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Science communication is important in today's technologically advanced society. A good part of the adult community is not science saavy and lacks the background to make sense of rapidly changing technology. My blog attempts to help by publishing articles of general interest in an easy to read and understand format without using mathematics. I also give free lectures in community events - you can arrange these by writing to me.

Wednesday, 28 November 2018

Ethics of Eating Meat - We Need to Factor-in Sustainability

Whether eating meat is ethical or not is a subject that arouses passion and interesting debate (see and comments).  What is lacking in most such discussions is the realisation that ethics is not a fixed entity but evolves to encompass the changing values of the society.  For background on ethics, please see - particularly the section on behavioural ethics(In this blog, I shall assume that ethics and morality refer to the same thing)

Humans are omnivores - meat and plants have always formed their diet.  It is only recently that we have questioned the ethics of eating meat. Ironically, the control of fire increased meat consumption that resulted in the human brain to outgrow brains of other animals, allowing us to ask questions about ethics and morality of eating meat.  
What people ate in the past, while a worthy subject for discussion, must not be the reason for deciding what we should be eating in the future. Life is very different now than what it was even 100 years ago, and looking forward, we need to appreciate the new reality of the 21st century, and develop the ethics of what we eat including meat accordingly. 

What is the new reality?  With reference to food - in rough proportions-   

(1) 15% of the world population is undernourished, while 40% is overweight or obese.  
(2) A third of the agricultural produce is wasted/destroyed by failure to efficiently manage our food resources.
(3) We have switched, in a big way, to animal-farming that is 10 times more inefficient than harvesting plant-based nutrients.
(4) A good proportion of corn and soya crops are used to raise cattle.  This could be used to feed the hungry people in the world. Bio-fuels take away further food resources.
(5) Agriculture has gone big - 'agriculture is the way by which oil is converted into edible food' and in that process is doing serious harm to the environment and climate.
(6) Population numbers keep growing and are expected to reach more than 9 billion by 2050.  Coupled with increased consumption per capita, much more food will be needed in the future.

We ignore these realities at our peril.  The ethics of what we eat has to be decided by what is sustainable - essentially what type of the world we want to live, and leave for future generations? That is the moral/ethical question.  I have addressed this in my recent blogs (1, 2, 3).  Reducing red meat consumption is a definite conclusion from these analyses.

I can already hear the howls and shrieks from some that without eating meat human body cannot survive  - not enough protein, not enough B12 - we shall become weak and be not able to fight diseases.  That will be the end of human race.

The situation is not that way at all.  Apart from 4 years in the 1960s, I have been a vegetarian, I do not ever take supplement vitamins, kept a constant weight (with BMI of 23) for the past 40 years and visit my doctor once a year for a blood test.  I might have considered adding meat to my diet but the current methods of meat production and processing flag a clear message to me to stay away from eating meat.  

So far, this has been a rational discussion - taking some prudent steps, it might even be possible to solve the food crisis the world is facing.  But that is where life gets more complex - humans love power, have a selfish streak to their nature and there are some who can just not tolerate others do better or even equally well. Then, there is the human mind which can be irrational some of the time (actually I should write - quite a lot of the time).  Essentially, what I want to say is that those who have power will exercise it to grab far more than their fair share.  The so-called developed world has done so (imperialism  and slavery in the past; waste and overconsumption now) and the new 'developed' countries like China and India are following the OECD example. 

Pseudoscience is also raising its profile.  Our political leaders no longer care to set examples that we can follow.  Lying in the face of evident truth is almost acceptable - thanks to our great new leader.  
I must say that I do not feel much hopeful that our moral compass will define a sensible, viable route for the future.

Thanks for reading...

Monday, 26 November 2018

A Magic Square based Party Game

Sometime ago, I had published a version of this game as part of a general blog on magic squares. From the feedback, it seems that people would like more instructions about how to use it, and also how to change it to suit their own usage.  I shall try to help in this through the following blog.

Let us start with a six by six grid that I have constructed - later I shall explain how to make such a grid yourself.  The game is described in the next four slides.  Yes, you can use negative and/or decimal numbers as well.
(click on a slide to see full page image; press Esc to return to main text)

Remember that the number you choose must not be on the scored out numbers (I have shown them masked in this illustration)

The point of the game is that one can choose any combination of the numbers as described above and the sum will always come out to be 50 - very convenient if the birthday or anniversary you are celebrating is the 50th.  

But what if the sum you want is different, say 20 or 70 or something else.  I shall describe how the make a grid with a different outcome for the sum.

Suppose you wish the sum to be equal to the number N.
To play with a six by six grid, you should choose 6 + 6 = 12 numbers that sum to the number N.

let us choose a,b,c,d,e,f,p,q,r,s,t,u for the 12 numbers - they must sum to N.  

