Measuring Air Pollution: Methods And Tools For Assessment

Air pollution is a pressing issue that affects the health and well-being of people worldwide. To address this problem, various organisations, including governments, local councils, and environmental groups, are tasked with monitoring and measuring air quality. This process, known as pollution measurement, involves using techniques such as active or passive sampling, biomarkers, and calibrated microphones, to assess pollution levels and their impact on both human health and the environment. One commonly used tool for measuring air pollution is the Air Quality Index (AQI), which assigns numbers on a scale to indicate the level of air pollution and the potential risk to human health. Additionally, advancements in technology have led to the development of mobile monitoring platforms, such as those onboard road vehicles, aircraft, and even balloons, which provide horizontal and vertical air quality data. These innovations, along with traditional ground-based measurements, contribute to a comprehensive understanding of air pollution and its effects.

Active vs passive measurement: Active devices are automated or semi-automated and tend to be more complex, while passive devices are relatively simple and low-cost

Air pollution measurement is broadly categorised into two types: passive and active. Passive devices are relatively simple and inexpensive. They work by absorbing or otherwise passively collecting a sample of the ambient air, which is then analysed in a laboratory. Active devices, on the other hand, are automated or semi-automated and tend to be more complex and sophisticated than passive devices. They use pumps or fans to suck in the air, filter it, and either analyse it automatically or store it for later analysis.

Passive air sampling collects air pollutants without using a mechanical pump. Instead, it relies on the natural diffusion of air pollutants onto a sorbent material, such as a filter or chemical trap. This method is popular for long-term monitoring due to its simplicity and low cost. Passive samplers can be left in the field for extended periods, making them ideal for assessing average pollutant levels over time. They require little to no maintenance and are easy to use, with no need for power or mechanical parts. However, they have limited temporal resolution, as they rely on the slow diffusion of pollutants, and may have lower sensitivity than active samplers.

Active air sampling, on the other hand, uses a mechanical pump to draw a known volume of air through a collection device. This method provides more precise and immediate data on air pollutant concentrations. It offers high temporal resolution, making it suitable for detecting rapid changes in air quality. Active samplers can detect lower pollutant concentrations and provide controlled sampling conditions, reducing variability and improving accuracy. However, they are generally more expensive and complex, requiring power sources, regular maintenance, and calibration. They also have limited deployment time due to their need for power and maintenance.

Both passive and active air sampling methods play crucial roles in environmental monitoring and are suited to different applications. Passive sampling is ideal for long-term average pollutant concentration monitoring, compliance monitoring, and epidemiological studies. Active sampling is preferred for real-time monitoring, industrial hygiene, emergency response, and urban air quality monitoring.

Air quality sensors: These range from small handheld devices to large-scale static monitoring stations and remote monitoring devices used on planes and satellites

Air quality sensors vary in size, portability, and cost. They can be as small as wearable devices or as large as static street-side monitoring stations. They can be inexpensive portable sensors or very expensive static stations.

Small, portable, and inexpensive sensors like the Air Quality Egg and PurpleAir are constantly sampling particulates and gases, producing moderately accurate, almost real-time measurements that can be analysed by smartphone apps. Their data can be used to build maps of pollution over wide areas. They can be used for both indoor and outdoor environments and can measure five common forms of air pollution: ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Some measure less common pollutants such as radon gas and formaldehyde.

These sensors can be worn by individuals to monitor their local air quality levels, and are sometimes referred to as low-cost sensors (LCS). A recent review by the European Commission's Joint Research Center identified 112 examples, made by 77 different manufacturers.

Static monitors, on the other hand, are fixed in public places such as busy railway stations to continuously sample and measure the air quality in a particular urban location. Some static monitors provide immediate feedback on local air quality. For example, in Poland, EkoSłupek air monitors have small lamps on top that change colour to signal the healthiness of the surrounding air.

At the other end of the spectrum are the large, very expensive, static street-side monitoring stations that constantly sample the various different pollutants commonly found in urban air for local authorities. These make up metropolitan monitoring systems such as the London Air Quality Network and the Automatic Urban and Rural Network (AURN) in the UK. In the US, the Environmental Protection Agency (EPA) maintains a repository of air quality data through the Air Quality System (AQS), with data from over 10,000 monitors.

Air quality can also be measured remotely, from planes and satellites, through methods such as gas filter correlation. Some of the earliest satellite pollution monitoring efforts were GOME (Global Ozone Monitoring Experiment) and NASA's Mapping Pollution with Satellites (MAPS) in the 1990s.

