Air Quality Measurement Units: Understanding Air Pollution Better

Air pollution measurement is the process of collecting and measuring the components of air pollution, notably gases and particulates. The amount of pollutant present in the air is usually expressed as a concentration, measured in either parts-per notation (parts per billion or parts per million) or micrograms per cubic meter. Air quality is also measured using the Air Quality Index (AQI), which is an indicator developed by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. Modern air pollution measurement is largely automated and carried out using many different devices and techniques, such as satellites that monitor what's in our air.

Air Quality Index (AQI)

Air pollution measurement is the process of collecting and measuring the components of air pollution, notably gases and particulates. Modern air pollution measurement is largely automated and carried out using many different devices and techniques. These include simple absorbent test tubes known as diffusion tubes and highly sophisticated chemical and physical sensors that give almost real-time pollution measurements, which are used to generate air quality indexes.

The Air Quality Index (AQI) is a unit used to measure air quality. The AQI is a scale that runs from 0 to 500, with higher values indicating higher levels of air pollution. An AQI of 50 or below is considered safe, while readings above 100 are deemed unhealthy. The AQI tracks five major air pollutants: ground-level ozone, nitrogen dioxide, sulfur dioxide, PM2.5, and PM10. These pollutants are tied to human and environmental health impacts.

AQI values are typically grouped into ranges, with each range assigned a descriptor, a colour code, and a standardized public health advisory. The AQI can increase due to an increase in air emissions, such as during rush-hour traffic or an upwind forest fire, or from a lack of dilution of air pollutants. The AQI for an individual location is the highest of the AQI values for each pollutant being monitored at that location.

Air quality monitors are used to detect specific pollutants and can be outfitted with sensors or use lasers to scan particulate matter density in a cubic meter of air. Satellites, such as the GOES-R Series and JPSS satellites, can also provide particle pollution measurements and monitor the movement of aerosols. Additionally, air quality databanks process readings from governmental, crowd-sourced, and satellite-derived air quality monitors to produce an aggregated AQI reading.

UNEP, in collaboration with IQAir, developed the first real-time air pollution exposure calculator in 2021, which combines global readings from validated air quality monitors in 6,475 locations across 117 countries, territories, and regions. This database prioritizes PM2.5 readings and uses artificial intelligence to calculate each country's population exposure to air pollution on an hourly basis.

Parts-per notation

The amount of pollutant in the air is usually expressed as a concentration, which can be measured in parts-per notation, or micrograms per cubic meter (μg/m³). Parts-per notation is a commonly used unit for measuring air pollution, and it is often presented as parts per million (ppm) or parts per billion (ppb). This unit measures the volume mixing ratio of the pollutant in the air. Parts-per notation is used to quantify both gaseous pollutants and particulate matter.

Gaseous pollutants, which are commonly found in urban areas due to fuel emissions, include nitrogen dioxide, sulfur dioxide, and carbon monoxide. Particulate matter, on the other hand, refers to solid and liquid particles suspended in the air, such as soot, fly ash, and microscopic particles like PM2.5. PM2.5 particles are very fine, measuring only 2.5 microns in width, and can infiltrate people's respiratory tracts, reaching their lungs. High levels of PM2.5 can lead to a haze in the sky and have been linked to lung and heart diseases. Therefore, measuring the concentration of PM2.5 is crucial for developing policies to control and reduce air pollution and its associated health risks.

Air pollution measurement is the process of collecting and measuring the components of air pollution, notably gases and particulates. Modern air pollution measurement is largely automated and carried out using many different devices and techniques. These include simple deposit gauges and sophisticated sensors that provide real-time pollution measurements. Satellites orbiting above Earth also play a significant role in monitoring air pollution, providing measurements of particle pollution, aerosol concentrations, and carbon monoxide levels from wildfires.

The Air Quality Index (AQI) is a commonly used tool for communicating about outdoor air quality and health. The AQI works similarly to a thermometer, with higher values indicating greater levels of air pollution and health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. The AQI is based on measurements of particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) emissions.

Micrograms per cubic meter

The amount of air pollution is usually expressed as a concentration, measured in either parts-per notation (parts per billion or parts per million) or micrograms per cubic meter (µg/m³). Micrograms per cubic meter are commonly used for measurements of both gaseous pollutants, such as nitrogen dioxide, and coarse (PM10) and fine (PM2.5) particulate matter.

PM2.5 refers to particulate matter with a diameter of less than 2.5 micrometers. These fine particles can be harmful to human health as they can penetrate deep into the respiratory tract. According to the US EPA, the annual fine particulate matter standard is set at 12 µg/m³ of air. Concentrations above this level indicate worsening air quality. For example, a concentration of 35 µg/m³ of PM2.5 corresponds to an Air Quality Index (AQI) of 101, which is considered unhealthy for sensitive individuals or populations.

Air quality monitors are equipped with sensors to detect specific pollutants, such as nitrogen dioxide, sulfur dioxide, and particulate matter. These monitors may be static, like the EkoSłupek air monitors in Poland, or satellite-based, like the GOES-R and JPSS satellites. The data collected by these monitors is used to generate air quality indexes, such as the AQI, which helps assess the health risks associated with air pollution.

In addition to monitoring, efforts are also made to control and reduce air pollution. For example, the Clean Air Act in the UK was implemented after the Great Smog of London in 1952, which caused the deaths of 12,000 people. Similarly, the #BeatPollution strategy by UNEP aims to address air, land, and water pollution through coordinated action.

Satellite imaging

Air pollution is typically measured by collecting and measuring the components of air pollution, such as gases and particulates. The amount of pollutant in the air is usually expressed as a concentration, measured in either parts-per notation (parts per billion or parts per million) or micrograms per cubic meter. Modern air pollution measurement is largely automated and carried out using various devices and techniques, from simple diffusion tubes to advanced chemical and physical sensors.

Satellite data can indicate criteria air pollutants, such as PM2.5, PM10, ground-level ozone, nitrogen dioxide, and sulfur dioxide, as well as greenhouse gases like CH4 and CO2. These pollutants are tied to human and environmental health impacts. The GOES-R Series and JPSS satellites provide particle pollution measurements, with the latter offering higher-resolution measurements of aerosols over the entire planet once a day.

Satellite remote sensing applications have been used in research to scan areas such as the LA Basin, detecting trace gases, aerosols, and greenhouse gases. This technology has also been employed by the California Air Resources Board to estimate PM2.5 concentrations in California between 2006 and 2012, contributing to our understanding of air pollution trends.

Additionally, satellite data can fill spatial gaps in ground monitoring, providing air quality information in regions without ground monitors. This is particularly relevant for areas with sparse monitoring, such as Africa, Central Asia, and Latin America. Satellite imaging, combined with AI, has led to the development of models like AQNet, which can predict various pollutants and create an "air-quality index" for comparing air quality across different regions.

Deposit gauges

The amount of pollutant in the air is usually expressed as a concentration, measured in either parts-per-notation (parts per billion or parts per million, also known as the volume mixing ratio) or micrograms per cubic meter. Modern air pollution measurement is largely automated and carried out using many different devices and techniques.

The bottle is removed after a period of time (usually from a week to a month) and the contents are taken away for analysis of water (such as rain, fog, and snow), insoluble matter (such as soot), and soluble matter. Deposit gauges are still used today, although air pollution is more likely to be measured with automated electronic sensors.

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