Question

Most of the ultraviolet radiation reaching the Earth's atmosphere from the Sun is absorbed by the layer of stratospheric ozone and never reaches the Earth's surface. Between 1969 and 1986 , the layer of stratospheric ozone over North America thinned, decreasing by about 3 percent. Yet, the average level of ultraviolet radiation measured at research stations across North America decreased over the same period. Which one of the following, if true, best reconciles the apparently discrepant facts described above? (A) Ultraviolet radiation increases the risk of skin cancer and cataracts; the incidence of skin cancer and cataracts increased substantially between 1969 and 1986. (B) Between 1969 and 1986, the layer of stratospheric ozone over Brazil thinned, and the average level of ultraviolet radiation reaching the Earth's surface in Brazil increased. (C) Manufactured chlorine chemicals thin the layer of stratospheric ozone. (D) Ozone pollution, which absorbs ultraviolet radiation, increased dramatically between 1969 and 1986. (E) Thinning of the layer of stratospheric ozone varies from one part of the world to another and from year to year.

Short answer

Option D reconciles the discrepancy by explaining increased ozone pollution absorbing UV radiation.

Step-by-step solution

Understand the Problem Statement

The situation involves two key changes over time: the thinning of stratospheric ozone and a decrease in ultraviolet radiation levels at North American research stations. We need to identify a factor that explains how ultraviolet radiation levels decreased despite a thinned ozone layer.

Analyze Each Option for a Possible Explanation

Examine each provided option to see if it could plausibly explain the observed phenomenon of decreased ultraviolet radiation despite ozone thinning: - **Option A:** Discusses health risks related to UV radiation but does not address why radiation levels decreased. - **Option B:** Talks about ozone thinning and UV increase in Brazil, unrelated to North America. - **Option C:** Identifies a cause of ozone thinning, but does not explain decreased radiation. - **Option D:** Mentions an increase in ozone pollution, which could absorb more UV radiation, potentially explaining decreased UV radiation. - **Option E:** States geographical and temporal variability, but does not directly link to the decreased radiation in North America.

Select the Best Explanation

The question asks for the explanation that best reconciles the discrepancy. Option D, which explains an increase in ozone pollution that absorbs ultraviolet radiation, effectively accounts for the decreased UV radiation measurements despite ozone thinning.

Key concepts

Stratospheric Ozone

The stratospheric ozone layer is a vital shield protecting Earth from harmful ultraviolet (UV) radiation. This layer, located in the stratosphere, absorbs most of the Sun's harmful UV rays, preventing them from reaching the surface. By doing so, it plays a crucial role in safeguarding both human health and the environment. The ozone layer is formed by the reactions of ultraviolet light with oxygen molecules, creating ozone (O₃).
However, since 1969, there has been a measurable thinning of this layer over areas like North America. The use of manufactured chlorine chemicals, often found in refrigerants and aerosol sprays, has significantly contributed to this depletion. As ozone levels decrease, more UV radiation can penetrate through, increasing risks to life on Earth. Understanding these changes is key in grasping how they impact our atmosphere and health.

Ultraviolet Radiation

Ultraviolet radiation is a type of energy emitted by the Sun. It is invisible to the human eye but can have significant effects on skin health. UV radiation is divided into three types: UVA, UVB, and UVC.

• UVA is the most abundant form reaching the Earth's surface and can age skin.
• UVB is less abundant; however, it can burn the skin and is a major cause of skin cancer.
• UVC is absorbed by the stratosphere and usually doesn't reach the surface.

Given its harmful potential, it's crucial to monitor UV levels. The scenario in the original exercise highlights a decrease in measured UV radiation over North America despite thinning of the ozone layer. This decrease indicates other factors may be influencing UV absorption, such as increased ozone pollution, which is not part of the stratospheric ozone layer but can still absorb some UV rays.

Problem-Solving Skills

Problem-solving skills involve the ability to approach complex situations systematically and logically. The original exercise is a perfect example of using problem-solving strategies. In scenarios where changes are observed, like the thinning of the ozone layer yet reduced UV levels, identifying the right connections is crucial.
To solve such problems, it's essential to:

• Gather all relevant data and facts.
• Identify discrepancies or anomalies.
• Consider alternative explanations or factors.
• Evaluate different hypotheses against the data.

In the exercise, understanding that increased ozone pollution could explain the decreased UV levels requires analyzing available information and making connections between various factors.

Critical Thinking

Critical thinking is the ability to assess situations or statements and reach a logical and fact-based conclusion. The exercise about ozone and UV radiation is a great scenario requiring critical thinking. It demonstrates how different variables can influence results and why considering multiple angles is essential for a well-rounded conclusion.
Effective critical thinking involves:

• Questioning assumptions and explored possibilities.
• Analyzing relationships between known data points.
• Recognizing patterns and potential influences.
• Drawing informed conclusions from evidence.

In this context, evaluating the role of ozone pollution over North America in the face of a thinning stratospheric ozone layer requires discerning the relationship between observed data and potential explanations. Such critical assessment is what leads to the most plausible reconciliation of apparently contradictory data.