Ozone depletion is primarily caused by the release of chlorofluorocarbons (CFCs) and other halogenated compounds into the atmosphere. These compounds are used in various industrial and commercial applications, such as refrigeration, air conditioning, and aerosol propellants.

CFCs and other halogenated compounds release chlorine and bromine atoms into the stratosphere. These atoms act as catalysts, initiating a chain reaction that leads to the breakdown of ozone molecules.

Lightning strikes produce high-energy ultraviolet radiation, which splits oxygen molecules (O₂) into individual oxygen atoms (O). These atoms then combine with other oxygen molecules to form ozone (O₃).

The biosphere contributes to the production of ozone-depleting substances through the release of methane (CH₄) and nitrous oxide (N₂O). These gases can react with chlorine and bromine atoms in the stratosphere, leading to the formation of ozone-depleting compounds.

Ozone depletion in the stratosphere leads to increased ultraviolet (UV) radiation reaching the Earth's surface. This can have various adverse effects, including an increased risk of skin cancer, cataracts, and immune system suppression.

Asthma is not a direct consequence of increased ultraviolet radiation. However, UV radiation can exacerbate respiratory conditions, including asthma.

Ozone depletion can have various negative impacts on marine ecosystems. It can harm phytoplankton, which are the base of the marine food web, leading to disruptions in the entire ecosystem. Additionally, it can cause coral bleaching and damage to coral reefs, and it can also contribute to the growth of harmful algal blooms.

The Montreal Protocol is an international agreement that aims to protect the ozone layer by phasing out the production and use of ozone-depleting substances. It was adopted in 1987 and has been instrumental in reducing the levels of these substances in the atmosphere.

The biosphere plays a role in the recovery of the ozone layer by releasing compounds that react with ozone-depleting substances, breaking them down into less harmful substances. This helps to reduce the levels of ozone-depleting substances in the atmosphere and allows the ozone layer to recover.

It is estimated that it will take approximately 100 years for the ozone layer to fully recover from the damage caused by ozone-depleting substances. This recovery period is dependent on various factors, including the continued implementation of the Montreal Protocol and the natural processes that contribute to the formation and replenishment of the ozone layer.

Phasing out ozone-depleting substances poses several challenges. These include the high cost of alternative substances, the lack of availability of suitable substitutes for certain applications, and the long lifespan of existing ozone-depleting substances. These challenges require ongoing efforts to develop and implement effective strategies for the transition to ozone-friendly alternatives.

The observed increase in ozone levels in the troposphere is primarily attributed to human activities, particularly the burning of fossil fuels. This process releases nitrogen oxides and volatile organic compounds into the atmosphere, which react to form ozone in the presence of sunlight.

Tropospheric ozone is harmful to human health as it can cause respiratory problems, aggravate asthma, and increase the risk of cardiovascular diseases. In contrast, stratospheric ozone is beneficial as it absorbs harmful ultraviolet radiation from the sun, protecting life on Earth.

To reduce tropospheric ozone levels, strategies include reducing emissions of nitrogen oxides and volatile organic compounds, promoting the use of renewable energy sources, and improving energy efficiency in transportation and industry. These measures aim to decrease the production of ozone precursors and mitigate the formation of tropospheric ozone.

Individuals can contribute to reducing tropospheric ozone levels by taking actions such as using public transportation or carpooling to reduce vehicle emissions, conserving energy at home and in the workplace, and choosing products with low volatile organic compound (VOC) content. These efforts help to decrease the release of ozone precursors into the atmosphere.