chemistry

Leighton relationship

Leighton relationship is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Leighton relationship rather than just read about it. In short: In atmospheric chemistry, the Leighton relationship is an equation that determines the concentration of tropospheric ozone in areas polluted by the presence of nitrogen oxides. Ozone in the troposphere is primarily produced through the photolysis of nitrogen dioxide by photons with wavelengths (λ) less than 420 nanometers, which are able to reach the lowest levels of the atmosphere, through the following mechanism…

Key takeaways

Leighton relationship belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Leighton relationship to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Leighton relationship from memory before moving on to harder problems.

Reference excerpt

In atmospheric chemistry, the Leighton relationship is an equation that determines the concentration of tropospheric ozone in areas polluted by the presence of nitrogen oxides. Ozone in the troposphere is primarily produced through the photolysis of nitrogen dioxide by photons with wavelengths (λ) less than 420 nanometers, which are able to reach the lowest levels of the atmosphere, through the following mechanism:

The symbol M represents a "third body", an unspecified molecular species that must interact with the reactants in order to carry away energy from the exothermic reaction. The 3P designation on the atomic O species is the term symbol for its electronic state, indicating that it is in a spin triplet state, which is the ground electronic state of atomic O. This series of reactions creates a null cycle, in which there is no net production or loss of any species involved. Since O(3P) is very reactive and O2 is abundant, O(3P) can be assumed to be in steady state, and thus an equation linking the concentrations of the species involved can be derived, giving the Leighton relationship:

[ O 3 ] = J 1 [ NO 2 ] k 3 [ NO ] {\displaystyle [{\ce {O3}}]={\frac {J_{1}[{\ce {NO2}}]}{k_{3}[{\ce {NO}}]}}}

This equation shows how production of ozone is directly related to the solar intensity, and hence to the zenith angle, due to the reliance on photolysis of NO2. The yield of ozone will therefore be greatest during the day, especially at noon and during the summer season. This relationship also demonstrates how high concentrations of both ozone and nitric oxide are unfeasible. However, NO can react with peroxyl radicals to produce NO2 without loss of ozone:

RO2 + NO → NO2 + RO thus providing another pathway to allow for the buildup of ozone by breaking the above null cycle. This relationship is named after Philip Leighton, author of the 1961 book Photochemistry of Air Pollution, in recognition of his contributions in the understanding of tropospheric chemistry. Computer models of atmospheric chemistry utilize the Leighton relationship to minimize complexity by deducing the concentration of one of ozone, nitrogen dioxide, and nitric oxide when the concentrations of the other two are known.

References

Worked examples

Example 1 — a first encounter with Leighton relationship

Start with the simplest possible case. Write down what Leighton relationship claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Leighton relationship before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Leighton relationship ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Leighton relationship

In research: Leighton relationship appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Leighton relationship in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Leighton relationship is common in secondary-school and first-year university syllabi. It links to neighbouring topics Atmospheric chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Leighton relationship outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Leighton relationship in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Leighton relationship means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Leighton relationship out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Leighton relationship in simple terms?

Why does Leighton relationship matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Leighton relationship?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Leighton relationship.