Personal air quality sensors: Small, inexpensive, portable, and sometimes wearable sensors that can be used for both indoor and outdoor environments

Personal air quality sensors are small, portable, and sometimes wearable devices that can be used to monitor air pollution levels in both indoor and outdoor environments. These sensors are generally inexpensive and provide a convenient way to measure air quality. Here are some examples of personal air quality sensors:

• Atmotube Pro Portable: A small, keychain-sized air quality monitor that can be attached to a backpack or belt clip. It measures various parameters, including PM1, PM2.5, PM10, VOCs, temperature, humidity, and barometric pressure. The data can be accessed via the Atmo app, which is available for Android and iOS devices. The Atmotube Pro offers impressive accuracy, with a range of 86-98% across different conditions. However, its battery life is shorter than expected, especially when measurements are taken more frequently.
• PurpleAir Zen: An indoor-outdoor air quality monitor that uses the EPA AQI colour scale to indicate air quality: green for good, yellow for moderate, orange for unhealthy for sensitive groups, red for unhealthy, purple for very unhealthy, and deep violet/maroon for hazardous. The Zen can be linked to PurpleAir's Real-Time Air Quality Map, contributing to crowd-sourced data. It offers an easy-to-see colour scale and has been tested in various weather conditions, from hot and humid summers to cold winters.
• Govee Smart Air Quality Monitor: A budget-friendly option priced under $40. It measures PM2.5, temperature, and humidity. The Govee Smart has an easy-to-use app and can be paired with Govee air purifiers. While it may be less sensitive than more expensive models, it still provides valuable information about air quality.
• Temtop M2000 2nd Generation: A handheld air quality monitor that tests for a wide range of pollutants, including CO2, HCHO (formaldehyde), PM2.5/PM10, temperature, and humidity. It has been widely used, including by the New York State Education Department, and offers built-in calibration. The device includes an audible alarm for high contaminant levels and has high consistency across multiple units. However, it does not function in temperatures below freezing, limiting its outdoor use in colder regions.

Large-scale pollution monitoring: Large, very expensive, static street-side monitoring stations that constantly sample various pollutants for local authorities

Large-scale pollution monitoring involves the use of large, static street-side monitoring stations that continuously sample various pollutants. These stations are typically very expensive and are operated by local authorities to monitor the air quality in urban areas.

These monitoring stations are designed to constantly sample the different pollutants commonly found in urban air, such as nitrogen dioxide, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen oxides. The data collected by these stations is used to generate air quality indexes (AQIs) that provide a representation of air pollution concentration levels.

The sensors used in large-scale pollution monitoring systems are highly accurate and provide near real-time measurements. They are often part of metropolitan monitoring systems, such as the London Air Quality Network and the Automatic Urban and Rural Network (AURN) in the UK. In the United States, the Environmental Protection Agency (EPA) maintains a repository of air quality data through the Air Quality System (AQS), collecting data from over 10,000 monitors.

These large-scale monitoring stations play a crucial role in identifying and regulating air pollution sources to ensure that air quality remains within legal limits mandated by regulatory bodies. The data collected helps local authorities assess the impact of changes in the urban environment, such as modifications to the road network or the construction of new buildings, on air quality. Additionally, health experts can utilise this information to understand the effects of air pollution on the well-being of people residing in the monitored areas.

The size and cost of these monitoring stations are significant, requiring substantial investments from local authorities. However, the insights gained from the continuous sampling of urban air pollutants are invaluable for making informed decisions to improve and maintain air quality, ultimately safeguarding the health of the public and the environment.

Remote sensing: Air quality can also be measured remotely, from the air, by lidar, drones, and satellites

Remote sensing is a powerful tool for measuring air quality from a distance, using technologies like lidar, drones, and satellites. These technologies offer unique advantages over traditional ground-based monitoring stations, providing unprecedented flexibility, accuracy, and coverage.

LiDAR Technology

LiDAR (Light Detection and Ranging) is an optical remote sensing technology that measures the light reflected by objects and converts it into highly accurate digital elevation models. It has emerged as a popular solution for vegetation management and infrastructure monitoring. LiDAR can be used to scan portions of forests, detect changes in elevation, and even estimate tree growth and health. Its compact design has made it more accessible and cost-effective, especially when used in combination with drones. However, LiDAR data interpretation can be complex and time-consuming, often requiring external expertise.

Drone Technology

Drones, equipped with cameras and photogrammetry capabilities, are increasingly being used for detailed surveys and inspections. They offer a flexible and safe way to gather data and perform inspections without putting personnel at risk. Drone inspections, combined with satellite imagery, provide valuable insights into the health of vegetation and can help identify potential issues along power lines or in other critical infrastructure.

Satellite Imagery

Satellite imagery has become a go-to solution for many organizations, especially in the protection of critical infrastructure. With thousands of satellites in orbit, this technology is becoming increasingly affordable and accessible. Satellites can cover large areas with high accuracy, providing timely and precise data updates. When combined with LiDAR and drone technologies, satellite imagery offers a comprehensive view of the environment, making it a powerful tool for monitoring and managing vegetation and linear infrastructure.

In summary, remote sensing technologies like LiDAR, drones, and satellite imagery offer unprecedented capabilities for measuring air quality and managing critical assets from a distance. These technologies are revolutionizing the way we monitor and protect our environment, infrastructure, and natural resources.

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