In 2014 and 2015, Flint, Michigan, faced a public health crisis when high levels of lead and other contaminants were found in municipal drinking water. As a result, a Legionnaires’ outbreak killed 12 people, and many more were severely sickened. While the lead pipes caused unsafe lead levels in drinking water, proper emission detection may have prevented the outbreak.
Emission sensors play a vital role in monitoring and controlling environments in industrial, medical, research, and everyday life. Many types of emissions can have negative impacts, such as high levels of lead or radiation in water, and monitoring these emissions can safeguard human health, preserve the environment, conserve process performance, ensure compliance with regulations, and provide quality control. This article examines various types of sensors and the emissions they’re designed to monitor.
Particulate emissions
Particulate matter emissions include compounds like dust, smoke, pollutants, volatile organic compounds (VOCs), bacteria, chemicals, and more. Given the broad nature of particulate emissions, a variety of sensor technologies are used for detecting particulate emissions in water and air. The most common term for this family of sensors is “water or air quality sensors”, but the technology that powers them can be drastically different, depending on the application.
Air particulate & VOC sensors
Lasers are an integral tool for sensing microscopic particles in the air. For example, the Honeywell HPM Series Particle Sensor utilizes a laser light source to illuminate particles passing through its detection chamber. As the light reflects and scatters off the particles, a photodiode detector analyzes the received laser signal to detect ultra-fine particle matter. This sensor series detects particulate matter (PM) ranging from PM1.0, PM2.5, PM4.0, and PM10 particles, allowing them to be used in air quality monitors for cleanrooms, HVAC systems, and air purification devices. PM1.0 – PM10 particles range from under 1 to 10 microns wide and include particles such as dust, pollen, spoors, bacteria, viruses, and smoke.
VOCs can cause major health issues, and they vary in size and composition. VOC sensors like SensirionAG’s SGP40-D-R4 integrate a CMOSens sensor system based on metal-oxide sensor technology. In the presence of VOCs, specifically designed metal-oxide film changes the resistance of a semiconductor material, which subsequently sends an electrical signal to indicate the detection of VOCs on the film. Metal oxide sensors can also be tuned to detect other materials, including specific gases, by manipulating the semiconductor’s characteristics and changing the sensor temperature.
Water quality detection sensors
Two common sensor technologies are used to detect particulate matter in water. Electrochemical sensors detect minerals, metals, and pH levels, while optical sensors detect dispersed solids, color, and clarity.
For example, Analog Devices’ CN0428 sensor employs electrochemical reduction-oxidation (redox) reaction sensing by measuring the transfer of electrons from one reactant to another via detection probes. This method is used to detect heavy metals like lead, as well as other unwanted chemicals, bacteria, and biological particulates in water.
The other common type of water quality sensor utilizes optical transmitter/receiver systems to detect water turbidity, commonly called water clarity. Turbidity can be affected by suspended particles such as clay, silt, microplastics, algae, sediment, or other organic matter. Analog Devices’ CN0409 sensor utilizes infrared emitters and photodiodes to measure water turbidity ranging from 0 to 1000FTU, with a +/- 0.5FTU tolerance. For reference, the EPA limit for turbidity of drinking water is 1 FTU.
Gas emission sensors
Gas emissions are most associated with greenhouse gas and automotive emissions such as CO2, nitrogen oxide, and carbon monoxide. However, gas emissions can originate from industrial facilities, electric utilities, paints, solvents, chemical vapors, and even natural sources like volcanoes.
Carbon dioxide, the most famous of greenhouse gas emissions, is one of the most monitored gases in a variety of applications. For example, CO2 sensors such as SCD4X can be used for traffic light indicators, demand-controlled ventilation, agricultural greenhouses, and indoor air quality monitoring. This sensor utilizes a thermal-mass measurement principle, integrating a MEMS calorimetric sensor and a micro-heating element to generate a temperature profile during gas flow. As different gases flow across the membrane, the heat profile changes. This change is used to indicate the concentration of various gases present on the membrane.
Ozone is a harmful pollutant that can cause heart and lung disease. When nitrogen oxides (the byproduct of the combustion of fossil fuels) are in the presence of VOCs, heat, and sunlight, gaseous chemical reactions can create high concentrations of ozone. In high concentrations, ozone can damage soft tissue, harming human, animal, and plant health. Because of this, ozone sensors are very common in urban settings and are used to alert authorities when high levels of ozone are present. Ozone sensors like SEN0321 use the same electrochemical principles as metal-oxide sensors mentioned above and can detect ozone concentrations ranging from 0 to 10 ppm.
Lastly, gas emissions can be measured at incredibly high accuracy using infrared gas detectors. These highly specialized sensor assemblies measure gas composition by emitting specified frequencies of infrared light through a sample of gas. If a target gas is present in the sample, specific wavelengths of the infrared light are absorbed. Depending on the absorption rate, the concentration of the specific gas can be detected by the infrared detector. Infrared gas detectors range from small devices like KEMET’s USEQGSEx series to very large, specialized sensor assemblies that simultaneously detect a wide range of gases.
The importance of emission sensors and detection
Emission detection is a critical tool for monitoring and controlling environments in the industrial, medical, municipal, and research sectors. The Flint, Michigan, water crisis highlighted the need for proactive monitoring and detection systems for safeguarding public health.
The various sensors and technologies mentioned in this article can detect an array of emissions. Nearly every emission detection application has a solution. Governments, businesses, and researchers should leverage emission sensors to create a safer, healthier, and more sustainable environment for all.
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