There are several methods for measuring air quality! Today, many technologies are available to measure our air quality. These technologies include traditional reference-grade FRM/FEM monitors, mobile air quality sensors, low-cost stationary sensors, satellite monitoring technology, as well as alternative monitoring to successfully identify air pollution sources. As the push for improved data on air quality rises, we will see further innovation in monitoring systems to help satisfy these demands. In addition, monitoring on a smaller scale, local monitoring, for example, has become increasingly common as a higher level of environmental awareness has developed. This article will talk about the types of air quality monitoring systems.



Traditional Monitoring Systems

The scientific standard for monitoring air quality is classified as either FRM (federal reference method) or FEM (federal equivalent method). This equipment meets stringent performance measurement criteria and is often used to assist in decision making, policy creation, and evaluating air quality at federal and state levels.


FRM, federal reference method, equipment was specifically designed to fulfill air quality monitoring criteria established by regulatory agencies such as the Environmental Protection Agency. FEM monitors use alternative technologies, but they must still deliver a comparable degree of performance compared to established standards.


Because these monitoring systems provide high-quality data, they are used as the standard of measuring air quality monitoring technologies. Because FRM and FEM data are utilized in making critical decisions, they must meet more stringent operational criteria for accuracy, drift, measuring range, and precision. Furthermore, because these systems can last beyond most other systems, ten years or more, they are used at the federal level in the United States with proper calibration and maintenance.


Although they are considered the “Gold Standard,” these technologies have their downsides. The first drawback is the expense.  These monitors are expensive, costing between $15,000 and $40,000 each. In addition, operating this equipment necessitates a controlled environment, regular maintenance, and proper calibration by expert technicians, making the expense higher. 


Because they require a specialized electrical supply and data shelters for equipment housing, they are often rigid in terms of placement considerations. Additionally, the higher cost means fewer monitors are placed than technologies that cost less. Because of these constraints, air quality is often monitored on a regional scale, resulting in substantial data gaps in assessing local air quality levels.


Air Quality Monitoring


Mobile Air Quality Monitoring

Unlike stationary monitors, mobile air quality monitoring evaluates the quality of air across a specific region or city in a specified timeframe. This method produces a regionally diversified but temporally constrained dataset that provides a snapshot of the air quality throughout an area at a set point in time.


The high spatial resolution at which measurements may be taken is one advantage of mobile air quality monitoring. In addition, air quality measurements can be acquired at sites not generally covered by a standard FRM/FEM air quality monitoring network by employing a “block by block” strategy of capturing data for a large number of data points across a region.


However, mobile air quality monitors might have variable data quality, making them unsuitable for regulatory usage. In addition, the image of air quality provided by mobile monitoring may provide less informative information than fixed monitoring networks.


Because these monitors are moving constantly, it is more likely to miss a pollution hotspot or local trend because it was not in the region when a pollution event happened. While this type of monitoring can gather data on air quality at a higher spatial resolution, it does not ensure that the information captured can be evaluated for trends in air quality over time for local air quality events. 


Mobile Air Quality Monitoring


Stationary Monitoring 

Low-cost stationary air quality sensors are in between traditional and mobile monitoring in terms of spatial and temporal resolution. This category of monitoring technology is broad due to the extensive range of low-cost sensors available, having an equally broad performance range. Some low-cost sensors are promoted for outdoor and indoor use but are best for home use. 


Aside from the quality of data and services, low-cost sensors require different infrastructures to operate based on brand.  The operating requirements can impact the locations and conditions deployed, whether they require dedicated electrical services or WIFI. When it comes to the deployment of low-cost sensors around the world, self-sufficient sensors that link to the cloud for data collecting can have significant advantages.


Compared to low-cost mobile monitoring, low-cost stationary sensors may still provide high spatial data coverage, including temporal patterns. Flexible siting implies that areas that would most benefit from increased air quality monitoring coverage during network design, such as those near a pollution source, may be prioritized.


Low-cost stationary sensors help construct sensor networks in locations with no reference network or to help supplement reference-grade monitors in areas with more data points due to their low purchase and operations costs, flexible deployment, and scalability.


