The World Health Organisation (WHO) says that Air Pollution Kills 600,000 Children Every Year Medscape - Oct 29, 2018
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In 2016, Outdoor Air Pollution was responsible for premature death of up to 4.2 million people globally (40000 in the UK). A further 3.8 million deaths are attributed to household (indoor) air pollution, mainly in developing countries. The science of air pollution is well understood, what needs to be done is known, international standards of air quality have been set out; but our inability to control air pollution tells us something about the way our societies function.
Most sources of air pollution are well beyond the control of individuals and demand/require concerted action by local and national level policy-makers working in sectors like transport, energy, waste management, urbal planning, and agriculture.
Last week the pollution in Delhi reached 'astronomical levels' and this has driven me to write this blog. I wish to discuss here
1. The nature of air pollution,
2. Adverse health effects of air pollution
3. Recommended safe limits,
4. Geographical areas worst affected,
5. Sources of air pollution, and
6. Some ideas as to what we can do to control and mitigate
the harmful affects of air pollution.
Air pollution comes in two forms - as gases (Oxides of nitrogen and sulphur, carbon mono-oxide, ozone, and poly-aromatic hydrocarbons or PAHs) and as particulate matter (dust, carbon, metal compounds etc.). Most of the time we do not see the pollution - although serious smog does give us a visual reminder - the invisible killer is at work 24 hours of the day, particularly in our cities where more and more people now live.
Air pollution mostly enters our bodies through inhaling ambient air which deposits the pollutants in the lungs and subsequently in the blood stream.
In my course on Climate Change, I had discussed the properties of our atmosphere - the slides may be found here.
We shall emphasise pollution due to particulate matter (PM) in this blog. PM are particles suspended in air, their concentration is measured by the mass of such particles in a m3 of ambient air. It is not only the particles but also the adsorbed harmful chemicals on their surface that do the real damage to our body.
The relevant PM are:
PM10 -- all particles smaller than 10 micrometres (μm) in diameter.
PM2.5 -- all particles smaller than 2.5 μm in diameter.
How far a particle penetrates the respiratory system depends on its size; and that also determines how such foreign material is removed from the body.
Additionally, for the same mass, PM2.5 present a far bigger area for adsorption of harmful chemicals and therefore are responsible for much greater damage than bigger particles. Due to their small size PM2.5 are also much harder to filter out by masks.
Following slides provide some details about particulate matter and their invasion of our respiratory system.
From the above slides we note, that mostly it is the particles in the range from 0.01 to 2 μm diameter, like soot and smoke, that reach the blood stream and cause health issues in humans. For a given mass, small particles have much larger surface area; and pollutant gases, hydrocarbons, PAHs, metal compounds etc. are adsorbed in larger amounts on the surface of the particles.
Each 10 μg/m3 increase in fine particle air pollution is associated with a
4% increase in all-cause mortality
6% increase in cardio-pulmonary mortality
8% increase in lung-cancer mortality.
A recent sudy (October 2018) in asthma related hospital visits found that 5 to 10 million annual asthma emergency room visits (representing 4 to 9% of total visits) globally could be attributed to PM2.5. Anthropogenic emissions are responsible for ~73% of PM2.5 impacts. The numbers of visits due to inhalation of atmospheric ozone were more than twice as large.
The largest impacts were in China and India.
How Do PM2.5 Cause Diseases? Understanding the molecular mechanisms of PM2.5 induced respiratory diseases may contribute to the development of targeted drugs and preventable treatments. In recent years much work has been done in the investigation of the role of PM2.5 (with adsorbed toxic chemical pollutants) in the pathogenesis (the development of a disease and the chain of events leading to that disease) of lung cancer and chronic airway inflammatory diseases.
PM2.5 and accompanying toxic
chemicals induce epigenetic changes (epigenetic changes, without modifying DNA
sequence, can switch genes on and off and determine which proteins are
transcribed) that may result in oncogene activation and tumour suppressor gene
inactivation in lung cancer. PM2.5 may also induce and aggravate
asthma and COPD (chronic obstructive pulmonary disease) by activating inflammatory-associated cells
and triggering oxidative stress. This is
explained in the next two slides.
