Infographic: Understanding How the Air Quality Index Works
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Understanding How the Air Quality Index Works

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Understanding How the Air Quality Index Works

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

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 in the 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

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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The Biggest Carbon Emitters, By Sector

The manufacturing and construction sector contributed to 6.3 billion tonnes of global greenhouse gas emissions in 2019.

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The following content is sponsored by Northstar Clean Technologies

The Biggest Carbon Emitters, By Sector

It’s no secret that greenhouse gas emissions need to decrease drastically in order to fight the effects of climate change.

As countries across the globe ramp up efforts to reduce global warming, every industry needs to do its part. So who’s lagging and who’s leading?

Although often less discussed, the manufacturing and construction sector is a large contributor to global greenhouse gas emissions.

The above graphic from Northstar Clean Technologies takes a look at the biggest contributors by sector in relation to greenhouse gas emissions.

Breakdown Of Emissions

The manufacturing and construction sector is a growing one, and as population and infrastructure expand, it’s vital that we take all actionable paths to reduce emissions.

Manufacturing and construction contributed to 6.3 billion tonnes of global greenhouse gas emissions in 2019. Let’s look at the breakdown of greenhouse gas emissions by sector over the years from Our World In Data.

In 2019 electricity and heat were the biggest carbon emitters, while transport came in second place.

Manufacturing and construction overtook the agriculture sector in 2007 to become the third largest contributor to global greenhouse gas emissions.

Building a Solution

One solution to reducing the impact of the manufacturing and construction sector is to repurpose materials. This reduces emissions and waste while also being both energy and cost-efficient.

Take a material like asphalt shingles as an example. This product is found on the roofs of approximately 75% of single-family detached homes in the U.S. and Canada.

In 2018, 86% of total asphalt shingles waste was dumped in landfills where they do not decompose or biodegrade. Reusing and recycling existing materials like asphalt shingles is a vital step in reducing greenhouse gas emissions in the industry.

Northstar Clean Technologies repurposes the three primary components of asphalt shingles which are then recycled back into the market.

By reprocessing asphalt shingles into three primary components, Northstar’s clean technology has been shown to reduce CO₂ emissions by 60% compared to virgin production of liquid asphalt.

Click to learn how Northstar Clean Technologies is becoming one of the top material recovery providers in North America.

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Mapped: Carbon Dioxide Emissions Around the World

This graphic maps out carbon emissions around the world and where they come from, using data from the European Commission.

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mapping carbon dioxide emissions worldwide

Mapped: Carbon Dioxide Emissions Around the World

According to Our World in Data, the global population emits about 34 billion tonnes of carbon dioxide (CO₂) each year.

Where does all this CO₂ come from? This graphic by Adam Symington maps out carbon emissions around the world, using 2018 data from the European Commission that tracks tonnes of CO₂ per 0.1 degree grid (roughly 11 square kilometers).

This type of visualization allows us to clearly see not just population centers, but flight paths, shipping lanes, and high production areas. Let’s take a closer look at some of these concentrated (and brightly lit) regions on the map.

China, India, and the Indian Ocean

As the two most populated countries and economic forces, China and India are both significant emitters of CO₂. China in particular accounts for about 27% of global CO₂ emissions.

And looking at the oceans, we see how much shipping adds to emissions, with many shipping lanes east of China clearly outlined as well as the major Indian Ocean lane between the Strait of Malacca and the Suez Canal.

The United States and Central America

The United States is one of the world’s biggest carbon emitters. While other countries like Qatar and Saudi Arabia technically have higher emissions per capita, their overall emissions are relatively low due to smaller populations.

Across the U.S., the most brightly lit areas are major population centers like the Boston-Washington corridor, the Bay Area, and the Great Lakes. But also lit up are many of the interconnecting highways linking all these population centers, even in the less-populated middle of the country.

With so much traffic in and out of the U.S., the oceans become a murky mix of shipping and flight paths. To the south, very clearly visible is the major concentration of people around Mexico City and the traffic flowing through the Panama Canal.

South America’s Network of Emissions

Like the other regions, some of South America’s most populated areas are also the biggest emitters, such as São Paulo and Rio in Brazil and Buenos Aires in Argentina. This map also highlights the continent’s rough terrain, with most of the population and highway emissions limited to the coasts.

However, the cities aren’t the only big emitters in the region. There are clear lines intersecting the Amazon forest in many sections where cities and roads were constructed, including the economic hub city of Manaus along the Amazon River. Likewise, the oceans have many major shipping lanes highlighted, particularly East of Brazil.

Europe and North Africa

Germany is one of Europe’s biggest carbon emitters—in 2021, the country generated almost 644 million tonnes of CO₂.

Also making an impression are Italy (which is the second-highest CO₂ emitter after Germany) and the UK, as well the significant amount of trade along the English Channel.

Compared to the intricate network of cities, towns, and bustling highways spanning Europe, across the Mediterranean are far clearer and simpler lines of activity in Northern Africa. Two major exceptions are in the Middle-East, where Egypt’s Nile River and Suez Canal are massively lit up, as well as Israel on the east of the sea.

But a more significant (albeit murkier) picture is drawn by the massive amounts of shipping and flight paths illuminating the Atlantic and Mediterranean at large.

Net Zero by 2050

To mitigate the negative effects of climate change, countries around the world have made commitments to reach net-zero emissions.

Imagining the global map of emissions with these commitments in action requires a complete transformation of energy production, consumption habits, transportation infrastructure, and more. And even then, a future generated map wouldn’t be fully dark, as “net-zero” is not equivalent to zero emissions but a balance of emissions and removal.

How might this map of global emissions look in the near and distant future? And what other interesting insights can you generate by browsing the world this way?

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