Now, outside the grid, place the first six numbers (a to f) horizontally and the other six numbers (p to u) vertically.  In each cell, write doen the sum of the horizontal and vertical numbers as shown in the next slide.  This completes the grid and you are ready to play the game. Simple!
You do not need to have 6 x 6 grid.  You can work with m x m grid but choos 2m numbers to add to N.

Pass the web link of the blog to friends and family.

Sunday, 25 November 2018

Why Do Humans Have two Front-Facing Eyes? An Analysis and Some New Ideas.

"Eyes in the front, the animal hunts. Eyes on the side, the animal hides."

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Humans are primates and all primates have two front-facing eyes.  Why?  

Currently, the explanation goes like this: The binocular vision provides stereoscopic or three-dimensional (3D) view that helps to locate and pin-point objects more precisely.  This is good if you are hunter/predator; and it helps in arboreal living - gives ability to swing and jump more accurately between tree branches - good if you live in trees

Early primates were indeed tree dwellers; and besides finding insects to eat, they ate plant leaves and fruits.  None of the primates were predators in the usual sense of the term. Chimps are the closest relatives of humans; and among the great apes, only humans and chipms eat meat but only infrequently.  Traditional human societies appear to have relied more heavily on plant-based diets

So one might think that more likely front-facing eyes evolved to help in arboreal living - living in trees helped early primates to stay safe from predators and also allowed easy access to tree leaves and fruits.  The problem with these theories is that the earliest primates were actually nocturnal and relied on smell more than vision.  But see also.

For many millions of years, great apes have lived mostly on ground and have not been hunters.  I would think that input from the front facing eyes serves a more fundamental purpose and is not necessarily wholly related to predation or arboreal living. I base this suggestion on the fact that in the human brain, neurons devoted to visual processing number in hundreds of millions and take up about 30% of the cortex - as compared with 8% for touch and just 3% for hearing.  Each of the two optic nerves, which carry signals from retina to the brain, consists of a million fibres; each auditory nerve carries a mere 30,000.  It would be unusual for evolution to invest so much energy in visual processing if it only helped humans to carry out relatively minor activities of hunting and tree dwelling. 

So, why do primates have front facing eyes?  In this publication, I want to examine this question in more detail - (1) by looking at the evolution tree of primates, (2) I shall discuss the pros/cons of having front-facing eyes against eyes on the sides of the head. Lastly, (3) I shall argue that the complex society/environment, that humans have been living for the past million years or so, requires the most elaborate vision system and a good part of the 'new brain' was earmarked for processing the 'superior' visual signals possible by having two front-facing eyes.  

(1) Primates: Let us look at the evolution of primates that goes back to some 60 million years.  The next two slides summarise the evolution tree of primates:
(please click on a slide to see full page image; press Escape to return to main text)

Let us start with Prosimians - the first primates. Prosimians are nocturnal, have large eyes with a tapetal (retro-reflecting) layer behind the retina to help night vision, but their eyes are not as well positioned for 3D vision as are the eyes of other primates. They have well-developed sense of smell and hearing; a larger proportion of prosimian's brain is devoted to the sense of smell than the sense of vision.  Prosimians are insectivorous, also eating fruits.  It is plausible that two front-facing eyes helped the prosimians to live in trees and search for insects during the night. However, it is only about 20 million years ago that in the apes, eyes developed to have the full bony sockets, full colour vision etc. 
For completeness, I list some common traits that primates (apes) share:

Among the apes, humans are unique in having a much larger brain relative to the body mass - human brain is 1.3 kg that is almost 3 times the size of a chimp brain even though they have similar body mass.  This divergence is due to the rapid development of the preforntal cortex in humans starting some 2 million years ago.   

(2) Vision with side-facing and front-facing eyes: Most animals have either front-facing or side-facing eyes.  Conventional wisdom is that hunters/predators have front-facing eyes as the binocular vision provides greater accuracy in determining distance and location of the prey; animals, who are preyed on, have side-facing eyes as the monocular vision provides almost a 360 degrees view and helps in detecting an approaching predator.
I have drawn the following slide to explain the difference:
Depth Perception:  In binocular vision, we perceive depth/distance of objects by receiving information from two different angles.  If we close one eye - we have monocular vision as many two-eyes-on-the-sides animals also have. However, with one eye only, our depth perception does not seem to be enormously different; the question arises how can/do animals perceive distances of objects with monocular vision?  

We can do this because the brain uses a variety of depth cues.  The brain has a big memory bank and large processing power; and it seems to do a pretty good job of interpreting depth cues. Binocular vision just makes the depth perception so much better. For animals, it is a trade off between limited 'good' coverage of about 180 degrees or nearly full 360 degrees 'good-enough'/functional coverage.  One chooses what gives the best chance of survival.
Wiki has a detailed article on depth cues; here, I shall discuss only some of the most important cues: 

Relative Size Cue:  If two objects (e.g., two trees) are known to be the same size and if one subtends a larger visual angle on the retina than the other, the object that subtends the larger angle appears closer.

