Reducing Air Pollutants (College Board AP® Environmental Science) : Study Guide

Jacque Cartwright

Written by: Jacque Cartwright

Reviewed by: Alistair Marjot

Updated on

Methods of reducing air pollutants

  • Methods to reduce air pollutants include regulatory practices, conservation practices, and alternative fuels

  • These strategies help in:

    • Reducing the sources of pollution

    • Promoting cleaner technologies

    • Encouraging sustainable living

Conservation

  • Reducing energy usage is key to reducing air pollutants

  • Methods include:

    • Carpooling and mass transit release fewer pollutants

    • Combine this with more compact cities and now you are traveling even less

    • Make the cities greener with more energy-efficient buildings, green roofs, and improved municipal waste management

Alternative fuels

  • Reducing pollution from the combustion of fossil fuels is one reason for finding alternative fuels

  • Cleaner alternative energy sources like biofuels, solar, wind, hydro, and hydrogen reduce greenhouse emissions and eliminate particulates from combustion

  • Many buildings can be retrofitted for wind and solar and reduce dependence on the power grid

Regulations

  • To combat air pollution, numerous laws and procedures have been put into place

The Kyoto Protocol (1997)

  • This was signed by UN members and aims to reduce global warming-causing greenhouse gas emissions

  • Human CO₂ emissions were the most likely cause of global warming, the committee said

  • The protocol listed reducing carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HCFs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF₆)

The Paris Agreement (2016)

  • The goal is to limit global temperature rise to below 2°C of the pre-industrial average

  • This requires adapting and mitigating anthropogenic carbon dioxide

The United States' Clean Air Act (CAA)

  • This US federal legislation governs fixed and mobile air pollution

  • The legislation mandates states to prepare strategies to meet and maintain National Ambient Air Quality Standards (NAAQS) for specified pollutants

Montreal Protocol

  • This international convention ends production and consumption of ozone-depleting substances to safeguard the ozone layer

  • Many are also greenhouse gases, so limiting their use can help combat climate change and improve air quality

European Union's Air Pollution Thematic Strategy

  • This approach is a comprehensive plan to lower air pollution in the EU and its member states

  • It consists of steps to cut emissions from a range of sources, including households, transportation, industry, and agriculture

Beijing Action Plan

  • This is a strategy created by the Beijing administration to deal with the air pollution issues in the city

  • It restricts car use, closes polluting factories, and promotes the use of clean energy

Vapor recovery nozzle

  • A vapor recovery nozzle is an air pollution control device on a gasoline pump that prevents fumes such as benzene (which is a known carcinogen) from escaping into the atmosphere when fueling a motor vehicle

  • There is a separate tube inside the filling nozzle that captures vapors and returns them to an underground storage tank beneath the gas station

  • The nozzle reduces VOCs, which contribute to smog and irritate the respiratory tract

Catalytic converter

  • Catalytic converters are devices fitted to gasoline and diesel vehicles along with kerosene heaters to reduce harmful emissions

  • They contain a series of transition precious metal catalysts, such as platinum and rhodium

  • The metal catalysts are in a honeycomb within the converter to increase the surface area available for reaction

  • The system is attached to the exhaust system and converts toxic gases like CO, NOₓ, and hydrocarbons into less toxic compounds like CO₂, O₂, N₂, and water

  • In many countries, it is compulsory for vehicles to have catalytic converters

Diagram of a catalytic converter showing gases from the engine (CO, NOx) entering, passing through a catalyst, and exiting as clean gases (N2, CO2).
Diagram of a catalytic converter with labeled parts: gases (CO, NO, O2) enter, pass through a honeycomb structure, and exit as CO2, N2, and O2.
Catalytic converters are designed to reduce the polluting gases produced in car exhausts

Wet and dry scrubbers

  • Companies must reduce smokestack pollution under EPA requirements

  • Scrubbers remove building exhaust gases and particles

  • Wet scrubbers

    • Wet scrubbers use limestone to neutralize sulfur dioxide before it leaves smokestacks

    • These pipe exhaust gases through a water-sprayed chamber

    • Particulates and dissolved gases are then filtered from the liquid

    • After cleaning (scrubbing), the exhaust is emitted

    • There is a sludge collection system that traps polluted water for later disposal

  • Dry scrubbers

    • Exhaust gases are neutralized or converted by dry reagent scrubbers

    • The converted materials are recovered from the gas stream, with the cleaned gases being emitted

    • Calcium oxide is a common dry scrubber additive which reacts with SO₂ to form calcium sulfite

Flue gas desulfurization (FGD)

  • FGD is important because SO₂ emissions are a health and environmental hazard

  • FGD systems can remove up to 95% of SO₂ from flue gases

  • FGD is the main way to reduce sulfur dioxide emissions from coal-fired power stations

    • Emissions are passed into a scrubbing chamber where

      • They are sprayed with a wet slurry of calcium oxide and calcium carbonate 

      • The calcium compounds react with sulfur dioxide to produce calcium sulfate

      • The cleaned gas is then emitted from the chimney

Flue gas desulfurization

Diagram of a flue gas desulfurization unit showing waste gases entering, reacting with calcium slurry, producing clean gases and calcium sulphate.
Flue gas desulfurization

The scrubber sprays a lime slurry over the waste gases to remove 90-95% of the sulfur dioxide

Electrostatic precipitators

  • Coal-fired power stations use electrostatic precipitators and scrubbers to remove dust and smoke from emission gases to control air pollution

  • It works by using a high-voltage screen that filters waste gases so particles are ionized

  • Gases are passed across positively and negatively charged electrodes, creating ion particles in the gas stream

  • Collector plates attract the ionized particles and remove them from the gas stream into a collection hopper for disposal in landfills

Diagram showing the process of removing smoke particles from waste gases using charged plates, with labels explaining each step in the process.
Diagram showing the method of electrostatic precipitation

You've read 0 of your 5 free study guides this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Jacque Cartwright

Author: Jacque Cartwright

Expertise: Geography Content Creator

Jacque graduated from the Open University with a BSc in Environmental Science and Geography before doing her PGCE with the University of St David’s, Swansea. Teaching is her passion and has taught across a wide range of specifications – GCSE/IGCSE and IB but particularly loves teaching the A-level Geography. For the past 5 years Jacque has been teaching online for international schools, and she knows what is needed to get the top scores on those pesky geography exams.

Alistair Marjot

Reviewer: Alistair Marjot

Expertise: Biology & Environmental Systems and Societies Content Creator

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.