Smart Home Sensors: Understanding Air Quality

Smart home sensors provide a practical and affordable means to monitor air quality. These smart devices detect pollutants like particulate matter (PM), volatile organic compounds (VOCs), carbon dioxide (CO₂), and nitrogen dioxide (NO₂), transmitting data to local or remote platforms for analyses or can be used in automations to trigger actions.

Below is an overview of all the different types of air quality measurements and examples of what might cause the readings.

Particulate Matter (PM)

Particulate matter (PM) refers to a mixture of solid particles and liquid droplets suspended in the air. These particles vary in size and composition, and are categorised based on their aerodynamic diameter. The size of these particles determines how deeply they can penetrate into the respiratory system and their potential health impacts.

Particulate matter can be measured using Ecowitt Air Quality sensors. The Ecowitt WH41 is an outdoor air quality sensor that measure particulate matter (PM). There are other Ecowitt sensors for indoors, they are the WH46D (has a built-in display, WH46, WH45 and the WH43. All of which monitor various levels of particulate matter.

For Information: There are 1000 micrometres in 1 millimetre. A human hair is about 75 micrometres wide

Volatile Organic Compounds (VOC) 

Volatile Organic Compounds (VOCs) are individual organic chemicals that easily evaporate into the air at room temperature

Total Volatile Organic Compounds (TVOC) represent the combined concentration of all VOCs present in the air at a given time. TVOC measurements provide an overall indication of indoor air quality but do not identify specific compounds. 

VOCs encompass a wide range of organic chemical compounds that easily become vapors or gases. Common indoor sources include:

• Building materials: paints, varnishes, and adhesives
• Household products: cleaning agents, air fresheners, and cosmetics
• Furnishings: new furniture and carpets
• Combustion activities: cooking and tobacco smoke

VOC concentrations are typically measured in milligrams per cubic meter (mg/m³). According to various guidelines:

• Less than 0.3 mg/m³: Low concern
• 0.3 to 0.5 mg/m³: Acceptable
• 0.5 to 1 mg/m³: Marginal concern
• 1 to 3 mg/m³: High concern
• Above 3 mg/m³: Very high concern

Prolonged exposure to elevated VOC levels can lead to health issues such as headaches, dizziness, respiratory irritation, and in severe cases, damage to the liver, kidneys, or central nervous system.

Carbon Dioxide (CO₂) and Carbon Monoxide (CO)

Carbon dioxide (CO₂) and carbon monoxide (CO) are both colorless and odorless gases, but they have distinct properties, sources, and health implications

Carbon Dioxide (CO₂):

• A naturally occurring gas produced by respiration, combustion, and fermentation.
• Commonly found in exhaled breath and as a by product of burning fossil fuels.
• Can accumulate indoors without proper ventilation.

Carbon Monoxide (CO):

• A toxic gas resulting from incomplete combustion of carbon containing fuels.
• Produced by malfunctioning or improperly ventilated appliances like gas stoves, heaters, and fireplaces.
• Dangerous even at low concentrations

Nitrogen Dioxide (NO2)

Nitrogen dioxide (NO₂) is a reddish-brown gas with a pungent odor, commonly produced during the combustion of fossil fuels. It is a significant air pollutant, both outdoors and indoors, and poses various health risks.

• Common sources of NO2 include Vehicle emissions, Industrial processes and home gas stoves and heaters
• Annual mean should not exceed 10 µg/m³
  
• 1 hour mean should not exceed 200 µg/m³
• Good Ventilation will prevent build-up of NO2
  
  

Ozone (O₃)

Ozone (O₃) is a gas composed of three oxygen atoms. It plays an important role in the upper atmosphere by shielding the Earth from harmful ultraviolet radiation, at ground level, ozone becomes a significant air pollutant with adverse health effects.

• Producers of Ozone include air purifiers, laser printers, photocopiers and UV lamps
• Safe Levels: Indoor ozone concentrations should remain below 0.1 mg/m³ (approximately 0.05 ppm) to protect health.
• Hazardous Levels: Concentrations above this threshold can lead to respiratory issues, especially in the vulnerable such as children, the elderly, and those with pre-existing respiratory conditions.
  
  

Humidity

Humidity refers to the amount of water vapour in the air. It’s usually measured as relative humidity (RH) — the percentage of moisture in the air compared to the maximum it could hold at a given temperature.

Indoor Humidity Monitoring

• Comfort: RH between 40% and 60% is ideal for most people. Too low feels dry, too high feels muggy.
• Health: High humidity encourages mould, dust mites, and bacteria. Low humidity can dry out skin, eyes, and airways.
• In Home: High moisture can damage furniture, electronics, and walls. Low moisture can crack wood and cause static electricity.

Outdoor Humidity Monitoring

• Weather forecasting: Outdoor humidity affects how hot or cold it feels (heat index or wind chill).
• Pollution interaction: High humidity can worsen air pollution by trapping particles near the ground.
• Allergies: Damp conditions can lead to more mould spores or affect pollen levels.

Conclusion

Smart home air quality sensors can measure lots of different pollutants, and it’s common for them to occasionally show high or ‘unsafe’ readings. Often, these spikes are caused by everyday activities like using deodorant spray, which are usually harmless and pass quickly. However, if you’re seeing regular or persistent spikes, it’s worth looking into. In many cases, simply opening a window will help, unless the problem is coming from outside.