Air pollution kills. Some studies estimate that bad air quality is responsible for 10,000 pre-mature deaths every day. Aerosol particles with diameters smaller than 2.5 micron (a millionth meter), so called PM2.5, is especially threatening Human Health. If more mass is suspended in the air in form of such particles, the bigger the health thread. It is well known that industry, traffic and other human activities, such as cooking or heating, emit such particles. However, how do large numbers of them accumulate? Moreover, why is severe haze still happening in urban China and other highly industrialized regions? Stricter and stricter controls and better filtration techniques should prevent the massive direct emissions of large particles during the last decades.
The answer are so-called secondary processes, already explained here. Many aerosol particles are not directly emitted into the atmosphere, but form in the air from gases. In 2014, a study showed that even if the particles are born at a size of 1 nanometer, they can grow up to 1-2.5 micron during the following days, causing severe haze in Beijing. This means they grow by a factor of 1000 in size, having 1 billion times the mass compared to their weight at birth: Imagine a human baby born with 3 kg, reaching 3 million tons when reaching adulthood.
However, for a long time, it was unclear, if this new particle formation mechanism is causing the haze. Or would severe pollution also occur, when there are no newborns? Could all the mass also be consumed by the adult aerosols, that they become so heavy that the air becomes difficult to breath? Our new study, published in Faraday Discussions, makes a strong argument that the newborns are much more effective in building haze. Well, most of you might know the hunger of newborns, so this seems no surprise to you?
Scientifically it is. Without the formation of new particles, severe air pollution caused by aged aerosols would occur later and hence less frequently throughout the year. Our study therefore suggests that if we fix the formation of small clusters in the atmosphere, we could fix the problem of bad air quality in modern megacities!