Global guideline from the World Health Organization (WHO) on air pollution
On the evening of Sep 22, Vietnam time, the World Health Organization (WHO) has just announced the latest information on the Global Air Quality Guidelines (AQGs) 2021. This is the first update for AQGs since its initial publication in 2005
Over the past 15 years, the quality and quantity of evidence regarding the impact of air pollution on various aspects of human health have significantly increased. For this reason, the World Health Organization’s 2021 air quality guidelines provide recommendations on air pollutant concentration thresholds for six major air pollutants: PM₂.₅, PM₁₀, NO₂, O₃, SO₂, and CO. Some of these thresholds will be lower than those in the 2005 guidelines.
Here below are some of the information in the newest AQGs by WHO:
Summary of the guideline:
NEW GUIDELINE ON AIR QUALITY BY WHO
What is the WHO Global Guideline on air quality?
Based on existing scientific evidence, the guideline document (GLD) identifies the necessary air pollutant concentration thresholds for protecting public health globally. AQGs also serve as a reference document for assessing exposure levels for a population group.
The thresholds set for specific pollutants in this GLD can be used as a reference document to provide evidence for regulatory agencies to establish legally binding air quality management standards and targets at the international, national, and local levels.
What’s new in the 2021 document?
Since the 2005 guidelines, there has been a wealth of evidence, both in terms of quantity and quality, about the health effects of air pollution. Therefore, after a systematic review of the available evidence, some values in the AQG 2021 GLD are adjusted lower than 15 years ago (see Table 1). Currently, there is a clearer understanding of emission sources and the impact of air pollutants contributing to the global burden of disease.
Compared to the last WHO GLD, the new AQGs:
- Uses newer methods to collect evidence and construct guidelines;
- Solidifies evidence on health effects;
- Provide stronger evidence on health effects at lower levels of pollutants;
- Provide additional AQGs thresholds, such as peak season of O₃, 24h NO₂ and CO threshold, as well as new thresholds and target recommendations (interim targets);
- Provide good practice recommendations in controlling different types of dusts (black carbon / elemental carbon, ultrafine particles, and dust and sandstorm-derived particles).
Table 1. Recommended 2021 AQG levels compared to 2005 air quality guidelines
| Pollutant | Average period | AQG 2005 | AQG 2021 |
|---|---|---|---|
| PM₂.₅, µg/m³ | Annual | 10 | 5 |
| 24-houra | 25 | 15 | |
| PM₁₀, µg/m³ | Annual | 20 | 15 |
| 24-houra | 50 | 45 | |
| O₃, µg/m³ | Peak seasonb | – | 60 |
| 8-houra | 100 | 100 | |
| NO₂, µg/m³ | Annual | 40 | 10 |
| 24-houra | – | 25 | |
| SO₂, µg/m³ | 24-houra | 20 | 40 |
| CO, mg/m³ | 24-houra | – | 4 |
µg = microgram
a 99th percentile (meaning: 3–4 exceedance days per year).
b Average of daily maximum 8-hour mean O3 concentration in the six consecutive months with the highest six-month running- average O3 concentration.
Note: Annual and peak season is long-term exposure, while 24 hour and 8 hour is short-term exposure.
What is air pollution and what sources are contributing to daily air pollution?
The pollutants with the clear evidence of health impacts include particulate matter (PM), ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and carbon monoxide (CO). Notable health risks include the effects of particulate matter with a diameter of less than or equal to 2.5 micrometers (PM₂.₅)
PM₂.₅ và PM₁₀ have the ability to deeply penetrate into the lungs, and PM₂.₅ can even enter the bloodstream, affecting the cardiovascular and respiratory systems. In 2013, the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) classified outdoor air pollution and particulate matter as carcinogenic agents.
The main sources of air pollution caused by human activities may vary in different geographic regions, but generally include sources from energy production, transportation, household cooking and heating, waste sites, industrial and agricultural activities. Combustion is the largest contributor to air pollution, especially uncontrolled burning of fossil fuels and biomass for energy production.
How are the thresholds in the AQG decided?
WHO’s guidelines strictly follow the process of screening and evaluating evidence, with various expert groups participating under different roles.
During the development process of the air quality guidelines (AQG) on air quality, more than 500 studies were systematically collected and reviewed to identify the latest evidence for establishing new AQG levels. These guidelines do not include recommendations for situations of exposure to multiple pollutants (multi-pollutant exposure).
Why does the AQGs play an important role in health protection?
Air pollution increases the rate of hospitalization and death from respiratory and cardiovascular diseases - the leading causes of death worldwide. Air pollution also increases the burden of disease from lower respiratory tract infections, increases the risk of preterm birth, and other causes of death in children and infants - these are the main causes of disease burden in low- and middle-income countries.
According to WHO’s estimates, around 7 million premature deaths are mainly caused by non-communicable diseases, due to both indoor and outdoor air pollution. Outdoor air pollution alone has resulted in the loss of hundreds of millions of years in expectancy, with the majority of the burden of disease falling on low- and middle-income countries.
In 2019, more than 90% of the global population lived in areas where the concentration of long-term exposure to PM₂.₅ exceeded WHO’s AQG 2005 levels. Air pollution, in general, is widespread in most low- and middle-income countries.
How is the burden of disease due to air pollution distributed around the world?
One important thing to note is that in 2019, over 90% of the world’s population lived in areas with PM₂.₅ concentrations exceeding the AQG guideline of 10 µg/m³ set by WHO in 2005. And with the AQG threshold in 2021 lowered from 2005, the burden of disease from air pollution will increase in all countries. In 2019, the highest population-weighted average PM₂.₅ concentration was in the Southeast Asia region.
How to use this guideline?
AQG is a set of guidelines with clear evidence to protect community health from the impact of air pollution. Although these guidelines do not provide legally binding recommendations, they can still be used as a reference tool to help policy makers establish legally binding standards and objectives for air quality management at the international, national or local level. The standard set is also useful for researchers and national and local government agencies in developing plans and impact assessments, thereby enhancing monitoring, surveillance and in-depth research.
How many lives would be saved or improved health-wise if nations achieved the new AQG thresholds?
The world could avoid about 80% of deaths related to PM₂.₅ exposure if countries achieve an annual average PM₂.₅ concentration equal to the recommended level in the AQG guidelines.
Achieving the UN sustainable development goals (SDG) target 4 for PM₂.₅ (i.e., equal to the AQG level of 2005) would help reduce nearly 48% of total deaths related to PM₂.₅ exposure. The highest reduction rate is observed in the Southeast Asia and Africa regions (at 57% and 60%, respectively).
Is there a possible connection between air quality and COVID-19?
Air pollution is a significant factor contributing to the disease burden due to COVID-19. NOx - a pollutant closely related to transportation - has significantly decreased due to lockdown measures. Data from some European cities show a decrease of up to 50% in NO₂ levels, and in some cases up to 70% compared to pre-lockdown times.
COVID-19 is catastrophic, but at the same time, the measures taken to cope with COVID-19 have shown how policies related to transportation and how people work, study, and consume can contribute to better air quality.
How to reduce air pollution and as well as climate change?
By promoting sustainable environmental activities linked to protecting public health, we can gain significant progress in reducing climate change and achieving sustainable development goals.