Measuring Air Pollution: Scientists' Methods And Tools

Air pollution is a serious issue that affects the health of both humans and the environment. Scientists use a variety of methods and technologies to measure air pollution, including passive and active devices, ground-level sensors, and satellite imaging. Passive devices, such as diffusion tubes and deposit gauges, collect air samples that are then analysed in a laboratory. Active devices, on the other hand, are automated or semi-automated and use physical or chemical methods to analyse air samples. Ground-level sensors and satellite imaging are also used to detect specific pollutants, such as particle pollution, ozone, carbon monoxide, and sulfur dioxide. These measurements are used to generate air quality indexes, such as the Air Quality Index (AQI), which help governments and organisations identify air pollution hotspots and take targeted action to improve air quality and protect public health.

Air Quality Index (AQI)

The Air Quality Index (AQI) is a system used to communicate about outdoor air quality and health. The AQI is a numerical system that measures the level of air pollution in a given region. The higher the number, the worse the air quality. The AQI is measured using instruments on the ground and satellites orbiting the Earth. These instruments collect information about the particles in the air, such as smoke particles from wildfires, airborne dust, urban and industrial pollution, and ash from erupting volcanoes.

The AQI is divided into six colour-coded categories, each corresponding to a range of index values and a different level of health concern. The six categories are:

• Green (0-50) - Good: Air pollution is of little to no risk.
• Yellow (51-100) - Moderate: While air quality is acceptable, some may be at risk, particularly those who have heightened sensitivity to air pollution.
• Orange (101-150) - Unhealthy for Sensitive Groups: People with sensitivities may experience negative health effects, but the general public is less likely to be affected.
• Red (151-200) - Unhealthy: The general public may experience health effects, and those with sensitivities may experience more serious effects.
• Purple (201-300) - Very Unhealthy: Health alert, everyone may experience more serious health effects.
• Maroon (301-500) - Hazardous: Health warning of emergency conditions, the entire population is more likely to be affected.

The AQI is an important tool for public health officials and individuals to understand the level of air pollution and its potential impact on human health. By monitoring the AQI, people can take proactive measures to protect their health and reduce their exposure to air pollution when necessary. Additionally, the AQI helps raise awareness about air quality issues and can inform policies and strategies to improve air quality and protect public health.

Passive and active measurement devices

Air pollution is broadly measured in two ways: passively and actively. Passive devices are relatively simple and low-cost. They collect air samples, which are then analysed in a laboratory. Diffusion tubes are a common form of passive measurement. They are fastened to lamp posts to absorb specific pollutant gases. After a period of time, they are sent to a laboratory for analysis. Deposit gauges, large funnels that collect soot and other particulates, are another type of passive device.

Active measurement devices are automated or semi-automated and tend to be more complex and sophisticated than passive devices. They use fans to suck in the air, filter it, and then analyse it automatically or store it for later analysis. Active sensors use either physical or chemical methods. Physical methods measure an air sample without changing it, for example, by seeing how much of a certain wavelength of light it absorbs. Chemical methods change the sample through a chemical reaction and then measure it. Most automated air-quality sensors are examples of active measurement. They range from small handheld devices to large-scale static monitoring stations in urban areas. Remote monitoring devices are also used on aeroplanes and satellites.

Personal sensors can empower individuals and communities to better understand their exposure to air pollution. Small, inexpensive, portable (and sometimes wearable) internet-connected air pollution sensors can be used to monitor local air quality levels. In contrast to low-cost monitors, static monitors continuously sample and measure the air quality in a particular, urban location. Active air quality monitors are sometimes fixed in public places, such as busy railway stations, to measure levels of nitrogen dioxide and other pollutants. Some static monitors are designed to give immediate feedback on local air quality.

Direct-reading air quality monitors provide information at the time of sampling, enabling rapid decision-making. They can be used to identify oxygen-deficient or oxygen-enriched atmospheres, immediately dangerous conditions, elevated levels of airborne contaminants, flammable atmospheres, and radioactive hazards. They are particularly useful for identifying point source contamination, such as gas leaks.

Air pollution calculators

Air pollution is typically measured using the Air Quality Index (AQI), a numerical system that indicates the level of air pollution in a given region. The higher the AQI value, the worse the air quality. The AQI is measured on a scale of 0 to 500, with different ranges corresponding to different colours, levels of concern, and health effects.

There are various methods and devices used to measure air pollution, including both passive and active devices. Passive devices, such as diffusion tubes and deposit gauges, collect air samples or pollutants, which are then analysed in a laboratory. Active devices, on the other hand, are automated or semi-automated and can provide real-time pollution measurements. They use physical or chemical methods to analyse air samples, with physical methods measuring the sample without altering it, and chemical methods involving a chemical reaction to measure the sample.

Additionally, air pollution sensors can range from small handheld devices to large-scale static monitoring stations in urban areas. These sensors can measure various pollutants, including ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The data collected by these sensors can be used to create maps of pollution levels over wide areas and is crucial for understanding and addressing air pollution and its impacts on human health and the environment.

Air quality monitors

Low-cost air quality monitors are typically designed for indoor use and can be purchased by consumers. These devices use one or more sensors to detect specific air pollutants like particulate matter (PM) or carbon dioxide, as well as environmental factors such as temperature and humidity. Some low-cost monitors have a single sensor that measures only one pollutant or environmental factor, while others have multiple sensors that can detect a combination of pollutants. The accuracy and precision of these monitors can vary, and they may not always be reliable.

More expensive and sophisticated air quality monitors are often used by government agencies and environmental organizations to monitor air quality on a larger scale. These monitors are typically stationary and may be placed in urban areas or remote locations. They can provide real-time data and are considered the gold standard for air quality monitoring. The Clean Air Act of 1970, for example, requires nationwide ambient monitoring of six criteria pollutants: particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen oxides, and lead.

Some popular air quality monitors on the market include the Airthings View Plus, the PurpleAir Touch Indoor Air Quality Monitor, the QP Lite Air Quality Monitor, and the AirVisual. These monitors can measure a range of pollutants and environmental factors, including PM2.5, CO2, temperature, and humidity. They often use color-coded displays or indicators to show the air quality, with green indicating good air quality and red or purple indicating poor air quality.

Satellite data

NASA, in particular, has been at the forefront of using satellite data to measure air pollution. Its satellites, along with airborne and ground-based sensors, constantly collect data on major pollutants in the Earth's atmosphere. NASA-funded scientists track the sources and concentrations of these pollutants and their movement through the atmosphere. They provide this data to managers and policymakers to inform decisions around air quality for economic and human benefit.

One example of a NASA satellite is the Aura satellite, which has an Ozone Monitoring Instrument that can detect atmospheric gases such as nitrogen dioxide, a common emission from cars, power plants, and industrial activity. Another example is the Multi-Angle Imager for Aerosols (MAIA) mission, which combines the expertise of planetary scientists and epidemiologists to answer the question of which types of air pollutant particles are most harmful to human health. MAIA does not measure particulates directly but instead measures how they interact with light.

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