Improving Indoor Air Quality

TL;DR

Indoor air quality (IAQ) is essential for health, comfort, and productivity in every indoor environment. This page provides a clear overview of key indoor pollutants such as carbon monoxide (CO), ozone, radon, and particulate matter (PM1), explains relevant standards like WELL and RESET, and offers practical guidance on selecting accurate, certified sensors. You'll also find actionable strategies to improve air quality at home and work, empowering you to create healthier spaces.

Welcome to your guide on indoor air quality — the invisible ingredient that shapes your well-being every day. We’ll start by grounding our discussion in trusted standards like WELL, then explore what poor air quality really means, and finally, what practical steps you can take to breathe easier and live better, whether at home or in the office.

The First Ingredient: Air That’s Fresh, Clean, and Safe

Before you automate anything, before you plug in a purifier or install a dashboard — start with the air. It’s the base stock of your smart home recipe. And while there’s plenty of hype around air quality, the truth is both simpler and more actionable than you might think.

😷 What Makes Air “Bad”?

CO₂ from human respiration and gas appliances — causes drowsiness, headaches, poor concentration
PM2.5 and PM10 from cooking, candles, traffic — fine particles linked to asthma, heart disease, and other health issues
VOCs from furniture, cleaning products, paints — can trigger allergies, nausea, and long-term illness
Humidity extremes — too high = mold and dust mites; too low = dry throat, irritated eyes
Radon, carbon monoxide, formaldehyde — invisible but dangerous, especially in enclosed spaces

PM1 is an emerging concern due to its tiny size, allowing it to penetrate deeply into lungs and bloodstream, posing serious health risks. While not yet widely regulated, monitoring PM1 alongside PM2.5 and PM10 offers a fuller picture of indoor air quality and helps target mitigation more effectively.

And it's not just pollution

Viruses and bacteria can remain airborne by attaching themselves to measurable pollutants like dust, particulate matter, and organic debris—even though the microbes themselves are too small to detect directly. These pollutants act as carriers, allowing pathogens to travel farther and persist longer in indoor air. Factors such as low humidity, poor ventilation, and stagnant airflow amplify this effect, while high humidity can breed mold spores, which are harmful in their own right and can also serve as carriers for pathogens.

Hong Kong Air & Weather Dashboard

Select AQHI station:

AQHI Index

—

Risk: —

Last updated: —

Weather

Temperature

— °C

Humidity

—%

UV Index

—

Rain

— mm

Last updated: —

Pollutants (µg/m3)

—

Last updated: —

These Are real time readings from EPD AQHI, HKO Weather, EPD Pollutants
🙏 Thanks to Hong Kong EPD & HKO for open data.

🌍 What Do Standards Say About Air Quality?

Pollutant	WELL v2	RESET CI	HK AQOs	HK Urban Avg	HK Urban Max
PM2.5 µg/m³	≤ 15 AA	≤ 35 HA	≤ 37.5 24HA	20–40 Daily Avg	80–120 Daily Max
PM10 µg/m³	≤ 50 24HA	≤ 75 HA	≤ 75 24HA	30–60 Daily Avg	100+ Daily Max
CO₂ ppm	≤ 800 IN	≤ 1000 HA	≤ 1000 Good	n/a	n/a
TVOC µg/m³	≤ 500 IN	≤ 500 HA	≤ 600 Good	n/a	n/a
CO ppm	≤ 9 8HA	≤ 9 HA	≤ 6.1 Good	0.5–1.5 Daily Avg	3–5 Daily Max
NO₂ µg/m³	≤ 40 AA	≤ 100 HA	≤ 200 1HA	40–80 Daily Avg	150–200 Daily Max
O₃ µg/m³	≤ 100 8HA	≤ 100 HA	≤ 120 8HA	50–100 Daily Avg	200+ Daily Max
Formaldehyde µg/m³	≤ 27 30MA	≤ 50 HA	≤ 100 Good	n/a	n/a

Note: The three columns to the left are interior air quality, while the others are exterior.

Abbr.	Definition	Abbr.	Definition
µg/m³	Micrograms per cubic meter	ppm	Parts per million
AA	Annual Average	HA	Hourly Average
24HA	24-Hour Average	8HA	8-Hour Average
1HA	1-Hour Average	30MA	30-Minute Average
IN	Instantaneous (real-time)	Max	Highest daily value recorded (peak exposure)
Good	HK IAQ Objective classification meaning pollutant levels are within acceptable health limits for general indoor environments. “Good” is less strict than “Excellent” but still considered safe for most occupants.

WELL is a leading framework used in commercial spaces to define healthy indoor air. It’s built around measurable thresholds for pollutants like:

CO₂ — WELL recommends keeping levels below 800 ppm for optimal cognitive function
PM2.5 — Fine particles under 15 μg/m³ are considered safe for long-term exposure
VOC levels — Formaldehyde under 27 ppb, total VOCs under 500 μg/m³
Carbon monoxide, ozone, radon — All have strict limits to prevent acute and chronic health risks

Hong Kong’s Indoor Air Quality Certification Scheme and Air Quality Objectives (AQOs) echo many of these thresholds, especially for public buildings and offices. While these standards are designed for workplaces, they’re increasingly relevant for homes — especially high-rise flats with limited ventilation.

What Can You Realistically Do?

