Warning: breathing can harm your health

On December 4, 1952, a dense cloud of smog began to form over London. There was nothing out of the ordinary about it, so why worry? But that week, there were 4,000 more deaths registered than usual, and the effects of the killer cloud lasted for months. What happened? The victims' respiratory problems suggested a flu epidemic. But five decades later, epidemiologists and researchers specialized in air quality managed to reconstruct the case and identify the culprit: pollution. Heavy coal combustion had turned the city's air into poison.

Last month, Madrid and Barcelona, not to mention Milan, Naples, Rome and a number of other cities, should have issued the warning: "Breathing this city's air is a health hazard." In recent weeks, some air quality control stations in Madrid have registered nitrogen dioxide levels of up to 400 micrograms per cubic meter, much higher than those considered harmful by the World Health Organization (WHO). Three stations have already surpassed the maximum permitted by EU regulations for an entire year.

One would think that in the last few decades, cities in the developed world would have learned to control their air. International experts have focused most of their warnings on the megapolises that are now growing uncontrollably in Asia and Latin America, where residents breathe an increasingly toxic flow. But no. Modern-day Europe isn't free from urban pollution, either.

What's more, in the 21st century the problem has gone global. Humanity has been altering the atmosphere for two centuries since the industrial revolution, and the effects are now planetary. The chemical makeup of the sky has changed, and as a result, we have a darker planet and clouds loaded with chemical substances that were never there before. What will be the mid- and long-term effects of this? How does this new chemical makeup affect the millions of microorganisms - bacteria, funguses, viruses, etc. - that travel each day, stuck to atmospheric dust (yes, this is another recent surprise: microorganisms migrate through the air and can establish themselves wherever they land).

Only now - thanks to satellite data, DNA chips and hypersensitive sensors - are scientists starting to study these phenomena in depth. Let's take a look at the latest cutting-edge research regarding the air we breathe.

It's rush hour in Madrid. Cars, many of them with diesel engines, start up, move a few meters, stop and start up again. Every time they stop, they spew out a stream of copper, antimony, tin, magnesium, zinc and barium, metals that come from the wearing away of brakes, wheels and tarmac to make what is known as "road dust." And with every rev of the engine, nitrogen and sulfur oxides, above all, are emitted into the atmosphere. Together, they make up one big toxic soup that will end up in buildings, in the soil and inside the city's inhabitants. All the major Spanish cities went over the permitted levels of some contaminants in 2010. Madrid has 2,100 cars per square kilometer; Barcelona, 6,010; Valencia, 2,600; London, 1,300; Oslo, 400.

Xavier Querol, from the Institute for Environmental Diagnostics and Water Studies of the Spanish National Research Council (CSIC), has spent over a decade studying the "ingredients" of the air in cities all around Spain, using some of the most sensitive instruments available at this time. In Madrid, his team "sees" everything from the arsenic given off by the few remaining coal-fired boilers to the cocaine molecules in suspension - a real demonstration of how sensitive these instruments are, since both substances are only present in tiny amounts. Querol concludes that the average makeup of Spanish urban air is 15-percent road dust, around 35 percent ultrafine particles (millionths of a millimeter) from engines, 30 percent nitrogen oxides and 15 percent mineral dust (mainly from construction work).

These numbers are not good news. They indicate that the vast majority of urban pollution comes from traffic, and that "the levels of some contaminants are not dropping in our cities, despite efforts from the automobile industry to reduce vehicle emissions," Querol says. Diesel engines, which are increasingly common, give off more ultrafine particles and gases, making the problem even worse.

There are more and more indicators that ultrafine particles, the smallest specks of dust, are dangerous. Current European legislation on urban air quality takes into account particles larger than 2.5 thousandths of a millimeter, 100 times smaller than the thickness of a human hair; but many think that it should also consider the ones that are just millionths of a millimeter in size.

"Thick particles, when inhaled, are deposited in the bronchial tubes and can aggravate respiratory problems," says the epidemiologist Jordi Sunyer, from the Environmental Epidemiology Research Center (CREAL) and the Municipal Institute for Medical Research (IMIM) of Barcelona. "But finer particles are deposited in the alveoli and can find their way into the bloodstream. They can also affect the cardiovascular system." In the next few years, Sunyer will lead a European Union research project to find out whether ultrafine dust might even reach the brain and interfere with children's cognitive development.

Today, the planet is darker than it was three decades ago. A research team in the United States compiled data on atmospheric visibility gathered between 1973 and 2007 at 3,250 meteorological stations around the world. After comparing them with satellite observations, they attributed the phenomenon to pollution. Their work was published last year in the prestigious magazine Science.

