Air pollution
Air pollution is the contamination of the indoor and outdoor environment by any substance or chemical that changes the nature of the atmosphere. Many pollutants come from the factory's and vehicles like cars, trucks and boats, however many air pollutants also come from natural sources like volcanoes, dust (mostly from deserts) and forest fires. Air pollutants have a major effect on human health. Studies have shown that air pollutants can cause heart and lung diseases. Air pollutants with major health concerns are particulate matter, carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide. Data has shown that almost all people on planet earth breathe in air that contains high levels of pollutants and especially low and middle-income countries get exposed to the highest amount of air pollutants. Many of the air pollutants are also Greenhouse gases and therefore the polluted air is directly connected to the earth's Climate change and Ecosystems. Seemingly the best choice would be to remove all the air pollutants as much as possible, however, it is more complex than it looks.
Aerosols
Aerosols are little specs that are emitted into the atmosphere. Some aerosols have a relatively short timeframe in the atmosphere. Aerosols can have a cooling as well as a warming effect. Aerosols can be from a natural source like dust, volcano ash and vapours or it can be due to a human-made source like agriculture dust, vehicle exhaust, emission mine and so on. Many climatologists use a typical type of labelling for grouping aerosols including sulfates, organic carbon, black carbon, nitrates, mineral dust and sea salt. However, no labelling is perfect and it is difficult to have correct labelling for aerosols.
How do aerosols work?
Besides the health effect of aerosols, they also play an important role when it comes to weather. Aerosols overall have a cooling effect of the earth and they are relatively short in the atmosphere (week to months). Meaning if we would stop emitting any aerosols into the atmosphere we would see the effect within weeks to months. When there is no cooling effect anymore because of the aerosols we would see the full effect of greenhouse gases. This would result in an acceleration of climate change. Therefore cutting out all the aerosols emissions in a short period of time can have serious consequences and is best to be avoided. The best option would be slowly removing all aerosols and at the same time removing greenhouse gasses as fast as possible.
Aerosols and clouds
Aerosols play a very important role when it comes to clouds. Aerosols serve as cloud condensation nuclei (CCN). The aerosol particle acts like a sort of cloud seed and the water vapour condenses on the aerosol particle. There are two effects depending on the number of aerosols:
Twomey effect
A low amount of aerosols means a low amount of CCN which means that the same amount of water is condensing on a lower amount of nuclei. As a result less and bigger waterdrops in the clouds. When there is a high amount of aerosols in the atmosphere meaning a high amount of CNN results in a lot of small raindrops. Small drops of water have a higher albedo meaning that they reflect more sunlight and thus have a higher cooling effect. The cloud albedo based on the number of aerosols is called the Twomey effect.
Albrecht effect
When there are a low amount of aerosols and thus a low CCN the droplets in the clouds are bigger and rain will fall more quickly. When the CCN is high and thus there are many aerosols the droplets are smaller and the cloud has more time to grow and it takes longer before the cloud will start raining. When the amount of aerosols in the atmosphere is high the result will be that the rain gets more catastrophic because the cloud gets more time to grow before the rain falls and a single cloud holds more water when the CNN is higher. The higher amount of aerosols will result in more floods and extreme weather. A higher amount of CNN means an increase in cloud life. The cloud's lifetime based on the number of aerosols is called the Albrecht effect.
Aerosols as a solution for Climate change
Solar engineering is a type of engineering where particles like aerosols are released into the stratosphere to reflect sunlight and slow the process of global warming. Solar geoengineering mimics the result that happens from massive volcano eruptions which result in a cooling of the earth for about 1 year. Solar engineering is focussing on releasing chemicals that reflect the sunlight but do not cause any harm to the environment like calcium carbonate or sulfates. The cooling of the earth due to solar geoengineering slows down the global warming process, reduces heatwaves and reduces sea level rise. However as mentioned before with more aerosols in the air the chances of extreme weather, flooding and droughts become bigger. Right now there are a few projects about solar geoengineering including a project that releases sea salt spray into the atmosphere in Australia during the warm periods resulting in thicker clouds en thus whiter clouds that reflect more sunlight to minimize Bleaching event. Solar geoengineering can never be a solution to climate change however it can be a tool to slow down the process so we have more time to cut our carbon dioxide emissions to 0.
