Many of us are familiar with the idea that pollution can reduce the quality of the air we breathe outdoors and affect our health. But air pollution is not just something that happens outside.
The quality of air indoors can be reduced by common activities like cooking or using a boiler.
These can give off harmful gases like carbon monoxide, which can be fatal in extreme cases. Even carbon dioxide, which is produced naturally when we breathe, can reach harmful levels if several people are confined in a room with poor ventilation. These gases can cause symptoms like headaches, dizziness and nausea.
Such symptoms have been reported by people like office workers who spend long hours in an enclosed building. The phenomenon is called sick building syndrome and poor air quality is thought to be one of its risk factors.
Poor air quality can exacerbate symptoms in people with respiratory conditions like asthma, or those with allergies. Pollen carried in from the outdoors, dust and cigarette smoke can all contribute to poor air quality.
Indoor air pollution from volatile organic compounds
Volatile organic compounds (VOC) are another common but less known source of air pollution indoors. VOCs sources in the home and at work include:
● Cleaning products
● Cosmetics
● Furnishings like carpets
● Sofas and mattresses
● Paint and varnishes
● Photocopiers
● Newspapers
VOCs are highly volatile and tend to give off an unpleasant smell. They include compounds such as formaldehyde, acetone, benzene and chloride.
They can cause symptoms such as headaches, nausea and irritation to the eyes, nose and throat. They can also affect people with respiratory conditions.
Improving air quality with an air purifier
If you live or work in a building with poor air quality then dealing with the cause is best way to improve the air quality. For instance, you might need to improve the ventilation. If this isn’t an option, or you are particularly sensitive to poor air quality because of a condition like asthma, then an air purifier can help clean the air.
Air purifiers often use one or more different kinds of filtering technology to deal with different kinds of pollutants. The types of filters available include:
● Activated carbon: These use carbon which has been processed to be incredibly porous, so there’s a larger surface area to adsorb particles. This makes them good at removing VOCs.
● Ultraviolet light: UV light has long been used as a steriliser to destroy microorganisms, including airborne viruses which can cause diseases like flu.
● Photocatalytic: These use a photocatalyst to oxidise water to produce hydroxyl radicals. The radicals are capable of damaging a wide range of pollutants including VOCs and airborne pathogens.
Air quality sensors
Some air purifiers have in-built sensors which can monitor the ambient air quality. Depending on the amount of pollutants detected by the sensor, the air purifier can then automatically adjust how hard it works.
Manufactures like SGX Sensortech produce sensors which detect a wide range of gases, including VOCs.
Stand-alone rather than in-built VOC sensors can also be used to monitor the performance of air purifiers. This helps provide extra peace of mind that the air purifier is indeed improving the air quality, if VOCs are present.
SGX Sensortech’s range of VOC sensors make use of cutting-edge technology. Sensors using metal oxide semiconductors and micro-electro-mechanical systems (MEMS) technology can detect VOCs with a high degree of sensitivity.
MEMS technology allows small but powerful sensors to be created. Not only can the devices pick up subtle changes in the level of VOCs, across a wide detection range, they can do so in real time.
Some of the devices are particularly handy because they can simply be plugged into a power socket where they operate at low power with a high energy efficiency.
SGX Sensortech also create VOC sensors which can indicate the level of carbon dioxide present, which is often used as a proxy for determining air quality.
In future, SGX Sensortech is looking at creating VOC sensors which can monitor other factors affecting air quality, such as humidity and temperature. They may also be customised by their owners so they can choose which factors to measure.
Measuring the efficiency of air purifiers
The efficiency of air purifiers is determined by the type and variety of particles they can remove from the air, as well as the speed at which they do so.
In the US, air filters are given American Society of Heating, Refrigeration, and Air-conditioning Engineer ratings to indicate their efficiency.
Purifiers approved by the Association of Home Appliance Manufacturers are assigned a Clean Air Delivery Rate to indicate their efficiency. This indicates how many cubic feet of air is purified per minute.
