Air Pollution Measurement Methods: Understanding The Techniques

Air pollution is a serious issue that can have detrimental effects on both human health and the environment. It is therefore important to be able to measure the quality of the air we breathe so that we can understand the extent of the problem and develop strategies to combat it. The methods used to measure air pollution vary depending on the type of pollutant and the required timescale of assessment, from simple, low-cost passive devices to highly sophisticated, automated active sensors.

Air Quality Index (AQI)

The Air Quality Index (AQI) is a scale that runs from 0 to 500, with higher values indicating greater air pollution and health risks. An AQI of 50 or below is generally considered safe, while readings above 100 are deemed unhealthy, first for sensitive groups and then for everyone as values increase. The AQI is divided into six colour-coded categories, each representing a range of index values. For instance, an AQI value over 300 represents hazardous air quality.

The AQI is a tool developed by the EPA to communicate information about outdoor air quality and health. It tracks five major air pollutants regulated by the Clean Air Act: ground-level ozone, PM2.5, PM10, nitrogen dioxide, and sulfur dioxide. These pollutants are monitored by instruments on the ground and satellites orbiting the Earth, such as the GOES-R and JPSS series of satellites. The data collected by these instruments and satellites is processed by air quality databases, which produce an aggregated AQI reading.

The AQI is an essential tool for understanding the health effects of air pollution and taking targeted action to protect and improve human and environmental well-being. It helps identify air pollution hotspots and provides information on how to avoid the health effects of air pollution. Given that, according to the World Health Organization, 99% of the global population breathes unclean air, and air pollution causes approximately 7 million premature deaths annually, the AQI is a critical tool for addressing this crisis.

Satellite imaging

Satellite data can be used to estimate the amount of ground-level air pollution, specifically the amount of tiny airborne particles called PM2.5. These particles have a diameter of less than 2.5 micrometers and have been shown to have a dramatic effect on human health due to their ability to travel deep into the lungs. Satellites can measure the concentration of these particles by observing how much light reaches the surface of the Earth and how much is reflected off the particles. This measurement is called aerosol optical depth or aerosol optical thickness.

Recent innovations in satellite technology and machine learning have further improved the accuracy and spatial resolution of air pollution measurements. For example, researchers at Duke University used 10,400 images to train a model to predict local levels of PM2.5 using only satellite images and weather conditions. Their model was accurate to within 24% of actual PM2.5 levels measured at reference stations, with a much higher spatial resolution capable of predicting levels down to 40,000 square meters.

Satellite data of atmospheric pollutants are becoming increasingly important for decision-making and environmental management activities in the public, private, and non-profit sectors. They are used for a variety of applications, including estimating emissions, tracking pollutant plumes, supporting air quality forecasting, and evaluating air quality model output. By combining satellite data with ground measurements and advanced AI models, we can gain a more comprehensive understanding of air pollution and its impact on human health and the environment.

Laser scanning

The NIST laser frequency-comb system has been designed to emit laser beams containing various wavelengths or frequencies of light, with each "tooth" of the comb representing a different frequency. By analyzing the absorption of these different frequencies, researchers can determine the concentration of different gases in the atmosphere. The more of a specific gas that is present, the higher the absorption of the corresponding frequency. This technique allows for continuous measurement of greenhouse gases over substantial distances, providing valuable data for studying urban air quality and the impacts of events like wildfires.

Real-time exposure calculators

The first real-time air pollution exposure calculator was developed by the UN Environment Programme (UNEP) in collaboration with IQAir, a Swiss air quality technology company. This calculator is based on the world's largest air quality data platform, which was also launched by UNEP and IQ Air. By combining global governmental, crowd-sourced, and satellite-derived air quality data with population data, the calculator employs artificial intelligence to determine each country's population exposure to air pollution every hour. Specifically, it calculates exposure to fine particulate matter (PM2.5), which is largely responsible for deaths and illnesses linked to air pollution.

The data is displayed on an interactive air quality map in a live data box that specifies the exposure level per age group across the world's population. This allows for the identification of air pollution hotspots and facilitates targeted actions to protect and improve human health and the environment. The calculator prioritises PM2.5 readings, which, when inhaled, are absorbed into the bloodstream and are linked to illnesses such as stroke, heart disease, lung disease, and cancer.

The development of this calculator is a significant step towards utilising technology to support cleaner air and improve public health. It is part of a broader effort that includes increasing the collection of air quality data, conducting joint research, developing new technologies, and sharing best practices to combat air pollution and climate change. UNEP also plans to enhance the calculator to assist cities worldwide in improving their air quality, as more than 80% of urban residents are exposed to air pollution levels exceeding WHO guidelines.

Monitoring human and environmental health impacts

Human Health Impacts:

Air pollution can have detrimental effects on human health, and vulnerable populations such as children, the elderly, and those with pre-existing health conditions are at an increased risk. The main pathway of exposure is through the respiratory tract, leading to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body. This can impact various organs, including the lungs, heart, and brain. The specific diseases associated with air pollution exposure include stroke, ischaemic heart disease, chronic obstructive pulmonary disease, lung cancer, pneumonia, and adverse pregnancy outcomes such as low birth weight. Long-term exposure to air pollution has also been linked to an increased risk of cognitive and emotional problems in adolescents and young adults.

To monitor and assess human health impacts, organisations like the World Health Organization (WHO) and the European Environment Agency (EEA) conduct systematic reviews and provide guidance. The WHO's Air Quality Guidelines, for example, offer recommendations on safe air quality levels. Additionally, the U.S. Environmental Protection Agency's Air Quality Index (AQI) is a numerical system that categorises air quality based on levels of concern, with higher numbers indicating worse air quality. These tools help raise awareness, inform public health policies, and guide preventive measures.

Environmental Health Impacts:

Air pollution also has significant environmental health impacts, affecting natural ecosystems, groundwater, and soil. It can lead to negative changes in water and soil quality, disrupt weather patterns, contribute to acid rain, and drive global warming. The European Green Deal, for instance, aims to address these issues by aligning European Union (EU) air quality standards with WHO recommendations and setting targets to reduce air pollution to levels no longer considered harmful to health and ecosystems.

To monitor environmental health impacts, organisations like the EEA collect and analyse data on air pollutant concentrations, premature deaths, years of life lost, and population-weighted concentrations. This data informs policy decisions and the development of emission reduction strategies, such as the revision of industrial emissions directives and the introduction of stricter emission standards for road vehicles. Additionally, models like the WHO's Household Multiple Emission Sources (HOMES) help policymakers understand household air pollution levels and their impact on the environment.

Frequently asked questions