International Standards of PM10 and PM2.5 emissions; 'Safe Limits': In 2006, based on extensive scientific evidence relating to air pollution and its health consequences, the World Health Organisation (WHO) had published its Air Quality Guidelines (AQGs).
3-5 μg/m3 and the WHO guideline limits are aimed to achieve the lowest possible concentrations of particulate matter. By reducing PM10 pollution from 70 to 20 μg/m3 air-pollution related deaths could be cut by 15%.
The 2016 update makes grim reading about the implementation of the AQGs - 91% of the global population is living in places where WHO air quality guidelines are not met.
WHO estimates that in 2016, some 58% of outdoor air pollution-related premature deaths were due to aschaemic (coronary) heart disease (CHD) and strokes, while 18% of deaths were due to COPD, 18% due to acute lower respiratory infections, and 6% of deaths were due to lung cancer.
Global Air Pollution Data: We shall look at some slides showing the global air pollution data and premature deaths that it causes. What comes through is that the developed countries have the lowest pollution, the developing countries (including India and China) are severly polluted. But, first the data:
Air pollution is largely a problem of urban areas due to concentration of road vehicles, large numbers of households sending pollutants into the ambient air and industrial activity in nearby areas.
Air pollution is also much worse in developing world. For example, in Delhi in 2015 the PM2.5 level was 226 μg/m3. In several monitoring stations the reported air quality index was 999 (maximum readable on the meters) - this is equivalent to smoking 45 to 50 cigarettes a day See also.
What are the Sources of Air Pollution? There is some background air pollution from natural sources. The mean level of background particulate concentration is estimated at 3 to 5 μg/m3. It arises due to
wild fires,
volcanic eruptions,
emission of volatile organic compounds from plants etc.
The man-made air pollution comes from various sources; For example,
burning of fossil fuels in electricity generation,
transport - road, rail, sea and air,
households - cooking etc.,
mining, chemical and agricultural industries,
waste treatment,
burning of crop residues, etc.
Of all the sources of pollutions, in urban centres road transport is the most serious. In Central London, road transport is responsible for 54% of particulate matter PM10 emissions and for 48% of the harmful oxides of nitrogen. The issue of transport in cities is a complex problem - petrol and diesel vehicles are generally blamed for the pollution. However, with near zero emission standards, the main problem will be the particulate matter generation by brake wear and tyre wear (BWTW). BWTW is equally important for electric vehicles and it seems that PM emissions will continue to be a serious health hazard in cities until a better way to move people is found.
What can you do to minimise exposure to air pollution: The obvious thing to do - may be not too practical - is to live as far away from the city centre as possible. Growing urban population is a well established megatrend and shall happen - by 2050 it is expected that 75% of the world population will be living in cities. Air pollution will be even more relevant for global health.
Air quality inside the houses is not necessarily any better than outside and staying indoors may not help much. In fact, during the cold months, houses are well insulated, windows are not opened for most of the time and indoor air pollution - supplemented by biological pollutants like dustmites, mold and dampness etc. - can be quite harmful. Using air-purifiers with HEPA filters (high efficiency particulate air filters which absorb all particles greater than 0.3 μm size) can reduce the impact of indoor pollutants.
In big cities like London, most people walk. It will help to choose side-streets and quieter roads with less traffic. Studies have found that pollution levels inside the cars are actually greater than outside - so walking is best. One can wear dust masks.
Final Word: New health problems caused by air pollution are being identified. There is some evidence that pollution might be causing hearing and visual impairments, cognitive decline and other health problems. Children are specially vulnerable to the damage done by pollutants and there is nothing much one can do about it.
Populations in developing countries tend to suffer far worse air pollution levels. Moreover, air pollution is worse in neighbourhoods where less affluent people live.
We have forsaken fairness, and thrown sustainability out of the window.
Thanks for reading.
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