Many of the gases and particles that darken the urban sky rise remain in the atmosphere for weeks and even stray from where they originated. Meanwhile they change, physically and chemically. Nitrogen oxides, for example, turn into extremely toxic tropospheric ozone when exposed to sunlight. Sulfur oxides turns into sulfuric acid, which returns to the ground in the form of poisonous acid rain. These ultrafine particles have an electrical charge, which makes them clump together into microscopic discs. In any case, pollution is not confined to the city sky, and over the centuries, it has managed to surround the planet in a very faint layer which is nevertheless able to block the sun.

These suspended particles are called aerosols. They can be natural, such as dust from the Sahara, but in recent decades the levels of this type of aerosols have not changed as much as the ones generated by humans. The question is, how does planetary pollution affect us? "This is one of the most active fields of research right now," Querol confirms.

The role of aerosols is not clear. We know that they are important, specifically when it comes to how the global climate behaves, but how? One would think that they would cool down the surface because they reflect sunlight into space - and, as we have said, darken the planet. But in some regions, they have the opposite effect: they absorb the heat reflected by the earth's surface and warm up the atmosphere. Querol thinks that this is exactly what is happening in Spain.

Sergio Rodríguez, from the Izaña Center for Atmospheric Research (National Weather Agency), is studying aerosols in Tenerife. His work consists of analyzing clean air, or rather non-polluted air, using local sources. He "captures" it at an altitude of 2,400 meters at Izaña, an observatory that has become a mecca for meteorologists from all over the world. In the Canary Islands, trade winds create a layer of clouds that isolate the peaks. This means that pollution from the islands' vehicles doesn't reach Mount Teide, where the Izaña observatory is, but rather air from the mid-Atlantic, which moves up to 4,000-5,000 meters before descending upon Tenerife.

The instruments use quartz microfiber sheets to filter the air, and analyze the size and chemical composition of the aerosols that get trapped. Thus, the researchers are able to distinguish between particles generated by human activity and the dust of the Sahara Desert, for example. In the last few months, Rodríguez and his team have made a surprising discovery. Contrary to what they thought, many of the anthropogenic aerosols that find their way to Izaña don't come from Europe, but from refineries and fertilizer factories in North Africa. "The dust is covered in sulfates, nitrates and ammonium, and that really changes the way it affects the climate," says Rodríguez. "When they're covered in contaminants, the aerosols reflect even more light into space. It also changes the way that they favor cloud formation, like seeds."

One of the consequences of climate change is that it will worsen droughts and the amount of African dust in the atmosphere will therefore rise. In fact, this prediction is already coming true: the drought in the Sahel has drawn out for over three decades now. Rodríguez's findings suggest that the dust will reach Europe covered in more and more contaminants, as a consequence of development in North Africa. This is something that climate models will have to take into account.

Contaminants aren't the only thing that sticks to the 60 to 200 million tons of dust that come out of the Sahara each year. Dust is, in itself, rich in nitrogen, phosphorus and iron, and it plays an important role in fertilizing oceanic plankton and even tropical jungles. But the dust also carries stowaways: millions and millions of microorganisms. Back in the late 19th century, Louis Pasteur proved that germs travel through the air, but only recently have scientists discovered that bacteria, funguses and viruses travel thousands of kilometers stuck to particles. Satellite images show clouds that are sometimes as large as the entire Iberian Peninsula.

Until recently, it was assumed that the atmosphere is a hostile environment. Dust travels at altitudes of 2,000 to 4,000 meters, where the dryness and sterilizing UV radiation are very intense. But in recent years, researchers have warned that microorganisms find a way to protect themselves, preserving their ability to colonize when they reach their destination.

Isabel Reche, from the University of Granada, and Emilio O. Casamayor from the Blanes Center for Advanced Studies, have directed an international project financed by the BBVA Foundation to study the phenomenon. These researchers aspirated air from areas without local contamination, specifically from mountain lakes, filtered it and extracted the DNA of the organisms it contained. "Traditional methods showed far fewer organisms than are actually present," says Reche. "That's why, until now, we only knew about less than 0.1 percent of the 500 bacteria present in each liter of air. DNA analysis, however, detects the majority of organisms in the sample."

To their surprise, says Reche, they discovered microorganisms in the lagoons of the Sierra Nevada and the Pyrenees which had also been found in the soil of Mauritania. The project also includes lakes in the Austrian Alps, in Patagonia (Argentina), the Bylot Islands in the Arctic Ocean (Canada) and the South Shetland Islands (Antarctica).

With climate change, the number of traveling microorganisms multiplies - more drought means more atmospheric dust. Again, researchers are wondering about the consequences. Coral populations in the Caribbean already seem to be suffering from excess dust, and the possible effects of "bacterial clouds" on human health are also being studied. It's time to take a deep breath, and seek out the root causes of these problems.