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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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Energy

Visualizing China’s Energy Transition in 5 Charts

This infographic takes a look at what China’s energy transition plans are to make its energy mix carbon neutral by 2060.

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China Energy Mix

Visualizing China’s Energy Transition in 5 Charts

In September 2020, China’s President Xi Jinping announced the steps his nation would take to reach carbon neutrality by 2060 via videolink before the United Nations Assembly in New York.

This infographic takes a look at what this ambitious plan for China’s energy would look like and what efforts are underway towards this goal.

China’s Ambitious Plan

A carbon-neutral China requires changing the entire economy over the next 40 years, a change the IEA compares to the ambition of the reforms that industrialized the country’s economy in the first place.

China is the world’s largest consumer of electricity, well ahead of the second place consumer, the United States. Currently, 80% of China’s energy comes from fossil fuels, but this plan envisions only 14% coming from coal, oil, and natural gas in 2060.

Energy Source20252060% Change
Coal52%3%-94%
Oil18%8%-56%
Natural Gas10%3%-70%
Wind4%24%+500%
Nuclear3%19%+533%
Biomass2%5%+150%
Solar3%23%+667%
Hydro8%15%+88%

Source: Tsinghua University Institute of Energy, Environment and Economy; U.S. EIA

According to the Carbon Brief, China’s 14th five-year plan appears to enshrine Xi’s goal. This plan outlines a general and non specific list of projects for a new energy system. It includes the construction of eight large-scale clean energy centers, coastal nuclear power, electricity transmission routes, power system flexibility, oil-and-gas transportation, and storage capacity.

Progress Towards Renewables?

While the goal seems far off in the future, China is on a trajectory towards reducing the carbon emissions of its electricity grid with declining coal usage, increased nuclear, and increased solar power capacity.

According to ChinaPower, coal fueled the rise of China with the country using 144 million tonnes of oil equivalent “Mtoe” in 1965, peaking at 1,969 Mtoe in 2013. However, its share as part of the country’s total energy mix has been declining since the 1990s from ~77% to just under ~60%.

Another trend in China’s energy transition will be the greater consumption of energy as electricity. As China urbanized, its cities expanded creating greater demand for electricity in homes, businesses, and everyday life. This trend is set to continue and approach 40% of total energy consumed by 2030 up from ~5% in 1990.

Under the new plan, by 2060, China is set to have 42% of its energy coming from solar and nuclear while in 2025 it is only expected to be 6%. China has been adding nuclear and solar capacity and expects to add the equivalent of 20 new reactors by 2025 and enough solar power for 33 million homes (110GW).

Changing the energy mix away from fossil fuels, while ushering in a new economic model is no small task.

Up to the Task?

China is the world’s factory and has relatively young industrial infrastructure with fleets of coal plants, steel mills, and cement factories with plenty of life left.

However, China also is the biggest investor in low-carbon energy sources, has access to massive technological talent, and holds a strong central government to guide the transition.

The direction China takes will have the greatest impact on the health of the planet and provide guidance for other countries looking to change their energy mixes, for better or for worse.

The world is watching…even if it’s by videolink.

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Energy

Visualizing 50+ Years of the G20’s Energy Mix

Watch how the energy mix of G20 countries has evolved over the last 50+ years.

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G20 Energy Mix share

Visualizing 50+ Years of the G20’s Energy Mix (1965–2019)

Over the last 50 years, the energy mix of G20 countries has changed drastically in some ways.

With many countries and regions pledging to move away from fossil fuels and towards cleaner sources of energy, the overall energy mix is becoming more diversified. But shutting down plants and replacing them with new sources takes time, and most countries are still incredibly reliant on fossil fuels.

This video from James Eagle uses data from BP’s Statistical Review of World Energy to examine how the energy mix of G20 members has changed from 1965 to 2019.

G20’s Energy History: Fossil Fuel Dependence (1965–1999)

At first, there was oil and coal.

From the 1960s to the 1980s, energy consumption in the G20 countries relied almost entirely on these two fossil fuels. They were the cheapest and most efficient sources of energy for most, though some countries also used a lot of natural gas, like the United States, Mexico, and Russia.

