Measuring Pollution: Effective Strategies For Accurate Assessments

Measuring pollution is a critical step in identifying its causes and implementing strategies to reduce or regulate it. Air pollution, in particular, has gained prominence due to its adverse effects on human health, the natural world, and the built environment. While the measurement of pollution dates back to the 19th century, modern techniques have evolved to include automated and semi-automated devices that provide near real-time data. These devices range from simple diffusion tubes to advanced chemical and physical sensors. Governments and industries use these measurements to assess the effectiveness of control strategies and ensure compliance with regulations. The data collected helps public health officials make informed decisions to improve air quality and protect the well-being of their communities.

Air quality sensors: small handheld devices to large static stations, and remote devices on planes/satellites

Air quality sensors are an important tool for measuring pollution and can range from small handheld devices to large static stations, as well as remote devices on planes and satellites. These sensors help public health officials and researchers understand and address the impacts of air pollution on human health and the environment.

Handheld air quality monitoring devices offer an ultra-portable option for measuring air pollution in real-time. These devices often feature swappable sensor heads for flexibility and can be used to simultaneously measure particulate matter and gaseous pollutants.

Static stations, on the other hand, are typically equipped with a small number of costly, high-quality sensors and numerous low-cost micro stations. While data from micro stations may be more prone to noise and errors, it can be calibrated using methods such as the Spatio-Temporal Calibration Model (STCM). This model employs dual encoders to capture temporal and spatial dependencies, improving the accuracy of air pollution data collected by micro stations.

Remote sensing instruments provide another means of measuring air pollution and can be deployed on satellites, aircraft, or ground-based stations. Satellite remote sensing, in particular, can fill in spatial gaps in ground monitoring by providing data on criteria air pollutants and greenhouse gases. For example, the California Air Resources Board (CARB) has utilised satellite data to estimate ambient PM2.5 concentrations and to identify air pollution hotspots and trends.

Overall, air quality sensors play a crucial role in quantifying and addressing air pollution, with each type of device offering unique advantages and contributing to a better understanding of air quality.

Passive vs active measurement: passive soaks up samples, active uses fans to suck in air

Air pollution is a pressing issue, and accurate measurement is the first step in identifying its causes and implementing strategies to reduce or regulate it.

There are two broad methods of measuring air pollution: passive and active. Passive devices are relatively simple, low-cost, and do not require pumping air to collect samples. They work by soaking up or passively collecting ambient air samples, which are then analysed in a laboratory. Diffusion tubes, for example, are fastened to lamp posts to absorb specific pollutant gases. Deposit gauges, large funnels that collect soot and other particulates, are another type of passive device.

On the other hand, active measurement devices are automated or semi-automated and tend to be more complex and sophisticated. They use fans to suck in air, filter it, and either analyse it immediately or store it for later laboratory analysis. Active sensors use physical or chemical methods to analyse the samples. Physical methods, such as measuring light absorption, do not change the sample, while chemical methods analyse the sample through a chemical reaction. Most automated air-quality sensors are examples of active measurement.

While passive devices are more affordable and convenient, they are limited to measuring gases and vapours. Active devices, on the other hand, can be used to collect samples of gases, vapours, and particulates. Active devices also have the advantage of a variable flow rate, allowing for more control over the sampling time period. However, they are generally less user-friendly and more costly than passive devices.

Air pollution sources: industrial emissions, wildfires, organic burning, vehicle emissions

Air pollution is a pressing issue that has serious implications for human health, the environment, and the economy. By measuring air pollution, we can gain valuable insights to inform policies, strategies, and research that aim to mitigate its negative effects. This is especially important for communities located near industrial facilities, wildfire-prone areas, and regions with a high volume of vehicle traffic.

Industrial Emissions

Industrial emissions, particularly the combustion of fossil fuels, contribute significantly to air pollution. To monitor and measure the impact of industrial emissions, various methods can be employed:

• Fixed Automated Monitoring Stations: These are large, government-sanctioned stations situated in fixed locations, especially in areas with a higher likelihood of exposure to harmful pollutants. They measure major pollutants following World Health Organization (WHO) guidelines and present the data as an Air Quality Index (AQI). While these stations provide high accuracy and reliability in real-time, they are also expensive to install and maintain.
• Air Emissions Monitoring: This involves gathering and interpreting data to determine compliance with regulatory requirements set by environmental protection agencies. It includes ambient air quality monitoring, which compares current air pollutant levels with historical information and clean air standards, and stationary source emissions monitoring, which focuses on individual stationary emissions sources such as facility output and emissions control devices.

