Reducing Emissions

This lesson covers the strategies and technologies used to reduce emissions of greenhouse gases and atmospheric pollutants, as required by AQA GCSE Chemistry specification (5.9.2 and 5.9.3). You need to understand the range of approaches available — from individual actions to international agreements — and be able to evaluate their effectiveness and limitations.

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Why Reducing Emissions Matters

The emission of greenhouse gases and atmospheric pollutants from human activities is causing:

• Climate change — rising global temperatures, sea level rise, extreme weather events.
• Air pollution — respiratory diseases, acid rain, global dimming.
• Environmental degradation — loss of biodiversity, ocean acidification, damage to ecosystems.

Reducing emissions is essential to limit these impacts and protect the environment, human health, and the economy.

Exam Tip: When discussing reducing emissions, always explain WHY it is important before describing HOW to do it. This shows the examiner that you understand the context and significance of the topic.

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Strategies for Reducing Greenhouse Gas Emissions

1. Switching to Renewable Energy Sources

Replacing fossil fuels with renewable energy sources eliminates greenhouse gas emissions from electricity generation. The main renewable energy sources are:

Source	How It Works	Advantages	Limitations
Solar	Photovoltaic cells convert sunlight to electricity	No emissions during operation; abundant	Intermittent (no sun at night/in cloudy weather); large land area needed
Wind	Turbines convert kinetic energy of wind to electricity	No emissions during operation; can be offshore	Intermittent; visual impact; noise; can harm birds
Hydroelectric	Water flowing through turbines generates electricity	Reliable; no emissions during operation	Requires suitable geography; can damage ecosystems; limited sites
Tidal	Tidal movements drive turbines	Predictable; no emissions during operation	Very expensive; limited suitable locations; environmental impact on estuaries
Geothermal	Heat from within the Earth used to generate steam and electricity	Reliable; no emissions during operation	Limited to geologically active areas; drilling is expensive
Biomass	Burning plant material or biogas	Carbon neutral (in theory); uses waste materials	Releases CO₂ when burned; land use competition with food crops

2. Nuclear Energy

Nuclear power does not produce CO₂ during electricity generation (only during construction and fuel processing). However, it produces radioactive waste that must be stored safely for thousands of years, and there are concerns about safety (e.g. nuclear accidents) and the high cost of building and decommissioning plants.

3. Carbon Capture and Storage (CCS)

Carbon capture and storage (CCS) is a technology designed to capture CO₂ from power stations and industrial processes before it enters the atmosphere, and store it permanently underground.

The process involves three stages:

flowchart LR
    A["1. Capture<br/>CO₂ separated from<br/>flue gases at source"] --> B["2. Transport<br/>CO₂ compressed and<br/>piped or shipped"]
    B --> C["3. Storage<br/>CO₂ injected deep<br/>underground into<br/>geological formations"]

    style A fill:#2980b9,color:#fff
    style B fill:#e67e22,color:#fff
    style C fill:#27ae60,color:#fff

Advantages of CCS:

• Allows continued use of fossil fuels while reducing CO₂ emissions.
• Can be fitted to existing power stations (retrofitted).
• Suitable geological storage sites exist in many countries (e.g. depleted oil and gas fields, saline aquifers).

Disadvantages of CCS:

• Very expensive — significantly increases the cost of electricity.
• Energy-intensive — the capture process uses 10–40% of the energy produced by the power station.
• Not yet proven at large scale — very few commercial CCS projects are operating worldwide.
• Risk of CO₂ leakage from underground storage.
• Does not address other pollutants (NOₓ, particulates, SO₂).

Exam Tip: CCS is a technology that is often mentioned in exam questions about reducing greenhouse gas emissions. You need to know the three stages (capture, transport, storage) and be able to discuss both advantages and disadvantages.

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Strategies for Reducing Pollutant Emissions

1. Catalytic Converters

As covered in the previous lesson, catalytic converters fitted to vehicle exhaust systems reduce emissions of carbon monoxide (CO) and nitrogen oxides (NOₓ):

2CO + 2NO → 2CO₂ + N₂

2. Flue Gas Desulfurisation (FGD)

FGD removes sulfur dioxide (SO₂) from power station exhaust gases:

CaCO₃ + SO₂ → CaSO₃ + CO₂

This reduces acid rain. The by-product (calcium sulfate / gypsum) is used in construction.

3. Diesel Particulate Filters (DPF)

Modern diesel vehicles are fitted with diesel particulate filters that trap soot particles in the exhaust. The trapped particles are periodically burned off at high temperatures (a process called "regeneration").

4. Electrostatic Precipitators

Power stations use electrostatic precipitators to remove particulates from flue gases. The particles pass through a strong electric field, become charged, and are attracted to collecting plates where they are removed.

5. Low-Emission Vehicles

Vehicle Type	Emissions Comparison
Petrol car	CO₂, CO, NOₓ, some particulates
Diesel car	CO₂, CO, NOₓ, more particulates
Hybrid car	Reduced CO₂ and pollutants (uses electric motor at low speeds)
Electric car (EV)	Zero tailpipe emissions (but emissions depend on how electricity is generated)
Hydrogen fuel cell car	Only produces water; zero CO₂ at tailpipe (but producing hydrogen may generate emissions)

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Government and International Action

Legislation and Regulation

Governments can introduce laws and regulations to reduce emissions:

• Vehicle emission standards — setting maximum limits for CO₂, NOₓ, and particulate emissions from new vehicles (e.g. Euro 6 standards in the UK and EU).
• Clean Air Zones — restricting the most polluting vehicles from entering city centres.
• Banning coal — several countries have phased out or are phasing out coal-fired power stations.
• Building regulations — requiring new homes to be energy-efficient and well-insulated.

International Agreements

Agreement	Year	Key Commitment
Kyoto Protocol	1997	Legally binding emission reduction targets for developed countries
Paris Agreement	2015	Aim to limit global warming to well below 2°C (ideally 1.5°C) above pre-industrial levels; all countries set voluntary targets
COP conferences	Annual	Regular meetings to review progress and strengthen commitments

Economic Instruments

• Carbon taxes — a direct tax on carbon emissions, making polluting activities more expensive.
• Emissions trading schemes (ETS) — cap-and-trade systems where companies buy and sell permits to emit CO₂. The total cap is reduced over time.
• Subsidies for renewables — financial incentives for installing solar panels, wind turbines, and other renewable energy systems.

Exam Tip: If asked about international efforts to reduce emissions, mention the Paris Agreement by name and state its aim (limit warming to 1.5–2°C). This shows specific knowledge. If asked about UK-specific measures, mention Clean Air Zones, the ban on new petrol and diesel car sales, or the phase-out of coal power.

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Evaluating Emission Reduction Strategies

No single strategy is sufficient on its own. A combination of approaches is needed: