SO₂ - How Sulfur Dioxide
Affects the Way We Live & Breathe

Published by the US EPA
Office of Air Quality Planning & Standards
November 2000

Over the past 30 years, sulfur dioxide emissions have decreased by more than a third. EPA has implemented innovative, flexible programs to continue the national reductions, prevent degradation, and improve local air quality.

EPA-456/F-99-005 [courtesy of EPA - Environmental Protection Agency]

Table of Contents
SO₂: What is it? Where does it come from?
Chief Causes for Concern
Health and Environmental Impacts of SO₂

SO₂: What is it? Where does it come from?

Sulfur dioxide, or SO₂, belongs to the family of sulfur oxide gases (SOx). These gases dissolve easily in water. Sulfur is prevalent in all raw materials, including crude oil, coal, and ore that contains common metals like aluminum, copper, zinc, lead, and iron. SOx gases are formed when fuel containing sulfur, such as coal and oil, is burned, and when gasoline is extracted from oil, or metals are extracted from ore. SO₂ dissolves in water vapor to form acid, and interacts with other gases and particles in the air to form sulfates and other products that can be harmful to people and their environment.

Over 65% of SO₂ released to the air, or more than 13 million tons per year, comes from electric utilities, especially those that burn coal. Other sources of SO₂ are industrial facilities that derive their products from raw materials like metallic ore, coal, and crude oil, or that burn coal or oil to produce process heat. Examples are petroleum refineries, cement manufacturing, and metal processing facilities. Also, locomotives, large ships, and some nonroad diesel equipment currently burn high sulfur fuel and release SO₂ emissions to the air in large quantities.

Pie chart showing sources of SO2
courtesy of EPA - Environmental Protection Agency

Chief Causes for Concern

SO₂ contributes to respiratory illness, particularly in children and the elderly, and aggravates existing heart and lung diseases.

SO₂contributes to the formation of acid rain, which:

damages trees, crops, historic buildings, and monuments; and
makes soils, lakes, and streams acidic.

SO₂contributes to the formation of atmospheric particles that cause visibility impairment, most noticeably in national parks.

SO₂ can be transported over long distances.
SO₂ and the pollutants formed from SO₂, such as sulfate particles, can be transported over long distances and deposited far from the point of origin. This means that problems with SO₂ are not confined to areas where it is emitted.

Silhouette of child using inhaler to treat asthma

People with asthma are particularly affected by peak levels of SO₂.
[courtesy of EPA - Environmental Protection Agency]

Short-term Peak Levels

High levels of SO₂emitted over a short period, such as a day, can be particularly problematic for people with asthma. EPA encourages communities to learn about the types of industries in their communities and to work with local industrial facilities to address pollution control equipment failures or process upsets that could result in peak levels of SO₂.

Health and Environmental Impacts of SO₂

SO2 causes a wide variety of health and environmental impacts because of the way it reacts with other substances in the air. Particularly sensitive groups include people with asthma who are active outdoors and children, the elderly, and people with heart or lung disease.
	Respiratory Effects from Gaseous SO₂ Peak levels of SO₂ in the air can cause temporary breathing difficulty for people with asthma who are active outdoors. Longer-term exposures to high levels of SO₂ gas and particles cause respiratory illness and aggravate existing heart disease. Respiratory Effects from Sulfate Particles SO₂ reacts with other chemicals in the air to form tiny sulfate particles. When these are breathed, they gather in the lungs and are associated with increased respiratory symptoms and disease, difficulty in breathing, and premature death.
	Visibility Impairment Haze occurs when light is scattered or absorbed by particles and gases in the air. Sulfate particles are the major cause of reduced visibility in many parts of the U.S., including our national parks.
	Acid Rain SO₂ and nitrogen oxides react with other substances in the air to form acids, which fall to earth as rain, fog, snow, or dry particles. Some may be carried by the wind for hundreds of miles.
	Plant and Water Damage Acid rain damages forests and crops, changes the makeup of soil, and makes lakes and streams acidic and unsuitable for fish. Continued exposure over a long time changes the natural variety of plants and animals in an ecosystem.
	Aesthetic Damage SO₂ accelerates the decay of building materials and paints, including irreplaceable monuments, statues, and sculptures that are part of our nation's cultural heritage.

Reference: http://www.epa.gov/air/urbanair/so2/index.html

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Indoor Air Quality and Pollution

SO2 - How Sulfur Dioxide Affects the Way We Live & Breathe

SO2: What is it? Where does it come from?

Chief Causes for Concern

Health and Environmental Impacts of SO2

SO₂ - How Sulfur Dioxide
Affects the Way We Live & Breathe

SO₂: What is it? Where does it come from?

Health and Environmental Impacts of SO₂