The World Health Organization has released new guidelines for air quality, for the first time since 2005. The most important change is much lower guideline levels for PM2.5 and NO2, two key air pollutants. The update marks official recognition that these pollutants are dangerous at much lower levels than understood two decades ago.
Enormous health benefits
The update was long overdue given what we know about the health impacts of air pollution. Based on the latest studies on the global health impact of PM2.5, only about half of the deaths caused by PM2.5 exposure would be avoided if the entire world met the WHO 2005 guideline. Meeting the new guideline would avoid 3/4 of these deaths globally. This means 3–8 million deaths avoided every year, depending on the exact study and estimate used.
This situation varies widely by country: in very highly polluted countries such as India, the vast majority of air pollution deaths would be avoided by meeting the old WHO guideline. In others, such as the United States, air pollution is still responsible for hundreds of thousands of deaths per year, but these impacts take place almost entirely at levels below the old guideline.
One tragic impact of NO2 pollution is its contribution to new cases of childhood asthma globally, with an estimated 4 million children affected every year. The authors estimate that the risk of asthma in children increases starting from a concentration of 4 µg/m3 (range: 0–10 µg/m3), again a tenth of the guideline level. Our health impacts tool estimates that meeting the new WHO guideline worldwide would limit this impact to 1.3 million children per year, avoiding more than 2.5 million new cases of asthma per year.
Our health impacts tool lets you look at the health impacts of meeting different standard and guideline levels in detail by country or globally.
Where do countries stand?
Few countries have aligned their legally binding standards for annual average PM2.5 concentration to the WHO 2005 guideline of 10 µg/m3, so what does it matter that the guideline is strengthened further to 5 µg/m3? At the very least, this marks recognition of the latest science, and increases the gap between the guideline and current national standards to a clearly unacceptable level. The European Union’s standard is 25, China’s 35 and India’s 40, for example. The update puts pressure on these jurisdictions, and many others, to strengthen their standards — and above all improve their air quality, as even the current standards are being violated in parts of each region.
In the case of NO2, many countries, including China, India, European Union, Vietnam and Brazil, already base their standards on the WHO guideline. Therefore, the update of the guidelines should directly imply that national standards need to be revised.
Other jurisdictions, most notably the U.S., have NO2 standards that are even far weaker than the old guideline, having failed to keep up with the science already earlier. The U.S. has a standard of 100 µg/m3, ten times as high as the new guideline.
Our air quality standards tracker lets you compare the current legal standards of different countries to the WHO guidelines.
Meeting the guidelines means drastically cutting the use of fossil fuels
Putting stronger guidelines and targets on paper is only the first step to avoiding the heavy toll of air pollution on our health. Emissions from the key polluting sector will have to be reduced sharply to achieve good air quality across the world.
The main sources of PM2.5 are globally are industry, power generation, transport, agriculture, residential fuel use and forest fires, with differing shares across regions.
NO2 comes almost entirely from human sources, mainly fossil fuels used in transport, industry and power plants. Note though that we tend to equate “transport” with private cars, but in many cities, heavy vehicles such as trucks and buses are at least as large emitters. In much of developing Asia, two-wheelers are also a major source.
The key solutions are stronger emissions standards for those sectors, and eliminating or significantly reducing the burning of fossil fuels and biomass.
For both PM2.5 and NO2, reaching the new guideline levels means in effect eliminating much of fossil fuel and biomass burning, especially in cities and highly populated areas. Air pollutant control technologies, “end-of-pipe” measures, such as catalytic converters in cars and trucks and scrubbers and filters at power plants, have delivered impressive improvements in air quality in all countries that have deployed them effectively, but these technologies are never 100% efficient and can only go so far.
For PM2.5, there is a natural background of dust, sea salt and other types of natural particles that amounts to at least a few micrograms per cubic meter in most of the world. This means that reaching the new guideline requires cutting emissions from human-made sources effectively to zero. In arid, dusty regions such as much of the Middle East, North Africa and Central Asia, the natural background is substantially higher. Targeting near-zero particles from fossil fuels and biomass-burning makes sense in these regions as well — and aiming to slow down or reverse desertification, where that is contributing to dust levels.
What about SO2?
One possible source of confusion in the new guidelines is the weakening of the guideline for SO2, another health-harming pollutant. The old guideline was 20 µg/m3 for 24-hour average concentration, now raised to 40. Controlling SO2 emissions from power plants and industry has been the centerpiece of China’s highly successful clean air efforts, as well as efforts in Europe, North America, Japan and others. In other countries, such as India and South Africa, the question of whether to require coal power plants to install SO2 controls is being debated fiercely. What’s important to note is that the main reason to regulate SO2 emissions has always been that SO2 turns into particulate matter (sulfate aerosols) in the atmosphere, making a major contribution to PM2.5 pollution. So the guidelines give all the more reason to mitigate SO2 emissions, not less.