The potential health effects from ambient air pollution
highlight the importance of control measures to reduce
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
Particles <2.5ìm (PM2.5) & Particles <10ìm
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
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
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
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
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
"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
- 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
- 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
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.