A repeat of this scene on opening ceremony day would be a PR disaster
By Finlo Rohrer
BBC News Magazine
Beijing is taking drastic measures to improve its air quality in the run-up to the Olympics. But is it possible to conquer air pollution in a short space of time?
In China's capital city, emergency measures are afoot.
It is nine days until the games begin. Beijing has a reputation for bad air pollution and if the national stadium is shrouded in smog on the first day of the games, the embarrassment will be palpable.
Driving through the city is restricted to cars with even or odd number plates on alternating days. Factory emissions have been reduced and some building sites shut down.
The aim is to reduce air pollution so when athletes and tourists arrive for the Olympics, they can see blue sky above the bird's nest stadium. They also want competitors concerned over health risks to rest easy.
But the BBC's James Reynolds has been monitoring air quality in Beijing since the measures came into force and the results are not good. A measurement of PM10 (particles smaller than 10 micrometres) shows things got worse - at a given snapshot moment each day - for five successive days after the introduction of the measures.
Despite lower emissions, levels of pollution are still bad. The authorities are even talking about more severe "ultra-emergency" measures immediately prior to key events, with 90% of cars off the roads and much industry shut down.
Whether the weather
It is possible to tackle air pollution in the short term, says Hugh Coe, professor of atmospheric composition at Manchester University.
"It isn't like climate change where you put carbon dioxide in the atmosphere and it lasts for decades. Air quality is a short term problem. If you stop emitting, your air quality could improve very quickly."
But it's not quite as simple as just turning off the pollution tap, says Prof Coe.
"It's about the rate at which you pump this stuff into the atmosphere and the meteorological conditions. There is not too much you can do about the latter."
The weather is the great variable in any efforts to clear the air.
Frank Kelly, professor of environmental health at King's College London, says the worst case scenario is "very, very low winds, high atmospheric pressure, an anti-cyclone building up above the city - it acts like a saucepan with the lid on".
Pollution needs to be able to rise into the atmosphere and blown by winds to properly disperse.
The worst case scenario is a situation like London's Great Smog of December 1952. Then there was almost certainly increased coal burning because of the cold weather, but the main culprit was a rather nasty weather pattern, known as an inversion layer.
Normally the air gets colder the higher you go. In an inversion layer, this is reversed with a layer of cold air held in place by a warmer "lid". The result in 1952 was a city choked with smog and at least 4,000 extra deaths.
"The weather conditions were unique. The whole of London's pollution didn't go anywhere," says Prof Kelly.
BBC Weather forecaster Dan Corbett says meteorological patterns in Beijing over the summer are not conducive to dispersing pollution, with high pressure and inversion layers common.
"It is like taking a pan of soup off the hob. It steams, but put a lid on it and everything just sits under the lid."
And as well as weather conditions trapping smog in, there are conditions that suck in pollution. Take a coastal city like Newcastle. When the wind blows out to sea it's perfect for dispersing pollution, but should there be a south-easterly wind it can bring in new pollution from continental Europe and boost readings.
In Beijing the issue is serious, with winds carrying pollution from all over the surrounding region as well as dust from the Gobi desert in spring.
Then there's the effect of sunlight. Nitrogen oxide and hydrocarbons can form ozone as long as there's bright sunlight. Ground-level ozone is hazardous and a major component of photochemical smog.
In London in 1952, the concentration of the pollution was visible, largely a result of coal, which produces black smoke consisting of large particles. The sulphurous type of coal then used also produced large quantities of sulphur dioxide that caused smog.
In the West today, less and cleaner coal is used. Now the threat is usually less visible and comes in the form of nitrogen dioxide, volatile organic compounds - such as paint thinner or solvents - and smaller particulate pollution under 10 micrometres in size, known as PM10.
"Modern pollution is coming from motor vehicles," says Prof Kelly. "Particles emitted are much, much smaller. They are not as visible, people feel safer but the real problem is that because they are smaller they get deep down into the lungs where the coal particles didn't get."
And being of a size that can penetrate deep into the airways and settle in the lungs, these PM10 particles are among the most dangerous forms of air pollution, says environmental epidemiologist Prof Tanja Pless-Mulloli, of Newcastle University.
Santiago's geography and weather patterns lead to chronic smog
"People who already have asthma more likely to have an asthma attack. There is an impact on the number of hospital visits and there is an impact on mortality, even at concentrations that many countries experience."
