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Understanding How the Air Quality Index Works

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Infographic explaining how the air quality index (AQI) works

Understanding How the Air Quality Index Works

Air quality levels have received a lot of attention in recent years.

In the wake of COVID-19 lockdowns, many places reported a marked increase in air quality. Northern India captured the world’s attention when it was reported that the Himalayan mountain range was visible for the first time in decades.

On the flipside, later that summer, wildfires swept over the Pacific Northwest and California, blanketing entire regions with a thick shroud of smoke that spanned hundreds of miles.

How is air quality measured, and what goes into the health scores we see?

Measuring the Air Quality Index

When we see that air quality is “good” or “unhealthy”, those public health categories are derived from the Air Quality Index (AQI).

In the U.S., the AQI is calculated using five major air pollutants regulated by the Clean Air Act:

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

Some countries have a slightly different way of calculating their scores. For example, India also measures levels of ammonia and lead in the air.

To make these readings more accessible, the AQI has a scoring system that runs from 0 to 500, using data collected from air monitoring stations in cities around the world. Scores below 50 are considered good, with very little impact to human health. The higher the score gets, the worse the air quality is.

To make communicating potential health risks to the public even easier, ranges of scores have been organized into descriptive categories.

AQI Score RangeAQI CategoryPM2.5 (μg/m³)Health Risks
0-50Good0-12.0Air quality is satisfactory and poses little or no risk.
51-100Moderate12.1-35.4Sensitive individuals should avoid outdoor activity.
101-150Unhealthy35.5-55.4General public and sensitive individuals in particular are
at risk to experience irritation and respiratory problems.
151-200Unhealthy55.5-150.4Increased likelihood of adverse effects and aggravation
to the heart and lungs among general public.
201-300Very Unhealthy150.5-250.4General public will be noticeably affected.
Sensitive groups should restrict outdoor activities.
301+Hazardous250.5+General public is at high risk to experience strong
irritations and adverse health effects. Everyone
should avoid outdoor activities.

Particulate Matter

While all the forms of atmospheric pollution are a cause for concern, it’s the smaller 2.5μm particles that get the most attention. For one, we can see visible evidence in the form of haze and smoke when PM2.5 levels increase. As well, these fine particles have a much easier time entering our bodies via breathing.

There are a number of factors that can increase the concentration of a region’s particulate matter. Some common examples include:

  • Coal-fired power stations
  • Cooking stoves (Many people around the world burn organic material for cooking and heating)
  • Smoke from wildfires and slash-and-burn land clearing

Wildfires and Air Quality

Air quality scores can fluctuate a lot from season to season. For example, regions that are reliant on coal for power generation tend to see AQI score spikes during peak periods.

One of the biggest fluctuations occurs during wildfire season, when places that typically have scores in the “good” category can see scores reach unsafe levels. In 2020, Eastern Australia and the West Coast of the U.S. both saw massive drops in air quality during their respective wildfire seasons.

Air quality in wildfire season

In June 2023, a storm system sent a thick blanket of smoke from Canadian wildfires down to Northeastern states, blocking out the sun and turning the sky over Manhattan into a dull shade of orange.

wildfire smoke raises AQI air qualities scores in NYC and other U.S. cities

Luckily, while these types of fluctuations are extreme, they are also temporary.

Correction: Graphics and article updated to include nitrogen dioxide.

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Ranked: Top 20 Countries by Plastic Waste per Capita

Visualizing plastic waste per capita reveals a surprising list of countries that you may not have expected.

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Ranked: Top 20 Countries by Plastic Waste per Capita

This was originally posted on our Voronoi app. Download the app for free on iOS or Android and discover incredible data-driven charts from a variety of trusted sources.

Single-use plastic waste is perhaps one of the biggest environmental issues of our time. Every year, millions of tons of plastic end up in oceans and landfills, harming wildlife and ecosystems.

To make matters worse, plastics take hundreds of years to decompose, leading to long-term environmental and health hazards as they break down into microplastics that contaminate water and food sources.

In this graphic, we visualized the top 20 countries that generated the most single-use plastic waste per capita in 2019, measured in kilograms per person. Figures come from research published in May 2021, which we sourced from Statista.

Data and Key Takeaways

The data we used to create this graphic is listed in the table below.

RankCountryKg per personPounds per person
1🇸🇬 Singapore76168
2🇦🇺 Australia59130
3🇴🇲 Oman56123
4🇳🇱 Netherlands55121
5🇧🇪 Belgium55121
6🇮🇱 Israel55121
7🇭🇰 Hong Kong55121
8🇨🇭 Switzerland53117
9🇺🇸 U.S.53117
10🇦🇪 UAE52115
11🇨🇱 Chile51112
12🇰🇷 S. Korea4497
13🇬🇧 UK4497
14🇰🇼 Kuwait4088
15🇳🇿 New Zealand3986
16🇮🇪 Ireland3986
17🇫🇮 Finland3884
18🇯🇵 Japan3782
19🇫🇷 France3679
20🇸🇮 Slovenia3577

Countries from all around the world are present in this ranking, highlighting how plastic waste isn’t concentrated in any one region.

It’s also interesting to note how most of the countries in this top 20 ranking are wealthier, more developed nations. These nations have higher levels of consumption, with greater access to packaged goods, take-out services, and disposable products, all of which rely on single-use plastics.

Where’s China and India?

Note that we’ve visualized plastic waste per capita, which is different from the total amount of waste produced by a country. It is for this reason that major polluters, such as China and India, are not present in this ranking.

It’s also worth noting that this focuses on the demand side of plastics, rather than where plastic products were initially created or produced.

If you’re interested to see more visuals on plastic waste, check out Which Countries Pollute the Most Ocean Plastic Waste?.

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