Wildfires

Wildfires generate large amounts of smoke that can have far-reaching impacts on air quality and human health, even in locations far downwind from the fire. To measure the pollution caused by wildfires:

• Smoke Monitoring Networks: These networks, such as the one operated by the US National Park Service (NPS), use permanent or temporary air quality monitors and low-cost sensors to measure levels of particulate matter (PM), a primary component of smoke. During wildfires, this data helps track air quality, inform potential health risks, and guide management decisions.
• Satellite Monitoring: Satellites, such as the Sentinel-5P from the European Space Agency (ESA), play a crucial role in forecasting poor air quality by imaging the Earth from space. They provide global coverage of air pollution data and contribute to monitoring services like the Copernicus Atmosphere Monitoring Service (CAMS).

Organic Burning

Organic burning, or open burning, includes activities such as agricultural burning of crop residues, forest fires, and the combustion of household waste. It releases various air pollutants, including soot, particulate matter (PM), carbon monoxide (CO), methane (CH4), volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs). To measure the impact of organic burning:

• Emissions Inventories: Organizations like the US Environmental Protection Agency (EPA) sponsor emissions inventory improvement programs to collect data on the release of pollutants from open burning. This data is used to develop emissions inventories that quantify and categorize the types and amounts of pollutants emitted.
• Air Quality Index (AQI): The AQI is a numerical system that measures the level of air pollution in a given region. It categorizes air quality from good (0-50) to hazardous (301 and higher), with corresponding colors and levels of concern. Public health officials use the AQI to make recommendations on outdoor activities and provide guidance for sensitive groups.

Vehicle Emissions

Vehicle emissions are a leading cause of urban air pollution worldwide, with a growing number of vehicles contributing to the problem. To measure and monitor vehicle emissions:

• Gas Analyzer Technology: Installing reference air quality monitoring systems based on gas analyzers can provide data on vehicle emissions. However, these systems tend to be bulky and expensive, limiting their placement and resulting in insufficient data resolution during traffic peaks.
• Mobile Monitoring Instrumentation: Air quality can be measured on moving vehicles, such as trucks or airplanes equipped with appropriate instruments. This flexible and cost-effective approach is useful for monitoring communities and rural areas that lack fixed monitoring stations.
• Roadside Networks: Smaller, more cost-effective monitors can be deployed in dense, targeted networks along roadsides to measure roadside emissions accurately. These monitors have shorter logging intervals, providing a more detailed picture of air pollution during peak exposure times.

Air quality indexes: combine data on common air pollutants to produce a single number

Air quality indexes (AQIs) are a way to communicate air quality to the public. They are designed by government agencies to indicate how polluted the air currently is or how polluted it is forecast to become. As air pollution levels rise, so does the AQI, along with the associated public health risk.

AQIs are calculated using an air pollutant concentration over a specified averaging period, obtained from an air monitor or model. Concentration and time together represent the dose of the air pollutant. Health effects corresponding to a given dose are established through epidemiological research. Each country's AQI reflects that country's national air quality standards and considerations. For example, the European AQI reports on five separate pollutants, while the India AQI reports on those same five pollutants and ammonia (NH3).

The AQI is usually presented as a number within a category, with a descriptor, a colour code, and a standardised public health advisory. For example, the US Environmental Protection Agency's AQI is split into six categories, with a different colour and level of concern for each. The categories range from "Good" (0-50) to "Hazardous" (301 and higher).

The AQI can be used to inform the public about the risk of air pollution and to provide health advice. For instance, when the AQI is high, government bodies often recommend that people reduce physical activity outdoors or avoid going out altogether.

Air quality monitoring: qualitative, by observing effects on plants, or quantitative, using devices

Air quality monitoring can be done in two ways: through qualitative observation of the effects of pollution on plants, or through the use of devices that provide quantitative data.

Qualitative Monitoring: Observing Effects on Plants

Monitoring air pollutants via plants is an economic, convenient, and credible method. Plants exhibit different damage symptoms in response to different air pollutants, which can be used to determine the species of air pollutants. The mass concentration scope of pollutants can be estimated by observing the extent of damage to plants and the duration of exposure. For example, moss is a sensitive indicator plant that will turn black or brown when exposed to air pollution. In the long term, moss communities will decline and the species diversity will continue to decrease until they disappear.

Quantitative Monitoring: Using Devices

Air quality monitoring devices are designed to assess the levels of pollutants and environmental conditions within indoor spaces. These devices measure various parameters, including particulate matter (PM), volatile organic compounds (VOCs), carbon dioxide (CO2), temperature, and humidity, providing a comprehensive overview of air quality. By identifying pollutants and potential health hazards, these devices help ensure a healthier indoor environment.

Data collected by these monitors can be used to improve ventilation, control pollution sources, and guide the maintenance of HVAC systems, ultimately enhancing occupant comfort, well-being, and productivity. Additionally, monitoring air quality can promote health and well-being, achieve building certifications, improve facility management, encourage a return to physical workspaces, optimize energy usage, and increase property value.

Some examples of air quality monitoring devices include:

• Wireless humidity and temperature monitor
• Handheld carbon monoxide meter
• Indoor air quality meter
• Datalogging indoor air quality meter

Frequently asked questions