Country (Energy Mix - 1965)OilCoalOther
🇦🇷 Argentina83%3%14%
🇦🇺 Australia45%50%5%
🇧🇷 Brazil66%8%26%
🇨🇦 Canada47%13%40%
🇨🇳 China8%87%5%
🇪🇺 EU47%45%8%
🇫🇷 France49%37%14%
🇩🇪 Germany34%63%3%
🇮🇳 India24%67%9%
🇮🇩 Indonesia86%2%12%
🇮🇹 Italy66%11%23%
🇯🇵 Japan56%31%13%
🇲🇽 Mexico61%3%36%
🇷🇺 Russia29%50%21%
🇸🇦 Saudi Arabia98%0%2%
🇿🇦 South Africa19%81%0%
🇰🇷 South Korea20%77%3%
🇹🇷 Turkey46%47%7%
🇬🇧 UK38%59%3%
🇺🇸 U.S.45%22%33%

But the use of oil for energy started to decrease, beginning most notably in the 1980s. Rocketing oil prices forced many utilities to turn to coal and natural gas (which were becoming cheaper), while others in countries like France, Japan, and the U.S. embraced the rise of nuclear power.

This is most notable in countries with high historic oil consumption, like Argentina and Indonesia. In 1965, these three countries relied on oil for more than 83% of energy, but by 1999, oil made up just 55% of Indonesia’s energy mix and 36% of Argentina’s.

Even Saudi Arabia, the world’s largest oil exporter, began to utilize oil less. By 1999, oil was used for 65% of energy in the country, down from a 1965 high of 97%.

G20’s Energy Mix: Gas and Renewables Climb (2000–2019)

The conversation around energy changed in the 21st century. Before, countries were focused primarily on efficiency and cost, but very quickly, they had to start contending with emissions.

Climate change was already on everyone’s radar. The UN Framework Convention on Climate Change was signed in 1992, and the resulting Kyoto Protocol aimed at reducing greenhouse gas emissions was signed in 1997.

But when the Kyoto Protocol went into effect in 2005, countries had very different options available to them. Some started to lean more heavily on hydroelectricity, though countries that already utilized them like Canada and Brazil had to look elsewhere. Others turned to nuclear power, but the 2011 Fukushima nuclear disaster in Japan turned many away.

This is the period of time that renewables started to pick up steam, primarily in the form of wind power at first. By 2019, the G20 members that relied on renewables the most were Brazil (16%), Germany (16%), and the UK (14%).

Country (Energy Mix - 2019)Natural GasNuclearHydroelectricRenewablesOther
🇦🇷 Argentina49%2%10%4%35%
🇦🇺 Australia30%0%2%7%61%
🇧🇷 Brazil10%1%29%16%44%
🇨🇦 Canada31%6%24%4%35%
🇨🇳 China8%2%8%5%77%
🇪🇺 EU22%11%4%10%53%
🇫🇷 France16%37%5%6%36%
🇩🇪 Germany24%5%1%16%54%
🇮🇳 India6%1%4%4%85%
🇮🇩 Indonesia18%0%2%4%76%
🇮🇹 Italy40%0%6%10%44%
🇯🇵 Japan21%3%4%6%66%
🇲🇽 Mexico42%1%3%5%49%
🇷🇺 Russia54%6%6%0%34%
🇸🇦 Saudi Arabia37%0%0%0%63%
🇿🇦 South Africa3%2%0%2%93%
🇰🇷 South Korea16%11%0%2%71%
🇹🇷 Turkey24%0%12%6%58%
🇬🇧 UK36%6%1%14%43%
🇺🇸 U.S.32%8%3%6%51%

However, the need to reduce emissions quickly made many countries make a simpler switch: cut back on oil and coal and utilize more natural gas. Bituminous coal, one of the most commonly used in steam-electric power stations, emits 76% more CO₂ than natural gas. Diesel fuel and heating oil used in oil power plants emit 38% more CO₂ than natural gas.

As countries begin to push more strongly towards a carbon-neutral future, the energy mix of the 2020s and onward will continue to change.

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