By observing the angle projected by the object on the retina, the brain can determine the absolute distance of the object using the previous knowledge of its size.

Similarly, the brain uses perspective (parallel lines converging in the distance) to reconstruct relative distances of two parts of some large object (a building or landscape features)
Motion Parallax:  

Transverse Motion:  Parallax is the apparent change in position of an object relative to distant background objects resulting from a change in position of the observer.  
The relative motion of an object against the background objects gives hints about its distance; for example, when travelling in a train or a car, nearby objects pass quickly while far off objects appear stationary. The use of motion parallax for depth perception is widespread throughout the animal kingdom.  Birds bob their heads to achieve motion parallax, squirrels move in lines perpendicular to an object of interest to locate its position etc.

Radial Motion:  If an object is moving towards you, its image on the retina increases in size - the changing image size enables the observer to not only see the object as moving but also to perceive the distance and the speed of the moving object.  

Accommodation:  Mammals, birds and reptiles vary the optical power of the eye by changing the shape of the elastic lens.  Fish and amphibians vary the power by changing the distance between a rigid lens and the retina. 

The far point may usually be taken as a distant point at infinite distance and focusing on an object at finite distance allows the brain to perceive its distance.

The muscles inside the eye (ciliary muscles) bring about the mechanical changes in the lens.  The sensation of contracting or relaxing of the ciliary muscles in focusing on a nearby object is sent to the visual cortex where it is used to interpret distance/depth of the object.  Accommodation is most effective in judging distances less than 2 metres. In humans, the accommodation amplitude can be up to 15 Dioptres.

Recent Work:  Some fascinating work has been done in quantifying the superiority of binocular vision over monocular vision.  An interesting conclusion is that for large distances of greater than about 25 metres, the two visions have similar precision; but for closer objects, binocular vision precision, depending on the availability of depth cues from the surrounding, can be up to 40 times better than for monocular vision (see 1, 2). 

Visually Guided Behaviour:  Studies with visually guided behaviour like walking over and around obstacles have observed that walkers were quicker by about 10% when using binocular vision and also  judged the height of obstacles with greater precision.  There was higher uncertainty in monocular vision, leading to greater reliance on feedback (from depth cues) in the control of movements. 

Seeing Objects behind Obstacles 

It is not only in depth perception that binocular vision is superior, but significantly, results from recent research point to advantages of binocular vision in carrying out many aspects of daily activities

Structure of the Eye:  Actually, nobody tells you about the scrappy and incomplete information about the surrounding environment that the eye sends to the brain - the brain fills in the voids, and this can be dodgy.  To understand 'the trip-wire act' that vision processing is, we need to learn how the eye collects visual data about the surroundings.  Essentially, one thinks of the retina as an extension of the brain and it is at the retina that external light is received to generate the electro-chemical signals which are then processed in different parts of the brain (see Section 2). The interpretation of the results again requires the brain to fill in lot of details using guesswork and can also be dodgy.  It is surprising that, most of the time, the brain appears to make a decent job out of the whole process.
First, I describe the anatomy of the eye and the retina in the following slides. 

In humans, the retina is a 0.5 mm thick layer of cells and covers 72% of the spherical eyeball of 22 mm diameter. The retina covers about 150 degrees vision area in front of the eye. 
The optical disc  where the bundle of 1 million nerve-fibres leave the retina is an area of about 3 mm square. It contains no light-sensitive detectors creating a blind spot in the vision.
Light detectors are called rods and cones.  There are 100 million rods (sensitive to the brightness of light but not its colour), while the 7 million cones in the retina are sensitive to colour but not very sensitive to brightness.

Cones are primarily concentrated in the central retina (see slide) as  hexagonal mosaic in the fovea and its surrounding macula (diameter = 5.5 mm). Fovea is the region of sharpest visual acuity, is very small in size and contains no rods.  The pit in the macula (parafovea) is 1.5 mm diameter. The area surrounding the fovea has the largest concentration of rods and has the most sensitivity to light.  
The fovea of the eye sees the spatial details and full colour of the objects with the greatest sharpness - but that is a tiny angular range - of the order of a few degrees.  The reason, that we can see the bigger picture spanning almost 130 degrees range without moving the head, is  that our eyes constantly dart about, fixating for a fraction of a second and then moving on.  The jerky movements are called saccades.  We make about three saccades per second, each lasting between 20 and 200 millionth of a second; we have no concious control on saccades - the brain manages it.  While saccades are happening, we are effectively blind. The brain does not use information picked up during a saccade but uses guesswork to fill in the details.

