What comes to mind when you think of indoor vs outdoor air pollution? How do they compare? Understanding the difference between indoor vs outdoor air pollution is the most effective strategy to limit its impact on your health.

Indoor air pollution is caused by smog, tobacco smoke, and household products. It is found in higher levels compared to outdoor air pollution, which may come as a surprise. Man-made and natural sources such as fossil fuel combustion and agricultural activities can cause outdoor air pollution. The health effects also vary significantly. 

Many resources are required to meet the demand of the high population growth. The by-product is air pollution, divided into indoor vs outdoor air pollution. 

So whether you’re inside or outside, you’ll likely feel the effects of air pollution. It’s essential to understand the main differences. This way, you know the potential impact on your health. 

In this article, we’ll break down indoor vs outdoor air pollution. We’ll discuss some major causes and solutions. Furthermore, to provide you with a clear picture of the health effects, we’ll analyze both the long-term and short-term implications.

What Is Indoor vs Outdoor Air Pollution?

To better understand indoor vs outdoor air pollution, we must first define indoor vs outdoor air pollution.

What Is Indoor Air Pollution

Whether you’re in an office or simply at home, we spend more than 90% of our time indoors. And while we often focus on the air pollution outdoors, we rarely consider the air quality we’re breathing indoors.

Indoor air pollution is the air quality contamination in buildings caused by dust, dirt, and other pollutants. It is broken down into particle matter and gases. Particle Matter (PM) consists of soot and dust in the air. While gases include carbon monoxide, nitrogen oxide, and sulfur oxide are a few examples.

What Is Outdoor Air Pollution?

On the other hand, outdoor air pollution is air contamination outside a building. It is mainly divided into Sulfur dioxide, Ozone, Carbon dioxide, and Hydrocarbon gases. 

Outdoor air pollution is primarily a result of emissions from various sources like factories, fossil fuels, cars, and more, depending on the area.

Indoor Vs Outdoor Air Pollution

What Are Sources of Indoor vs Outdoor Air Quality?

Sources of indoor vs outdoor air pollution can take various forms. Some sources are naturally occurring, while others are man-made. 

It is important to note that the concentration of each source varies depending on the city and climate. Warmer climates, for example, may worsen the prevalence of these air pollutants. Nevertheless, below is a breakdown of the leading sources of indoor vs outdoor air pollution.

Sources of Indoor Air PollutionSources of Outdoor Air Pollution
– Mold and mildew
– Tobacco smoke
– Household products
– Toxic gas
– Pet dander
– Fossil fuels
– Landfills
– Factories
– Mining
– Vehicles
– Agriculture

The Sources of Indoor Air Pollution 

There are several causes of indoor air pollution, some of which are evident, but others may go unnoticed. Inadequate ventilation can raise indoor pollutants by preventing clean air from entering the building.

Moreover, high temperatures and humidity can raise the number of air pollutants indoors. That being stated, below are a few familiar sources of indoor pollution.

Mold and Mildew 

Mold is a sort of fungus that grows from spores in humid areas of buildings. It consumes the materials it comes into contact with, multiplying on various surfaces.

It is most common in damp or humid environments and colder months. Because there are different types of fungus that cause mold, it can look different. Mold comes in white, black, green, and yellow varieties. The texture can be scratchy, rough, or slimy at times.

Mold can be bad for your health because it releases harmful containments into the air. It can cause respiratory issues, especially in older people and newborns.

Tobacco Smoke

Cigarettes, pipes, or cigars release tobacco smoke. Tobacco smoke is a substantial source of indoor air pollution. There have been more than 40 000 fatalities annually in the United States alone due to tobacco smoke. 

It is especially harmful to children, causing severe respiratory issues, ear problems, and other illnesses. Furthermore, cigarette smoke contains more than 70 carcinogens and other cancer-causing substances. 

When inhaled indoors with inadequate ventilation, it can cause chronic obstructive pulmonary disease (COPD) and cardiovascular disease.

Household Products

Many of the products we use in our homes daily might cause indoor air pollution. For example, cleaning products, paint, beauty products, and disinfectants. These products produce volatile organic compounds (VOCs).

They can cause health problems such as eye and throat inflammation and severe migraines. In addition, they can cause cancer in severe or long-term exposure.

Toxic Gases 

Toxic gases can accumulate inside a building. While they are often rare to find indoors, they still pose a significant danger. 

Heating appliances can produce carbon monoxide. On the other hand, you can find natural gases indoors, even though they are in lower concentrations than outdoors. 


Chemicals in furniture, electronics, and homes can cause indoor air pollution. Asbestos, formaldehyde, and lead, for example, can be found in building materials.

You won’t find chemicals like Asbestos often because newer products do not have Asbestos. However, in an old building, you may discover Asbestos. In the United States, Asbestos is prohibited. Other chemicals in building materials, such as Radon, can also contribute to indoor air pollution.

