Outdoor air pollution is a widespread and deadly problem.

As recently as 2020, the cost of air pollution was shockingly high, resulting in over 160,000 deaths in the five biggest cities alone and linked to 3-4 million premature deaths worldwide.^1,2,3

But outdoor air pollution is not a monolith. Some areas may experience continuously high levels of air pollution due to vehicle traffic and industrial emissions, but others may be affected by temporary but extreme sources like wildfire smoke or agricultural burning.⁴

Outdoor air pollutants can also penetrate indoor spaces or enter into vehicle cabins, rising undetected to dangerous levels in the absence of air quality monitoring or air filtration.

Real-time, accurate outdoor air quality monitoring is critical to understanding hyperlocal air pollution and responding accordingly with air pollution mitigation strategies and high-efficiency air filtration.

Read on to learn:

• which outdoor air pollutants are most dangerous to human health
• how to choose the best outdoor air quality monitor for particles and gases
• tips to reduce your daily exposure to outdoor air pollution

Outdoor air pollutants

The exact sources of outdoor air pollution can vary widely from place to place, but there are two main categories of air pollutants: particles and gases.

Particle matter

Particulate matter, or PM, consists of solid particles that range in size from 10 microns to as small as 0.003 microns.⁵

Some PM comes from natural sources like dust storms and wildfire smoke.^6,7 But most PM results from human activity, such as vehicle exhaust, industrial emissions, and crop burning – all of which have become more acute as the world population expands and industrializes.⁸

The most common outdoor particle pollutants include:

• PM10: Coarse particles ranging from 10 microns to 2.5 microns, including dust, pollen, mold spores, and large combustion particles. These particles can get into your airways and irritate the eyes, nose, and throat in high concentrations, causing short-term symptoms like coughing, sneezing, and itching.
• PM2.5: Fine particles ranging from 2.5 microns to 0.3 microns, mostly comprising smaller particles from combustion sources like vehicle exhaust, industrial emissions, and smoke from wildfires and tobacco products. PM2.5 is considered the most common and most dangerous particle pollutant. PM2.5 is small enough to penetrate into lung tissue and into the bloodstream, where it can build up in the circulatory system and increase your risk of heart and lung diseases.
• PM1: Fine particles ranging from 1 micron to 0.3 microns. PM1 particles can also get into the bloodstream and affect numerous organs throughout the body. PM1 particles have a larger overall surface area than typical PM2.5 particles, allowing PM1 particles to carry toxic chemicals on their surface and cause even more harm in the body.
• Ultrafine particles (UFPs): Tiny airborne particles smaller than 0.1 microns. UFPs can also be breathed into the lungs and pass into the bloodstream. UFPs cause widespread oxidative stress to the body, resulting in a wide variety of health effects like heart disease, lung disease, and brain damage.

Gas pollutants

Gases are substances with no solid shape or size, comprising molecules that are so small that they move erratically in the air due to Brownian motion, bumping around into other molecules in the air.⁹ This behavior can make many airborne gases difficult to monitor accurately in real time.

Gas pollutants, especially greenhouse gases like carbon dioxide (CO₂), have become an increasing air quality problem as the global climate warms and traps gases in the atmosphere.^10,11,12 Outdoor CO₂ also poses a health threat to indoor air quality as rising outdoor CO₂ intermingles with indoor CO₂ that builds to dangerous levels when ventilation is poor.

The warming climate has also increased the length and severity of wildfires worldwide, generating even higher amounts of carbon emissions each year.¹³

The most common outdoor gas pollutants include:

• Carbon dioxide (CO₂): Carbon dioxide is a gaseous molecule made up of one carbon and two oxygen atoms. Measured in parts per million (ppm), CO₂ isn’t considered harmful around 400 ppm. But above 1,000 ppm, CO₂ can displace oxygen in your lungs and lead to cognitive and health symptoms. Above 5,000 ppm, CO₂ can be deadly.
• Ozone (O₃): Ozone is a naturally occurring molecule made up of three oxygen atoms. High in the atmosphere, ozone is a natural barrier to harmful ultraviolet (UV) radiation from the sun. But ground-level ozone created when heat from sunlight reacts with chemicals in emissions can cause symptoms like shortness of breath, coughing, and sore throat. Over time, ozone exposure can damage the lungs and worsen conditions like asthma and emphysema.

Outdoor air quality monitoring technology

When outdoor PM or gases like CO₂ reach high levels, it’s advised for the general population to consider how much outdoor air pollution they may be able to tolerate in order to perform necessary daily tasks. Sensitive groups, such as those with respiratory conditions or children and the elderly, should be especially cautious due to increased health risks.

However, no amount of air pollution should be considered safe for human health. This is especially true for PM2.5, one of the most dangerous airborne pollutants.

