The effect of nitric acid on aerosol particles in the atmosphere may offer an explanation for the smog seen engulfing cities on frosty days.
Under laboratory conditions, researchers at CERN in Switzerland observed the formation of atmospheric aerosols and discovered new information on the link between nitrogen oxides, originating in traffic and the energy industry, and the climate and air quality. These findings were published in the Nature and Science Advances journals.
Based on the findings, nitrogen compounds can, depending on the circumstances, either slow down or accelerate the growth of aerosol particles. This means that reducing sulphur dioxide is not on its own enough to prevent the smog problem seen in large cities. Instead, a comprehensive understanding of the atmospheric particle formation process is needed.
Earlier, nitric acid was not thought to have a significant effect on the formation or early growth of aerosol particles, even though nitrate compounds often occur in larger particles. However, the study published in Nature demonstrates that, in cold climates, nitric acid can boost particle growth to a marked degree, and even form particles together with ammonia in temperatures under -15°C. This is significant, as there are up to a thousand times more nitric acid and ammonia than sulphuric acid in the atmosphere.
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