Pet Dander

You may not believe that pet dander can contribute to air pollution, but allergy sufferers will disagree. Tiny skin particles shed by pets make up pet dander. It can trigger coughing, sneezing, watery eyes, and difficulty breathing.

Indoor Air Pollution

The Sources of Outdoor Air Pollution

There are several sources of outdoor air pollution. Let’s have a look at some outdoor air pollution sources.

Combustion of Fossil Fuels

The combustion of fossil fuels is a well-known source of outdoor air pollution. You can quickly notice the smoke from factories or the burning of wood. Fossil fuels release toxic gases such as sulfur dioxide from coal, nitrogen oxides, and carbon monoxide from power plants. 


Waste from landfills releases toxic methane gases. Methane’s combination with other gases can also produce harmful and hazardous gases.

Industries and Factories

Factories emit a significant amount of carbon monoxide and other harmful gases. For example, petroleum refineries emit hydrocarbons, contributing to outdoor air pollution.

Mining Operations

Mining-related activities that remove minerals from the soil emit chemicals and dust into the atmosphere. These chemicals contribute to outdoor air pollution and cause health problems for workers and people living in the surrounding area.

Emissions from Vehicles

Vehicles can emit air pollutants such as Particles Matter, nitric acid, NO2, carbon monoxide, etc. These emissions contribute to outdoor air pollution and adverse health conditions.

Agriculture-Related Activities

Agricultural activities, such as burning old crops to prepare the land for sowing, are a common source of outdoor air pollution. Furthermore, the usage of insecticides produces toxic gases such as ammonia.

Outdoor Air Pollution

What Are the Health Effects of Indoor Vs Outdoor Air Pollution?

When considering indoor vs outdoor air pollution, many often ask which has the most significant effect on health. The health impacts are determined by the concentration levels of air pollutants.

Health Effects of Indoor Air Pollution

According to WHO, indoor pollution is responsible for 4 million deaths every year. Over the last decade, there has been an increase in scientific findings shedding light on the health effects of indoor air pollution. 

People exposed to indoor air pollution for an extended time are at a higher risk of developing major health problems. There is even a condition called “sick-building syndrome”. It primarily affects persons who spend a significant amount of time indoors.

It’s important to highlight that indoor air pollution can frequently cause significant health problems. But there hasn’t been enough scientific research done to determine what levels of exposure can cause these effects.

In addition, people also react differently to indoor air pollution. Here are some common short and long-term effects of indoor air pollution.


These health issues include inflammation of the eyes and throat. The symptoms usually appear right after being exposed to air pollution. Additionally, you will feel headaches and dizziness. These symptoms are generally manageable. In general, treatment entails reducing one’s exposure to indoor air pollutants.


Long-term health effects can emerge after years of exposure or only after prolonged exposure. These side effects include significant respiratory diseases. If the person is exposed to high air pollutants, it can lead to cancer and cardiovascular disease. 

Person Indoors

Health Effects of Outdoor Air Pollution

A research study conducted by WHO noted that at least seven million deaths occur each year from air pollution. Outdoor air pollution was responsible for nearly 4.2 million deaths these figures.

Having stated that, there are several health effects of outdoor air pollution. These health effects can be classified as either short or long-term.


The short-term health effects of exposure to outdoor air pollution include inflammation of the lungs and throat. Sulfur dioxide, for example, constricts the airways, causing breathing troubles, chest pains, and wheezing. High levels of sulfur dioxide can also cause a burning nose. 

Furthermore, it can worsen pneumonia and bronchitis, particularly in infants and toddlers who have been exposed to hydrocarbons and PAHs. 

One other short-term effect of outdoor air pollution is allergic reactions. Outdoor air pollutants such as Ozone can trigger existing allergic symptoms.


Long-term health effects from exposure to outdoor air pollution can result in an increased risk of cardiovascular and respiratory disease. Years of research have also revealed that outdoor air pollution such as Ozone and particle matter can increase the severity of heart disease.

People Outdoors

How to Reduce Indoor vs Outdoor Air Pollution

There have been a lot of efforts made to decrease indoor vs outdoor air pollution. Everyone can help to reduce air pollution by applying the actions and solutions listed below.

Reducing Indoor Air Pollution

If you’re experiencing indoor air pollution, how do you improve the air quality? Let’s have a look at some possible solutions.

Install HVAC Filters

You can install HVAC filters in your building to remove dust, spores, and other dirt particles. According to EPA, HVAC filters can trap and remove up to 99% of air pollutants ranging from 0.003 microns to 1 micron.

There are different types of HVAC filters on the market. You can purchase HVAC filters with varying efficacy and suitability for capturing certain air pollutants. 