The U.S. Environmental Protection Agency (EPA) air quality index (AQI) provides a globally recognized standard for health risks connected specifically to PM2.5 exposure, with PM2.5 concentrations measured in micrograms per cubic meter (μg/m³). A typical outdoor air quality monitor will use this standard to measure PM2.5 as an AQI reading.

From 0 to 50 (equivalent to 0 to 12 µg/m³), outdoor PM2.5 poses minimal risk to human health, even for those considered sensitive to air pollution. Beyond an AQI of 51, PM2.5 is increasingly dangerous to human health (see Figure 1), especially above 100.

Figure 1: U.S. AQI levels from 0-301+, equivalent PM2.5 standards by μg/m³, and health recommendations for each level. Source: IQAir

Because PM2.5 can contain particles as small as 0.3 microns (encompassing PM1 particles, too), highly sensitive and accurate air quality monitoring technology is critical to measure and forecast air pollution in order to make informed decisions that help protect your health.

Outdoor monitoring technology for PM2.5 is highly advanced and has been widely available for years.¹⁴ Leading outdoor air quality monitors also use artificial intelligence and machine learning to generate air quality forecasts based on hyperlocal PM2.5 and weather data.¹⁵

But particles below 0.3 microns are much more difficult to monitor due to their tiny size and erratic behavior in the air.

AirVisual Outdoor air quality monitors detect PM10, PM2.5, PM1, and CO₂ as well as temperature and humidity to high degrees of accuracy.

PM is measured using light-scattering laser sensor technology that shines light onto particles in ambient air (see Figure 2). The light scatters and is then measured by a light detector (or photometer) that can accurately calculate PM concentrations down to 0.3 microns.

Figure 2: A diagram illustrating how AirVisual Series PM sensors work. Source: IQAir

The 3-PM / CO₂ model also detects CO₂ levels with sensors designed to measure both gas and particle pollutants.

As air passes through the CO₂ sensors, a light source shines infrared (IR) light on CO₂ molecules and measures the remaining IR light that reaches a light detector in the sensor to estimate how much of the air contains CO₂ (see Figure 3).

Figure 3: A diagram illustrating how AirVisual Series CO₂ sensors work. Source: IQAir

Outdoor air pollution levels can be monitored through the AirVisual app or a custom air quality dashboard for multiple outdoor sensors.

When air pollution levels are high, AirVisual Outdoor air quality monitors can alert a user with health recommendations based on the immediate air quality, giving the user the ability to mitigate risk and advance notice before even higher concentrations are reached.

AirVisual Series air quality sensors – including both indoor and outdoor monitors – are also compatible with smart-home technology and automated building management systems (BMS).

For example, a custom IFTTT applet can be written for an AirVisual Outdoor monitor to alert a BMS or smart-home HVAC system when outdoor PM or CO₂ levels reach a defined threshold considered undesirable by the home or facility owner (i.e., AQI of 51+ or CO₂ at 1,000+ ppm).

This IFTTT alert is sent to the BMS or smart home system and triggers HVAC fans to turn on. In an HVAC system containing high-efficiency air filtration rated MERV 16 or higher, this automated event can both ventilate CO₂ and filter PM.

How to reduce exposure to outdoor air pollution

Awareness of air pollution is only the first step. Responding to elevated air pollution levels and helping prevent air pollution are both critical to reducing your exposure and protecting your health.

Here are some ways to help reduce your exposure to outdoor air pollution throughout your day:

• Close windows and doors when outdoor air pollution levels are high.
• Reduce your use of gas-powered vehicles and other appliances that use combustion engines. Consider buying a hybrid, electric, or hydrogen-powered car.
• Limit your essential trips to once a week or so to reduce your personal emissions.
• Walk, bike, or take public transportation whenever possible.
• Limit your use of gas or electric indoor appliances and switch them off when you’re not using them.
• Turn off lights and other electronics when you’re not using them.
• Transition to solar energy or other renewable energy sources to power your home.
• Use an air purifier to help reduce indoor air pollutants that seep in from outdoors or from indoor sources.
• Connect an air quality monitor to indoor HVAC systems so that air quality data can automatically turn on HVAC fans when detecting high levels of indoor pollutants.
• Wear an air pollution mask outdoors when particulate matter concentrations are elevated.

The takeaway

Outdoor air quality monitors provide a first line of defense in detecting airborne pollutants that are dangerous to your health.

A highly accurate outdoor air quality monitor uses sensors that detect both particle and gas airborne pollutants and can use that data to send essential health data to an app or automate ventilation and filtration.

Knowing more about what’s in the air can help reduce your risk of exposure to air pollution and empower you to take back control over air quality.