 In this video, we are going to learn about the effects on our health from a range of air pollutants. If you live in the city, you may already be aware of the effects of air pollution on your health. You may already have had some breathing discomfort or painful eyes. The ones that we'll be focusing on in this video are particulate matter called PMs, ozone, O3, nitrogen oxides and sulfur dioxide. More often than not, these pollutants exist as a direct result of human activity. One such human activity is the burning of fossil fuels in power stations or cars. Particulate matter is a mixture of sulfate, nitrate, ammonia, sodium chloride, carbon, mineral dust and water. It consists of a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. These particles are identified according to their aerodynamic diameter, as either PM10 particles with an aerodynamic diameter smaller than 10 microns or PM2.5. These have aerodynamic diameters smaller than 2.5 microns. In comparison, the average size of a human hair is 60 microns. PM2.5s are more dangerous since, when inhaled, they may reach deep into the lungs and interfere with gas exchange. The health effects of particulate matter are felt in both the developed and developing world. Chronic exposure to particles contributes to the risk of developing cardiovascular and respiratory diseases, typically asthma, as well as lung cancer. Ozone O3 absorbs harmful UV rays from the sun in the upper atmosphere and can help prevent the increased risk of skin cancer. However, ground level ozone causes problems. It does so by a photochemical reaction, which is triggered by the absorption of light. The reactions between nitrogen oxides and volatile organic compounds lead to the formation of a photochemical smog and ground ozone. You see this more often in the summer, and it can appear as an orange-brown haze over a city. This smog, including the ground ozone, causes breathing problems, can trigger asthma attacks and lead to lung disease. Next, nitrogen dioxide emissions come from cars and factories where fuels are combusted. You may recall, oxygen forms about 21% of our atmosphere, whilst nitrogen forms 79%. In a hot engine, a tiny amount of nitrogen atoms join with oxygen atoms to form mixtures of nitrogen oxides, called NOx. Studies have proven that there is a causal relationship between the symptoms of bronchitis, a respiratory disease being seen in children with asthma, as a result of long-term exposure to this pollutant. Finally, there is sulfur dioxide. Can you think how this chemical might be formed? Pause the video and continue when ready. The correct answer is that any sulfur combusted in the presence of oxygen, typically coming from fossil fuels, which naturally contain tiny amounts of sulfur, and also the smelting of mineral ores, lead to the formation of sulfur dioxide. In turn, these pollutants affect the respiratory system and cause irritation of the eyes. If you breathe this in, you are more likely to cough or secrete more mucus, and will be at a higher risk of developing chronic bronchitis. In summary, all are causing unnecessary deaths, especially where the emissions of these pollutants can be avoided through the use of catalytic converters in cars and by scrubbing of power station gases.