Understanding AQI Meaning: How Climate Change Affects Air Quality

The Air Quality Index is a scale of 0-300+ that measures the threat level of air pollutants to human health. In the United States, the national ambient air quality, or outdoor air quality, is measured by taking levels of five key pollutants:

• Ground-level ozone
• Particle pollution, also known as particulate matter
• Carbon monoxide (CO)
• Sulfur dioxide
• Nitrogen dioxide

These are the most common hazardous substances likely to be found in our air. Exposure to air pollution from any of these five sources can cause acute and long-term health problems, like:

• Coughing
• Wheezing
• Trouble breathing
• Fatigue
• Dizziness
• Asthma attacks
• Heart attacks
• Migraines
• Blood poisoning 

Since it would be hard for the average person to keep an eye on the levels of all five major pollutants each day, the AQI was developed as a useful shorthand. 

Source:  Christian Lue on Unsplash

This helps keep the public safe - they can check local air quality each day. An AQI value of 100 generally means the air is safe for normal outdoor activities for most people - though people with health conditions that make them unusually sensitive to air pollution may need to be extra careful. 

High levels of air pollution mean you probably need to take protective steps, like not exercising or doing yard work outside, or even trying to stay indoors entirely. For people who work outdoor jobs, respirators may be necessary during high AQI days. 

We'll take a deep dive into how AQI is calculated, what these five pollutants mean for your health, and how you can protect yourself as air quality across the planet steadily worsens. 

Protective Measures: Are Gas Masks Becoming the Future Norm? 

We're all familiar with wearing cloth or medical masks to try to prevent the spread of viruses. Wearing air-filtering face masks - or even industrial-grade respirators - might become a new norm in heavily polluted cities. 

In much of Asia, for example, wearing N95 masks is common on bad air quality days. These masks help to filter out P2.5, which is tiny fragments of inhalable matter. But it doesn't do much against other chemicals

Air filtering face masks work by actually purifying the air through a charcoal filter. This means that the wearer only breathes in clean air. 

BUY NOW: Emergency air filtering face masks for adults and children 

Air Purifying Mask Scenarios 

If you spend a lot of time working hard outdoors, AQI can have a huge impact on your health. People in physically demanding jobs may want to wear an air-purifying mask when working outside on bad air quality days.

Similarly, localized pollutants, like lead from a waste incinerator, can cause local spikes. You should keep an eye on local air quality alerts and wear an air purifying mask on days with additional risk. 

Source: Mira Safety

Finally, anyone with respiratory conditions like asthma or COPD should consider protecting themselves with a respirator. 

Risks of Long-Term Respirator Wear

Some wearers try to extend the life of their respirator filters as long as possible. We don't recommend this, as the efficiency drops with excessive use.

Additionally, respirators need to be cleaned and sanitized properly to remove any contaminants that might stick to them. It's important to take time to remove, clean, and fully dry your respirator in between wears.

READ NOW: How long do gas mask filters last? 

Components of AQI (Air Quality Index) 

The Air Quality Index is a handy way of explaining the level of air pollution in any given area at a specific time. 

Five of the most common air pollutants are measured by local stations. These levels are then calculated into a standardized score according to a formula determined by the environmental protection agency (EPA). 

We'll cover the sources and health effects of each of the main five pollutants. 

Ground-level ozone

What is it? Ground-level ozone is a reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) when exposed to heat and sunlight. 

What causes it? Industrial emissions, car exhaust, chemical solvents, and gasoline vapor all produce NOx and VOCs. They're most likely to react and create ground-level ozone in hot, enclosed environments, like a city in the summer. 

What are the risks? Ground-level ozone damages lung tissue. Healthy people experience coughing, throat irritation, or chest pain. People with chronic respiratory conditions like bronchitis and emphysema will feel their conditions get worse. 

Particulate Matter 

What is it? Particulate matter is the mixture of microscopic pieces of liquids and solids. PM10 is matter that is less than 10 microns in diameter, meaning it's small enough to be inhaled into a human's lungs. PM2.5 is even smaller (2.5 microns in diameter or less). These are the two most common types of particulate matter discussed in AQI. 

Where does it come from? PM10 is created by construction sites, combustion of any substance (wood, gasoline, oil), dust, pollen, and more. Think of it as the "grit" in the air. PM2.5 is formed mostly by emissions or by the chemical reactions of different gasses in the atmosphere. 

Source: California Air Resources Board 

What are the risks? Microscopic particles are inhaled and collect on people's airways and lungs. Some studies show that this can stunt lung development in children and they lead to many hospital visits each year. 

