Smog is a phenomenon strongly affected by the weather. Without favourable conditions, its formation isn’t possible. What are the dependencies between the weather and smog? Before breaking them down, let’s take a closer look at the smog itself.
Even though it has become a permanent element of many urban landscapes, many still don’t really understand its phenomenon. Smog is a relatively new word that comes from a combination of smoke and fog. It perfectly describes its essence since it can be easily confused with an ordinary morning mist – but sometimes it’s enough to take a deeper breath to notice its terrible influence on the lungs. Breathing with smog can be harmful to your health and affect the respiratory system as well as other organs.
There are two kinds of smog – the photochemical and sulphurous, or, in other words, the Los Angeles and the London type. Each of them requires different conditions to occur and has a different chemical composition.
The photochemical smog is often named the Los Angeles one since it’s symptomatic for this biggest Californian metropolis. However, the phenomenon is spread worldwide, appearing in the urban spaces on all the longitudes, from São Paulo to Delhi. It’s particularly common to the subtropical spheres and forms mainly in the summer months.
In the chemical composition of the photochemical smog, it’s the nitrogen oxides and carbon oxides that dominate. It may also contain aromatic hydrocarbons that are particularly dangerous for human health. The Los Angeles smog is caused mainly by exhaust fumes.
The weather conditions play a significant part in the formation of this type of smog. The lack of wind stops the air pollution from spreading, whereas the high solar exposure drives the photochemical reactions.
Note that this type of smog can also appear in different latitudes than the subtropical ones. In countries like Poland, where the sulphurous smog is notorious, the photochemical ones can also appear in the summer months. Particularly in recent years, due to climate change, it was observed annually.
The sulphurous smog is also known as the London one due to the history of the British capital. In the industrial era, it has been the most polluted city in the world. Many of its inhabitants suffered health problems or even died as a direct result of exposure to smog. In 1952, as a result of the high concentration of sulphurous oxides in the air, thousands of Londoners died. These tragic events have led to the introduction of regulations that helped to lower the emissions of toxic gases and particulate matter. Today, London has cleaner air than it used to, but the label has stayed with it.
The sulphurous smog is typical of the moderate climate and appears mainly in the colder seasons. The reason lies in its origins – the burning of fossil fuels. It consists mainly of sulphur oxides, carbon oxide, dust, and soot.
In its case, the weather conditions are also crucial. The lack of wind facilitates the formation of the London smog, but there’s a weather phenomenon that makes it even easier – thermal inversion. It causes the rise of temperature in the higher layers of the atmosphere. As a result, it is impossible for the air masses to mix.
The weather conditions are crucial to the formation of smog. How do they influence it?
The more windy the area is, the less probable is the formation of smog. The wind can spread the pollutants, lowering their concentration in a particular space. However, that doesn’t mean that they disappear.
High temperature with high sun exposure can fuel photochemical reactions. The thermal inversion can make it impossible for the pollutants to move to higher altitudes, trapping them on the Earth’s surface. The convection – mixing the masses of warmer and lighter air with the cooler and heavier ones – facilitates it.
High pressure is associated with stable weather. The air masses move much slower in such circumstances, which creates favourable conditions for smog. Low pressure, on the other hand, creates higher humidity and makes the masses of the air move fast. It can lead to precipitation which washes the pollution out of the atmosphere.
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