COVER STORY
Indoor air quality – quick and straightforward solutions for measuring the key parameters
Air quality is recognised by global studies as having a direct correlation to population health. Whilst it is natural to think mainly about outdoor air quality, however indoor air quality is equally as important, recent studies indicate that the quality of the air inside our homes, workplaces and other buildings can be, on average, between two to five times more polluted than outdoor air. As we spend the majority of our lives in indoor spaces, this makes us more vulnerable to the effects of poor air quality. These effects are not just to our respiratory system, they can also affect our cognitive performance and increase our stress levels. As homeowners and the operators of public and commercial buildings become aware of the risks and their potential liability, there is a rapidly growing opportunity to create devices that monitor for the most common pollutants. In this month’s edition, Gregorio Vidal, field application engineer at Anglia, outlines the key compounds and gases which affect indoor air quality (IAQ) and how they can be effectively detected and measured using innovative sensor solutions from Sensirion. The company not only offers solutions for each of the major pollutants but has also recently launched a compact and convenient air quality sensor detecting multiple pollutants and measuring other air quality parameters.
Common pollutants
Let’s start by looking at the sources of indoor pollutants, whilst these can be many and varied, they can be broadly grouped into four common categories of pollutants which any effective indoor air quality monitoring system should focus on: VOC: Volatile organic compounds are organic chemicals which are naturally released into the air from certain materials or produced during manufacturing processes. This encompasses hundreds of substances, some are harmless but many can be toxic and have long term effects on humans, examples of these include Acetone found in nail varnish removers, Toluene commonly used in paints and glues, Formaldehyde from building materials, cooking with gas stoves and smoking. NOx: Nitrogen oxides are a group of gases which are produced during the combustion of fuels. They are usually less abundant than VOCs around indoor spaces due to their instability, however they can reach dangerous level for humans if there is a constant source, for example living nearby major roads. CO2: This gas is formed naturally when humans exhale during breathing, it is also formed when any carbon-based fuel is burned. High concentrations of CO2 are clinically proven to adversely affect human performance and wellbeing. PM: Particulate Matter is classed as a mixture of solid particles and/or liquid droplets present in the air. They are classified by the size of the particles, for example PM2.5
10 November 2022 Components in Electronics
refers to particles which are 2.5 micron or smaller in diameter, a micron is 1 millionth of metre. High concentrations of particulates in the air can lead to long term respiratory issues.
Sensirion air quality monitoring solutions With over 20 years of experience, Sensirion is the global leader in developing and manufacturing environmental sensor solutions covering a wide range of applications from monitoring temperature and humidity, gas flow, pressure sensing and detection of harmful compounds and particulates in the air.
MOXSense Technology for VOC and NOx detection
Sensirion MOXSense devices are sensors based on the principle of a heated surface coated with a metal oxide that when exposed to certain types of gases changes its electrical resistance accordingly based on the oxygen content on its surface. Oxidizing gases such as NOx provide oxygen therefore, they increase the resistance of the MOX element. Conversely, VOCs absorb oxygen which reduces the resistance of the MOX element.
Sensirion’s MOXSense technology comprises of several MOX elements, or pixels, with different formulations
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for different gases, over a temperature-controlled plate. Processing the signals from the different pixels provides a complete and accurate measurement of various gas families. In addition, this technology is resistant to siloxanes. Siloxanes are compounds of silicon and oxygen which are present in perfumes or detergents and which can reduce the sensitivity of the MOX layers. Sensirion’s novel MOXSense technology means the sensors are highly sensitive and reliable over time. Sensirion products based on this technology include the SGP40 (VOC) and SGP41 (VOC + NOx) which are well-suited for constantly monitoring VOC and/or NOx concentrations. Their small size (2.44 x 2.44 x 0.85 mm) allows them to be designed into a wide variety of applications including portable monitoring devices, the MOXSense technology employed
Figure 1. MOX technology
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