Carbon Monoxide 

What is it? Carbon monoxide (CO) is an odorless gas that naturally occurs in nature. High levels can cause health problems. 

Where does it come from? Carbon monoxide comes from natural sources like volcanic eruptions and respiration. It also comes from car exhaust and industrial emissions. 

What are the risks? Breathing in CO causes serious health problems. Low level exposure causes headaches and dizziness. High level or prolonged exposure causes unconsciousness and death. 

Sulfur Dioxide 

What is it? Sulfur dioxide (SO2) is a gas made of sulfur and oxygen. 

Where does it come from? Industry is the main source. Ships and trucks burning high levels of sulfur also cause some sulfur dioxide to be released into the air. 

What are the risks? SO2 makes breathing difficult, especially for children and people with asthma. 

Nitrogen Dioxide 

What is it? Nitrogen dioxide (NO2) is a key component of smog and can react with water to create acid rain. 

Where does it come from? NO2 mainly comes from burning fuel. 

What are the risks? Acid rain can damage forests and waterways, and the wildlife living in them. People experience more serious health effects the longer they are exposed to NO2, and the elderly and children are more susceptible. 

Lead 

Lead is sometimes used in the AQI if there are particularly high levels affecting local air quality. 

What is it? Fine particles of lead can be suspended in the air as dust. 

Where does it come from? High levels of lead are often found near smelting plants, waste incinerators, and airfields. 

What are the risks? Lead exposure is very dangerous to young children, leading to brain damage. It can also damage the reproductive, kidney, and nervous systems. 

AQI Categories and Their Significance 

It would be too hard for most people to check the levels of the five major air pollutants each day, so monitoring agencies calculate them into a daily air quality standard called AQI. 

AQI is calculated on a scale of 0-500. AQI is divided into six categories:

• Good (0-50)
• Moderate (51-100)
• Unhealthy for Sensitive Groups (101-150)
•  Unhealthy (151-200)
•  Very Unhealthy (201-300)
• Hazardous (301-500)

Source: AirNow

Health advisories are associated with each quality level to protect public health. Color coding helps immediately communicate the threat level. Specific warnings include:

• Good - No warning
• Moderate - Sensitive groups should reduce outdoor exertion
• Unhealthy for Sensitive Groups - People with lung disease, children, and the elderly are likely to be affected and should avoid heavy or prolonged outdoor exertion
• Very Unhealthy - Vulnerable groups should avoid all outdoor exertion 
• Hazardous - Everyone should avoid all outdoor exertion 

These warning levels help people make informed decisions about when to exercise outdoors or allow their children to play outside, and when to limit exposure to protect health. 

How AQI is Calculated 

Outdoor concentrations of pollutants are detected at over 4,000 monitoring stations across the United States. These stations measure the air quality daily and send the data to the EPA's database, Air Quality System (AQS). 

Satellites also monitor air quality. This includes NASA's Tropospheric Emissions: Monitoring of Pollution (TEMPO) mission and privately-owned companies. 

The EPA also tracks emissions from vehicles and industry. This data is mainly estimates based on samples of real emission levels in various places. This data is stored in the Air Emissions Inventory database. 

Levels are calculated for the main six categories of pollutants listed above. Each pollutant is given a different weight in the formula depending on the health risks associated with it. This produces a number from 0 to 500 that is focused on the overall level of health threat to humans on a given day. 

Global Variations in AQI Standards 

Each nation measures the daily air quality index differently. For example, Australia's AQI ranges from 0-200+, and India measures eight different pollutants, not six.

Different parts of the world have different risk factors. National air quality is also measured differently because of differing environmental policies. Legislations in different regions includes:

• Clean Air Act (USA) 
• Air Quality Guidelines (WHO)
• National Clean Air Programme (India)
• 2030 Emissions Reduction Plan (Canada) 

Impact of Climate Change on Air Quality 

The amount of these toxic materials in the air fluctuates constantly. This is why we measure AQI regularly. Several elements of climate change affect air pollution levels. 

Wildfires 

Wildfires are twice as common as they were 20 years ago. Hotter and drier weather, combined with a pileup of dry wood, make forest fires common across North America.

These fires release particle pollution into the air through ash and smoke. Winds can blow these particles across large distances. Intense forest fires also destroy plant life needed to help process excess carbon dioxide and release more oxygen. 

Rising Temperatures

Remember, a key ingredient to ground-level ozone is warm temperatures. Emissions from vehicles used in closed-in cities can create "hot boxes" where excess ozone is produced. 