The health concerns over air pollution have prompted some places to employ drastic measures along the lines of Beijing.
Athens tried the odd/even registration plate restrictions, starting in the 1980s. Not the hardest restriction to circumvent, many motorists bought an old banger with the other plate. Atlanta put traffic restrictions in place for the 1996 Olympics.
On 1 September 1990, Dublin banned the sale and burning of bituminous coal. A study published in the Lancet by Luke Clancy, Pat Goodman, Hamish Sinclair, and Douglas W Dockery - comparing the six years before the ban and the six years after - found dramatic results.
Black smoke concentrations in Dublin fell 70%, and the authors estimated there would have been 116 fewer respiratory deaths and 243 fewer cardiovascular deaths a year in the city after the ban.
And in Santiago, Chile, short-term emergency action was taken in the 90s when there were extraordinary bursts of smog, says Nigel Bell, professor of environmental pollution at Imperial College London.
"It put a lot of babies in hospital. Santiago has got a ring of mountains round it and a lot of vehicles. They closed a lot of factories. The smog went but I don't know how much one could ascribe it to the actions taken."
Cirrus clouds are thin and whispy
And one dramatic change in the atmosphere came after 9/11, says Prof Coe. All flights were grounded in the US and the vapour trails which form many cirrus clouds were thereby removed. These cirrus clouds reflect some radiation from the sun, as well as absorbing some of the heat energy escaping to space from the earth.
The difference in radiation levels at the surface would have been measurable during the grounding, says Prof Coe.
Emissions can be controlled, particularly by aggressive government action, but no power on earth can control the weather patterns that carry those emissions around our atmosphere.
Switching off air pollution is possible, but only if the weather lets us.
Send us your comments using the form below.
The interesting thing to see will be if China reverts to "business-as-usual" once the Olympic Games has finished. Curbing emissions levels for a short space of time purely for PR reasons seems like a very pointless exercise if emissions will rise significantly again afterwards.
Stuart, Aberdeen, Scotland
The run up to the Beijing Olympics hopefully adds another wake up call to the reality of years of consumerism without thought for the environment. Are we at last learning very visibly that we literally get out what we put in? In that case, well done China.
Mike Wood, Stockport
Can I just point out that there is a significant difference between classical smog (as in 1952) and photochemical smog (as in Santiago). Classical smog is due to the combination of particles from the burning of coal, and fog. Photochemical smog is, however, entirely to do with the photochemical reactions of pollutants (most notably hydrocarbons, ozone, and NOx). Though a temperature inversion is required to trap the pollutants, and a temperature inversion can create fog, the two types of smog are independent of each other.
One question is why China was so keen to put their showcase stadium in a highly polluted city. Certainly the Olympics have been billed as the "Beijing" Olympics, but everyone knows that events take place over a wide range of areas - surely they could have found a place where pollution wasn't so much of a problem, but still near enough to be called Beijing? Pity the poor athletes, having two choices - competing in masks to try and filter out the pollution, or breathing in high levels of dangerous particles. What a choice.
Anne Boyce, Halifax, West Yorkshire
I truly believe it is a pity that governments refuse to take pollution seriously unless it affects their short term plans or their economy. In Mexico, we have a few measures to improve air quality, but just as you mentioned, the results are not the expected, because the are many more vehicles every day, and people who can´t afford a new one, will buy a cheaper one that is of course much more polluting.
Marcela Melendez, Mexico City
The smog in Santiago is still very much here. Vehicle restrictions operate permanently throughout the winter and there have already been a number of air pollution alerts this year during which more vehicles are prohibited from circulating and industry is shut down. But people still use log fires as they are more concerned with keeping warm as cheaply as possible rather than the health of their own children.
Edward Cook, Santiago, Chile
Having lived in Santiago since 1990 I am afraid I don't concur with my namesake's comments(Professor Nigel Bell) that the smog in Santiago "went". The smog is as bad as ever and in fact is getting worse every year as there is less rain in the winter months, more construction (and therefore more dust) and an increase in the number of cars on the streets. The idea of banning certain digits on number plates each day is also not working as many people have 2 or 3 cars especially to avoid the ban. There is no short term solution: a possible long term solution would be to move industry out of the city and build up a more effective system of public transport to avoid the over dependence on cars.
John Campbell Bell, Santiago, Chile
The BBC may edit your comments and not all emails will be published. Your comments may be published on any BBC media worldwide.