However, just with mobile monitoring, the quality of data provided by fixed low-cost sensors might vary. As a result, it is critical to evaluate the efficacy of the low-cost sensor you want to use as part of an air quality monitoring network. 


Monitoring Netoworks


Satellites Monitoring for Air Quality.

Unlike ground-based monitors, technologies on satellites, like NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS), may be used on a broader scale to monitor the pollution incidents and trends around the world. Satellite monitoring technology is complicated in that it must deal with atmospheric chemistry. Aerosol optical depth (AOD) is one sort of measurement that quantifies aerosol particle density and measures differences in solar radiation from the top of the Earth’s atmosphere and those that reach the surface. Satellite-based monitoring works by observing how sunlight scatters by ambient particulates; however, weather conditions, atmospheric mixing, pollutant particles, and other factors in space can easily disturb this method. Because it relies on sunshine, this type of monitoring cannot function on overcast days.


Air quality monitoring by satellite is often combined with ground observations in numerous applications to understand our air quality better. Combining various data points from the satellite monitor, such as AOD with wind speed and direction or cloud optical thickness, with ground-level air quality index (AQI) and knowledge of recent fire locations, for example, can contribute to a more accurate forecast of air quality during wildfires.


NASA uses an ozone monitoring instrument (OMI) or TROPOspheric Monitoring Instrument (TROPOMI) aboard satellites as another form of air quality monitoring. They can measure ozone and nitrogen dioxide, sulfur dioxide, and formaldehyde based on the intensity of reflected sunlight at various wavelengths and identify the absorption properties of atmospheric gases. This monitoring technology can observe the planet in a single day and track air quality changes as time goes on.


However, they cannot collect data when it is cloudy, as the technology relies on sunlight reflected in space. Nevertheless, satellite air quality monitoring can fill in gaps from ground monitors. This includes monitoring remote regions where there are no ground monitors.  


Satellite monitoring also helps track air pollution, which is far more geographically extensive than current monitoring systems. However, compared to ground-based monitoring, satellite air quality monitoring presently has a limited temporal and geographical resolution and fluctuating degrees of accuracy due to calibration biases. In addition, satellite-based models must also be ground-truthed by ground-based monitoring; therefore, they will most likely supplement existing monitoring methods.


Satellite Monitoring


Other Techniques for Monitoring Air Quality

In addition to the methods of measuring air quality above, there are additional ways to measure air quality without using sensors. For example, because air pollution is frequently invisible, in some instances, we can use our senses of sight and smell to determine if air quality good or bad.


One alternative and intriguing way to monitor air quality has been researched in Portland, Oregon. A study was conducted in 2016 to explore using particular forms of moss on trees to assess air quality. The analysis discovered dangerous heavy metal levels, like cadmium and arsenic, surpassed the state’s guidelines. Researchers utilized this data to construct maps showing where state regulators may place air quality monitors in Portland.


Plants such as moss and lichen have long been used to monitor air quality in woods; however, this study was the first time it was effectively used in a metropolitan setting. This alternate monitoring technique is conceivable because moss works as a natural air pollution sensor, absorbing gases from its surroundings and reflecting small changes in the air.


Employing moss for monitoring the air quality is comparatively inexpensive compared to other methods of monitoring. While this monitoring approach is intriguing, it requires other monitoring methods to supplement and evaluate air quality. Given its lack of precision, it is best employed as an indication rather than a data source for measuring air pollutant concentrations. Using moss to gather air quality data can complement an area’s current monitoring networks. This method can only be used in geographic areas where moss or lichen grows naturally.


Non Traditional Monitoring Alternatives


Caring for Our Air

Advancements in air quality monitoring technology provide intriguing prospects for the future of air quality management. However, traditional and new monitoring technologies have their own strengths and weaknesses. In the future, the most effective air quality monitoring systems will be those that capitalize on each technologies strengths. Air quality impacts all of us, and ensuring we do our part to ensure a brighter future for everyone is imperative! At Filti, our mission is to manufacture quality products that help improve air quality at home and work environments.  Check out our website to find our more about Filti, and our products!

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