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In 2018, the World Health Organization (WHO) and the UNFCCC secretariat (UN Climate Change) organized the first global conference on air pollution and health. In advance of this groundbreaking meeting, WHO Director-General Tedros Adhanom Ghebreyesus, Ph.D., declared air pollution and the toxic air billions breathe every day “a silent public health emergency.”

We agree. That’s why, since 2008, GPS has designed and introduced innovative technologies and products that help improve indoor air quality (IAQ). Our patented needlepoint bipolar ionization (NPBI™) technology targets particulate matter (PM), one of the most common and harmful indoor air pollutants.

In this article, we provide a high-level overview of air quality in the United States, including sources of pollution, environmental and health impacts, and how and why air quality is monitored.

We also take a deeper dive into PM, including the potential health effects of airborne PM and the importance of reducing indoor PM levels.


What is air pollution?

Air pollution is the contamination of the indoor or outdoor environment by harmful solids, liquids or gasses in higher than usual, or recommended, concentrations.

As described in the Clean Air Act of 1970 — a comprehensive federal law that regulates air emissions to protect public and environmental health — the six most prevalent and harmful air pollutants are:

  • Particulate matter: A mixture of solid and liquid droplets suspended in the air, either emitted directly from a source (e.g., construction sites, unpaved roads) or formed by chemical reactions (e.g., sulfur dioxides emitted from power plants and automobiles).

  • Ground-level ozone (O3): A natural gas created when nitrogen oxides and volatile organic compounds chemically react with one another. In the upper atmosphere, ozone is protective, reducing the amount of harmful UV radiation reaching the Earth’s surface. High levels in the lower atmosphere are harmful because, according to the Environmental Protection Agency (EPA), ozone can trigger a variety of health problems.

  • Carbon monoxide (CO): A colorless, odorless, tasteless gas produced by burning gasoline, wood, propane or other fuels. Improper ventilation may allow carbon monoxide to accumulate to dangerous levels.

  • Sulfur dioxide (SO2): A colorless, pungent, toxic gas formed by burning sulfur in air, primarily from diesel engines, industrial boilers and other industrial processes.

  • Nitrogen dioxide (NO2): A gas composed of nitrogen and oxygen, primarily formed from burning fuel (e.g., emissions from cars, trucks and buses, power plants and off-road equipment).

  • Lead (Pb): A naturally occurring element found in small amounts in the Earth’s crust and in the environment (air, soil and water). Lead is also emitted from some industrial sources.

How does air pollution impact the environment?

Airborne contaminants have a significant effect on the environment. For instance, air pollution contributes to:

  • Acid rain: This occurs when wet (rain, fog and snow) or dry (particulates and gas) precipitation contains toxic amounts of nitric and sulfuric acids that acidify water and soil environments and damage trees, farms and buildings.

  • Haze: Formed when fine particles are dispersed in the air and reduce the transparency of the atmosphere, haze is primarily caused by gas emissions from industrial facilities, power plants, cars and trucks.

  • Climate change: Some airborne pollutants contribute to changes in the Earth’s climate. For example, black carbon — a particulate pollutant from combustion — absorbs light and converts solar radiation to heat, warming the air and accelerating the melting of glaciers, snow cover and sea ice.

How does air pollution affect human health?

WHO data shows that almost everyone (99% of the global population) is breathing air that exceeds WHO guideline limits for levels of the most common pollutants, contributing to more than 7 million premature deaths worldwide annually while also harming the health of billions more. Low- and middle-income countries are disproportionately affected and suffer from the highest exposure.

According to WHO data on household air pollution and ambient (outdoor) air pollution, health effects vary by pollutant but generally can include:

  • Temporary discomfort (irritation of the eyes, nose, skin and throat, as well as breathing difficulties and headaches)

  • Respiratory infections

  • Stroke

  • Heart disease

  • Lung disease, including chronic obstructive pulmonary disease (COPD)

  • Immunological disorders

Longer cumulative exposures are correlated with more severe health outcomes, with some populations being more susceptible (American Lung Association):

  • Infants, children and teens

  • People with lung disease, especially asthma and COPD

  • People with cardiovascular disease

  • People of color

  • Current or former smokers

  • People with low incomes

  • Obese individuals

  • People living in areas with high levels of air pollution

How is air quality measured and reported?

While there is no one standard that affirmatively quantifies good air quality, the EPA’s Air Quality System database consolidates air quality data from thousands of monitoring stations across the U.S. These data inform the Air Quality Index (AQI), a nationally uniform, color-coded index for reporting and forecasting daily air quality.

The EPA establishes an AQI for each of the six major air pollutants regulated by the Clean Air Act (PM, O3, CO2, SO2, NO2 and Pb). Each of these pollutants has a national air quality standard set by the EPA to protect public health.