If you have a pet, vacuuming is an excellent way to reduce indoor air pollution. Vacuuming at least four times a week will remove air pollutants like pet dander.

Improve Ventilation

Another solution to reducing indoor air pollutants is increasing clean air ventilation. Open windows and doors, especially if you are cooking, painting, or anything else that emits pollutants. Kitchen and bathroom fans can also increase ventilation indoors when placed in an appropriate location.

Reducing Outdoor Pollution 

To improve outdoor air quality, you need to make some changes. The following are some possible solutions to help reduce outdoor pollution.

Public Mode of Transportation

Use public transportation to reduce the amount of outdoor air pollution. Also, if your colleagues are traveling in the same direction as you are, consider carpooling. It will decrease the concentration of outdoor air pollution and save you money.

Reduce Fossil Fuels Combustion

Swap out fossil fuels for renewable energy where possible. In addition, we can replace coal plants with natural gases to lessen fossil fuel emissions.

Reducing Indoor And Outdoor Pollution

Indoor vs Outdoor Air Pollution Conclusion 

The key takeaways here are that there is a lot of difference between indoor and outdoor air pollution. Outdoor air pollution is contamination occurring outside a building, whereas indoor occurs inside a building. 

With indoor air pollution, ventilation is critical. It helps improve the air quality by preventing the accumulation of air pollutants. Using HVAC filters can also help remove harmful air pollutants. You can consult our experts if you need assistance choosing the best HVAC filter for your building.

While with outdoor air pollution, lessening fossil fuel combustion can reduce outdoor air pollution levels. That said, we hope this article has given you better insight into the key differences between indoor vs outdoor air pollution.

FAQ’s about Indoor vs Outdoor Air Pollution

What Are Volatile Organic Compounds (VOCs)?

Volatile organic compounds (VOCs) are gases released from manufacturing man-made products such as paints and pharmaceuticals. They are also found in petroleum fuels and paint thinners. In addition, they include a variety of substances that have long-term and short-term health effects. VOCs are found at higher levels indoors compared to outdoor. 

What Is an HVAC Filter?

An HVAC filter removes indoor air pollutants such as dust, pollen, mold spores, and other tiny particles. These particles are captured in the HVAC filter to improve the air quality inside the building. Typically, the higher the MERV rating, the more effective the filter captures and removes air pollutants. Therefore, you want to ensure a filter with a good MERV rating for your needs.

What Is Indoor Air Quality?

Indoor air quality refers to the effects of air quality in a building on a person’s health. It considers the temperature, humidity, levels of ventilation, and other factors. Currently, the indoor air quality (IAQ) standard provides guidelines on air quality levels deemed harmful to a person’s health.

How Can I Tell if There Is a Low IAQ in My Building?

People in buildings with low IAQ will notice odors or may find it difficult to breathe. They may also notice that the building is hot or dusty. However, the primary symptoms are headaches and feeling tired. Prolonged exposure to low IAQ can cause respiratory problems such as Asthma and pneumonia. 

Is There a Test That Can Find Out the Indoor Air Quality?

You can check the temperature and airflow in the building. You also take humidity readings as an extra precaution. Inspecting the building’s air ventilation will also help determine air quality. An odor inspection may also be beneficial, as the odor is a dead giveaway of poor indoor air quality. However, the best way to check indoor air quality is by using a monitor. 

How Do Air Quality Monitors Work?

Air quality monitors come in a variety of sizes. Some need a Wi-Fi connection, while others don’t. They all, however, work the same way by analyzing and detecting any air pollutants indoors. Air quality monitors are great for detecting common air pollutants that affect indoor air quality. These include gases and VOCs.

Which Air Pollutants Are of Concern?

Air pollutants from vehicles are a significant concern because they release toxins that cause adverse health effects. Although several air pollutants, nitrogen oxide and particle matter, including PM10 and PM2.5, lead to profound health implications. You also have to watch out for dust particles because they can cause respiratory diseases.

Who Is Responsible for Managing Air Quality?

The Environmental Health Agency sets quality standards in the country, among other national bodies such as the National Health Council. These agencies regulate and issue indoor and outdoor air quality standards. 

What Is the Safe Level of Air Pollution to Protect My Health?

Since everyone is exposed to different levels of air pollution, there is no scientific evidence on the safest level of air pollution. However, according to WHO, there are some guidelines on what levels you should avoid. And regulations on what is deemed safe under specific conditions. For example, for particle matter, the concentration levels need to be 35 micrograms or less to lessen the effects on your health.

How Is Outdoor Air Quality Monitored?

Government environmental bodies are usually responsible for monitoring outdoor air quality levels through a set of criteria. The monitoring procedure involves implementing stations that capture and analyze air pollutants. In addition, they also have a defined process that requires special equipment which is certified by national and international bodies.

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