle. And as far as PM2.5 is concerned all the indexes are identical. In December 2012, in recognition of the fact that it is probably the most harmful ambient air pollutant, the standard for PM2.5 became more stringent. Since September 2013, all countries use the same conversion scale to calculate the index for these particulates.


 Controlling exposure

The World Health Organization (WHO) states that "outdoor air pollution is a major environmental health problem affecting everyone in developed and developing countries alike". A 2013 assessment by WHO's International Agency for Research on Cancer (IARC) concluded that outdoor air pollution is carcinogenic to humans. The potential health effects from ambient air pollution highlight the importance of control. As far as John's assignment in China was concerned, the emphasis was on straightforward and pragmatic measures to control exposure.

 "The measures we recommended depended on the building. Some had no form of mechanical ventilation systems, ie. they were naturally ventilated. The ventilation came from opening and closing windows, cracks in the building itself and gaps around door seals and window seals. In situations such as these the ventilation is driven by wind pressure on the building and by temperature differences. The ventilation in the building will vary from day to day and there will be no active filtration of particulates. The only filtration will be that which the building itself offers. Thin gaps in the building, for example, will remove particles from incoming air as the particles impact the sides of the gap. In addition, there will be some deposition on surfaces. As a result you will tend to get lower levels of ambient air pollution inside the building than outside. But, of course, it also has to be remembered that there are indoor pollutants. For example, photocopiers will generate ozone and particulates in a range of sizes. Human beings generate carbon dioxide." After assessing each naturally ventilated building John was able to give specific advice. This ranged from measures such as simply closing the windows on high pollution days to the use of stand-alone air purifier units. For PM10 and PM2.5 these needed to be fitted with HEPA (high efficiency particulate air) filters. These are often referred to as absolute filters.

 Stand-alone air purifiers pull in the contaminated air, remove particulates and gases and recirculate that air through the building. Effectively it is a dilution process. But because air purifiers should not be the default control measure. They could, for example, be restricted to days when the air quality index is high. John concedes that control of ambient air pollution in naturally ventilated buildings can be difficult. There is little control over where the air enters, how much enters and where it goes once it has entered. Nor can you filter the air coming into the building. But simple steps, such as keeping doors and windows shut, can help as can improving the seals around doors and windows and the use of draught excluders.

"One of the buildings we visited had a gap around a glass door that was so large that when it was shut you could easily get your fingers around the edge of it."

 But John sounds a note of warning. "You don't want the buildings to be too tightly sealed. You do need some exchange with the  outside air otherwise you could end up with other problems. For example, a small office with several people in it could end up with raised CO2 levels. And, of course, the building itself may cause pollution. For example, furniture and fittings can release gases into the room when new." The holistic approach to controlling exposure taken by John and his colleagues meant they also had to look at exposure in the home. So would the advice for people in their homes be similar to that for people in naturally ventilated buildings? After all most homes are naturally ventilated. "When we talked to employees a lot of them would actually open windows in the belief that they were letting fresh air in. This belief might well be reinforced if, for example, they were cooking. We also found that in the home many employees went down the route of air purifiers." Of course, a big problem for air purification units, particularly for individuals, is their expense.

"For a Chinese factory worker a high end range air purifier can cost several months wages. And of course the unit should be  fitted with pre-filters, HEPA filters, and carbon filters (for gases and vapours), which need to be regularly replaced." It is easier when considering buildings with mechanically ventilated systems, which many UK offices have, as the air handling unit will usually contain a filtration system. How adequate this is at removing PM2.5 and PM10 needs to be assessed. For indoor work environments therefore, it is possible to take steps to minimise the degree of pollution in the ambient air. Protection for people when they are outdoors can be more difficult.



The protective mask has now become a prominent feature of the Chinese urban landscape. People wear these (usually disposable) masks in an attempt to eliminate or at the very least reduce their exposure to ambient air pollutants. To be effective these must be capable of filtering out the specific contaminants to which the wearer is exposed. However, many disposable masks are designed purely to deal with particulates.

 But simply buying a mask is not enough. Mask failures do not usually happen because the filter fails (provided that is the filtration has been properly selected). Most failures happen because the seal between mask and face is not good enough. To overcome this problem in the workplace, those who have to wear personal respiratory protection to reduce exposure to workplace contaminant must undergo a fit test. This ensures that the seal between mask and face is good enough to control leakage of contaminant into the mask. A poorly fitting mask will result in a fit test failure - as can facial hair. It should also be noted that even people with ordinary looking faces may, unfortunately, have difficulty achieving a good fit. All of which emphasises the importance of a properly conducted fit test.

 But, of course, fit testing is not easy for a member of the public buying a disposable mask for protection when, for example, walking in central London (the smog alert back in April reportedly resulted in many face masks being seen on London streets). But if you do want to wear one, to get the best protection, the general advice would be to:

  • Make sure you buy a mask which is suitable (check with the manufacturer whether it is for use against particles and/or gases).
  • If masks come in different sizes make sure that you select the size that best fits your face.
  • Read and follow the manufacturer's instructions on how to wear the mask. For example, if there is a metal strip fitted into the mask make sure you bend it over the bridge of your nose to get a better fit.
  • Be aware that facial hair, eg. beards or even designer stubble can compromise the fit between mask and face.
  • Be aware of the limitations of the mask you select.


It is interesting to note that, in the UK, government advice associated with the Daily Air Quality Index does not mention the use of personal RPE, and people who do choose to wear face masks outdoors need to be aware of their limitations - when worn properly masks inevitably make the act of breathing more difficult, even for healthy people. In workplaces, guidance document HSG53 recommends that they not be used for longer than an hour at a time.



The strategies and technology to monitor and control ambient air pollution have never been better. But the challenge is always changing.

For example, the growth of nanotechnology has triggered fears that ultrafine particles (particles <100ìm in diameter) may also start to contaminate the environment. But they already have. Vehicle exhausts, for example, have been associated with ultrafine particle emissions, and measurements taken at Los Angeles International Airport2 have revealed high levels of these particles (ultrafine particles are abundant in jet exhaust). There are concerns that these particles can be even more harmful than PM10 and PM2.5 as they can be very efficiently deposited in the respiratory tract. Ultrafine particles have been associated with increases in respiratory and cardiac deaths.





Author: Nick Cook for RoSPA

Contributors: John Saunders, Owen Butler, Mike Hemingway, Ian Pengelly, Riannon Mogridge and Shirley Frost.

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