Examples of Secondary Pollutants and How They’re Formed

, Staff Writer
Updated June 23, 2020
car exhaust leaks nitrogen oxides
    car exhaust leaks nitrogen oxides
    milehightraveler / E+ / Getty Images

Primary issues lead to secondary problems, such as how primary pollutants lead to secondary pollutants. Explore what secondary pollutants are, along with different examples of secondary air pollutants like nitrogen dioxides and smog.

Primary Pollutants vs. Secondary Pollutants

When it comes to pollutants, there are two different types: primary and secondary pollutants. The difference between them is how they are formed.

Primary Pollutants

Primary pollutants come right from the source. For example, the exhaust from a car burning gas is an example of a primary pollutant. Another primary pollutant is crude oil leaking from a pipe into the ocean.

Secondary Pollutants

However, when primary pollutants mix with the Earth’s atmosphere, they make new compounds called secondary pollutants. For example, the fumes from your exhaust mix with the oxygen in the air to make nitrogen dioxide. This is a secondary pollutant.

Secondary pollutants are created in response to primary pollutants messing up the precarious balance in the atmosphere. And, they can wreak havoc on our world. Let’s check out different examples of secondary air pollutants you might be familiar with.


Examples of Secondary Air Pollutants

In chemistry, you know that when you mix one chemical with another, it forms a new substance. That’s exactly what happens with secondary pollutants. The byproducts individuals and factories release into the air from burning fossil fuels, such as burning coal to make electricity, mix with the atmosphere in the air to create new compounds. And these new compounds cause all types of issues.

Ground Level Ozone (Photochemical Smog)

The ozone layer is detrimental to human existence when it’s in the right place. High up in the atmosphere, it protects people from harmful sun rays. However, near the ground, it’s harmful to humans. It’s also a major component of photochemical smog. This is the brownish haze that you might notice around large major cities, but winds can carry it to other places too.

When factories and cars burn fossil fuels, they release nitrogen oxide into the air. Now that would be all fine and dandy if nitrogen oxides didn’t mix with the ultraviolet light of the sun. When they mix, they create photochemical smog. Not only does smog make it harder to see, but it’s harmful to trees, plants, and humans.


Acid Rain

When you hear acid rain, you might think of droplets that melt metal in the movies. But real acid rain isn’t as potent as that. Instead, when factories release sulfur dioxide and nitrogen oxides, the chemicals react with water and oxygen in the air to create nitric and sulfuric acids. These acids get mixed up with water molecules to form clouds and are eventually rained down onto earth. While these acids aren’t any good for the lakes, streams, and soil, they also cause weathering to rock and mountains.

Nitrogen Dioxide

When you ride in a car or truck, your exhaust leaks nitrogen oxides. When those nitrogen oxides go in the air, they mix with oxygen creating a new compound called nitrogen dioxide (NO2). While nitrogen dioxide can be found in both smog and acid rain, it’s also dangerous on its own in the form of particulate matter. You can breathe in this gas, which can cause airway and lung irritation.


Harmful Secondary Pollutants

Primary pollution is harmful enough, but when it mixes with the atmosphere, it creates damaging secondary pollutants like smog and nitrogen dioxide. These secondary pollutants can affect other areas too by creating acid rain. Interested in exploring more about pollution? Read about the 7 different types of pollution.