Airborne pollutants pose a continual threat to human health, safety, and quality of life. Pollutants also pose a challenge to maintaining safe indoor air quality and to the outdoor environment.

Knowing which pollutants are most common and their sources is an important step towards protecting yourself against their negative health impacts. The following are some of the more frequently encountered and dangerous pollutants to be aware of.

PM2.5

PM2.5 is a concentration measurement of particulate matter (PM) in the air with a diameter of 2.5 microns or less.

Of all the listed pollutants, PM2.5 poses the greatest health threat to human health.¹ This is because PM2.5 can lodge deep into the most sensitive part of the respiratory tract upon inhalation andtriggerrespiratory illnesses such as asthma, bronchitis, and emphysema.

PM2.5can enter the bloodstream and travel to the heart, increasing the potential for cardiovascular problems such as arrhythmic heartbeats and heart attacks.

PM2.5can originate from both organic and inorganic sources. Common sources include:^3,4,5

• soil
• dust
• soot
• smoke
• smoking
• combustion emissions
• construction and demolition

PM10

Like PM2.5, PM10 is suspended particulate matter which can appear in either a liquid or solid forms. PM 10 differs from PM2.5 only in terms of size.

While PM2.5 is particulate matter that has a diameter of 2.5 microns or less, PM10 is particulate matter with a diameter between 10 - 2.5 microns.PM10 is the larger, coarser particle of the two types.

PM10 is not as dangerous as PM2.5 because it’s relatively larger size prevents it from being easily absorbed into the bloodstream. It can, however, cause irritation to the eyes, nose, and throat, while long term exposure can impact the lungs and heart.⁶

Sources for PM10 include:^7,8

• dust and dirt
• pollen
• mold
• smoke
• combustion

Black Carbon

One of the possible components of particulate matter is black carbon. Black carbon is a major element of soot.

Sources of black carbon include:⁹

• emissions from diesel engines and vehicles
• residential burning such as wood and coal burning
• agricultural waste field burnings
• forest and vegetation fires

Black carbon can create problems in respiratory and cardiovascular symptoms and can result in premature death.

Ozone (O₃)

The ozone molecule is anaturally occurring compound that plays a vital role in blocking out harmful ultraviolet light from the sun. At the ground level, however, ozone is toxic.¹⁰

While other pollutants are emitted directly into the air by various sources, ozone iscreated by sunlight chemically reacting withnitrogen oxidesand volatile organic compounds (VOC) in the air.Ozone is one of the most pervasive and most difficult to control of all airborne pollutants.

Symptoms can include:^11,12

• chest pain
• lung and throat irritation
• wheeze and coughing
• increased asthma attacks
• continued lung damage after symptoms end

Nitrogen dioxide (NO₂)

Nitrogen dioxide is a pollutant with acharacteristic acrid odor. In high concentrations, it appears as a reddish-orange gas.¹³

Nitrogen dioxide is either formed naturally during thunderstorms or from combustion processes, such as running car engines. Indoor sources include unvented heaters and gas stoves.¹⁴

Nitrogen dioxide is a precursor for pollutants like ozone (or smog)and particulate matter.

Health impacts from exposure to high concentrations of nitrogen can include:¹⁵

• Coughing and wheezing
• lung irritation
• reduced lung function
• increased asthma attacks
• cardiovascular damage
• lower birth weight
• risk of premature death

Carbon monoxide (CO)

Carbon monoxide(CO) is an odorless, colorless, tasteless gas. Accidental carbon monoxide poisoning poses a serious threat to life; its imperceptible nature causes it to be known as the silent killer.

Carbon monoxide can be created through incomplete combustion in vehicles, heating, coal-fired power generation, and biomass burning.^16,17

Symptoms and health problems from carbon monoxide poisoning can include:

• headaches
• dizziness
• weakness
• fatigue
• nausea
• confusion
• blurred vision
• death¹⁸

As reported in a 2015 study published in Obstetrical & Gynecological Survey, high levels of CO can also be especially harmful to pregnant women and newborns.¹⁹

Sulphur dioxide (SO2)

Sulphur dioxide is a colorless gas with a strong, pungent smell. Sulfur dioxide is almost entirely from man-made sources.²⁰

Sulfurdioxide is formed when energy sources containing sulfur, like coal and oil, are burned in industrial processes. Emissions can also result from fuel combustion in vehicles.

When inhaled, sulfur dioxide can cause several health problems, including:²¹

• nasal mucus
• choking
• irritation to the ears, eyes, and throat
• wheezing
• chest tightness
• shortness of breath

Long term, sulfur dioxide exposure can cause acute respiratory illness and permanent changes in the lungs' biology.

Volatile organic compounds (VOCs)

Volatile organic compounds (VOCs) are gases that are emitted from liquids or solids. Like nitrogen dioxide, VOCs contribute to the creation of the pollutants PM2.5 and ozone.

VOCs can be found in vehicle emissions and can also be emitted from many indoor and outdoor sources, such as fuels, household cleaners, and combustion. ^22,23

VOCs can be toxic, depending on their composition. Health impacts of VOCs include: ^24,25,26,27

• irritation of the eyes, nose, and throat
• headaches
• breathing problems
• sick building sickness (SBS)
• allergies and asthma
• cancer
• kidney damage

Ammonia

Ammonia is a colorless and corrosive gas with a pungent smell. When combined with nitric and sulfate acids, ammonia can create ammonium salts, a harmful form of PM2.5.²⁸

Ammonia comes from both natural and man-made sources, such as:

• decaying organic matter
• human and animal waste
• fertilizer manufacturing
• industrial processes
• waste disposal sites

Health implications for ammonia exposure include:

• eye, nose, throat, and skin irritation
• severe cardiovascular and respiratory effects
• decreased lung function
• asthma aggravation
• premature death

Carbon dioxide

Carbon dioxide is a colorless, odorless gas. It's the primary greenhouse gas emitted through human activity.

Carbon dioxide is created naturally through animal respiration, oceans, and decaying plants. However, most greenhouse contributions come from human activities, such as transport, industry, and fuel burning for electricity and heating.

Direct exposure to high concentrations of carbon dioxide can have several negative health impacts on people, including: ²⁹

• feeling lethargic
• clumsiness
• emotional upset
• headaches
• difficulty concentrating
• dizziness
• vomiting
• nausea