Changes in Weather Patterns 

Increased temperatures lead to more condensation and therefore more moisture in the air. This can give additional fuel to powerful storms, which sweep across the planet and cause intense damage. These strong storms can also carry pollutants across regions, damaging the air quality in relatively rural areas. 

Case Studies: Climate Change and AQI 

Human activity affects air quality in numerous ways. Three case studies show some of the most significant implications for climate change on local and global air quality. 

Case Study 1: California Wildfires

Wildfires are a natural part of the ecosystem's self-renewal process. In California alone, such fires became five times more severe between 1996 and 2001. 

Smoke from forest fires is full of PM2.5, which can shorten life expectancy, trigger asthma attacks, and cause heart attacks. 

These forest fires have an enormous impact on the economy. Recent estimates show that federal and state governments spend over $3 billion per year. Another $5 billion is spent per year on prevention and mitigation efforts. This doesn't account for the healthcare costs, which are most likely billions more in costs to both the State and individual citizens. 

Case Study 2: Urban Heat and Ozone in Cities

Cities are covered with asphalt and concrete, which absorbs sunlight during the day and releases it as heat at night. Cities also lack plants, which would otherwise help metabolize some of the energy into water and evaporation. These areas are often called "urban heat islands."

All this means that cities are up to 10 degrees Fahrenheit warmer than surrounding suburban and rural areas. This may not seem like much, heat is a key ingredient in ground-level ozone. This affects the AQI value dramatically. 

Source: My NASA data

Los Angeles is a prime example of an urban heat island leading to health concerns. Sensors reporting daily air quality show neighborhood-level data that reveals much higher risk in central LA when compared to suburban and rural surroundings. 

Source: Climate Central 

New York City, the most populous city in the U.S., is also a notorious urban heat island. Neighborhood-level data shows that air quality is well into the purple (dangerous) zone thanks to trapped heat. 

Source: Climate Central

Finally, Beijing, home to over 22 million people frequently suffers from poor air quality. For China's AQI, numbers over 130 mean vulnerable people may experience more serious health impacts.

Source: The World Air Quality Index Project 

Case Study 3: Agricultural Burning in Southeast Asia

One of the fastest ways to clear land for farming is by burning the trees. Unfortunately, this wreaks havoc on the air quality.

Burning releases PM2.5, carbon dioxide, carbon monoxide, nitrous oxide, and VOCs into the air, all of which have negative health impacts on humans when breathed in. 

Recent examples include Indonesia, where poor farmers often burn forest to graze animals or plant crops. Smoke drifts to other countries, like Thailand and Singapore, causing health problems there. 

India and Pakistan even have a seasonal "crop-burning haze" that strikes each fall as Northern farmers burn the stubble left over from harvested crops to prepare fields for new planting. This makes it hazardous to be outside for many days during that season. 

Alternative Strategies to Improve Air Quality 

Air quality is a complex measurement. There are some things individuals can do to protect themselves from high index values. Group-based efforts can help in other ways.

Policies

Many nations have made commitments to improve their AQI, including:

• ASEAN Agreement on Transboundary Haze Pollution
• U.S. Clean Air Act (1970) 
• Australia's National Clean Air Agreement 
• The Paris Agreement (2015) 

Other countries are trying to work towards using more renewable energy, like wind or solar, to avoid releasing so many pollutants into the air.

READ NOW: Could BioDiesel be the answer to bad air quality? 

Community Actions 

People living in high-threat areas still have some options to protect themselves and their neighbors.

• Building and maintaining local green spaces, like public parks, help prevents Urban Heat Islands from forming 
• Checking on the elderly to minimize their risk of going outside on high-threat days
• Carpooling to reduce emissions 

Individual Protective Actions 

Each of us should take steps to stay safe on the days that local air quality is bad. Some simple steps: 

• Check to see how clean or polluted your air is on a given day. 
• Use an air purifier in your home - make sure to get one appropriate for your square footage
• Stay indoors if possible 
• Drink extra water to keep your respiratory passages clear
• Wear a high quality respirator if you must work outside on high AQI days 

Conclusion 

AQI measures the five major air pollutants regulated by the U.S. government. An AQI value of 50 or less generally represents good air quality. AQI levels over 100 are generally thought to pose health risks.

As temperatures across the planet rise and emissions show little sign of slowing down, we can expect air quality to be an increasing concern for more people. 

Stay informed and safe by checking the AQI for your area regularly and taking appropriate precautions. Children, the elderly, and people with asthma and other lung conditions need to be especially careful.