Given the great variety of substances present in the atmosphere, numerous classification methods have been proposed: firstly it can be classified according to the chemical composition, for which we mainly speak of compounds that contain sulfur, compounds that contain nitrogen, which contain carbon and halogen compounds.
Secondly, it can be classified according to the physical state: gaseous, liquid or solid; finally, it can be divided according to the degree of reactivity in the atmosphere, into primary or secondary substances. The main effects that pollutants cause in the environment are the greenhouse effect, and acid rain, then of course they also lead to other problems such as the ozone hole and other less visible problems on flora and fauna.
The greenhouse effect: it is a climatic phenomenon that consists in the heating of the lower layers of the atmosphere, due to the shielding that some gases contained in it (greenhouse gases) offer, the latter are transparent to radiations of shorter wavelength and opaque to those with a wider wavelength, this means that the radiations with a shorter wavelength are able to cross these gases reaching the earth's surface, where they are partly absorbed and partly reflected; the absorbed part is released in the form of infrared rays which have a longer wavelength and therefore remain trapped by greenhouse gases.
The increase in the greenhouse effect following the industrial revolution was mainly caused by the release of fossil CO2 into the atmosphere. The study: Introductory lecture: air quality in megacities, published on the Faraday discussions, questions how smog can affect the quality of life of people in the world's largest cities.
We can read: "Urbanization is an ongoing global phenomenon as more and more people are moving from rural to urban areas for better employment opportunities and a higher standard of living, leading to the growth of megacities, broadly defined as urban agglomeration with more than 10 million inhabitants.
Intense activities in megacities induce high levels of air pollutants in the atmosphere that harm human health, cause regional haze and acid deposition, damage crops, influence air quality in regions far from the megacity sources, and contribute to climate change.
Great London Smog and the first recognized episode of Los Angeles photochemical smog seventy years ago, substantial progress has been made in improving the scientific understanding of air pollution and in developing emissions reduction technologies.
oxidation mechanisms; the formation and evolution of secondary particles, especially thos and containing organic species; and the influence of emerging emissions sources and changing climate on air quality and health. While air quality has substantially improved in megacities in developed regions and some in the developing regions, many still suffer from severe air pollution.
Strong regional and international collaboration in data collection and assessment will be beneficial in strengthening the capacity. This article provides an overview of the sources of emissions in megacities, atmospheric physicochemical processes, air quality trends and management in a few megacities, and the impacts on health and climate.
The challenges and opportunities facing megacities due to lockdown during the COVID-19 pandemic is also discussed. "