By the SightShield team · · 3 min read
Measure before you buy a solution
Air purifiers, fresh air systems and dehumidifiers all promise cleaner air, but without measurement you cannot tell which problem you have. A good indoor air quality monitor shows whether the issue is fine dust from traffic and construction, stale air from poor ventilation, chemical fumes from new furniture, or damp. Each needs a different fix.
What monitors measure
| Parameter | Main sources | Main fix |
|---|---|---|
| PM2.5 | Traffic, construction dust, cooking, incense, smoke | Filtration: purifier or filtered fresh air |
| PM10 | Road dust, construction | Filtration, cleaning, sealing gaps |
| CO2 | People breathing in closed rooms | Ventilation |
| VOCs | Paints, new furniture, cleaning products, perfumes | Ventilation and source control |
| Humidity | Weather, cooking, bathrooms | Ventilation, dehumidifiers, exhaust fans |
| Temperature | Weather, sun, appliances | Shading, AC settings |
Guideline values
These outdoor standards are useful reference points for indoor air too.
- PM2.5 under India’s National Ambient Air Quality Standards: 60 µg/m³ for 24 hours and 40 µg/m³ annual average.
- PM2.5 under WHO’s 2021 guidelines: 15 µg/m³ for 24 hours and 5 µg/m³ annual average — much stricter.
- CO2 indoors: around 1,000 ppm or lower is a common target.
- Relative humidity: roughly 40–60% is comfortable and discourages mould and dust mites.
Sensor accuracy
- Particle sensors in consumer monitors use laser scattering; good ones track trends well but can drift.
- CO2 needs an NDIR sensor for real measurement; “eCO2” values are estimates from VOC sensors.
- VOC readings are relative indexes, not exact concentrations — use them to spot changes.
- Humidity strongly affects particle readings during the monsoon.
- Compare a monitor with a reference or second unit before trusting exact numbers.
Placement
- Put it where people spend time: bedroom, living room, workstation zone.
- Keep it away from windows, AC vents, kitchens and direct sun.
- Place at breathing height, not on the floor or ceiling.
- Use a connected monitor that logs data so you can see daily patterns.
Reading the patterns
| Pattern | Likely cause | Action |
|---|---|---|
| PM2.5 spikes at cooking time | Kitchen smoke and oil | Use the chimney or exhaust; close kitchen door |
| PM2.5 high when windows are open | Outdoor pollution or nearby construction | Filtered fresh air instead of open windows |
| CO2 above 1,500 overnight in bedroom | Closed room, AC on | Fresh air with heat recovery |
| VOCs high after new furniture | Off-gassing | Ventilate well for weeks |
| Humidity above 70% in monsoon | Damp weather | Dehumidify; check for leaks |
Connected monitors and automation
Monitors that connect to Wi-Fi can do more than display numbers. Linked to a home or office automation system, a high CO2 reading can speed up the fresh air unit, a PM2.5 spike can switch on a purifier, and high humidity can start an exhaust fan. Logged data also shows whether changes actually worked, which is more reliable than judging by how a room feels.
Home automation and security together →An example
A family in a new Hebbal apartment complained of stuffiness and coughing. A week of monitoring showed bedroom CO2 above 2,000 ppm by morning with the AC on and windows shut, PM2.5 spikes whenever windows were opened during nearby construction, and high VOCs from new wardrobes. The fix was a compact ERV with fine filters for the bedrooms, keeping windows closed during construction hours, and airing the wardrobes. Readings dropped within days.
Fresh air ventilation for Bangalore homes →We can measure first
We measure air quality in homes and offices and recommend the right mix of ventilation, filtration and source control.
Fresh air ventilation service →Quick answers
What is a safe PM2.5 level indoors?+
WHO’s 24-hour guideline is 15 µg/m³; India’s ambient 24-hour standard is 60 µg/m³. Lower is better.
Does an air purifier fix CO2?+
No. Purifiers filter particles; CO2 needs ventilation.
Are cheap air quality monitors accurate?+
They show trends reasonably well, but CO2 needs an NDIR sensor and VOC readings are only relative.
Where should I place the monitor?+
At breathing height where people spend time, away from windows, vents and kitchens.
Why are readings high in the monsoon?+
Humidity affects particle sensors and damp air brings mould spores; check humidity alongside PM readings.