How is Visual Information Processed by the Brain:  
{This section may be missed out without loss of continuity}

The information from the eye is carried by the axons of the retinal ganglion cells to the midbrain.  In the brain,  visual processing is akin to an orchestra, where clusters of cells in different parts of the brain co-operate to process different components of visual information such as vertical or horizontal orientation, colour, size, shape, movement etc. 
The following two slides show a schematic of how visual information from the eye flows to the brain. I refer you to the original lectures for more information on this topic.

The visual information received is then analysed by various parts of the brain; the brain collects the results and constructs a picture of the external view.  Using memory and previously held information, the brain updates/fills-in any missing information to form a full picture. All of this is done in the blink of an eye!  Generally, it does a good job too.  
But a word of caution here:  It is not too difficult to  fool/manipulate the brain.  It uses past experience to construct from somewhat incomplete information that the eye sends and guesses what the missing information might be.  It is not too difficult for the brain to get the whole thing wrong.  The subject of optical illusions (see an infographic with many examples here) and hallucinations provide fascinating case studies where brain gets the results totally wrong. Eyes play a central role in meta-communications and bizarre effects like Uncanny Valley are observed directly as a result of brain's processing of visual signals. Dreaming is another example when teh brain creates visual perception when no external input is present.

And, it is not only in processing visual information, the brain is equally fallible in interpreting hearing, smell, taste, emotions and in many other decisions it makes.    

(3) Humans and Vision:  The above discussion leaves unanswered the question - 'why we have two front-facing eyes?' To some extent this is of academic interest only.  What we really want to understand is - why evolution has invested so much, almost 30-50% of brain resources - in processing vision related information. This is unique to humans and we shall try to speculate why such a large proportion of the increase in human brain size over the last 2 million years might have gone to vision related processing.

We learn about the world we live in through our senses - there are 21 accepted senses including 4 belonging to vision (brightness and 3 colours - red, green and blue). Vision, sound, smell and touch are the only senses that provide us information about the external environment.  Smell and touch are relevant only for short distances; sound may be good for medium distances of a few km or less but is of very poor spatial resolution. Vision is the only sense that properly connects us to the outside world and is our main way to interact with our surroundingsHumans rely heavily on vision to guide our behaviour and perceive the world.

Unlike all other animals who are mainly concerned with the search for food and safety from predators, humans have learnt to manipulate the environment for their benefit.  Many factors like learning to use tools, controlling fire, agriculture, living in societies with mutually accepted rule and regulations etc. have elevated humans to become the most powerful species that has ever lived.  This has been made possible by the visual input processed by the brain.  Imagine the amount of visual information that would be fed to the brain from the ever increasing activities that humans are involved with - that will require a massive supercomputer to handle .  It is no wonder that the human brain consumes greater than 20% of basal metabolic energy even though it is only 2% of the body mass.  The brain also consumes energy at a more or less constant rate of 20 Watts whether you are solving maths problems or sleeping or sitting quietly in the sofa - it has to organise itself to be ready for efficiently analysing the next input; (For comparison Titan supercomputer uses 4,000,000 Watts of electricity!)  
It seems the vision perception department is always looking for more resources and this might be the reason why the size of the human brain has increased so rapidly over the past million years or so.
Humans have retained the two front-facing eyes because the binocular vision provides a far superior depth perception than a monocular vision; and helps the brain to more accurately perceive reality.

The brain's perception of reality involves a lot of filling-in of missing information from guesswork, and the reliability of the resulting perception is a matter of discussion.  There are many examples when our perception is wrong by a long margin - but that is all we have just now.     

Thanks for reading. 
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Saturday, 17 November 2018

Air Pollution (Part 1) - The Invisible Killer; Particulate Matter PM2.5

Who am I?  Blog Index

The World Health Organisation (WHO) says that Air Pollution Kills 600,000 Children Every Year                                 Medscape - Oct 29, 2018

(please click on a slide to see full page view; Escape to return to main text)

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.   
What Effects do PM have on Human Health?: Many research groups have studied the effect of inhaling particulate matter on human health.  The next slide summarises the findings that are widely accepted.

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).  

For small particulate matter, no threshold has been identified below which no damage to health is observed.  The natural background of small PM is 
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.  
I hope to address pollutant emission in road transport in a separate blog.

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.  

In the end, the problem really boils down to the number of people living on the Earth. As more and more people move to western lifestyles with unbridled consumption; the human footprint, that is already too big, will increase further and our planet will just not be able to cope with the demands put on it. Air pollution is just one of the ways that the Earth is responding to our irresponsibility. 

We have forsaken fairness, and thrown sustainability out of the window.

Thanks for reading. 
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