Problem 41 - Chemistry in Context

Question

A certain city has an ozone reading of \(0.13 \mathrm{ppm}\) for 1 hour, and the permissible limit is \(0.12\) for that time. You have the choice of reporting that the city has exceeded the ozone limit by \(0.01\) ppm or saying that it has exceeded the limit by \(8 \%\). Compare these two methods of reporting.

Step-by-Step Solution

Answer

0.01 ppm exceedance is slightly inaccurate as an 8% exceedance should actually be reported as 8.33%.

Step 1: Understanding the Exceedance in ppm

First, we find how much the actual ozone reading of the city exceeds the permissible limit. The permissible limit is given as 0.12 ppm, and the city's reading is 0.13 ppm. Therefore, the exceedance in parts per million is calculated as the difference between the two values: \[\text{Exceedance (ppm)} = 0.13 \text{ ppm} - 0.12 \text{ ppm} = 0.01 \text{ ppm}\]

Step 2: Calculating the Percentage Exceedance

Next, we need to find by what percentage the city's ozone level exceeds the permissible limit. The percentage exceedance is calculated by dividing the exceedance in ppm by the permissible limit, then multiplying by 100 to convert it to a percentage: \[\text{Percentage Exceedance} = \left(\frac{0.01 \text{ ppm}}{0.12 \text{ ppm}}\right) \times 100\% \approx 8.33\% \]

Key Concepts

Air Quality Standards

Air quality standards are guidelines established to protect public health and the environment from adverse effects caused by pollution. They define the allowable concentration of pollutants in the air, such as ozone, in specific time frames. These standards are crucial for regulatory bodies to maintain air quality and ensure a safe and healthy environment for all citizens.

• Health Protection: Air quality standards are primarily set to minimize health risks, considering evidence-based research on the impact of pollution on human health.
• Regulation and Enforcement: Governments create regulations based on these standards to monitor and control pollutant emissions from various sources.
• Public Awareness: They also serve to inform and raise awareness among the public about the dangers of air pollution and encourage safer practices.

In our example, the permissible limit for ozone concentration is 0.12 ppm for one hour. This threshold is set to minimize potential health impacts to the individuals exposed.

Parts Per Million (ppm)

Parts per million (ppm) is a unit of measurement often used in science to describe the concentration of one substance in a million parts of another. It is especially common in the context of air and water pollution levels.

• Definition: One ppm indicates one part of a substance per one million parts of the total. In terms of air quality, if a substance measures 0.13 ppm, it implies that there are 0.13 parts of this pollutant in every million parts of air.
• Simplicity: Using ppm makes it easier to express very low concentrations that would be cumbersome in percentage terms.
• Comparison: It's also important for comparing pollutant levels easily against standards set by regulatory agencies.

In the context of the problem, the ozone concentration in the city was 0.13 ppm, slightly above the permissible 0.12 ppm, indicating a need for immediate attention to control air quality.

Percentage Exceedance

Percentage exceedance is a way to represent how much a measured value surpasses a standard or threshold in percentage terms. This is useful for effectively communicating the degree of violation in scenarios where precise ppm values might not be as meaningful to the general public.

• Calculation: To find the percentage exceedance, subtract the permissible limit from the measured value. Then divide this difference by the standard and multiply by 100.
• Interpretation: A key advantage is that percentage figures can more intuitively convey magnitude—seeing a percentage can often make the level of exceedance more relatable.
• Example Application: For the city with a reading of 0.13 ppm, exceeding the 0.12 ppm limit results in an approximate 8.33% exceedance.

Although both ppm and percentage exceedance methods help in understanding air quality issues, converting to percentage exceeds can often be more effective for public communication and awareness.