🏠 At home:

Use CO₂ and PM2.5 sensors to monitor air freshness and pollution
Run extractor fans during cooking or showering — especially in gas-equipped kitchens/bathrooms
Open windows when outdoor air is clean (check AQHI in our dashboard above, or use smart triggers)
Use air purifiers with HEPA filters for PM2.5 and VOCs
Ceiling fans rock! The move the air around, mixing it to a smooth consistency of temperature, humidity, CO₂ and more
Buy some plants, there are some varieties on plants that act like CO₂ extractors. And the look nice too
Avoid synthetic fragrances, scented candles, and harsh cleaning chemicals

🏢 At work:

Advocate for ventilation audits and WELL/RESET/HK AQO compliance
Use occupancy-based ventilation to reduce CO₂ buildup in meeting rooms (needs people counting, more in another post)
Install air quality dashboards to raise awareness and guide behavior (you can have ours or have us update to your requirements)
Encourage use of low-VOC materials in renovations and furnishings
And don't forget the plants. Not just great for the air, but great for the mind too
Try to discourage the use of scents and fragrances, these release chemicals and particles that can irritate lungs and trigger health issues.

Sensor Technologies and Selection

Choosing the right indoor air quality (IAQ) sensors is crucial for accurate monitoring and effective mitigation. It’s important to select sensors that are certified by recognized authorities, organizations, or government bodies to ensure their accuracy and reliability.

Certified sensors undergo rigorous testing and validation, providing confidence that the data they produce reflects real-world conditions. Additionally, look for sensors that support recalibration or replacement of parts, as this maintenance extends the sensor’s lifespan and maintains measurement accuracy over time.

An IAQ sensor without certification or maintenance support can be worse than having no sensor at all — inaccurate readings may lead to false reassurance or unnecessary alarm, undermining your efforts to improve air quality.

When selecting sensors, consider:

Certification: While UL and CE certifications cover safety, electromagnetic compatibility, and functional aspects of sensors, they do not guarantee measurement accuracy. For IAQ sensor accuracy, look for certifications and validations from specialized bodies such as RESET, WELL, ISO, or ANSI that focus on performance and data quality.
Maintenance: Ensure the sensor allows recalibration or part replacement to maintain long-term accuracy and reliability.
Measurement Range and Sensitivity: Match sensor capabilities to the pollutants of concern (e.g., CO₂, PM, CO, VOCs).
Integration: Compatibility with your smart home or building management system.
Data Transparency: Access to raw data and clear reporting.
Ongoing fees: It is common for vendors to charge annual fees to maintain access to your data or even access to your real-time data. Choosing a sensor with local communications, not reliant on the internet, can mitigate such fees. However, if long-term storage of readings is required for reporting, you may need to explore available options or create your own storage solution.

Want help selecting a monitor for you? Make sure you read our next post!

The Bottom Line

Air quality isn’t just a wellness buzzword — it’s the foundation of comfort, health, and productivity in every indoor space. Understanding what affects your air and how to measure it accurately empowers you to take meaningful action. With the right sensors, certifications, and maintenance, you can ensure the air you breathe supports your well-being and performance.

Coming up next

Now that we’ve established the importance of fresh, clean air as the foundation, the next step is to explore practical ways to achieve it. We’ll look at simple recommendations you can adopt immediately—like monitoring indoor air quality and choosing the right filtration methods—before moving into outline automation strategies that tie everything together. This is where smart controls for AC units, air filters, and extract fans come into play, creating a responsive system that not only keeps your atmosphere healthier but also adapts intelligently to changing conditions. In our upcoming post, we’ll show how these elements can be orchestrated to deliver a consistently cleaner, fresher environment with minimal effort.

Appendix: Specific Sensor Types and Technologies

Understanding the different sensor technologies available for indoor air quality monitoring helps you choose the right tools for your needs. Here are the key sensor types commonly used:

Optical Particle Counters (OPCs)

Measure particulate matter (PM1, PM2.5, PM10) by detecting light scattered by particles.
Provide size-resolved particle counts and concentrations.
Highly accurate for particulate monitoring but require regular calibration and maintenance.

Electrochemical Sensors

Detect gases like carbon monoxide (CO), ozone (O₃), nitrogen dioxide (NO₂), and others.
Work by producing an electrical current proportional to gas concentration.
Sensitive and selective but can degrade over time, requiring recalibration or replacement.

Metal Oxide Semiconductor (MOS) Sensors

Detect volatile organic compounds (VOCs) and some gases by measuring changes in electrical resistance.
Affordable and compact but less specific and can be influenced by humidity and temperature.

Photoionization Detectors (PIDs)

Measure VOCs by ionizing gas molecules with ultraviolet light.
Provide real-time VOC concentration data.
More expensive and typically used in industrial or specialized applications.

Nondispersive Infrared (NDIR) Sensors

Commonly used for carbon dioxide (CO₂) detection.
Measure gas concentration by detecting absorption of infrared light at specific wavelengths.
Reliable and stable with low maintenance needs.

Radon Sensors

Use solid-state detectors or scintillation counters to measure radon gas.
Often require longer sampling times for accurate readings.

Considerations When Choosing Sensor Technologies

Accuracy and Sensitivity: Match sensor capabilities to the pollutants you need to monitor.
Calibration and Maintenance: Sensors like electrochemical and OPCs need regular upkeep to maintain accuracy.
Cost and Scale: Balance budget with the number of sensors and coverage area.
Integration: Ensure compatibility with your building management or smart home systems.
Data Access: Prefer sensors that provide raw data and transparent reporting.