Daily AQI reports can be found at AirNow and on state and local agency websites. Some agencies also report the AQI via their local news media or by telephone hotlines.

The reports employ a color-coded system to help people interpret air quality:


  • Higher AQI values correspond with more air pollution and greater health concerns.

  • Ranges and values are shown on a continuum from 0 to 500 across six categories, from “good” to “hazardous.”

Guidance is included per category to help individuals and communities make informed decisions to minimize health risks. For instance, while most people may not be affected when the air quality is deemed unhealthy for sensitive groups, this information could be valuable for someone with asthma who may choose not to exercise outside on a day with this reading.

air quality index levels of health concern


What is particulate matter?

The air around us is filled with very small solid and liquid particles, also known as PM or particle pollution. Particles are typically divided into three groups by their diameter size in micrometers (µm):

  • PM10 : Coarse particles with diameters that are 10 µm and smaller

  • PM2.5: Fine particles with diameters that are 2.5 µm and smaller

  • PM1.0: Ultrafine particles with diameters that are 1 µm and smaller

For context, a grain of fine beach sand is around 90 µm, and a grain of salt is roughly 60 µm. The naked eye can see particles that range from between 10 µm and 40 µm. A sunbeam through a window helps us see some of these particles, which can include dust, dander, smoke and even certain viruses and bacteria.

According to the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE), virtually all particles (99.9%) found in a typical atmosphere are below PM1.0.

What are the primary sources of PM?

Particles are either directly emitted from a specific source or, more often, formed by complex chemical reactions:

  • For example, direct emissions, such as dust and debris, come from a construction site where materials are cut and/or grinded. They are also kicked up into the air on unpaved roads.

  • Indirect formation occurs when gaseous pollutants chemically react and form PM. Examples include soot from automobile exhaust or gas-burning fireplaces.

What are the harmful effects of exposure to PM?

The relationship between PM and adverse short-term and long-term health effects is well documented.

According to the EPA, exposure to inhalable particles can affect the heart and lungs. Any particle less than 10 µm can have a negative health impact, but particles that are particularly fine (less than 2.5 µm) or ultrafine (less than 1 µm) are more likely to be inhaled and become embedded in the lungs or, in some cases, enter the bloodstream.

People with heart or lung diseases such as coronary artery disease, congestive heart failure, asthma or COPD, as well as children and older adults, are at greater risk from PM exposure.

Specific health impacts include:

  • Eye, nose and throat, and lung irritation

  • Aggravation of coronary and respiratory disease symptoms

  • Premature death in people with heart or lung disease

How can we reduce PM exposure?

There are three key ways to reduce PM indoors:

  • Source control

  • Ventilation

  • Air cleaning

Passive approaches such as source control and ventilation are the initial lines of defense, helping minimize and dilute the pollutants that come and stay inside. But to achieve optimal IAQ, it’s important to add air-cleaning technologies that actively treat the air as part of a multilayered approach. These technologies make particles larger, in turn making it easier for HVAC systems to capture and remove them.


Research that goes back at least 20 years shows that filters, regardless of MERV rating, have a uniformly pronounced weak spot when it comes to capturing ultrafine particles, roughly between 0.10 µ and 0.4 µ. They counterintuitively perform better, capturing 0.01 µ than are at capturing particles that are 10 (0.10 µ) or 40 times (0.4 µ) larger before regaining their efficacy.

MERV curve

How does NPBI help reduce PM indoors?

Needlepoint bipolar ionization, or NPBI, is one proven technology that helps reduce indoor airborne particles through a process called agglomeration.

Here’s how it works:

  • NPBI ionization devices, manufactured by GPS, are installed in an HVAC system’s ductwork.

  • HVAC fans blow air through the ductwork and over the ionizer, producing positive and negative ions that are delivered to the indoor space.

  • These ions seek out and combine with particles, forming larger clusters that are more effectively captured by the HVAC system’s filter. NPBI can also help cluster the majority of mid-sized particles that are bouncing around in the space. Fewer particles mean cleaner indoor air.


Since the implementation of the Clean Air Act in 1970 — and thanks in large part to technological advances to mitigate air pollution — the EPA reports that air quality in the U.S. has steadily improved.

  • Between 1970 and 2020, the combined emissions of the six most common pollutants dropped by 78%.

  • Emissions of key air pollutants continue to decline from 1990 levels, driven largely by federal and state implementation of stationary and mobile source regulations.

AQI total days unhealthy for sensitive groups
But — even though we are headed in the right direction — we must all stay vigilant and do our part. At GPS, we are committed to improving indoor air quality with our proactive air cleaning approach.

Explore our NPBI technology to learn more about how it works to help reduce indoor PM levels.

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